Question regarding pressure signs/powder charge

[Bassnbow]

I have a relatively new Tikka 7 PRC rifle with a 22" Proof barrel with 110 rounds through it while fire forming brass. I just started load development and am testing Berger 175 Elite Hunter bullets. I contacted Berger for load data and they sent their data sheet for that bullet. Finally got out this morning to shoot my first ladder test using H1000. My brass is once fired Petterson and I'm using Federal Match Mag primers. The Load data Berger sent me was for a 26" barrel and their MAX load listed was 70.6 grains which produced 2973 max velocity. I purposely kept my max load at 69.8 grains and my ladder was done with .3 increments. At 68.9 grains I went over their max listed velocity and mine was 2989 with no signs of pressure. At 69.2 I was at 3003 and still no sign of pressure. 69.5 was 2996 and 69.8 was 3003, but both had very slight pressure signs with a slight bolt lift and very slight shiny spot on base.

I know I'm at pressure with their listed velocity and the signs I'm seeing, but I'm not sure if the pressure will increase or decrease with the brass now that it has been fired twice and likely fully formed. When I sized the once fired brass I purposely did not bump the shoulder back because I knew it was not fully formed yet. I used a #10 Redding Competition shell holder and it didn't move the shoulder at all. Fortunately I did locate a couple of promising nodes to explore in the mid 2850 range, but very curious about what would occur with the brass now that fully formed, will it speed up or slow down?

I do have two other strings to run, one with RL26 and the other H4831sc, so not sure if I might run into early pressure there also? Obviously very surprised with velocity with the 22" barrel. Please advise on your thoughts

 

[PddPdd]

During the forming of the brass the brass case will absorb some of the energy in the process of deforming to your chamber/bolt. After it is fully formed, that energy will not be diminished and should give you higher velocities and more pressure so you may want to back off a little instead of using the same load that was near max during fire forming.

 

[cajun]

So your getting more velocity with a 4" shorter barrel sign number one. Sign number 2 your adding powder but the velocity is not going up. Brass doesnt show pressure signs till around 70K. Peterson is tough brass with less internal volume so it takes less powder to get max velocity. With a 22" barrel you should be 2875-2900. PS Berger uses quickload for data. Get someone to run it with 22" barrel.

 

[Phil Rizzo]

Your rifle will be the judge, but it may prefer standard LR primers over Mags.
I generally try whichever I have the most of, first.
Unlike the H powders you listed, R26 has a tendency to pressure spike above 80-85 degrees. It may not cause a dangerous condition but will likely raise pressure enough to degrade precision. Learned it firsthand in my 7PRC last summer.
Good luck with it.
I'm using and liking Peterson also.

 

[MagnumManiac]

Apart from velocity differences, you have already reached the point of slight sticky bolt lift. This is a pure sign that safe pressure has been surpassed. I would not do anything else other than dropping that load by 2 grains and call that maximum. Work below that point to be safe. Sticky bolt lift is stressing your action…

Cheers.

 

[Bassnbow]

Thanks everyone for your replies/insight, that is exactly what I needed to hear. I will definitely back way off.

 

[Bassnbow]

Apart from velocity differences, you have already reached the point of slight sticky bolt lift. This is a pure sign that safe pressure has been surpassed. I would not do anything else other than dropping that load by 2 grains and call that maximum. Work below that point to be safe. Sticky bolt lift is stressing your action…

Cheers.

Thanks that is what I will do!

 

[Bob Wright]

That's a pretty decent speed for the H1000. Interesting to see RE26. In my experience the Reloder 23 powder will outrun the H powders and most of the loads in Reloder 23 could be slightly compressed loads. It just seems to have a flatter burn/pressure curve than Hodgdon and easier to find wider nodes. Never hit a pressure sign in a few of the rifles I have done. These 2 were compressed and stopped in that node.

 

[Phil Rizzo]

If you can find some that is…..
I've had good experience with it also in 2-3 rifles.

 

[WYMIKE]

I did not see what the accuracy was on any tests (i like 200 yards and 600 yards). Could bullet seating depth be an issue.?? VV N565 and VV N568 could be good powders to try. Stick with FED-215M primers.

 

[tracybartlein]

You guys have to keep in mind... just because you don't see pressure signs on the brass or heavy bolt lift etc... doesn't mean that your ammo isn't over pressure!

Ammo can easily go over pressure and you not see the signs any where.

I won't say the caliber but this is a good example. I was able to get brass and build a rifle in a spec caliber where it wasn't production made available yet to the public.

I worked up loads and did my testing like normal.

Because and only because we make the ammunition test barrels for different manufacturers I asked the one place that if I sent them some of my ammo and the next time at they're convenience when they have the p&v barrel set up again for this caliber would they run some of my ammo thru the test barrel for me? They said yes sure. Send it in and will all the load data and lot numbers of the components.

Per they're data and actual released loading data which came out about the same time... my one load at a .5gr over they're max load they recommended in the book my pressure was 5k psi over maximum recommended. My next load was 2gr more of a heavier powder charge and that bumped the pressure another 10psi but in my gun I had no pressure signs at all. So again just because you don't see any pressure signs doesn't mean that you have not exceeded the max pressure.

Later, Frank
Bartlein Barrels

 

[memtb]

Unlike the H powders you listed, R26 has a tendency to pressure spike above 80-85 degrees

While I'm not using R26 in my cartridge, potential temperature spikes is the primary reason that I only do load development on hot (90+ F) days.

While not a perfect solution, as the much cooler hunting season temperatures will reduce mv's and alter the group size findings. So now, the velocities/groups must be verified, and re-zero'd on a day replicating expected hunting season temperatures!

It does add a degree of difficulty and lengthens the process….but gives comfort that if shot on a hot day, you won't run into an excessive pressure situation! memtb

 

[Okanogan]

My experience with Berger load data is it tends to be very hot. (Same for Alliant load data) In general, I've found Hornady to be more in line with what I end up achieving, even though I might not reach the max velocity they publish. The current manual doesn't have 7 PRC data but their app does. For 7 PRC 175 ELDX they list max loads RE26 67.1/ 3000, H1000 67.1 / 2950, H4831SC 63.9/ 2950. The velocities are for a 24" barrel.
I've been working on load development for a 7 PRC Havak Element with a 22" barrel and a TBAC suppressor. I have been working with 175 ELDX, 175 EH, and 195 EH and Federal Premium 175 ELDX factory ammo. The Garmin Xero C1 makes it so easy, I've chrongraphed everything. I've been using both ADG and Peterson brass and have tried CCI250, F215M, F210M primers. I'm closing in on 250 rounds fired so far but am still working with virgin brass.
As others have pointed out, I suspect your posted loads were likely over pressure. I haven't seen any signs of pressure with my ADG or Peterson brass for the 7 PRC even when I exceeded Hornaday's max (but not nearly as high as you list). I worked up slow with all my powders and generally saw my ES/SD and group size get worse once I passed above Hornady's max loads. My best results for the 175 EH were close to the velocity range @cajun mentioned above 2860-2910 fps, using RL26.

Here are a few of my observations from the data I recorded which may or may not help in your efforts:

• 175 ELDX tended to be about 50 fps faster than 175 EH for the same charge
• F210M and CCI250 gave me similar results while F215M tended to give +30 fps higher
• the factory Federal ammunition gave me 2880 fps on average
• 175 EH, 180 Hybrid and 195 EH all had with-in a few thousand max COAL to the lands in my rifle and jumping them about 0.050 has given me the best results

Good luck with your Tikka and load development efforts.

 

[Shane Lindsey]

How did 69.8 shoot? Going from the lower node to the higher node will give you enough velocity to matter.

Going from 1gr difference doesn't give you enough velocity (especially down range that an animal is going to notice)to justify going higher pressure and trashing brass. If you can't get there, move 100 yards closer.