Chronographing the right way

[getitdone1]

I'm new to the chronograph and therefore could use some input.

Have a cheapy Pact that's new and just got it set-up. Very easy.

Have some concern about not blowing it away when using my high X scope along with .243 ctg. Best I can come up with is to bore sight it through the "uprights" and check scope picture at same time. Then, when shooting get same scope picture at same height. Directions say place chronograph 8 feet from muzzle of gun.

I have measured the distance between front and back of chronograph and it's 24" even, center to center--as per directions. I know this is critical if one is to obtain accurate readings.

Here's an important question:

What factory cartridges are very close in velocity to the reading I should get on my chronograph? My point is to use such cartridges to check the accuracy of my chronograph. I'm aware I must allow for barrel length and large, small or average sized chamber.

Instructions say the chronograph should vary no more than .5 more or less from actual velocity.

Is it alright to tape a sheet of paper fore and aft to chronograph with little bullseye on front one and after shot know exactly where bullet went through chronograph? My fast 55 gr bullets won't explode on this paper, will they? Guessing my MV about 3800 fps. If they did, to any degree at all could damage chronograph.

Don McCullough

[cutter]

Step number one- Don't shoot it. Trust me.


Note to self, the barrel on an AR is a lot lower than the sights.....

[bj94]

Be aware of where the bore line is, take care when setting up and don't get in a hurry, you'll do fine.

As for a "test", I've wondered the same thing. Seems that a .22LR would be a good test.

[Ram Hammer]

What factory cartridges are very close in velocity to the reading I should get on my chronograph? My point is to use such cartridges to check the accuracy of my chronograph. I'm aware I must allow for barrel length and large, small or average sized chamber.

Remember that every rifle shoots ammo to a slightly different velocity. I have Remington and Browning 30.06's with the same lenght barrels that shoot 100 fps different. But you are on the right track. Remember that factory ammo is loaded to a particular pressure. The velocity you achieve with factory ammo is an indicator of what you might achieve with a similar weight and type of bullet through handloading while maintaining safe pressures. I always use factory ammo when cronographing a new rifle for the first time and use that as a reference when handloading.

[Old Savage]

Can't really count on any factory ammo to be a gauge. When mine goes low battery it makes large errors in the hundreds of fps. I did have one that didn't have the elements aligned correctly (a chrony). It was consistently low. When that was corrected it worked alright.

[Don McDowell]

Don if you set your chrono on a tripod, and then adjust the height of the chrono to around 3 or so inches lower than the muzzle of the gun as it sits on the rest on your shooting bench will help a bunch.
Other wise just try and look down the side of the barrel to get things lined up.

I set my chrono up 15 ft from the muzzle to keep the false readings from muzzle blast to a minimum.
Don't count on centerfire rifle ammo to match factory numbers, it's the rare bird that'll match up. Some will be higher, some lower.
22 lr ammo is fairly consistent so firing a few rounds of that over the screens is a decent way to check if you're concerned about the accuracy of the chrono readings.

[Grizz]

I think you can use a .22 to benchmark the chrono. It will tell you when the battery is low and it's bleeding off speed. I think.

Grizz

[cas]

Tip #2. Don't store it in the trunk of your car year round.

[TedH]

Having mine too close to the muzzle has caused more errors than anything else. The bigger the gun the farther away it needs to be. Small handguns can be only a few feet away and do fine. My 338 Win Mag needs to be a minimum of 16 feet away to keep accurate readings.

[getitdone1]

How have some of you determined, for sure, that your chronograph gives accurate readings?

I need full confidence in the chronograph to make my time and effort meaningful.

I do believe the directions that came with this Pact chronograph are correct (hey, they are the experts)when they say it is capable of being within .5--that's 5/10 of 1%. That's pretty accurate and even more than I would expect.

A good battery and very accurate 24" between chronograph "windows" and I'm pretty confident the readings will be very close to actual fps.

Thanks for the tip about distance from muzzle to chronograph with various guns. I know muzzle blast can cause problems when too close.

I expect the only way to know for sure about the accuracy of my chronograph would be to compare it, side by side, with a PROVEN, second chronograph.

An in the ball park method would be to shoot factory loads--many at least--and subtract about 200 fps. I have read that a few factory centerfire rifle loads have fps close to actual. Which ones?

Don McCullough

[Dakota7]

I have used a PACT for a few years, no complaints. I wouldn't get too hung up on compairing it to factory rounds and what they say their velocity is supposed to be. No two guns will shoot the same ammo at the same vel. Too many other variables, barrel length, bore size and condition, temperature etc. In my experience it has been pretty usefull to compare my loads to some of my other loads. For the most part when your extreme spread is small the group size will be small also. Not always but most of the time.

[J Miller]

Question from someone else who don't know:

Since you have to set the chronograph away from the barrel to avoid false readings, how do you correct the reading to get the actual muzzle velocity?

Joe

[Dakota7]

Everybody gets too hung up on velocity. Chronograph are good for developing uniform loads. "Actual velocity" doesn't really matter. I have played the velocity game with all kinds of Ackley Improved stuff and it was a lot of fun but hard on barrels. In my experience, my best groups have showed up some where close to 2800 fps.
Since I started shooting BPCR, the chrono has been the most useful for developing uniform loads. I have developed some of my most uniform, best grouping loads using blackpowder. I would have never beleived that back in my Ackleyize era.

[Bronco]

Hey JM
There are a lot of ballistic programs free on the internet. In them they will have you imput the distance from muzzle that the crono is. They will give the MV.
John