Cut Down Chrome Lined Barrels?

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  • ericoak

    don't drop Aboma on me
    Feb 20, 2010
    6,806
    Howard County
    I got a good deal on some chrome lined barrels, and I am reading contradictory posts on whether they can be cut down or not. I see mostly older posts saying the chrome will flake, but no actual 1st hand reports. There seem to be a lot of companies like ADCO that have been doing it without any actual 1st hand reports of problems.

    Anyone have any experience here?
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,815
    I got a good deal on some chrome lined barrels, and I am reading contradictory posts on whether they can be cut down or not. I see mostly older posts saying the chrome will flake, but no actual 1st hand reports. There seem to be a lot of companies like ADCO that have been doing it without any actual 1st hand reports of problems.

    Anyone have any experience here?

    PM clandestine. He would know. And then get back to us?
     

    Doco Overboard

    Ultimate Member
    A machinist who is not a gunsmith told me hard chrome is a little different animal than regular chrome. They work on hard chromed tooling and industrial apparatus. When parting off he advised keeping the part cool and let carbide tooling do the work and approach the chromed surface tactfully.
    Theres plenty of jap barrels out there that have been cut but how could anyone ever speak to accuracy and they are ruined, because they're cut. Maybe EDM tech could be applied if it was available.
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    If its cut properly and threaded properly then the chrome is not going to be a problem. Looking for a 10.3/10.5 Colt Barrel and only finding chopped ones eh?

    Some people use the hand dies and/or annular cutters with the bore guides for non lethe work and that WILL damage the barrel.
     

    ericoak

    don't drop Aboma on me
    Feb 20, 2010
    6,806
    Howard County
    If its cut properly and threaded properly then the chrome is not going to be a problem. Looking for a 10.3/10.5 Colt Barrel and only finding chopped ones eh?

    Some people use the hand dies and/or annular cutters with the bore guides for non lethe work and that WILL damage the barrel.

    Thanks, was thinking of sending one to Adco eventually.

    No although I do see a lot of Adco chopped Colt barrels, and no one seems to be complaining about it.

    I got a great deal on Green Mountain chrome-lined 7.62x39 barrels. I can't find a chrome lined 4150 7.62x39 AR barrel under 16" to save my life. All the 11.5" I could find either were nitride/phosphate, or 4140 YHM. This barrel will be getting FA abuse.
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    That will be a neat setup.

    The GM CL 7.62x39 Barrels are some of the best. I do have concerns about it in full auto.

    Problem is modern production 7.62x39 barrels use a .124 Bolt Face Depth. This means the extractor is very weak. On full auto is you may break extractors so buy some spares. Try to use Colt Gold Extractor Springs if possible. They don't load the extractor as much since there is no need for the o ring.

    If you can find a Colt 7.62x39 upper, they are better. They use a .136 bolt face depth and have a much stronger extractor.
     

    ericoak

    don't drop Aboma on me
    Feb 20, 2010
    6,806
    Howard County
    That will be a neat setup.

    The GM CL 7.62x39 Barrels are some of the best. I do have concerns about it in full auto.

    Problem is modern production 7.62x39 barrels use a .124 Bolt Face Depth. This means the extractor is very weak. On full auto is you may break extractors so buy some spares. Try to use Colt Gold Extractor Springs if possible. They don't load the extractor as much since there is no need for the o ring.

    If you can find a Colt 7.62x39 upper, they are better. They use a .136 bolt face depth and have a much stronger extractor.

    Thanks, I'll pick up a couple of spare extractors. I just sent you a PM with the price and website I bought them from, it's a ridiculous deal frankly.
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    Can you use a Colt barrel with non Colt Bolt and vice versa? Or does the different bolt face depths make them not compatible?

    You would have a hard time finding a 7.62x39 Colt Bolt to stock as a spare part. You can use a 6.5 Grendel Bolt on a Colt 7.62x39 Barrel. The 6.5 Grendel Bolt Face depth and diameter is almost identical to the 7.62x39 Colt Bolt. The Colt is .136 depth and the Grendel is .135 depth. Worst case a little bolt lapping may be needed to get it to close on 7.62x39 CIP GO Gage.

    You would have to contact a barrel manufacturer to get a 7.62x39 setup with the Colt headspace spec. Most places that would do it make match barrels which are not optimal for this caliber and application. The way you are doing it is best. Chrome Lined, especially for steel cased 7.62x39 ammo.
     

    ericoak

    don't drop Aboma on me
    Feb 20, 2010
    6,806
    Howard County
    You would have a hard time finding a 7.62x39 Colt Bolt to stock as a spare part. You can use a 6.5 Grendel Bolt on a Colt 7.62x39 Barrel. The 6.5 Grendel Bolt Face depth and diameter is almost identical to the 7.62x39 Colt Bolt. The Colt is .136 depth and the Grendel is .135 depth. Worst case a little bolt lapping may be needed to get it to close on 7.62x39 CIP GO Gage.

    You would have to contact a barrel manufacturer to get a 7.62x39 setup with the Colt headspace spec. Most places that would do it make match barrels which are not optimal for this caliber and application. The way you are doing it is best. Chrome Lined, especially for steel cased 7.62x39 ammo.

    Probably just stick with the GM barrels then and combine them with a nitride toolcraft BCG for $100 shipped.

    http://skidtactical.com/store/toolcraft/7-62x39-bolt-carrier-group/
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    Probably just stick with the GM barrels then and combine them with a nitride toolcraft BCG for $100 shipped.

    http://skidtactical.com/store/toolcraft/7-62x39-bolt-carrier-group/

    If I can help in any way, let me know.

    If you use a Colt Gold Extractor Spring, and check for Correct Headspace and Correct Firing Pin Protrusion you should be good.

    These things are very magazine sensitive so buy a few good brands of mags when the upper is done from places that allow you to return them. Tape and number them and test the hell out of them. Return any ones that give you problems.
     

    TheOriginalMexicanBob

    Ultimate Member
    Jul 2, 2017
    32,176
    Sun City West, AZ
    Can you use a Colt barrel with non Colt Bolt and vice versa? Or does the different bolt face depths make them not compatible?

    You should be able to as long as each is within specs. There are + and - tolerances so it's always possible to find a barrel and bolt that don't work together. Colt barrels also are Milspec (well...most are) but many aftermarket barrels are not. That's not to say they're not good barrels...just that they haven't gone through the testing the military requires.
     

    ericoak

    don't drop Aboma on me
    Feb 20, 2010
    6,806
    Howard County
    If I can help in any way, let me know.

    If you use a Colt Gold Extractor Spring, and check for Correct Headspace and Correct Firing Pin Protrusion you should be good.

    These things are very magazine sensitive so buy a few good brands of mags when the upper is done from places that allow you to return them. Tape and number them and test the hell out of them. Return any ones that give you problems.

    I have another 7.62x39 upper, I haven't had a single malfunction once I swapped in an enhanced firing pin. The C Products Defense 30 round magazines have been great.

    I do have a question about 7.62x39 bolts though. I know they are much more likely to break lugs (at least the old ones), is that minimized by using either an adjustable gas system turned down or heavy buffer? Or is it just due to the increased recoil from the round on the same surface area, and not much you can do about it?

    Also, do you recommend any of the upgraded bolts like the LMT etc. or better off just buying 3-4 regular bolts for the same price?
     

    ericoak

    don't drop Aboma on me
    Feb 20, 2010
    6,806
    Howard County
    And I must say, I have enjoyed the 7.62x39 uppers much more than I thought. You feel like you are actually shooting a gun, 5.56 feels close to a pellet gun. Which is good, but not necessarily fun. They just have a bad stigma because the old magazines were definitely crap.
     

    babalou

    Ultimate Member
    MDS Supporter
    Aug 12, 2013
    16,019
    Glenelg

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