Dismal Results On Bolt Thrust Experiment #2

[Sixgun]

I hear 'ya Ben. Will do.

KWK,
I thought about that too. If that guy fired a 30-30 AI, you would think that the back of the case would blow out.......but, I thought there's no back thrust, but that......hey, wait.....this only concerns low pressure rounds and we all know that a cartridge is only as strong as it's case.

I'm going to bed. Screw this s@-t.----6

[Nath]

Stands to reson the tapered case...bit of a no brainer.

Has no body considered Mr Luger?

N.

[Ben_Rumson]

Luger... You mean its' toggle links? What?

[Nath]

Luger... You mean its' toggle links? What?

Yeah....nothing locks up does it IIRC. When the pressure drops the case then pushes back on the toggle. There was even a rifle developed.

N.

[Nath]

http://youtu.be/PEdRo0g-Mp8

[missionary5155]

Greetings
Me I would start the 1892 project with just a primer and a cork in the barrel. Should give you a good idea how fast a bolt can move about.
You should also remove the lever as it is connected to the bolt with that cross pin.
Mike in Peru

[Buck Elliott]

Now Fellers, I Was born at night -- 2:40AM, to be precise -- but it wasn't Last Night..!!

I'd surely appreciate it, if one of you "no bolt thrust" Jaybirds could kindly explain what forces may have been at work, that wrecked 4 '94 Winchesters (including a .375 Big Bore) and a nice 336 Marlin, back in the mid-1980s, when we set out to justify the need for a STRONGER action to safely contain the pounding of the .454 Casull cartridge, and its allowable 65,000 psi chamber pressure..

The angled locking lug of the 94 acts like a wedge or ramp, trying to force the rear end of the bolt up and out the top of the receiver.. the thrust force peens metal from the receiver, behind the lug recess, in the bolt guide raceways, and from the rear face of the bolt itself, while also stretching the receiver sidewalls to the point of dangerously-excessive headspace and insafe locking of the bolt.. These traits were accelerated in the AE Big Bore, due in great part to lack of supporting material in the right sidewall of the receiver.. The frame became so twisted that it was difficult/impossible to open/close the bolt, and peening behind the lug was very pronounced.

In the case of the poor Marlin, the locking lug became severely deformed, as did the locking recess in the bottom of the bolt.. Slots in the receiver for the lug also were severely peened, and the gun was deemed unsafe to fire, because it would not lock up properly..

All the above mentioned conditions are traceable directly to Bolt Thrust, and to nothing else..

I have examined older, heavily-used '86 and '92 Winchesters that have shown peening of the locking lugs.. they bear the imprint of the bolt on their forward faces..

It is not unusual to find locking lug recesses in bolt-action rifles which have been peened by the lugs, over the course of time..

Bolt thrust is real.. It is defineable and measureable, and it sure is observable...

[Chuck 100 yd]

What Buck Elliott said +1. Nuff said!!!

[Sixgun]

Buck,
Thank you for your knowledgable input. I believe 99% of us here are in your camp.

The controversy started with John Barsness's article in Handloader magazine. He stated that with LOW pressure rounds, there was little to no bolt thrust. When you hear a guy of his caliber state these so called facts, it makes us, (the readers) shake our head in wonder.

He states that P.O. Ackley proved this back in the forties by shooting an 1894 in 30-30 AI just by holding the bolt back with his hand after removing the locking bolt.

We do understand that with the pressures that your rifles are generating, that there is equal thrust on the case walls and the case head. The issue here is with low pressure cartridges.------Sixgun

[Ben_Rumson]

Nath....The way I see it The bolt is connected to the toggle..Spring pressure against the toggle keeps the bolt home... after ignition the bolt is driven in its carrier about a quarter inch rearward when then the toggle grasps get cammed up by the lobes on the frame, enough to cause the toggle to unlock...
I cant say if it is low pressure against the case that draws the bolt the rest of the way back and completes the extraction-ejection-loading cycle ...

[Buck Elliott]

Logic, reason and mathematics would say that all other factors being equal, higher pressure will transmit higher thrust..

If we take into account such variables as case strength (plasticity and elasticity) combined with friction between surfaces, we alter the equation, but not by any appreciable or significant amount.. In such an instance, a "lower-pressure" cartridge, which does not expand to fill the chamber and form a tight seal, may indeed TRANSFER A HIGHER PERCENTAGE OF ITS ENERGY (thrust) TO THE BOLT FACE, than a cartridge case which does firmly grip the chamber on firing..

BTW, the .45 Colt case gets "smoked" because it is a straight case, and in low pressure loadings, does not expand to fill the chamber completely, allowing powder gases to leak past the case mouth and "soot" up the outside of the case.. The .44 & .38 WCF cases are bottlenecked, and may or may not be of lighter construction than the .45s, but gas pressure against the shoulder angle helps shut off and seal the chamber better, at equal pressures..

When fired with VERY light loads, the WCF cases can be collapsed at the shoulder, from gas pressur finding its way back, past the unexpanded case mouth... A friend of mine was plagued by this problem, when trying to develop 'mouse-fanny burp' loads for an original '73 Winchester.

P.S.: Sadly, the only thing Proved by the Colt Lightning experiment was that the rifle functioned exactly as designed, while the experimenter displayed lack if sufficient knowledge about the gun's mechanics.. A waste of a "10-cent video.."

[Buck Elliott]

Looking at the shape of the hammer in the schematic the hammer itself acts as a locking lug......similar to the Remington rolling block action. The hammer in the forward position, such as it is when being fired, blocks the bolt from coming back. The key is can you cycle the action with the hammer forward?? I'm not familiar with the gun, but I'm guessing no.

The hammer Does Not look, act or function like the hammer in a rolling block.. If it served to hold the bolt closed, it would have to be cocked manually before the breech could be opened...

[Chuck 100 yd]

As a kid, My dad was a policeman and I got to see and handle a home made 'Zip' gun. I decided I was going to make one . The stock was wood, the barrel was a short length of car antenna taped to the stock. The antenna was just the right size to fit a .22 rim fire round. The firing mechanism was a hammer made of flat bar hinged on a nail through a hole drilled in the bottom and driven by a large rubber band. The hammer and rubber band was all that held the case in the chamber.thumbing the hammer back and letting it fly would fire the .22 long rifle round in the barrel.
I fired this thing exactly one time. The spent case came back out of the barrel with great force,hit me on the arm and raised a big bruise the size of a half dollar. It is a good thing I did not get hit in the eye.
That was my experiment in case thrust. It has been over 50 years ago and I will never forget it.

[Buck Elliott]

.22 LR ammo develops somewhere in the vicinity of 22,000 - 24,000 psi, and features a Straight Case...

[Nath]

I am usually wrong and if so so be it.
I thought nothing moved on a lugar until pressure dropped and there is no actual physical bolt lock.
I also understood there can be no lube present in a lugar chamber and was a reason why the rifle failed military trials.
All conjecture on my part.
I get where Buck is coming from too. Different cartridges have different charatistics. Chambers are polished more than others etc.
Our proof is two stage. The second stage is a action test with a greased cartridge to induce bolt thrust. This for me implys bolt thrust may or may not exist in part or other when the cartridge can bond to the chamber via pressure.
Nath.

[w30wcf]

It will be a couple of weeks yet before I get a chance to test the .44-40 as I mentioned earlier with cartridges loaded within SAAMI specs. We shall see if the case head touches the bolt face or if just the pressure against the primer is enough to keep the case in the chamber in this lower pressure cartridge........

w30wcf

[OldWin]

I'm definitely late to this party but have been loosely following along. I agree with Buck's comments on the 94'. The lockup operates in "shear", and while I own many and enjoy them, the older I get the less enamored I am with the design and don't load them up like I used to. I don't agree with the "strong" 94 belief. It's really fairly weak in my opinion.
As far as bolt thrust, I think it's very real and was understood by the designers from the start. The one thing all gun designs have in common is that they were made to sell and make a profit. Machining and manufacturing were difficult 100+ years ago. If it didn't need something, they wouldn't have put it in. I'm sure while they were working with engineering and production prototypes they tried and experimented with many things. In the case of Winchester, they were also at the forefront of cartridge design, and I would think understood the forces at work.
Anyway, what the h#ll do I know? I just shoot em and enjoy em all I can and wish I had the money to buy more. They were wonderful tools designed by brilliant men who had the ability to make something practical and pleasing to the eye at the same time.

[Old Savage]

In the case of the low pressure cartridge Buck described not sealing you not only have gas pressure inside the case but there is likely some down the outside of the case pushing on the rim.

[Griff]

Like herdin' cats, huh Buck?

Thanks for the info, sometimes it helps to get an understanding of how much we DON'T know... and while I consider myself a knowledgeable reloader, what you explained there very succinctly, helps me understand how those cowboy shooters can "stretch" a frame shooting very light .38Spl loads out of a '66 or even a '73.

[Model 52B]

This is my first visit to this thread and I have to say after reading page one, it ranked up there as absolutely one of the dumbest threads I've ever read. I couldn't bear to read much more of it.

Kudo's to JRD for pointing out the obvious difference between cycling the action via the slide, versus bolt thrust acting on the bolt face.

The folks prior to his post missed the obvious and worse - they didn't even think about it. Consider the following...

1) Has any of you ever fired a blow back operated .22LR? Ever wonder what made it "go"? There is the perfect example of bolt thrust driving the bolt back - against spring pressure even. So obviously there is enough bolt thrust in the lowly .22 LR to drive the bolt back and enough excess to require a spring to retard the motion of the bolt. That's with a just 40 grain bullet at around 1,200 fps and a case head area of only .0398 square inches.

2) Ever seen a blow back operated .380 ACP pistol? Of course you have. Most pistols smaller than .380 ACP are blow back operated as it's a simple and straight forward design. That's bolt thrust in action again, but this time with a 90 grain bullet at about a thousand fps and a case head area of 0.1098 square inches.

3) Ever wonder why you rarely see a blow back operated pistol in 9mm or larger? The bolt thrust increases to the point that you need an excessively heavy bolt along with an excessively heavy spring to absorb the energy and keep the slide velocity manageable. You see blow back operating systems sometimes in sub machine guns in 9mm and .45 ACP, but you'll also notice the heavy bolt and springs used. That either results in a long action like the Sten, the M3 or the Thompson, or it involves a telescoping bolt design like the Uzi, where the bolt over hangs or surrounds the chamber and initial portion of the barrel in order to get the needed bolt weight in a short over all weapon length.

If you ever knew, did, or wondered about 1, 2 or 3, then you already intuitively understood bolt thrust. You just failed (miserably) to apply a little bit of critical thinking and say "what's wrong with this picture?" when confronted with the Colt Lightning example. Knowing all of the things you actually know is totally useless if you don't stop and take the time to try to apply that information to new situations you encounter. It's not rocket science, it's just good 'ole practical common sense.

----

Along with this, have you ever wondered by they use brass in cartridge cases? Brass has a nice quality of expanding nicely under pressure, while being strong enough to contain a fair amount of pressure - and then relaxing slightly once the pressure is reduced. That allows the case to expand and efficiently seal the chamber and then relax to allow the fired case to be easily extracted.

Sealing the case requires a certain minimum amount of pressure, and it was common for older black powder lever action rifle cartridges to have a slight bottle neck. That slight bottle neck helped to seal the chamber early in the process, reducing the gas coming back into the action. If any of you have shot a straight walled .45 Colt with low pressure loads, you've noted the dirtier cases that you get compared to a stiffer load, and most of you have probably figured out a light charge of a fast burning powder will keep the action cleaner than a light charge of a slow burning powder. That's because the earlier pressure spike of the slow burning powder helps to seal the case more effectively before the bullet clears the case.

In terms of bolt thrust, if the case is adhered to the chamber wall then it increases the force needed before the case head can press back on the bolt head, so it will technically reduce the bolt thrust, at least initially. However, in practical terms there is just not that much brass in the web of the case in the area just behind where the case is stuck to the chamber wall, and the case will just stretch in that area until the head is against the bolt face, so any reduction in thrust is temporary, and probably minimal even early in the pressure curve.

[Ben_Rumson]

Hmmm... that's rather harsh... Oh well. Its just that the often referred to god of bolt thrust experimentation and pressure (in rifles at least)(Ackley) sold us on how a straight sided case expands so well the bolt thrust is minimal if the chambers are kept dry.....

[Sixgun]

Model 52B,
Yes, we understand.....but did you happen to read John Barsness's article on bolt thrust and what P.O. Ackley wrote in his book?

Let's pretend that Einstein came back to life and he told everyone that the sun revolved around the Earth and that what we thought was true was not. So, here are 6 billion people scratching our heads...........sound familiar yet?

While we know these things on bolt thrust, we want to know in terms that the average guy can understand, you know, solidification concerning the truth in our minds.

Not many of us have masters degrees in physics. It even had our very own highly intelligent AJMD scratching his head. That's a guy who makes his living healing people and has 8 years of education and passed the board. Dumb people cannot do that.

Not many of us here have their own rifle companies and it's combined knowledge of engineers.

If you read any of w30wcf's posts, he too, does not appear to be in total control of his previous physics
courses and I know Jack personally and can confidently claim that he knows more on loading for guns than all of us put together.

You had the chance to read all of the posts before you made a comment. Would have been nice to see what you would have said on page #1.

Would you like to go 1 on 1 on hundred year old single action Colts? Just because you don't know the difference between Henry Nettletown's cartouche from one of his sub inspectors does does make you "dumb".

So......next time don't wait until page 4 and a thousand readings before you call us "dumb". -----6

[Nath]

Here we have assumption again. A blow back auto does not necessary start blowing back at full pressure....it could just start after the case is no longer gripping the chamber some!
Just because it is called a blow back auto don't mean we can assume the full pressure is acting on the bolt.....surely the cases would come out a funny shape and be making the most awful noise.....no?

N.

[Chuck 100 yd]

Nath , I think you are spot on in your thinking there.
Count me in your camp .

[Sixgun]

I'm seeing plenty of "proof" from both sides by their "scientific" experiments and educated assumptions. But I have yet to see proof as the way the word has definition.

I sense frustration coming from the "proofers", along with changes of mind from some. Remember now.......LOW pressure loads.


Its time to call in the BIG DOGS! ---------------------6

[Old Savage]

That is what I said - " But I have yet to see proof as the way the word has definition.".

[vancelw]

Model 52B,
So......next time don't wait until page 4 and a thousand readings before you call us "dumb". -----6

He talks big behind his keyboard. Model 52B, my offer to sit down and visit over coffee stands.

That's what I'd do if I was the new guy in town...p!$$ everybody off right away and wonder why they shun me.

[Model 52B]

Ok, maybe I came off a bit harsh. I apologize for any offense that was taken.

It's still hard to watch the video and not catch the difference between operating the bolt via the slide and pushing it back via bolt thrust, or to consider blow back operation and make the connection that something is off in the conclusion made in the video.

People unfortunately are too quick to believe what they *told* or are led to be believe they are seeing. It's been making magic shows work for thousands of years.

I suspect if the author of the video had done the demonstration then just posted the question "what's going on here?" - prompting thought, instead of suggesting a conclusion - most people would have figured it out. Instead, as presented, it has the appearance of a valid experiment leading to a valid conclusion, when a critical piece of information (i.e the presence of a locking system) is missing and ignored.

There are 4 basic ways of knowing something and they tend to happen in this order in terms of frequency:

1) Authority - you know something because someone you feel is an authority told you that's how it is. (The potential pit falls here are that the "authority" can be wrong, can be taken out of context, or can be misleading you with their own agenda).
2) Observation / scientific method - you know it because you observed it. (The potential pit fall here is that true scientific experiments are rare, observations are often less than perfect, and that the conclusions made are only as valid as the underlying assumptions. Theories get developed, tested, and disproven all the time, even theories that have been around a long time. They fall by the way side when new observations and new information comes along.
3) Logic - you know when something is or is not potentially true based on how it logically relates to other knowledge. This often plays a big role in designing new experiments and observations that disprove theories from number 2, or far more often, poke holes in the theories suggested by "Authority". (The potential pitfalls are a number of logical fallacies that people fall prey to on a regular basis.
4) Philosophy - this is in essence a higher level integration of 1-3, to make sure everything fits, and to a lesser extent to recognize when various principles may be in conflict and prioritize what matters most.

Model 52B,
So......next time don't wait until page 4 and a thousand readings before you call us "dumb". -----6

He talks big behind his keyboard. Model 52B, my offer to sit down and visit over coffee stands.

That's what I'd do if I was the new guy in town...p!$$ everybody off right away and wonder why they shun me.

If I get to Montana this year, and you're there, I'll take you up on it. If you're in eastern NC, anytime drop me a line.

Model 52B,
Yes, we understand.....but did you happen to read John Barsness's article on bolt thrust and what P.O. Ackley wrote in his book?

I was thrilled to find a 1962 edition of P.O. Ackley's manuals in a pawn shop in North Florida several years ago, as I like a lot of what he has to say - but you have to be careful not to take it out of context.

When Ackley speaks about bolt thrust however, he's talking about the English method of measuring pressure via a crusher disk on the bolt head to measure pressure as bolt thrust. Ackley felt this was the most relevant method to the reloader as measuring pressure at right angles to the case wall was not quite as important since modern firearms seldom fail in the chamber wall given modern high tensile steel barrels.

The effect of minimum tapered case walls on reducing bolt thrust was the rationale used for minimum taper cartridges and sharp shoulders to maximize both case capacity and straight case wall area. Ackley illustrates this point with a discussion of experiments with a Savage 99 in 250 Savage where loads were be reached that made extraction impossible without using a rod to tap on the case, while pulling on the lever. But, after re-chambering for the .250/3000 Improved with minimum head space, minimum taper case wall and a sharp shoulder, the original load could be exceeded with no lock up issues, and he noted that as the load was progressively increased, something else would break on the 99 before extraction again became impossible.

He also discussed experiments with an old Model 94 Winchester resurrected from the junk pile where he rechambered it with minimum headspace and a 30/30 Improved cartridge with minimum taper and a sharp shoulder, then demonstrated the "stickiness" of the case by backing the barrel off a turn to increase head space and observing primer protrusion. That protrusion disappeared (replaced by an increase in base to shoulder length) when the case was oiled to prevent adhesion, thus demonstrating the effect of a straight, untapered case in reducing bolt thrust .

He concluded that straight, minimum taper case walls take some of the load off the bolt and that the case head itself will absorb at least some of the bolt thrust, suggesting that there is no absolute pressure limit on an action as the case design itself has some role to play in bolt thrust.

At no point however did Ackely ever say bolt thrust is non-existent, or that the case head is capable of handling all the thrust in a load, particularly, a high pressure load.

----

You might be able to argue that a low pressure .45 Colt load has little bolt thrust, being a straight walled case (.480" in diameter), but there are two problems with that argument.

The first problem is that the .45 Colt chamber itself was, and remains, tapered by .0056" from front to back. At the time it made sense to ease extraction in a straight walled black powder cartridge. But it also means that the case has to expand outward by .0056" at the rear to come in contact with the case walls. If you are observant, you'll notice the greater than average belling that occurs on a .45 Colt. Some shooters partial size it to avoid working the brass excessively, and many blame the sizing die for excessively sizing the case, when in fact it's just bringing the case back to spec, or close to it.

http://www.saami.org/PubResources/CC_Dr ... 20Colt.pdf

The second problem is that with an excessively light load, you may not be able to expand the rear of that case out the required .0056" to contact the case wall, and are thus reducing the ability of the case to accommodate some of the bolt thrust. However, you are also, by definition, dealing with low pressures in this case, and thus the bolt thrust is already greatly reduced, so any increase in bolt thrust due to poor case adhesion is more than offset by the reduction in bolt thrust over all. The major problem here is more gas coming back into the action, possibly reaching the shooter.

[Sixgun]

Model 52B,
So......next time don't wait until page 4 and a thousand readings before you call us "dumb". -----6

He talks big behind his keyboard. Model 52B, my offer to sit down and visit over coffee stands.

That's what I'd do if I was the new guy in town...p!$$ everybody off right away and wonder why they shun me.

Mr. Vance,
Mr. 52b thinks this is a dumb subject. If it's so dumb, why did P.O. Ackley and John Barsness say in print that there is little to no bolt thrust in LOW pressure cartridges? Mr. 52b sure does not sound like he is dumb, on the contrary, he appears to be very intelligent.

Who is the regular guy to believe, Mr. Ackley, who, in his lifetime forgot more that any of us will ever know collectively, or Buck Elliot, another respected gun crank?

I said nothing out of the way or demeaning to you or anyone else. Internet threads are like the TV, and that is, if you don't like the channel/thread, change it......move on and let the interested enjoy the time they have away from work and other life's stresses by interacting with each other.

By inserting hurtful words you are not helping the reputation that internet chat rooms have garnered.

Do us all a favor, if your not interested in a thread..........move on.------6

[Tycer]

I'm still enjoying this thread.

[Borregos]

I'm still enjoying this thread.

Me too

[Model 52B]

Mr. Vance,
Mr. 52b thinks this is a dumb subject. If it's so dumb, why did P.O. Ackley and John Barsness say in print that there is little to no bolt thrust in LOW pressure cartridges? Mr. 52b sure does not sound like he is dumb, on the contrary, he appears to be very intelligent.

Who is the regular guy to believe, Mr. Ackley, who, in his lifetime forgot more that any of us will ever know collectively, or Buck Elliot, another respected gun crank?

The irony here is that I'm defending what Ackley has said when others who apparently don't understand the limitations of what he's said are mis-appyling it.

You've expressed an excellent example of a major problem with the authoritarian way of knowing something. Who do you believe when there is disagreement? Any statement made by an authority is only as valid as the authority you heard it from, so you attempt to assign greater or lesser validity to one of the sources and then weight them accordingly. The answer to "who is the regular guy to believe?" then is that the regular guy should think and apply some common sense based on their own observations, which means going beyond just the "authoritarian" way of knowing and delving into observation and logic.

What makes the authoritarian way of knowing something fatally flawed at times is that people often don't fully understand the topic or the limitations of what the authority actually said and then over apply or over generalize it, taking it out of it's original context into areas where it's no longer valid. That's what happened here in this thread.

The subject itself isn't dumb, and that's not where I'm coming from in challenging the lack of critical thinking and mis application of "authoritarian" knowledge that was occurring in the thread - to the point of totally ignoring what common sense should have been telling us if we thought about it for more than about 30 seconds.

Personally, I put P.O Ackley right up there with John Browning in terms of firearms genius, but context is important and taking what he's said out of the high pressure rifle cartridge context does not make it magically support the idea that low pressure rounds have no bolt thrust. Ackley's printed comments will not support that contention no matter how many times people mis-quote them.

Re-read my post above. Ackley is talking about the reduction in bolt thrust that occurs when the straight walled, un-tapered section of a case adheres to the chamber. He is saying that long, straight walled cases with minimum taper will reduce the bolt thrust compared to their tapered and shallower shouldered counterparts. He never said low pressure rounds have no bolt thrust. The distinction is important.

If you still disagree and think "low pressure cartridges have no bolt thrust" is what he's said (and apparently don't have a copy of his work in front of you). Look at the lowly .22 rimfire for three separate examples and then wonder why those example are not consistent with that you think Ackley said:

1) The .22 LR runs at about 24,000 psi - low pressure by rifle standards, and only 3,000 psi more than the 45 ACP. The .22LR also has a straight un-tapered .226" diameter case, that is 2.71 calibers in length. If there is a round that is going to have no bolt thrust, this should be it. Yet they operate blow back operated .22 semi-autos with a great deal of reliability each and every day.

2) An even better example is the .22 WMR - .242" in diameter, un-tapered, and 5.5 calibers long with the operating pressure of 24,000 psi. Yet it again operates blow back semi-auto rifles with annoying regularity for a cartridge that should have no bolt thrust.

3) finally, lets look at the lowly .22 short and CB cap. If you have a semi auto load a "primer compound only" CB cap in it manually and pull the trigger. The bolt will probably move back slightly even with the recoil spring in place, and it will definitely move with the recoil spring removed. That's as low pressure as it gets, and there is still bolt thrust.

Now, you might be thinking that 24,000 psi is a lot of pressure for some pistol rounds and you'd be correct, as the .380 auto runs at only 21,500 psi. However you can load a .380 down to around 10,000 psi and still get reliable functioning in a blow back pistol. If you lighten the recoil spring, you can go even lower. Now...the area of the .380 case is larger, the brass is thicker than the .22 rimfires, and there is a slight taper, so you'll have to decide if those pros and cons in the .380 case add or takeaway enough to create the bolt thrust of the .380 even at low pressures.

The .45 Colt is the example at a hand and most folks who've shot low pressure loads in one have probably noted the greater degree of case staining lower on the case, reduced expansion of the straight case in the tapered .45 Colt chamber, and in extreme cases gas in the action. With those indicators of less adhesion at low pressures, I'm betting the bolt thrust is greater than zero. What do you think?

Theoretically, to have no bolt thrust at all, you'd need enough pressure to adhere the case to the chamber, yet at the same time have low enough pressure to allow the web of the case just below the part that sticks to hold the pressure without stretching. We all agree that there has to be a point on the case where it stops adhering, so for no bolt thrust, you'd have to have a point where the brass is still thin enough to stretch radially to adhere to the chamber and yet at a point only infinitesimally farther be strong enough not to stretch at all longitudinally under exactly the same internal pressure pressing the base of the case aft, retarded only by the tensile strength of the brass just behind the point where the case is adhered.

The construction of the web varies greatly in different case designs and that also has an impact on things. For example, an over used and abused .223 will separate relatively high on the case - about 1/3rd of the way up the case, and close to half way up the straight portion of the case - indicating that the lower third of the case does not adhere to the chamber to any great degree and that the web is a bit thicker than normal farther up the case. It's something Ackley would have pointed to as an example of a case design that increases bolt thrust, which was one of his points in the whole pressure discussion for the hand loader and wildcatter.

If you very carefully selected the cartridge design and carefully controlled the pressure you might create that ideal no bolt thrust condition under a very limited set of circumstances, but that does not happen in the real world. In the real world that particular spot in the case is the spot in the case where stretching, and eventually separation occurs. Ackley acknowledged that, claiming only some reduction in bolt thrust due to using minimum tapered cases.

----

I'm not the smartest guy on the planet by any means, but I've learned and been taught to think about what I read or am told and if necessary question the things that don't make sense and/or conflict with personal observations. That in a nut shell is "critical thinking" and it's a lack of critical thinking and an on going failure of our education system to teach or encourage critical thinking skills that's killing this country.

[Sixgun]

Well Mr. 52B,
I dont believe it could be said any better. I read your words carefully and cannot pick out anything suspect, using my limited ballistic knowledge.

Most guys here are serious guncranks and take for granted that the words coming from respected gunwriters to be truthful. We are too busy keeping food on the table and a roof over our families heads, or lack the proper IQ to fully understand the complicated science of ballistics.

I did not read what P.O. Ackley wrote. John Barsness quoted him in the latest issue of Handloader magazine. Handloader is the one magazine devoted to serious handloaders so we tend to believe what they say. I had a hard time believing it, hence, my very unscientific experiment with the Colt Lightning. Handloader is going to get a letter to remind them that not every reader they have does not belong to Mensa, (did I spell that right) and they have crazy shootists doing stupid experiments.

Although I can pull apart most guns blindfolded, I'm just a layman with no engineering degree to understand fully the mechanics of a brilliantly designed firearm as that Colt. I most likely can speak for the majority here.

Thank you very much for your detailed explainations and taking the time to post your obvious vast knowledge on ballistics. Speaking for myself, I am content with your explaination and hopefully, we can put this to rest. Whew........5 pages..........Got to admit boys, its been a good one!

Now, please tell us...what ammunition company do you work for? Your good and your words did not come out of a book, you typed as you thought. -------Thanks!---------Sixgun

[Ben_Rumson]

Please! Say It Aint So that Ackley never fired a Win 1894 with the locking block or locking bolt (not sure of the correct terminology) removed and the bolt did't fly out... I must have read that he did that at least a hunnert different times in about as many places here on the Internet...Thought sure it was true cause I'd seen it said so often... I can say positively though I have found it difficult over the years to get my hands on a hard copy of his actual printed words.....

[Nath]

I don't see where the conclusion is arrived that a 22 AT PEAK PRESSURE cycles the action!
Or any other cartridge.
Why does a gasser shotgun unlock when the load is several inches down the barrel?
Why does an auto rifle a gasser have it's bleed down the barrel?
Is it not so the pressure has dropped?
So why is it assumed a simple blow back action of a 22 operates AT PEAK PRESSURE?
The lower residual pressure in the barrel turns the empty shell into a piston driving the bolt back yes and inertia is given to the mechanism in an auto BUT NOT AT PEAK PRESSURE.....THINGS WOULD SOON BREAK!
Winchester 1300 and the like and their spring loaded lugs unlock on dropping the hammer but the shell does not come out with it's head ruptured or suffer a case head seperation. No the case bears on the bolt when it it self has let go of the chamber walls....after peak pressure.
I have held a block of steel on a makeshift 22 chamber and fabicated a small screwdriver to make a firing pin passing through the steel block....guess what....I felt nothing....no thrust at all....surely10-20,000psi would of done something!

Now...any low pressure or reduced load I have ever made has been discarded with any sign of gasses blowning back ALOT. The case is not likely gripping the chamber and sealing it. Apart from a lack of seal there is also quite likely very near full on bolt thrust for that load.

The variables are far to many to opine a blanket ruling on this matter.
Would I use a gun with no lock up? No.
Do I believe the lock is subject to peak pressure all the time? No.
Do I believe different cartridges behave differently with reguard to bolt thrust? Absolutely.

I need a lie down.....

N.

[Tycer]

..... been taught to think about what I read or am told and if necessary question the things that don't make sense and/or conflict with personal observations. That in a nut shell is "critical thinking" and it's a lack of critical thinking and an on going failure of our education system to teach or encourage critical thinking skills that's killing this country.

My hero.

[Sixgun]

Nath,
I hear 'ya on the "lie down" thing.

Mr. 52B says we need to exercise "critical thinking", which by the way, not many people want to do today. I believe we all have a finite capacity to critically think and once one's limit is reached, that individual hits a wall. My limit is reached once I load the cartridge into the chamber and pull the trigger. ---------------6

[Buck Elliott]

.... How many ballisticians or engineers can dance on the nose of a firing pin..?

The breech block in a blowback firearms begins to move at the time that the pressure ("force") of ignition overcomes the blocks inertia, and any recoil spring pressure and whatever friction there may be to deal with.. Whether this occurs at the precise moment of "peak pressure" depends on several factors. Functioning of the firearm depends on a balancing act, between pressure and resistence.. If pressure falls below the required threshhold, or resistence is measurably increased by some means, the mechanism will not cycle..

[vancelw]

If pressure falls below the required threshhold, or resistence is measurably increased by some means, the mechanism will not cycle..

As I found out trying to shoot game loads in my friends Browning Magnum Twenty Stupid bushings.
I'm going to buy a nice Semi-auto some day but it won't be an A5