How I ruined a good gun--is their hope?
A year and a half ago I bought a DPMS LR-30 .300 RSAUM and mounted on it an IOR scope. I was very impressed with its ability. It shot everything pretty well, factory loads grouped 1.25-1.5 @ 100yds, hand loads grouped such as 178 A-max/varget and 200 GK/R22 grouped .5-.75 inch @ 100 yds and sub MOA @ 300 yds. I tried lots of different loads and found the previously mentioned ones to be the best; nothing under 178 gr shot well, probably due to the 1-10 twist, not everything above that shot well either, but wasnít horrible. After spending a couple months grouping on paper, I moved to just shooting 1000yds and had great success. On good days with little wind I could typically keep it on a 12Ē gong 7/10 shots. I played around with different loads, upping powder and trying some Berger 190 VLDs and didnít find much improvement. After some time (~500 rounds) it seemed that my accuracy was slipping (I remember coming across a forum where someone mentioned taking this same gun to a competition and found that the gun shot great the first half of the day and horrible the last half, this could be any number of factors however.) Rather than putting it on paper again to confirm changes in accuracy, I just decided to get it barrel frozen (easier to clean, better groups, longer life?) and after it came back I decided to have a brake installed to improve the time needed for follow up shots, though the recoil wasnít bad to begin with (like a 12 gauge).
The first tests after getting it back from the gun smith were in the moonlight, and I did have some ok groups and was on target, but was taking it for granted because of the light conditions. The brake works wonderfully, however it did destroy the speaker on my M2 chrono. I have put about a hundred rounds through it since getting the work done and it wonít group my old favorites like it used to; 178 A-max group @ 1-1.3Ē, 200 gk group @ 1-2Ē. Before, I would get a vertical dispersion of groups (the actual group did not disperse vertically) between different loads, all remaining centerline of target, or close to, now some loads group high right, others low left, etc. I have had best groups with 185 Lapua scenars, some sub-MOA, but they are high and to the right of the 178ís. The 200 g are also high right with H4831 and high left R22. There also seems to be no correlation between group size and velocity S.D. Before having the work done I never had to touch my knobs, now I find myself playing with them trying to get everything somewhat centered.
Obviously the harmonics of my barrel have changed considerably for the worse. Before shooting it, the gunsmith told me his experience with cryo solved the problem of flyers, but opened up the overall group. I donít know what the major causal factor here is; cryo or brake. I am going to continue to try and tune some loads, and once I find a one that is acceptable I will try turning the brake out Ĺ turn at a time to see if it tightens things up. This is getting to be a really expensive waste of time and bullets.
The moral of the storyóif it ainít broke, donít fix it.
If anyone has any suggestions, please advise.