Irregular velocities with 7prc loads

[hunterbob]

I recently built a lightweight 7prc and started trying to work up a load. I am running into some odd velocities and wanted to see if anyone has experienced anything similar.

I am using ADG brass, h1000 powder federal gold medal match large rifle magnum primers and have tried 175 eld-x and 180 ELD-M bullets velocities are measured on a Garmin zero chrono

During my load work ups I am struggling to find any nodes at all and my velocities jump around a lot there have been 2 charge weights that gave decent which were 66.6grns and 67.5 grns after my initial testing I loaded 5 rounds of 66.6, 66.4 and 66.8 grns, the 66.6 grn group gave me an average velocity of 2815fps with and SD in the teens, 66.4 grns was an average of 2790 with a SD in the 20's and 66.8 had an average of 2754 with an SD in the 20's.

That's just an example and I've been seeing similar results across all charge weights if I load up 5 rounds at least 2 of them are 50-200fps different than the rest and it's had me pretty confused.

The other day I tried a few different primers with a load of 67.5grs and was kinda shocked. I loaded 5 rounds each with gold medal match magnums and Remington lrm primers the federals had an SD of 28 the Remington's had an SD of 9. I also loaded 2 rounds at the same charge with white river standard large rifle primers and the SD from those was 1.6, I know 2 shots is not a significant source of data but still definitely worth exploring more.

So it would seem that my rifle doesn't like the powder/primer combo I've been using and just wanted to see if anyone else has ran into something similar with this cartridge.

Just as a note so far every group I've shot with this rifle has been under 1" at 100yds but I haven't got it out to farther distances yet

I would try doing a factory crimp with the Lee factory crimp tool.
It made a big difference for me with 308 .

 

[Johrichal]

I finally got to shoot some more today. Shot 2 10 round groups of the same charge weights 67.5gr h1000 one with white river LRP and one with Rem. Lrmp the results were better and I think I'm on the right track the Remington magnums primers still didn't shoot great but the white river large rifles were good I'd really like to get my SD's into the single digits but an SD of 11 over ten shots is not bad at all. Groups with the WRLRP opened up a bit to right around 1.5" but I'm sure I can tweak my seating depth and get those down where I want them as well. My next step will be to pretty much start over with the WRLRP and do my standard load work up to see if I can find a good node. Thanks for all the help

 

[Dmagna]

Did you run into pressure signs while working up at all?

 

[Dmagna]

I ran into a lot of issues while starting my 7 prc adventure. ADG brass was showing ejector marks with h1000 at the minimum load. I believe it was because the brass might have had some slop in my chamber and the stopped after 2-3 firing. I use N570 now, so far it's the best powder I can find for the cartridge. I run a 180 Berger hybrid at 3050 with no pressure at all. I have also ran a 195 to 3050 with no pressure. Out of a 26" barrel.

 

[Johrichal]

@Dmagna - I got light ejector marks at around 68gr and stopped there this was after the case had at least 2 firings on them. I am running a 20" barrel with a silencerco 36M suppressor. also my primers seem to have a little cratering to them but it is at all charge weights and not bad so im guessing it's just the rifle

 

[sakoluvr]

I appologize if I missed it, how long is the barrel? Your velocity is pretty low.

I am getting 2975 fps with 180 Scenars over 67.0 H1000 and Fed 215M primers. Hornady brass. I do have a 26" Bartlein.

I have ADG on the shelf that I am going to start over with and find pressure with 180 ELD M's

 

[Koots]

I appologize if I missed it, how long is the barrel? Your velocity is pretty low.

I am getting 2975 fps with 180 Scenars over 67.0 H1000 and Fed 215M primers. Hornady brass. I do have a 26" Bartlein.

I have ADG on the shelf that I am going to start over with and find pressure with 180 ELD M's

Dont be scared that on first firing the adg may show ejector marks even at low charge. As said above ADG that I fired needed that first fire form to fit the chamber and grip well

 

[Dmagna]

@Dmagna - I got light ejector marks at around 68gr and stopped there this was after the case had at least 2 firings on them. I am running a 20" barrel with a silencerco 36M suppressor. also my primers seem to have a little cratering to them but it is at all charge weights and not bad so im guessing it's just the rifle

I think your inconsistent SD and ES is due to inconsistent pressure. Increasing powder might help and level out the load. ADG is sometimes weird, also have had the same issue with alpha