Back to square one

[El Chivo]

I brought this up seeking advice on the temporary forum, which turned out to be too temporary for me to see the replies.

Well, I had a shock at the range Thursday. I had loaded up a bunch of rounds of my best 30-30 silhouette load from testing back in March. This was 15.5 grains of SR 4759 over a 170 grain lasercast. It gave me a 5 shot cloverleaf, centered on the paper.

Thursday however, the group opened up to about a foot at 25 yards, with some keyholing. Then I moved it out to 50 yards, and only got one shot out of 15 on the 8.5 x 11" paper. They did all stay on the 24" cardboard.

One thought is temperature, it was about 85 degrees out and when the load was tested, it was probably about 60 or 65. Another is cleaning, I had cleaned the bore with Borescrubber to remove any copper and everything else. Earlier the bore wasn't quite that clean. A third possibility might be crimping, I crimped more firmly in the cannelure the second time, which shortened the OAL by about .040". In addition, the rifle now has a stronger hammer spring than before, so the primers are getting a good whack.

Any ideas? I was not smart enough to try the remaining rounds in my other 30-30 which I had with me. I was also not smart enough to go buy some factory rounds to try in the offending rifle.

[Andrew]

Hmmm, sounds like you might have a coulple starting points to look at.

I am not well versed in interior ballistics but there are those here that are. I like threads like this 'cause I get to learn something too.

[Old Time Hunter]

Check your crown. Something does not make sense here. Yes, it would be assumed that a 20 degree higher ambient temperature could cause a different POI, but the instability generally would be noticeable if the temperature would have been lower, not higher. The crimp, again might change POI, but not the instability. Did you chrono the loads? It sounds as though you are not getting enough velocity to stabilize.

[jdad]

Are you shooting a Marlin, with Ballard rifling? Both Jnyork and I have found that we could not shoot lead silhouette loads, but had great results with JFP's. 200m "barn door' groups to 6" groups, with the change of bullets. If it's a Winchester I have no suggestions.

[Hobie]

I hate trying to diagnose these things from a distance. I do so much better holding the gun in my own two hands... Anyway, I'd just run down the checklist, did the bullets match the bore (i.e. .001-.002" over groove diameter), are they the same (i.e. from the same lot, alloy, etc), same lube, same powder charge, same primer, etc. It is "boring" but necessary to troubleshoot this.

FWIW, 15 gr. IMR SR4759 is more than enough to stabilize the bullets, they should be doing 1900 fps or so. Hey, now there's an answer, they could be going a bit too fast for that bullet/bore combo. Drop the charge to 13-14 gr. in these summer temps and see what you get.

Got a chrony?

[Griff]

I'm w/Hobie, but some general thoughts: changing ANYTHING can change everything. Ambient temps can and do affect group size, but crimp, OAL changes would be my first first suspects. Crimp, as it changes the release of the bullet and internal pressure. OAL, as it determines the amount of "jump" before the rifling is engaged. Although you have seemingly insignificant variations, their cumulative effect can be disastrous. Going back to square one may seem a tad onerous, sometimes it provides a new oppurtunity to obseve and document just how we arrived @ our "best" load and how individual changes improve or diminish our accuracy. Good luck with your new load development project.

[O.S.O.K.]

The tumbling/keyholing got my attention. The bullets are not gripping the rifeling or are not going fast enough to stabalize.

I would definately check the diameter of the bullets - I also use Laser cast/Oregon Trail bullets and have found them to be consistent and of high quality - but you never know - check them first.

Also, if you still have some of the loaded rounds, pull a bullet and double check your load. Again, we all make mistakes from time to time... your load may be off due to reading the scale wrong, or something. It's easier to misread a scale than one might think.

The crimp being "much more" might also be the issue - I'd go back to your original crimp level if nothing else pops up. All's you need for the rifle bullets is enough crimp for consistent pull and to keep the bullet from being pushed into the case in the mag.

As far as cleaning the copper fouling out, that is usually an aid to cast bullet accuracy - not the reverse.

And Hobbie is right about the charge - if this propellant is temperature sensitive, it will make a difference. However, if you determine that this is the culprit, I would recommend going to a different propellant that's more consistent.

Just my 2 centavos - hope you get this worked out!

[Malamute]

" Going back to square one may seem a tad onerous, sometimes it provides a new oppurtunity to obseve and document just how we arrived @ our "best" load and how individual changes improve or diminish our accuracy."


Griffs comment caught my eye. It reminded me of the "optimal charge weight" concept. It's been a while since I reveiwed it, but I believe it had to do with working a load up to, and past, the sweet spot, then you have a bracket area to work with, instead of just barely reching a good point and stopping. The bracket gives a little leeway either way for minor variables to enter in without causing drastic changes. I may be mistaken in this,.....here's the link if you'd like to look at it.



http://home.earthlink.net/~dannewberry/ ... velopment/

[El Chivo]

Thanks for the suggestions, I'm going to load some more and go back to the original crimp/OAL. And I'll bracket the charge again and see what I get.

The rifle is a Winchester. The crown is probably ok, I use a coated rod and a wooden dowel to clean it with. All bullets were from the same batch. I was testing out three brands of primers but they all performed the same, and one was from the same batch as before. I'm pretty sure about the charge weight, according to the loadbook it's supposed to be 1500-1600 fps. If it is in fact 1800 I'll want to reduce the charge. I was going for 1500.

The guy at the reloading store was telling me to work up loads in the summer, not the reverse.

I also found a silhouette load for H4895 which I have as well. I also just got a batch of Lasercast 165 grainers. So I have my work cut out for me.

[El Chivo]

An update, I made it back to the range Thursday, it was quite hot, about 104 in the shade (by 10 am!).

This time I had matched everything I could, crimp, OAL, and double checked the scale and everything.

All the rounds using SR 4759 performed dismally, about 1 foot groups at 25 yards. I also tried some in the other rifle, with similar results.

I also loaded up some rounds with H4895, I found a cast bullet load on their website. These were just fine. I tried two OALs using 18 grains over a 165 gr Lasercast, and the shorter OAL gave me a nice 1" or so group.

So I think it does come down to powder. One thing, about a week before this I tried the SR 4759 in .357 with 180's. I got a great group, and it was pretty warm out then. I'll have to try some more of those in the heat. But it looks like the SR 4759 is temperature sensitive, at least in the rifle case.

[Andrew]

An update, I made it back to the range Thursday, it was quite hot, about 104 in the shade (by 10 am!).

This time I had matched everything I could, crimp, OAL, and double checked the scale and everything.

All the rounds using SR 4759 performed dismally, about 1 foot groups at 25 yards. I also tried some in the other rifle, with similar results.

I also loaded up some rounds with H4895, I found a cast bullet load on their website. These were just fine. I tried two OALs using 18 grains over a 165 gr Lasercast, and the shorter OAL gave me a nice 1" or so group.

So I think it does come down to powder. One thing, about a week before this I tried the SR 4759 in .357 with 180's. I got a great group, and it was pretty warm out then. I'll have to try some more of those in the heat. But it looks like the SR 4759 is temperature sensitive, at least in the rifle case.

Cool, I am glad you got it figured out. Thanks for sharing.

[Griff]

Thanks for the update. FWIW, 4759 is not noted for fine performance in the .30-30. My best results over a wide range of conditions have been w/RE-7, 3031, 4320 and 5744. I read & know guys that swear by BL/C(2) & 748. 4064 is also a good powder for this caliber.

If I may, IMR SR-4759: "This bulky handgun powder works great in the magnums, but really shines as a reduced load propellant for rifle cartridges. It's large grain size gives good loading density for reduced loads, enhancing velocity uniformit." My feeling is that you're pushing your loads too fast for this powder, it might be a great performer in the <1400fps range w/plain base cast bullets.

[HEAD0001]

I may be wrong but I find it very difficult to believe that a powder only difference would open up a group from 1" to 1' at 25 yards. IMO there is something else wrong.

You said you were shooting cast bullets?? Then why would you be cleaning out copper fouling after you shot cast bullets?? It has been my experience that it is very bad for accuracy to mix cast and jacketed bullets. This could be part of your problem. Tom.

[Hobie]

It doesn't surprise me, any combination of factors could be affected such that it would seem it is the powder. With temps at 104* instead of 60* and a powder charge that already propels the bullets at their limits, popping up another 100 fps could indeed destroy grouping. It could be that another bullet design of the same weight with more lube, or less (or diferent) bore contact could handle it. Just as all the variables can work in concert to give sub 1" groups at 100 yards, so can they combine to give abysmal accuracy in a particular firearm.