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How I ruined a good gun--is their hope?

 
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  #1  
Old 02-28-2008, 12:15 PM
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Join Date: Feb 2008
Location: Cedar City, Utah
Posts: 21
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.
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  #2  
Old 02-28-2008, 12:44 PM
Silver Member
 
Join Date: Jul 2007
Location: SW Wisconsin
Posts: 216
I had very close to the same experience on the first rifle I ever barreled. I started out with a new Shilen select match unturned blank in 7mm. I made up a 280 AI and turned down the barrel contour on the lathe as I wanted to do 'eveything' for my own education. Well as you might imagine I induced a bit of stress in that barrel and although it shot pretty well (3/4 MOA) it would start to walk a bit after several rounds. I had it cryo'd and that solved the problem of a drifting impact but the 140 and 150 gr bullet I shot out of it no longer grouped better than 1 1/2 MOA. Funny thing is it would take a 110gr (I think that was the one) Sierra and plug them into 1/2 MOA all day long. I even remember getting a little upset at that rifle at the range one day and thought OK, if you like these so well lets see how many of them you can take. I shot 12 or 13 rounds as fast as I could load and get a good shot. That barrel was smoking after that little display of stupidity but the rounds STILL all clustered into less than a 1" ball on target. Haven't shot that rifle in about 5 years, and thinking of rebarreling it to some other caliber.

With your thought of the muzzlebrake, if you plan on loosening the brake, I hope you're planning on using a spacer to butt it up tight on the tenon before shooting it.

I don't think you ruined your rifle, but you did change it's characteristics. You have to just go to a different bullet and play with more loads to see what it likes again.
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  #3  
Old 02-28-2008, 12:59 PM
Junior Member
 
Join Date: Feb 2008
Location: Cedar City, Utah
Posts: 21
Msalm, thanks for letting me know I am not alone. Education can be expensive. I am going to try some lighter bullets, though I like the heavies for elk and their long range performance. I have some 208 A-max on the way (those things are backordered everywhere) hopefully they will do something good. I think the ogive on the A-max lends itself to well to anything using a magazine and limited bullet length. The gun has always liked the A-max.
Thanks for making me realize the need to back up the brake. Anymore problems and I mught have to convert it to full-auto.
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  #4  
Old 02-28-2008, 04:09 PM
Bronze Member
 
Join Date: Feb 2005
Posts: 83
My AR10 shot inconsistantly (sometimes great, sometimes OK, somtimes terrible) until I bedded the upper & lower together. Now it always shoots great.

You can experiment by tying the upper & lower together with several large tie-wraps (pull 'em real tight with pliers) and try it out. If that helps-bed it.
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  #5  
Old 02-28-2008, 09:02 PM
Silver Member
 
Join Date: Jan 2008
Posts: 399
.dpms

This may not be your problem but its easy to check. Check your gas block, the set screws have a nasty habit loosening off. Mine has done this a couple of times and it will screw with the groups. When you tighten it make sure everything is lined up right.
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  #6  
Old 02-28-2008, 10:27 PM
Junior Member
 
Join Date: Feb 2008
Location: Cedar City, Utah
Posts: 21
things are looking better

I just got back from shooting and I am feeling better. Apparently the gun no longer likes any of itís old loads. It hates the 178 A-max and 200 GK with any powder combo, but I have been able to get down to ĺĒ with 185 scenars and 190 MK. It absolutely will not shoot anything with H4350, still loves varget and seems ok with 4831. I like the varget and have been getting single digit S.D. on velocity with most loads.

But I think the key is what DougH9 suggested. It totally made sense after putting more thought into it. The gun seemed to be losing accuracy before the work was done, but I didnít confirm it on paper. I had installed a little rubber thingy that I got from DPMS to tighten up the upper and lower assemblies since it loosened up over time. However, after I thought about it for a minute I realize that this thing could be causing some serious problems. It pushes the upper and lower apart in order to remove slack, but during firing this thingy is likely going to compress and could cause problems. light bulb Combine that with the fact it doesnít like the old loads anymore and I was in panic mode. So I chucked it, and replaced it with pieces of feeler gauge between the upper receiver just above the rear tack down pin. Tacked them in place with a little (very little) silicon. No more slop.

I think everything is going to be ok and the world is a better place now.

So thanks Doug, I think that little tidbit is what did the most good.
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  #7  
Old 02-29-2008, 09:11 PM
Silver Member
 
Join Date: Jan 2007
Location: Ohio
Posts: 163
This might be a silly question, but did you try seating your bullets out alittle??? .015 or .020 out might help too.
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