Range Report Factory Ammo: Velocity and Consistency

[chawk]

I shot some .308 FGMM 175gr and Black Hills Match 175gr across my chronograph this weekend. It was 45* and 55% humidity.

The Black Hills had an average velocity of 2578 fps and an extreme spread of 122 fps (high velocity 2618, low velocity 2496). The FGMM average velocity was 2610 fps with an extreme spread of 41 fps (high velocity 2629, low velocity 2588).

According to JBM, at 1000 yds the velocity variations I experienced with the BH 175's will translate into a 50" vertical difference in POI. The FGMM will have about a 16" impact difference between high and low velocity rounds.

For those of you that have done similar tests, do these results seem typical? Thanks.

 

[Lindy]

Re: Factory Ammo: Velocity and Consistency

At those temperatures, the velocities from those tests are about what I'd expect from those loads. In addition, at lower temperatures like that, your SD and your ES are both going to be higher than at, say 75 degrees.

Standard deviation of the muzzle velocity is a more useful metric than ES, which is of questionable utility. To see why, read Chronograph Statistics for Shooters.

 

[chawk]

Re: Factory Ammo: Velocity and Consistency

Thanks for the input. I forgot to mention, this is from a 20" barrel.

SD for the BH was 45fps and for the FGMM 11fps.

 

[Mo_Zam_Beek]

Re: Factory Ammo: Velocity and Consistency

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">
Standard deviation of the muzzle velocity is a more useful metric than ES, which is of questionable utility. To see why, read Chronograph Statistics for Shooters.
</div></div>


Good read.

While I only fired 10 of Fed GM the other day here is what I got out of a 22" Rock Creek, chrono 10', temp 56 degrees, 65% RH, 29.6" Hg.

<span style="text-decoration: underline">Federal Gold Medal Match</span>

10 round group = 0.879" or 0.839 MOA
2618 av velocity
SD = 15.53
ES = 41

Good luck

 

[chawk]

Re: Factory Ammo: Velocity and Consistency

Mo Zam Beek, Thanks for the information. It looks like your data is VERY close to mine.

 

[ChadTRG42]

Re: Factory Ammo: Velocity and Consistency

Wow! 41 fps and 122 fps! That's huge!! I finished a load work up on a 6.5x47 this weekend, and the ES was 2! Yes, 2 fps.
When doing a load work up, the loads that don't shoot so well run about 30-40 fps ES. The one's that shoot well normally run about 7-20 fps ES. If I planned to shoot longer ranges and didn't hand load, I think this would convince me to.

 

[chawk]

Re: Factory Ammo: Velocity and Consistency

How much brass prep (or sorting) is required to get velocities that consistent? Seems to me that case capacity variations alone could easily account for more then 20fps differences.

Thanks for your input.

 

[ChadTRG42]

Re: Factory Ammo: Velocity and Consistency

Not much, really. On new brass, I'll run the case up to kiss the expander ball to round out the neck. Then I'll chamfer the inside neck, prime and load. Keep the seating depth the same and consistant, and make consistant powder charges. If you have a round that the bullet seats very hard or too easy, mark it and use it as a fouler. When you find a good load, it all comes together. I use the chrono just as much (or more) as looking at group size when testing a load.

 

[chawk]

Re: Factory Ammo: Velocity and Consistency

That's impressive results you're getting. My only experience hand loading was years back for my 22-250, 25.06 and 7mmRM, although I never did achieve any more consistency then what the FGMM showed. I wish I had the opportunity to hand load now, but with two young boys i don't have the time to spend on it, or even a place to do it anymore.