Thread: Short barreled 7prc

The last time I shot a group next to Phil he did a slightly tighter group than what I did

The Duleys carried out a heap of very thorough testing in 7PRC with different powder & pills and measured actual chamber pressure & velocities. Running 175 - 180 ELDx or Ms and 180gn Bergers they reported 68.5 - 69.5 gn RL26 as max pressure, ie measured at 65k. So I sometimes wonder how accurate the theoretical calculations derived from GRT or QL are ? They certainly provide another sanity check of loads & safe starting points as well as some guide to max pressures but it’s hard to argue against real world hard data.

Originally Posted by chainsaw

The Duleys carried out a heap of very thorough testing in 7PRC with different powder & pills and measured actual chamber pressure & velocities. Running 175 - 180 ELDx or Ms and 180gn Bergers they reported 68.5 - 69.5 gn RL26 as max pressure, ie measured at 65k. So I sometimes wonder how accurate the theoretical calculations derived from GRT or QL are ? They certainly provide another sanity check of loads & safe starting points as well as some guide to max pressures but it’s hard to argue against real world hard data.

How did they measure chamber pressure? From what I have been told if used properly GRT is really accurate

Originally Posted by tibo

How did they measure chamber pressure? From what I have been told if used properly GRT is really accurate

Oehler

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Originally Posted by chainsaw

The Duleys carried out a heap of very thorough testing in 7PRC with different powder & pills and measured actual chamber pressure & velocities. Running 175 - 180 ELDx or Ms and 180gn Bergers they reported 68.5 - 69.5 gn RL26 as max pressure, ie measured at 65k. So I sometimes wonder how accurate the theoretical calculations derived from GRT or QL are ? They certainly provide another sanity check of loads & safe starting points as well as some guide to max pressures but it’s hard to argue against real world hard data.

The Duleys testing is likely for that exact combo a looser chamber will need more pressure, a different batch of powder the same, a different barrel, different batchs or manufacturers of brass, different seating depths the same.

A max load never transfers like for like. What was the Duleys velocity?

I don't trust GRT charges until I true it for that combination is powder cartridge and bullet. Once I do that I can extrapolate. What I do trust is that if GRT says that at X velocity im at pressure and I reach X pressure without pressure signs i shouldn't keep going unless im happy to be running over pressure (which i sometimes am).

Yep, Oehler 43 iirc.
The reported velocities were 2980 fps for 22in bbl & 3050fps for 24in bbl. Their data included several different rifles - factory & custom. Very comprehensive data set. Factory ammo & hand loads (Hornady & ADG brass). And yes there are differences as you’d expect. But the 68.5 gn RL26 load w 180s was reported in several configurations & barrels as max @ 65k psi.

Some interesting reading from Oehler

In fairness that difference is like 5% the Oehlers calibration is pretty critical and any error tends to read low. Regardless its could very well be right. 5% accuracy on GRT is good enough. It not like you hit 65kpsi and it explodes at 66kpsi. Hornady also pressure test and id say to a higher accuracy and have 66 grains as max. Id hypothesize Hornady use a min spec chamber to ensure so wiggle room in practice so the fuleys tests seem within reason being only a smidge higher. There velocity is a bit better but by about the same percentage as max charge weight varies (~4%). If your within a 100fps or so of factory data id feel fine personally and I usually work on 30fps expected lose per inch. I run an 18" 22 creed with 95s at 2980 which grt suggests is right at 65kpsi.

That ohler excerpt is strange really as pressure isnt the case of failure in actions. To actually burst a rifle from pressure you need like 2 or 3 mm wall thickness if I remember the US military testing. And if talking lug strength then you need to know the case head so you can find the bolt thrust as 65kpsi in a 223 is a lot less force than 60kpsi in a 338lapua.

I use grt as a guideline a lot I ignore the powder charge as it often doesn’t line up “sometimes it spot on” so I look at their psi for velocity both my rifles shoot less than max book charge to achieve max book velocity my saum won’t show other signs of pressure until velocity’s way up their but any more than 42 grains of 2208 with 150s and brass takes a hammering

Originally Posted by BRADS

Or just the bark off some totara trees in phils case.

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Why would he do that??? I mean Totara bark tastes terrible!!