I have about 700 rounds through my GD tuned Marauder. It has shot Ok although never as consistent as my neighbor's bone stock 25 Marauder. Mine will shoot very tight for 2 or 3 shots (cloverleaf 3/8" at 25 yards) but a 5 shot group usually has one or two fliers that open the group to 3/4" or 1". Again, I was able to shoot cloverleafs with my neighbor's stock gun. Also getting some variations in POI up to 1/2".
I kept shooting my gun to break it in. It was still doing pretty good, I'm mostly plinking targets at 25 yards that I could hit 19 out of 20 shots. Around 500 shots it started to shoot worse...opening up a bit and some slight shifting of the POI. I decided to clean the barrel for the first time using googone and weedwacker cord. It wasn't too bad, took maybe 10 patches or so. Once done I very lightly lubed my o-ring with a silicone lube and put some gun grease on my bolt.
Cleaning didn't really improve things. I'm shooting tethered and my tank has been in the 2400 - 2000 psi range as I have been noticing the worsening trend. Is it possible the gun just starts to open up a bit in the lower pressure range? I have not had my scuba tank refilled yet so have not been able to compare how well it shoots when I get it back to 3000 psi.
The gun reassembled fine after cleaning. Shroud is symmetric inside the barrel band. No signs of clipping seen. I'm shooting JSB Kings and Benji Domes which have been the best in this gun. Other than getting my tank refilled (of which I am skeptical as my neighbor's shoots fine from 2500 - 1800 psi) what else can I check? I'd call GD but have a real hard time getting ahold of him.