7prc Why am I so fast??

[camelcluch]

I have a 7prc built on a terminus action and a 20” proof barrel with 5” tb (thank you @RyanAvery ). There are about 120 shots through the tube. I have some federal eldx factory loads and hand loads with eldm’s. My barrel has constantly sped up each time I went out. My hand loads were about 2815 and the federal was about 2850 the first time I shot. The last time I shot I was up to 2940 with both loads and had heavy bolt lift. My loads are mild and using N560. Any ideas on this or what may have happened? The speeds are about the same with or without the can. The barrel was cleaned and scoped before the last time I shot. Again, 20” barrel with 5” tb.

 

[Benchrest Braxton]

borescope? I'd check for a carbon ring. Unless you are specifically cleaning for it, usually just the regular cleaning of the bore won't hit it.

I usually go at it with a one caliber oversized nylon brush on a fixed cleaning rod, use whatever flavor carbon solvent you want. Sometimes they can be a pita to get rid of.

Also, make sure your chamber is dry, flush with alcohol well, and patch out. Then preferably if you can, shove some compressed air or an electronic keyboard cleaner down the chamber to make sure everything is bone dry.

 

[nw nm hunter]

Once i don't think i got the chamber completely dry after cleaning and caused similar pressure spikes. But as said above double check for a carbon ring, I use a .338 bronze brush in the throat when cleaning as the 7mm brush doesn't get it out.

 

[camelcluch]

It was cleaned and scoped. Went to the range clean and no ring.

 

[Gulogulo]

Did you start with virgin brass then reload those cases?

 

[wind gypsy]

Got me stumped.. Maybe a tight bore but i dont know why you wouldn't have had pressure before break in if that were the case?

 

[Kimber7man]

What is your N560 load?

 

[benz1978]

Are you resizing brass? Are you taking measurements on resized brass? Measuring seating depth? Case capacity changes (from resizing or bullet seating) can impact pressure / velo in a hurry.

 

[Dave Thomas]

If you're having a heavy bolt lift, you are over pressure.

 

[Pilsner]

Unrelated to 7 PRC but my wife askes me that same question...
I'll see myself out now.

 

[camelcluch]

Sorry I was out for a bit. I started with ADG brass and it has been twice. My smith checked the head spacing and all measurements. You can eat off the barrel it’s so clean.
I reshot and still at 2900+ so I’ll rework the load but the gun did shoot better and I got my accuracy back. It’s not perfect yet but I think I’m close. The gun is way better than me so I’ll keep working at it.