View Full Version : Bulged Barrel Replacement--Barrel Extension Question, Etc.
Some time ago I posted about a possible bulged/ringed barrel, apparently from firing a CMMG unit and an obstruction that escaped my notice. A gunsmith who has seen a lot more of these than I have (none, up to now!) made the call and although there's not much to see, the tight/loose/tight patch down the bore pretty well tells the story.
I will probably pull the M4 type barrel and replace it with a pencil type myself. I have rebarrelled a couple of Garands without problems, and already have have headspace gauges for .5.56. Don't have the AR wrenches or clamping blocks but figure the usual approach of read the book, calculate twice, measure twice, go slow, should work out and I will have the satisfaction of doing it myself at about the same overall cost--and still have the tools.
I do have a question, though. Even with reviewing the USMC 16A2 manual and Kulek's books, I am a little hazy about whether the barrel extension comes as an integral part of a replacement barrel, if I am to use my take-off, or what. Also, what the matchup for M4/not M4 feed ramps might be. No doubt it's dirt simple once I see it, but I can't quite get my head around it with the manuals I'm using. :confused:If anyone can enlighten me I'd appreciate it.
The rifle currently has about 3400 rounds of 5.56 through it. I am thinking of replacing the bolt assembly and cam pin on principle at this time, so as to mate up a new bolt to the new barrel and wear these surfaces in all together.
Don't know what the moral of all this is other than be careful of possible squib rounds when using a .22 in rapid fire. I suspect that might have been the case and I got distracted when clearing a FTE. And I even checked the bore anytime I had a suspicion! At any rate, the conversion unit turned out to be an expensive option for low cost shooting. It may well be replaced by a 15-22 for practice.
Ideas or comments solicited. Thanks.
Robb Jensen
02-08-11, 13:15
Barrel extensions are made for barrel makers, not for armorers.
Get a receiver block and insert from Brownells, a GOOD barrel wrench, and a punch the size of your gas tube roll pin. Those are the basic tools you'll need.
Changing barrels is a pretty simple thing to do - remove the gas tube pin, then the gas tube. It may be in there TIGHT - a gas tube wrench might be a good idea, or WTH, just get a new gas tube and pin when you order your barrel. Then, clamp the upper in a vise using the receiver blocks and insert, remove the barrel nut, take it out of the vise, remove the barrel and reattach. Follow the instructions in the manuals about retightening the barrel nut. Make sure the gas tube hole and a notch in the barrel nut are aligned, and reinstall the gas tube. Make sure the carrier key engages the gas tube smoothly. If it does, then you're off to the races.
I don't recommend using Loctite in the barrel nut.
M4 feed ramps - depends on your upper. If your upper has the cuts then you'll need a barrel with M4 feed ramps, and vice versa.
You won't need to do anything with the barrel extension - once they're attached to a barrel they're pretty much permanently there.
You can't go wrong replacing the bolt and cam pin... you could keep the old one as a spare in case your new one breaks.
Thanks for the responses. I also talked to the Brownell's tech rep and now I know what I'm dealing with here...
Actually I intend to use some anti-seize on the barrel nut, just like the M1s. I've been a big fan of the stuff ever since I found that exhaust system studs and nuts coated with it removed easily even after being installed for years. Wonderful stuff, whether assembling or disassembling. (I really, really hate the feeling when a bolt snaps off :eek:.)
Robb Jensen
02-08-11, 20:40
Oh boy......:eek:
Atmosphere
02-09-11, 20:26
Actually I intend to use some anti-seize on the barrel nut, just like the M1s.
That is a good idea. Never know when it will have to come back off again.
The whole process really isn't bad as long as you have the right tools for the job! Be sure to buy or borrow a torque wrench to get everything snugged down properly.
Oh boy......:eek:
Meaning?
Meaning read some posts here and see what some people have done to their guns while trying to work on them or build them.
Take a look at the thread where a guy brought his Colt to 2 different "gunsmiths" and they screwed it up.
Meaning?
Meaning read some posts here and see what some people have done to their guns while trying to work on them or build them.
Take a look at the thread where a guy brought his Colt to 2 different "gunsmiths" and they screwed it up.
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What about the guy a week or so ago that moved his Gas Block out 2" so he would have a "Mid-Length"?? It blew his Hand Guards off because the Gas Port was uncovered.
IG, you commented on that one...but you kept your cool...you were cool. :)
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That is an excellent example. I almost forgot. :haha:
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What about the guy a week or so ago that moved his Gas Block out 2" so he would have a "Mid-Length"?? It blew his Hand Guards off because the Gas Port was uncovered.
IG, you commented on that one...but you kept your cool...you were cool. :)
.
Robb Jensen
02-10-11, 06:25
"Life's Tough, Get a Helmet"--Denis Leary
Meaning read some posts here and see what some people have done to their guns while trying to work on them or build them.
Take a look at the thread where a guy brought his Colt to 2 different "gunsmiths" and they screwed it up.
Ok. I thought that his exclamation had something to do with the use of anti-seize. Must remember that all statements made are not necessarily in response to the immediately preceding post.
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What about the guy a week or so ago that moved his Gas Block out 2" so he would have a "Mid-Length"?? It blew his Hand Guards off because the Gas Port was uncovered.
IG, you commented on that one...but you kept your cool...you were cool. :)
.
I'm sorry I missed that one!:haha: A little bit of knowledge really is a dangerous thing.
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What about the guy a week or so ago that moved his Gas Block out 2" so he would have a "Mid-Length"?? It blew his Hand Guards off because the Gas Port was uncovered.
IG, you commented on that one...but you kept your cool...you were cool. :)
.
I have GOT to look that one up!
I found this old post while checking up on M4 cuts and just reread it. To put an ending on it: on 4/22/11 I changed barrels. I had written up a composite set of instructions for myself from the references mentioned (and some of the ideas from posts). At the time I was recovering from rotator cuff surgeries, so enlisted a 13 year old friend of the family and shooter to help with some of the heavier torqueing and to keep me straight on the procedural steps I wrote up for myself. He was a real help, very interested, and found it worth his while. We proceeded very carefully at compound low speed and after about two hours had completed our first barrel change. Headspace was right on the money. About three days later I test fired it and rezeroed it. In addition to being lighter the new barrel seems more accurate than the old one was. I like it.
The tools may be coming out again to change the existing A1 upper on my daughter's AR to a flat-top one of these days. Not everyone likes the old A1s as much as I do, I guess.
The CMMG conversion unit is gone, replaced by a 15-22. Nice little practice carbine that is pure fun and doesn't give me any grief.
Gotta love happy endings.
Where is this thread with the moved gas block? I've heard about it a couple times but I can never find it!
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