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ANOTHER AR question (sorry)

bpostbpost Member Posts: 32,664 ✭✭✭✭
edited December 2014 in Ask the Experts
It seems buying barrels and installing them is not the way to go.

Is it OK to buy a UPPER without the Bolt Carrier Group and switch the BCG to the upper being used at the time?

OR; must each upper have its own BCG for safety and headspace?

Comments

  • v35v35 Member Posts: 12,710 ✭✭✭
    edited November -1
    As far as I know you can use the same bolt and carrier on different uppers.
    I've assembled four barrels (3-223/556 & 1-6mmx45) to flat top receivers and fired them with no problem using one BCG.
    The barrel should come with barrel nut (actual receiver) assembled or you have a bit of fitting to do.
  • nononsensenononsense Member Posts: 10,928 ✭✭✭✭
    edited November -1
    bpost,

    It is the fit of the extension to the barrel and fit of the bolt into the extension which determines headspace. If the new parts fall outside of the headspace requirements then it needs to be adjusted.

    Be aware that headspace on an AR runs about +0.002" to allow for the semi-auto to run unimpeded. So if your original bolt or bolt carrier group fits and allows for the headspace requirement you can most certainly use it. But if it doesn't, you will need to change the relationship of the extension to the barrel (chamber) or use a different bolt.

    Modern machining technology has reduced some of the problems associated with AR assemblies but those of us who do this kind of thing professionally, check everything since safety and reputation ride on it.

    Best.
  • asphalt cowboyasphalt cowboy Member Posts: 8,904 ✭✭✭✭
    edited November -1
    There are suppliers that carry barrel/bolt sets. It would be best though to make a call to insure they were head spaced as a set before ordering.
  • MobuckMobuck Member Posts: 13,735 ✭✭✭✭
    edited November -1
    "It seems buying barrels and installing them is not the way to go"
    An experienced mechanic with the right fixtures should be able to assemble a barrel(with extension head spaced) to an upper w/o serious difficulties. Generally speaking, new (in-spec) bolts mated to new(in-spec)barrels are safe and functional. I don't recommend "multi-using" bolts considering the current cost and availability.

    "The barrel should come with barrel nut (actual receiver) assembled or you have a bit of fitting to do."
    Not sure what you're saying in this statement. Barrel nut has little to do with barrel fit.
    I've "assembled" numerous AR platforms from scratch(box of parts) and have seen very few "misfits" relating to barrel installation. Some have been less than optimum but that was due to tolerance stacking in my estimation.
  • beantownshootahbeantownshootah Member Posts: 12,776 ✭✭✭
    edited November -1
    quote:Originally posted by bpost
    It seems buying barrels and installing them is not the way to go.


    That depends mostly on what you're trying to do.

    If you know what you're doing (and assembling the parts is not "rocket science" here), and are willing to make the appropriate investment in tools/fixtures, buying and installing barrels could be worthwhile. Obviously, putting in your own barrels gives you more flexibility in terms of what you "could" do.

    But you're fundamentally right that its not going to be cost-effective to do this if you're only building 1-2 rifles, and (IMO) especially not if you intend on building them in configurations that are otherwise commonly available.

    On swapping BCGs between guns, I think you've gotten "the answer" above. IMO, BCGs are cheap and available enough that there isn't a really good reason to do this short of some sort of emergency, but empirically people do get away with this.
  • martinetamartineta Member Posts: 2 ✭✭
    edited November -1
    Plenty of complete uppers for sale out there. Buy a complete upper with everything you need and then sell your old complete upper here.
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