The mini has a reputation for being problematical I agree but I have also seen a couple brought to Camp Perry and shot and I have heard of them getting down into the MOA range. I don't know any of the match gunsmiths that ever did any work on them like they did with M14/M1As.
I do know they were submitted to a 10,000 system life requirement at the factory.
I also know the M14 as it came from the govt lines had the worst accuracy we ever fielded on a gov't weapon. The match gunsmiths were given a free hand and now when they are worked over are capable of fine accuracy.
What propellants are you running? In our experience ball propellants are very rough on barrels which was proven time and again at Aberdeen PG.
The ammo companies love to use ball propellant as it meters quickly and uniformly in the loading machines.
When the M16A1E1 was submitted to Aberdeen PG by the Marine Corps for Technical Feasibility Testing utilizing FN made SS109 62 grain bullets loaded with WCC846 propellant the initial requirement was 12,000 round barrel life.
At the 4800 round point the barrels were right at rejection, at 6000 round point they could not be printed on a target 8 feet wide and 12 feet high beyond 600 meters and the group was about that size at 600 meters. Testing was halted and a conference was held with three recommendations:
1. Retest another three rifles the same way, this delivered same results.
2. Retest another three rifles with M193 ammo, similar results.
3. Retest another three rifles with genuine SS109 ammo loaded by FN. Barrels were right at rejection at 12,000 rounds. This was not a select lot but pulled down machinegun lot ammo. We got in 100,000 rounds and had to hand delink it.
The SS109 was the finest ball ammo I ever tested.
We ran 10,000 rounds a day for 14 straight days.
The XM855 ammo was terrible and was really rough on barrels and removed most of the chrome lining about three inches forward of the chamber.
We tested at 1200 round intervals. At 1200 rounds very little change, at 2400 rounds a little larger, at 3600 rounds much larger and at 4800 rounds there were going down but just barely in spec. Rejection was 7.2" at 100 yards and they were shooting 7".
Just remembered it was noted we got fliers out at 9 o'clock about the time the barrels were starting to open. If I remember correctly that started at 3600 rounds.
Unfortunately you can't get a borescope in you barrel for a close looksee but it would be interesting to run handloads loaded with Varget, 4895, and see what kind of differences you are getting. Oh yes you will want to be loading bullets without a cannelure.