View Full Version : Barrel worn out?
I've put about 6500 rounds through my AR in the last three years. Barrel is LMT chrome-lined 14.5", 1/7 twist. It used to shoot 2-3MOA groups @100 yds with 55grn ammo, now rounds are scattering all over the place in about a 8" circle. After cleaning the gun I benched & rested it on sandbags yesterday, and with match grade 69grn ammo got sub-MOA groups. I tried the 55grn again and got flyers all over the place again.
So, is the barrel done & dusted or is there anything that can be done to make it work with lighter bullets? I've still got about 1K rounds of 55grn that I'd prefer to shoot rather than sell to get expensive match grade ammo.
ICANHITHIMMAN
05-14-13, 13:05
I've put about 6500 rounds through my AR in the last three years. Barrel is LMT chrome-lined 14.5", 1/7 twist. It used to shoot 2-3MOA groups @100 yds with 55grn ammo, now rounds are scattering all over the place in about a 8" circle. After cleaning the gun I benched & rested it on sandbags yesterday, and with match grade 69grn ammo got sub-MOA groups. I tried the 55grn again and got flyers all over the place again.
So, is the barrel done & dusted or is there anything that can be done to make it work with lighter bullets? I've still got about 1K rounds of 55grn that I'd prefer to shoot rather than sell to get expensive match grade ammo.
It depends on a lot of things, to tell if its really smoked you need to have the head-space checked. That seams like a very large degradation in accuracy all at once and I think you should check your muzzle crown, if it became damaged during cleaning or whatever, its an easy fix to re do a crown. Also check out the entire weapon and your optic don't just assume its the barrel.
Since its still shooting good with good ammo I would have to think it could be a problem with the lighter cheap ammo. I could be wrong but I would think if its shot out or has a crown issue you would see it with the expensive ammo as well as the cheap stuff?
Heavy Metal
05-14-13, 13:25
Nevermind.
Its not a bench rifle to begin with, just shoot it the way it is suppose to be shot.
Its not a bench rifle to begin with, just shoot it the way it is suppose to be shot.
Yeah. But if it can't hold at least 4 moa with regular 55 grain, forget it.
I can't see the barrel being worn out with that low of a round count... unless those 6500 rounds was only a handful of range trips.. :confused:
Faster twist barrels will wear out faster than a slower twist 1-9 barrels, and who knows how fast he was putting rounds down range. 1-7 barrels prefer heavier bullets anyway.
Heavy Metal
05-14-13, 15:51
Faster twist barrels will wear out faster than a slower twist 1-9 barrels, and who knows how fast he was putting rounds down range. 1-7 barrels prefer heavier bullets anyway.
Not that much faster, only slightly faster.
Sounds like your rifle has probably a normal amount of Throat Erosion( 6,500 rnd's) which would explain why the shorter,( 55gr projectiles ) are producing a larger spread, and the longer projectiles are still producing tighter groups... Less bullet jump to the Rifling of the barrel... At least in theory...
You can probably continue too shoot the 55grainers, if you don't mind the accuracy, or step up to a longer projectile... 62-70grn and see how they perform...
Suwannee Tim
05-14-13, 16:15
My experience with worn out barrels is with 30-06 not 5.56 but here it is: Worn out barrels often, usually shoot stronger bullets better. In the case of 30-06 I have seen several rifles that would not shoot match ammunition worth a shit but would shoot the black tipped armor piercing bullets quite well. The AP bullets were longer and stronger than the usual 150 grain ball projectiles. The thinking was that a stronger bullet got gripped better by worn out rifling than a bullet of softer construction. You may be seeing a comparable situation.
justin_247
05-14-13, 16:59
1. Try the possibly bad ammo in another rifle, preferably as similar to yours as possible, and see how it performs.
2. Check the crown and the headspace of your existing barrel.
That's two folks that have suggested head space. I know that headspace issues can crop up with really long term rifle use, but wouldn't throat erosion occur LONG before that. In conversations with IG and a couple other armorers, they had very few occurrences of rifles having headspace issue before the barrel was worn out. What is worn out headspace? It's got to be totally hosed to not pass a field guage, and very few people have access to a set of guages to measure actual headspace.
I'm betting it's ammo related.
Ned Christiansen
05-14-13, 17:48
I'd be very, very surprised if headspace-due-to-round-count was the issue. I've sectioned several barrels with 20K plus through them and you can still see toolmarks on the shoulder of the chamber. Which is not to say the barrel extension and bolt could not have worn / stretched, but in these cases they had not.
It's the same thing that gets every barrel-- the throat. Some ammo will be more sensitive to it that others.
Same thing I was thinking. Either the throat is worn out, or the ammo is bad. I would definitely run it in another AR to be sure.
I'd be very, very surprised if headspace-due-to-round-count was the issue. I've sectioned several barrels with 20K plus through them and you can still see toolmarks on the shoulder of the chamber. Which is not to say the barrel extension and bolt could not have worn / stretched, but in these cases they had not.
It's the same thing that gets every barrel-- the throat. Some ammo will be more sensitive to it that others.
I had14,000+- a few hundred through my S&W 1/9 twist barrel before I replaced it. It would shoot 3-4" group all day with 55gr ammmo till it hit about 12,000 rounds then it opened up to over 6". I finally broke down and replaced it with a Rainer arms select barrel. Now it shoots 2" and under all day with 55gr and under 1" with BH 75gr match.
At 6,500 rounds, the barrel may not be worn out, yet there may be a combination of Throat Erosion, and Bolt Lug wear to decrease the accuracy of the shorter 55gr projectile... As some have stated not everyone has Head Space Gauges, or Calipers to check the Bolt Lugs...
As the round is fired in the chamber, the Bolt will get pressed back from the pressure, if the Lugs have some wear, in conjunction with Throat erosion, this could cause poor accuracy with the shorter 55gr projectiles, yet not with the slower less pressure, and longer 69 gr match loads...
At this point, if it can be deemed that the throat is indeed the issue, I would compare the cost of replacing the barrel versus selling the 55gr and using heavier loads for the foreseeable future. Given the current ammo situation, it may be more cost effective to replace the barrel.
New 16" barrel and BCG on the way--it was faster than leaving the rifle with the shop, and cheaper than buying more high grade ammo. I'll zero the new barrel with match grade 69grn and try out the 55grn XM193 again. Then the old barrel and BCG will go to the gunsmith for evaluation.
Ned Christiansen
05-15-13, 17:36
Using the ammo it still shoots well, it's gonna at some point go bad like all at once, that is, over a 200-round stretch.... that's my prediction. Not gonna say which 200 rounds...... that would be risky.;). Speaking of chamber throats wearing and causing accuracy issues, I......
<<static sound>>
We interrupt our regular program to pass on this little tidbit from my days with a guy I apprenticed with, who was a benchrest legend (Robert Simonson). A barrel that had proved itself a good grouper, he would shoot it a season or two, and could notice accuracy dropping off (like, 100-yard groups "opening up" to .290"). At that point he would remove it, and sometimes set it back a certain distance (I don't remember, I didn't say I was a good apprentice, but I'd say maybe 1/2"), but sometimes he would cut the chamber end off, crown it, and then thread and chamber the other end! Mind you these were barrels that were uncontoured and untapered-- the outer diameter was the way it was when it came as a blank-- like, 1 1/4" diameter-- they maybe had a light turn to make it concentric to the bore. These were "rail guns": a barrel, an action, a custom-made machine rest and a couple dial indicators.
sometimes he would cut the chamber end off, crown it, and then thread and chamber the other end!
Simply awesome
Would some copper cleaner help?
Alaskapopo
05-15-13, 22:35
Its not a bench rifle to begin with, just shoot it the way it is suppose to be shot.
8 inches at 100 yards is unacceptable for any rifle outside of a musket.
Pat
8 inches at 100 yards is unacceptable for any rifle outside of a musket.
Pat
This one gave me a chuckle...
8" at 100 yards is really far past acceptable accuracy for myself. I wouldn't tell anyone else to live with it either.
MUOTE=hkusp;1643476]I've put about 6500 rounds through my AR in the last three years. Barrel is LMT chrome-lined 14.5", 1/7 twist. It used to shoot 2-3MOA groups @100 yds with 55grn ammo, now rounds are scattering all over the place in about a 8" circle. After cleaning the gun I benched & rested it on sandbags yesterday, and with match grade 69grn ammo got sub-MOA groups. I tried the 55grn again and got flyers all over the place again.
So, is the barrel done & dusted or is there anything that can be done to make it work with lighter bullets? I've still got about 1K rounds of 55grn that I'd prefer to shoot rather than sell to get expensive match grade ammo.[/QUOTE]
My LMT barrel lasted to about 13k rounds before it started keyholing past 200 yards. And thats with shooting 90% Russian bi metal jacketed ammo and plenty of mag dumps.
Id contact LMT and have them take a peek.
Sounds like your rifle has probably a normal amount of Throat Erosion( 6,500 rnd's) which would explain why the shorter,( 55gr projectiles ) are producing a larger spread, and the longer projectiles are still producing tighter groups... Less bullet jump to the Rifling of the barrel... At least in theory...
You can probably continue too shoot the 55grainers, if you don't mind the accuracy, or step up to a longer projectile... 62-70grn and see how they perform...
In my humble first post, I think this is a bingo.
Man.. I have a couple of barrels with way higher round counts and throats so bad you can look into the chamber and see erosion... and they still shoot Hornady 55 FMJs good. :confused:
Man.. I have a couple of barrels with way higher round counts and throats so bad you can look into the chamber and see erosion... and they still shoot Hornady 55 FMJs good. :confused:
Thank you. I mearly meant to add some validity to what seemed a perfectly logical answer. If he actually has this barrel checked over by an excellent gun/barrel smith, then I will become the wiser. I understand that barrels produced along the same line on the same day will often show different accuracy potential and wear characteristics.
Yeah... each barrel is its own animal... and the longer bullet idea makes sense to me. I just haven't seen it first hand.
michael word
05-16-13, 11:36
8 inches at 100 yards is unacceptable for any rifle outside of a musket.
Pat
That would be unacceptable accuracy for me even out of my brown bess musket.
Robb Jensen
05-17-13, 05:30
I'd recommend pulling the flash hider off and cleaning all the carbon out of ii and cleaning the barrels crown. I'd also clean the bore with JB bore paste and then WipeOut-PatchOut copper remover along with their WipeOut-PatchOut accelerator.
I'd recommend pulling the flash hider off and cleaning all the carbon out of ii and cleaning the barrels crown. I'd also clean the bore with JB bore paste and then WipeOut-PatchOut copper remover along with their WipeOut-PatchOut accelerator.
Exactly what I would do. If it is shot out then a very aggressive cleaning cannot hurt it. My bet is that acceptable accuracy returns
Clean the barrel thoroughly before replacing it. Use solvents for removing both copper and powder fouling. I have made a few bad shooting rifles shoot a lot better after a thorough cleaning.
Clean the barrel thoroughly before replacing it. Use solvents for removing both copper and powder fouling. I have made a few bad shooting rifles shoot a lot better after a thorough cleaning.
Yep, cleaned old barrel thoroughly with lots of greenish residue coming out on the patches but still had accuracy issues. Can't take the flash hider off to clean the crown as it's pinned to meet the 16" OAL.
A new barrel from LMT solved all the problems and now it shoots like a laser beam again, even groups well with the 55grn M193.
wtheesfeld
06-04-13, 01:13
Can I have your old barrel :)
IMO likely-hood of issues, at that rd count, with a quality barrel.
1) fouling/obstruction at muzzle device
2) carbon build up IVO throat
3) throat erosion
4) excessive copper build up
Personally, I rarely clean barrels, time better spent on trigger. When I do, prompted by groups opening at 300m is the indicator. 50-100M groups may not show the spin "taking". My priority is carbon, then copper. Then a mag to re-foul.
If one has limited range facilities and pays for ammo your priorities may differ.
I have a krieger barreled, middy, 16.5" recce upper, a few thousand rds through it, never more than a bore snake. 10rds mk262mod1 all touching at 101m last zero verification.
I've put about 6500 rounds through my AR in the last three years. Barrel is LMT chrome-lined 14.5", 1/7 twist. It used to shoot 2-3MOA groups @100 yds with 55grn ammo, now rounds are scattering all over the place in about a 8" circle. After cleaning the gun I benched & rested it on sandbags yesterday, and with match grade 69grn ammo got sub-MOA groups. I tried the 55grn again and got flyers all over the place again.
So, is the barrel done & dusted or is there anything that can be done to make it work with lighter bullets? I've still got about 1K rounds of 55grn that I'd prefer to shoot rather than sell to get expensive match grade ammo.
It could be that the barrel is worn to the point that it will not stabilize bullets with shorter bearing surfaces. 6000 to 6500 rounds is about the point at which I replace a barrel on a match rifle, but my carbine barrels usually last 10,000 to 12,000 rounds.
I had a 1:9 twist LMT 16" light weight barrel make it to 10,000 rounds before I replaced it, but I did not perform a lot of mag dumps with the carbine.
but my carbine barrels usually last 10,000 to 12,000 rounds.
Wow. I've never had a barrel give up the ghost that quickly. :confused:
Wow. I've never had a barrel give up the ghost that quickly. :confused:
They are still safe to shoot, but do not meet my accuracy expectations.
They are still safe to shoot, but do not meet my accuracy expectations.
I see. I have an old one I swear has to have about 30k based on when I used to track the round count on the Silencer I got for it.
I'm going to have to shoot that one on paper to see if it's a 4 MOA train wreck this weekend.
7500-10000 rds is a reasonable expectation for a mil-grade chrome lined shorty on a rigorous institutional firing schedule.
10-12k with less heat build up and wear.
Use bimetal ammo, frange, and other specialty o questionable ammo... and who knows.
constructor
06-04-13, 13:01
Buy a .219" inspection pin from a machine shop tool house $3.10. McMaster Carr etc. (http://www.mcmaster.com/#plug-gauges/=n1rjjo)stick it in the muzzle. It shouldn't go in if the muzzle is in good shape but many go in apx 3/4" and stop. The bore land to land should be .218" If the muzzle is looser than the rest of the bore it will not shoot short bodied bullets well.
69s, 75s and 77s will shoot better than the lighter bullets.
Some barrels are made improperly and have a swelled muzzle new, others are cleaned from the front and the grit on the cleaning rod wears the lands down.
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