Power Pro Varmint weirdness

[LRRPF52]

Hello all, I've been lurking for quite a while, finally have something to post!

Inspired by Mel's recent trials of PPV I decided to give it another go. The only bullets I really have available at this time are 130eldm so that's what I'm using. I was velocity testing today, looking for pressure, and had a .6gr spread towards the top end where the velocity completely went flat. This doesnt make any sense to me, primers are rounded, no ejector swipes, etc.. Has anybody run into this before?

I'm shooting a 24" Liberty (yes I know) Grendel II (yes I know) chamber.
2.33" OAL
Starline brass
FED 205

Rifle is set up as a straight pull bolt, it's very easy on brass and I dont have any issues with the softer primers.

Charge weights are WAY over max, but again my OAL is long, as is the throat.

29.8- 2611
29.9- 2600
30.0- 2613
30.1- 2613
30.2- 2611
30.3- 2611
30.4- 2623 - very slight ejector swipe, stopped there.

There's nothing odd about seeing a flat spread when the charge weights aren't that different. You loaded up the ladder in .1gr increments, which won't show much resolution at all, as you confirmed.

Variance in case internal volume plus neck tension will have more of an effect on velocity than the spread of .1 gr increments you loaded.

Looking at Sierra's data for 130gr TMK, they show 28.5gr as the max load with that powder and a 2.260" COL, with 2450fps max speed from a 24" barrel.

You're loading to almost 2 grains over that with a longer COL at 2.330" and getting consistency over 2600fps.

Without pressure trace data, it's hard to say what chamber pressures you're reaching, but it's common to see a peak and a dip as excessive pressure signs in a rifle.

The SAAMI spec for Grendel brass max yield is 60,000psi, which is meant to be a factor of safety over the 50,000psi working pressure.

We don't want to get anywhere near that if we care about case life and case failures.

There's probably a general rule you can follow about longer throats and COLs equating to certain % of pressure reduction, which can then be filled with more charge weight to get back up to the Maximum Average Pressure listed by SAAMI. Does it allow an additional 2 full grains of powder in your case?

I think you've gone past that point, so I would be happy with the mid-29.x charge weight range and not tempt things beyond that.

Anything over 2500fps with a 130gr in a Grendel is normally in max pressure territory or beyond, but PPV seems to be one of the few powders to do that with.

I can't really give much advice in the absence of calibrating that chamber with pressure trace equipment, but I suspect you're well over 55,000psi, probably into or over 58,000psi.

AR15 bolt lugs and barrel extension teeth with wider cartridges than 5.56 will not do well with charges over 55,000psi. If you look at the .30 Remington AR, they used an AR10 bolt head diameter, but still with AR15-length lugs and teeth. It was limited to 55,000psi per SAAMI still when Remington submitted it, because they did extensive pressure testing and engineering analysis of the pressure containment components for the R-15 in 30 RAR.

I've gone close to your speeds with 129gr in a 22" Howa bolt gun using a 2.310" COL:

129gr SST
Lapua brass 1.215" headspace to datum
Rem 7 1/2 SRP
LEVERevolution
COL: 2.310"
60?F

Left string was shot first, then the right one
29.3 2370 2407
29.6 2393 2400
29.9 2448 2405
30.2 2453 2404
30.5 2504 2453
30.8 Error 2475
31.1 2485 2512
31.4 2530 2523
31.7 2534 2545
32.0 2572 2572

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