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AR-15 Bolt and Carrier Assembly Colt/Standard any difference?

Discussion in 'Rifle Country' started by birdbustr, Jan 19, 2008.

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  1. birdbustr

    birdbustr Member

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    I have a Colt M-4. Recently I purchased a spare bolt and carrier assembly from Coleman Tyler (exellent processing and shipping of product). When I received the assembly I noticed a difference between the Colt semi-auto bolt carrier assembly and the "Standard" bolt carrier assembly I received. From what I can tell Colt is the only manufacturer of the AR-15 types that cuts the bottom part of the assembly out, and the rest do not.

    More specifically, the rear part of the new bolt has metal that comes underneath the assembly, whereas the Colt factory does not. I have installed and cycled the action and dry fired. I cannot tell any difference in the way the action feels, but I am still a little apprehensive about firing live rounds through this different part. I thought these parts were interchangable, but now I'm not so sure. So will it make any difference?

    Here is a link to the new bolt carrier assembly. http://www.colemantyler.com/proddetail.php?prod=URBCADP
    Here is a pic of the rear portion of the Colt assembly.
    http://www.zediker.com/tubb/images/speedlock/burrclose200.jpg
     
  2. Chipperman

    Chipperman Member

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    It will work fine. A full-auto carrier will have more metal on the bottom to trip the sear. The semi-auto has thinned that area so it will not touch a sear. The Colt carrier with nothing on the bottom is just taking it one step further.
     
  3. battlecry

    battlecry Member

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    Check out a replacement bolt carrier from Colt for the Colt MT6700 HBARII.
    It has the full back. Works fine in an AR-15 semi.

    Don't ask em why they do these things.

    Regards,

    R
     
  4. Dave Markowitz

    Dave Markowitz Member

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    Make sure that the screws holding the carrier key on your replacement bolt carrier are properly staked in place. A lot of the aftermarket suppliers don't properly stake them.
     
  5. Slamfire

    Slamfire Member

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    A heavy bolt carrier will provide better reliability of feed. It also increases by a tiny tiny fraction the "dwell" of the rifle. This is better on brass as a slow opening bolt is less likely to stretch or rip the case in half.

    The HK91 opens so quickly that the Germans had to flute the blasted chamber.

    When the carrier is going forward, that extra inertial weight helps strip the round and close the bolt.

    The bolt carrier to bolt weight ratio is a measure of quality of a design. A design that has a lot of bolt carrier weight compared to the bolt is going to be a more reliable semi auto action.

    Just look at the AK as an example of good design. I have not weighed my HK91 components, but that rifle has a very heavy bolt carrier. You can feel it chugging its way forward.

    I have added David Tubb carrier weights and tried to find the heaviest carriers for all my Match AR's.
     
  6. Dave Markowitz

    Dave Markowitz Member

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    Comparing the HK91's bolt carrier with the AK or AR is an apples/oranges comparison. The AR and AK are locked breach, gas operated designs. The HK91 is a delayed blowback. It has to have much heavier reciprocating parts.
     
  7. TexasRifleman

    TexasRifleman Moderator Emeritus

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    No one has just said it plainly so I will. Colt ships M16 bolt carriers with theirs, most everyone else ships a semi model.

    That's why you are seeing the different cuts in the carrier.

    There is no reason to use anything other than the one that came with your Colt. If you want spare parts for whatever reason you can buy M16 carriers though it really won't matter.
     
  8. birdbustr

    birdbustr Member

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    M-16 and AR-15 bolt carriers are used interchangably on the internet. Some have the metal on the bottom and some don't. It looks as though the assembly will work with or without the metal on the bottom. The bolt carrier that I got from Coleman Tyler feels rock solid and I think for $102 + S/H it will make a very good clean spare to have on hand.
     
  9. TexasRifleman

    TexasRifleman Moderator Emeritus

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    I wonder more why you need a spare bolt carrier. If you break the carrier you've done serious damage to the rifle I suspect. :)

    I always carry a couple of spare bolts though, lots of things can go wrong there.....
     
  10. birdbustr

    birdbustr Member

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    Why? B/C I don't like putting up a dirty rifle for any frame of time, especially my SHTF rifle. Sometimes I can't get to cleaning my rifles right away after the range. I'm not trying to improve the Colt assembly, and it's not broken.
     
  11. rcmodel

    rcmodel Member in memoriam

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    I'd be more concerned about checking the headspace on the different bolts then about whether the M-16 carrier is cut or not.

    [​IMG]
    rcmodel
     
  12. birdbustr

    birdbustr Member

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    RC, Here's what I have found on the Headspacing matter:

    "bolt carrier assembly does not determine headspacing, etc. If you have multiple AR uppers you can use the same bolt carrier. However, headspacing on ARs is largely determined by the interface of the barrel extension to barrel, along with any bolt & lug wear."

    Almost no bolt & lug wear on the rifle <500 rds through the rifle. Does anyone else think the headspacing would be and issue?
     
  13. rcmodel

    rcmodel Member in memoriam

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    I know the bolt carrier has no bearing on headspace.
    I wasn't suggesting that it did.

    But minor variations between Colt's mil-spec bolt & barrel extension, and an unknown makers after-market bolt, in conjunction with your barrel extension being broken in with a different bolt, might make it prudent to check the new bolt's headspace.

    I know all AR-15 parts are "completely interchangeable", but sometimes they are not!

    [​IMG]
    rcmodel
     
  14. birdbustr

    birdbustr Member

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    I'll make some measurements to see if there are any differences in the two. If so I'll probably drop it by a gunsmith to see what he thinks.
     
  15. rcmodel

    rcmodel Member in memoriam

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    There is nothing you can measure without a head-space guage.

    You could try the old Scotch Tape trick on a loaded round though.

    Place one layer of Scotch Tape (about .002") on a case-head, and trim off the excess. See if it chambers (by hand with the rifle opened up) tight with the Colt bolt.
    If not, add another layer of tape (total of about .004") and try it again.

    When you start to notice resistance closing the bolt by hand, stop.

    Now try the new bolt with the same number of tape shims and see if it is the same.

    This will not tell you if the headspace is right or wrong!

    But it will tell you if the two bolts are the same or different when locking into your barrel extension.

    [​IMG]
    rcmodel
     
  16. birdbustr

    birdbustr Member

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    Sounds simple enough I'll try that tonight.
     
  17. taliv

    taliv Moderator

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    head space gauges are cheap. i check every rifle i buy/build or help others build.

    I have never actually found a bolt/barrel combo that wasn't properly headspaced,

    but still I check.
     
  18. Bartholomew Roberts

    Bartholomew Roberts Moderator Emeritus

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    If the bolt and barrel extension are both in spec, then it won't be an issue. I wouldn't be too concerned unless I was putting a well-used bolt into a well-used barrel. In that scenario, you might end up with excessive headspace.

    I've found exactly one and it was on a brand new bolt and barrel that was unfired :eek: That is why I always check now (at least the first time I use that bolt/barrel). Prior to that I would not always check and never had any issues.
     
  19. Onmilo

    Onmilo Member

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    Always check a barrel/bolt combination with at least a field headspace gage.
    I have received several barrels over the years that did not have fully finished chambers and should have.

    I would rather use M16 bolt carriers in all rifles, but my state can get real pissy with people having full auto parts in their rifles.
    Consequently I search out semi auto bolt carriers that have the minimum amount of machining to keep them from tripping an auto sear while maintaining enough mass to operate like the bolt carrier was designed.
     
  20. Slamfire

    Slamfire Member

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    Well, yes and no. Locked breech or delayed blow back, the Germans who designed the HK91 could have tinkered with the roller size, the cam angles and the trunnion recesses and played with the dwell to “delay” the “delayed blowback”.

    Take a look at your Brassey’s Military Small Arms, there are all sorts of design approaches.

    I believe the heavy bolt carrier is there because the Germans who designed this thing, after WWII remembered the cold, the mud, the rain, and the God awful conditions their Soldiers had to experience in that war. And they wanted that rifle to function. So they made an extra heavy bolt carrier.

    Strange they did not put on a forward bolt assist.

    But, it is just an opinion.
     
  21. Soybomb

    Soybomb Member

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    Link to what makes you say that (bcg, not a real machine gun of course)?
     
  22. Onmilo

    Onmilo Member

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    Contact these folks via e-mail if you want the skinny.
    http://www.isra.org

    I would recommend you avoid talking to any regulatory agency about this subject from up in Chicago or down in Springfield, especially if you live here.



    Addendum, I am sure there is something on the web,,,,,I am not going on a thread hijack because my state is restrictive.
     
    Last edited: Jan 20, 2008
  23. ckay

    ckay Member

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    Dirty ARs shoot fine. Unless you are pumping 3,000 rounds at one session, I don't think a single range session will dirty your AR to the point of failures.
     
  24. Soybomb

    Soybomb Member

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    There isn't the slightest bit of what the problem is available on the web?
     
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