Little bit O pressure testing for those who asked

**darkker** · 11-28-2017, 04:30 PM

So in another thread some asked about how pressure testing gets done. I need a little break from what I'm doing, so here is a pretty quick and dirty view of the process we did.

Cast the chamber and take GOOD, careful measurements at various points(stated in the instructions), then take good, careful measurements of the outside diameter of the barrel over the same points of the chamber. Carefully clean and bond the strain gauge to the barrel, looks like this.

Then just basically enter the measured dimensions into the program, follow directions, etc. Been too long ago, so I don't recall the specific calibration used. May have been reference ammo purchased from SAAMI, may have been a particular lot of ammo that discussed with the mfgr. In any case there was some cross-checking of numbers to ensure a reasonable level of accuracy.

So plug-in your strain guage to the cable going to the Pressure Trace, and connect(bluetooth) to your laptop.

Enter your current environs and shoot away!

For a bonus bit of testing we just completed over TurkeyDay, small primer testing.
I've been watching the fervor over Creedmoor brass being offered with small rifle primers. Better ignition, better pressure "handling ability" and various other claims of mystical properties.

I bought some Lapua small primer brass, and some Norma large rifle brass. Did two different loads, 100gr Sierra hp's, loaded with 748; Then 140gr Hornady SP's and IMR 4451. Used Wolf standard large primers, and Wolf Small Rifle Magnum primers. Same jump to lands, same powder charge, same brass for both loads. 748 normally doesn't have any issues in the Creed, but as it is now quite old tech, it will be harder to light than current powders. 4451 because it is the new hotness.
The small mag primers with 748 had terrible hang-fires, and a few rounds that flat didn't ignite. Once we pulled them apart, the primers had in fact ignited, but didn't have enough oomph to ignite the powder charge properly. No issues with the large, and no issues with the 4451.

Interestingly, the burning curves and rifle pressures were statistically the same, even with hang-fires. Also a good visible example why staring at primers don't tell you shyte about actual pressures in your rifle.

Had to block-out the rest of the curve in the above trace, because I didn't have the wire properly secured, and introduced noise, when I drug it across the bags during recoil and ejection..... I know, a DFO...

**Texas10** · 12-01-2017, 12:13 PM

Great post, Darkker and very timely as I just bought some Peterson small primer brass for my 6.5. Always enjoy your informative articles as you provide some very enlightening data backed by instrument based testing (maybe Santa will bring me a pressure test rig...LOL) and I find that refreshing!

I see you used Wolf primers and wonder how they stack up against CCI in your experience? I plan to use the 450's in my new brass.

**Evlshnngns** · 12-01-2017, 01:18 PM

I bought Starline small primer Creedmoor brass and imr4451, I drank the Koolaid.... Care to share how much powder was in the first test shown? And yes I am aware the pressure won't be exactly the same in my rifle with the same bullets, especially with my 140 rdf's.

**darkker** · 12-01-2017, 01:42 PM

Originally Posted by Evlshnngns

1) I bought Starline small primer Creedmoor brass and imr4451, I drank the Koolaid....
2) Care to share how much powder was in the first test shown?
3) And yes I am aware the pressure won't be exactly the same in my rifle with the same bullets, especially with my 140 rdf's.

1 - Nothing wrong with it. Just remember that magical claims outside of a Vegas show, aren't real. They should serve you quite well, keeping an eye on some certain conditions where ignition could be problematic.
2 - In the 4451 test? The short answer is not exactly. I don't have the measurements with me, and I load extruded by volume to keep after the burning curve control. That particular lot was notably different than the load data we had, but was a very accurate node in that particular rifle. Don't quote me, but I *THINK* it would have been roughly 3cc.
3 - RDF's won't have a significantly different pressure/velocity than any other similar shape bullet. I've tested the velocity/pressure claims of Berger, FlatLine, and RDF's because I have a small mountain of them. All are fine and dandy for what they are. But there is no statistical difference between them, in my testing against a classic projectile. The FlatLines were tested against a Pro-Hunter, Same relative jump to lands, same loads, will give you the same velocities and pressures.

Texas10 -
With standard brass and large primers(no small primers tested) I have tested swapping CCI's, Win, Wolf primers. When testing with 140gr bullets with H4350, Superformance, RL-17; you could interchange them and never know the difference. There could be some difference with other combinations, but not in anything I've tested so far.