Thread: My 7mm PRC is driving me nuts…

Some background:

Tikka action,
Hardy steel barrel 24”, profil similar to a medium Palma. Manson M1 reamer
Shooting suppressed.

Jumped on the new trend early when we only had Hornady brass. Made developing a load nightmare.
Tested H1000, H4831sc and Staball.
Finally found a load grouping well with h4831sc (66.3gn in middle of a 0.8gn nod) adg brass, 180eldm, fiocchi primer, 2990fps. Consistent sub 0.5moa five group shot, sub 0.3moa three group at distance up to 600m. Single digit ES among 20shot.
In short a shooter

I always let barrel cool down every three shot.

At around 400 rounds, it started to throw split group. Consistent 2 in one hole and one 1inch away. Every single group.
So far This is what I checked:
-different stock and chassis
-different action screws torque
-different scope
-different scope ring
-proper clean and bore scope inspected
-shot a new seating depth ladder from 85th to 10th
-shot it without suppressor
-I anneal every time
-not new to reloading

After that I was around 500 ish rounds. Measured throat erosion and it grew 55-60th from new.
Talked with some reloaded who do this for a leaving. That lead me to start questioning the load. Even if I had absolutely zero pressure sign this load was 2.3gn above Hornady book. We ran number on GRT and it is definitely well above max pressure. ADG has a podcast where they warn people their brass is stiffer than most brass and you won’t see usual pressure signs until it is way past max pressure.

So… if you still reading… shot another load ladder and found a nod between 63.6 and 64.2gn, sub Moa but all also grouping two in one hole one around one inch away. 64gn put me at 2900 which is almost bang on what Hornady gives for this charge. This is max book…

Reloaded a few pill and went to the range again. (Scope roughly zeroed as I did one last scope swap to make again sure it was not the scope).
Shot one group of 4 then 2x group of three (making sure barrel cooled down in between)
See the pic below. It is getting interesting when you superpose them. One main group of 4 then 3x separate group of 2 around it.

I’m out of options, two mates are professional reloaders and have worked on hundred of rifle, they said we pretty much tested everything. I’m now at 680rounds. I know it will still be a dead deer at distances but I’m struggling to leave something I can’t explain alone.
Anyone seen this before, could it be the barrel starting throwing shot consistently in different spot….?