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Posted: 7/28/2008 8:21:13 AM EDT
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Time to re-barrel? I have a Colt M4 upper with a 16” 1in9 chrome-lined Colt barrel in an M4 profile. The barrel is mounted under a medium KAC Free Float RAS. A Trijicon TA-31F ACOG tops off this upper. I have only ever run Q3131a and XM-193 through this rifle, and I would guess the round count to be somewhere in the neighborhood of 7k – 9k. Over the past few months, I have noticed that my groups are starting to really open up, especially as the distance increases. At a match this past weekend, my 200yd groups were a foot + w/ XM-193. Now while I know I have to do my part, I don’t believe my shooting skills have fallen that far, and I can still shoot sub-MOA with my LTR. So I guess my question is this? Is it time to start looking for a new barrel? One of my co-workers suggested giving the barrel a strong scrubbing with copper solvent to ensure that I do not have an excessive buildup of copper. While I admit I have never used a copper solvent in this barrel, I remain skeptical that this could be the source of my problems. Suggestions, Tips, Recommendations, etc…are welcomed. |
As a general rule you should swap to a new barrel when you start to see a significant change in MOA. There could be other issues like a damaged muzzle crown, etc., but trying to use the copper solvent may help. |
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I like Wipe-Out to remove copper. www.eabco.com/WipeOut.htm I would try the following: 1. Make sure the ACOG isn't loose or has other issues. 2. Use a good copper remover. 3. Check the crown. 4. Check throat erosion. 5. Shoot some 100 yard groups from the bench with good hand loads or match quality ammo. If it is still shooting 3+ MOA with good ammo then it is time for a new barrel. |
Yep, all that. |
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I received my KG cleaning supplies, that someone recommended and did a thorough cleaning. I went to the range yesterday and shot groups at 50m, 100m, and 200m; with a box of BH 50gr Amax, a box of BH 69gr SMK, and 50 rds of my reloads with 55gr Hornady FMJBT’s. The results were quite surprising. The lighter the round the better the rifle preformed. At 50m, 5rds each: 50gr Amax = Dime size group 55gr Hornady = Quarter size group 69gr SMK = 3inch group At 100m, 5rds each: 50gr Amax = Quarter size group 55gr Hornady = 2 inch group 69gr SMK = 8 inch + group At 200m, 5rds each: 50gr Amax = 1 inch group 55gr Hornady = 4 inch group 69gr SMK = Only one round out of five on a 10” x 10” target Any thought as to why it still shoots the lightweight 50gr so well, but as the weight increases; the groups start to fall apart? What concerns me is that this rifle used to shoot 55gr FMJBT’s at MOA. I don’t know what has happed to change this. Thanks in advance for your insight… |
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I can't answer why it will no longer shoot heavier bullets but copper fouling can have a HUGE effect on accuracy. Several years back I purchased an HK G3SG-1 from HK-USA. It was a Post-86 Dealer Sample. The rifle had been a weapon used by Germany's GSG-9. It shot minute of manhole cover at 200 yards. I figured the barrel was toast but I'g go ahead and clean it anyway. The first patch using Hoppe's No.9 came out GREEN. I cleaned on that bore off and on for two weeks before I was getting a clean patch. The result 2.5" - 3.0" groups at 200 yards. PursuitSS |
It is a Colt barrel, very clearly marked 1/9. Now I suppose it could possibly have been mismarked at the factory, but seems unlikely. As for the heavier weight rounds, no; all I have ever run through this barrel is Q3131a and XM-193...all 55gr. |
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I have seen high round count barrels shoot lighter bullets better than heavier bullets, that should shoot well for the twist rate. Sadly, with reading your posts, I think your barrel is toast for the heavier rounds, which is should handle well. You may get a few more years just shooting lighter bullets. I think the more you shoot it, the darker the toast will get. It still has a life as a golf ball launcher though. 
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Twists are not always as marked. More like an average range. I've seen them vary quite a bit. Try the jag and ruler method to measure actual twist. You might find you might have a 1/10 twist or less. I have a 16" colt HBAR 1-9 that measures 1/10.3. So, I limit it to light stuff. That is a low round count for a CL barrel to be toast in my opinion. |
I have noted the same thing. A barrel manufacturer should state the guaranteed twist rate. I steer clear of a barrel manufacturer who does not guarantee a twist rate, plus or minus a small amount. I saw a brand-name barrel with various twist rates, such as 1:9 to 1:10 to 1:8, back and forth throughout the barrel.  That was a hoot, and quite an embarrassment (or agitation) to the barrel manufacturer at the SHOT show.
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Thanks for all the feedback...I have already shipped my upper off to be re-barreled with a new Noveske. I don't have any real attachment to the Colt barrel or M4 contour, just happened to get a good deal on it at the time. This just gives me an excuse to upgrade now. Regards, Matthew (m4_a3) |
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