Range Report HELP! Fgmm powder temperature/velocity

[Crittermenot]

Truly dumb-founded here.

Fired 10 Rounds today to add data to my powder temp/velocity variation chart I started recently.
Case temps were 69 deg, averaged 2563 fps.

This is only the second time that I've gathered data for this chart, and what blows my mind is that the last time I went out, average case temperature was about 80 degrees, and the average velocity was 2652.

100 fps difference? I dont get it.

Same rifle, fouled bore, same chrono, 10ft from muzzle both times. Same ammo lot. I allowed the cartridges to adjust to ambient temperature for at least 10 minutes and verified with an ir thermometer.

What process do you guys use to cover all the variables and controls?
What kind of powder temp variations are you guys seeing with gold medal match 175's?

 

[ShtrRdy]

From what I've read the powder used in the .308 FGMM is IMR. That's not intended to be a temperature insensitive powder.

Also, I wonder if waiting 10 minutes is long enough to get the interior temperature to what you want.

 

[tnichols]

My experience has been that FGMM is very consistent MV wise in quite a wide range of temps. Now, I'm not chronoing to verify this, but I'm going off of results downrange. I typically shoot in temps ranging from 0 up to 75 degrees and the MV isn't varying by more than 10 fps give or take. 100 fps seems like a huge MV spread and I would guess there are other factors at play here.

 

[woodlandshooter]

Did someone mix in some 168's

 

[Greg Langelius *]

I am minded that this exercise appears to be intended as a foundation to predicting first shot precision. Twenty-some years of effort to determine whether that's occurring as part of my regular shooting regimen seems to indicate to me that this is not really a very valid goal.

I do not try to get first round perfection. IMHO, I think that for me, spotters are essential. They deliver real world performance verification, and prove, once again, that the only real indicator of performance, predictable or not, is the actual target.

This entire subject is recently covered in LL's topic about how yesterday's zero is not today's zero.

Where factory ammo is concerned, I have long considered FGMM, however fallible, to be the cream of the factory crop; and have been hard pressed to equal, let alone exceed, its performance with my handloads. I flatly refuse to look this particular gift horse in the teeth.

i have genuine trouble understanding how they can achieve such great performance out of an automated production line. If I had to make a guess at how it's done, I would have to think it's somewhere in charge weigh regulation and the way they manage neck tension.

I have managed to obtain and shoot a true clone recipe of FGMM 30-06/168 match, and find it to shoot remarkably well in my rifles. But nothing I do, with even that recipe, exceeds the performance of the real deal (but I may try neck lube next...).

Greg

 

[ShtrRdy]

Hey Greg -- when I first started using FGMM in my .308 I found the 168 gr worked best. Just for grins I measured the weight of the completed cartridge. I was amazed at how close the cartridge weights were to each other. I think Federal has put checks in place to make as much the same as possible when constructing the finished cartridges.

 

[Steel head]

I recently tried 260 Remington FGMM.
I was amazed.
SD and ES were not crazy good but certainly acceptable.

I’ve always been a fan of FGMM 69smk 223 ammo.

 

[918v]

Your 100 FPS variance is prolly due to your inaccurate optical chronograph.

 

[vh20]

Your 100 FPS variance is prolly due to your inaccurate optical chronograph.

My guess as well. Lighting conditions seem to affect their results, as well as being nearly impossible to place them exactly the same every time. I'd like to see if you still had the same variance using a MS or LR. Maybe you can borrow one and try again.

I've been through four chronos: Started with a Shooting Chrony. It was so inconsistent I gave up on it. Went to a Pro Chrono Digital. It was a lot better, but still a royal pain to set up (and you have to be very precise with the placement to be consistent - tape measure, and freakish attention to angle of the bullet path through the sensors). Moved to a MS3 and it was a great improvement, but I did experience POI shifts (no big deal) and group size changes (bigger deal - some folks don't but I did), which made it unreliable to use DURING load development, but it worked to check a load after accuracy was determined. Finally went to the LR. I ran it side by side with the MS3 for two 10-shot strings and MVs were never more than 3-4 fps apart from each other, so I trust them both. The LR is easier to set up, and doesn't affect the barrel harmonics, so it is a better choice for me when doing load development. It does have some peculiarities that have to be addressed if using with a suppressor or near other shooters. I just received a recoil-activated trigger for it made by a member here that I am going to test tomorrow. I believe it should eliminate any issues with either of these scenarios.

As tnichols stated, impacts downrange at distance will certainly tell you if you're truly getting that much variance.