Swapping BCGs in ARs

[mr_e]

A quick internet search showed that headspace in ARs was not easily modifiable. It was mostly a matter of checking that your Bolt Carrier Group met specs once installed.

Another site warned against swapping BCGs from one AR to another.

Why are most used AR uppers sold without a BCG? Of what use is the used BCG to the seller of the upper? Shouldn't it stay matched with the upper?

[Colorado Osprey]

Your correct, head space is a product of the barrel extension with the bolt face. The carrier is not actually involved...it is just that a carrier for that bolt. Think of the carrier as a bolt knob in a bolt action rifle.

Because the bolt and barrel extension wear, by changing to a newer or older bolt or switching the bolt into another upper you will prematurely wear these items as they wear into each other. So it is not advised to switch the bolt into another upper without checking to make sure you still have good head space with that combination.

Personally I would never buy a used upper with the bolt.....usually sold complete with a BCG. I do however see these as commonly as you do sold without a BCG. I believe that people do this to save money on not having to buy a new bolt with their replacement upper and it keeps cost down on the used upper to make it more economical to purchase.

There are a huge group of people that think that you can interchange bolts in uppers and have no worries. There are many stories of the Military putting all the BCG's and loose parts solvent tanks to clean and then re-assembling rifles from loose parts from many different rifles. I'm not sure if I believe these stories or would want to put my life on the line with these assembled rifles.

To conclude...if you buy a used upper..try and get the bolt with it. If you sell an upper, try and sell the BCG with it...some may not want to and you could and should pass on those folks.....at least I do.


EDIT:
Where is Paradise Colorado.??.....some would say anywhere you can't see your neighbor and they can't hear you shoot your gun.

[mr_e]

Thanks C.O., your explanation fits most of the info I've already found.

By the way, did you mean to say that you would not buy a used upper WITHOUT the BCG? That seems to be what you're implying with the rest of your explanation. Wear seems like it would apply to the upper receiver, the bolt carrier, the bolt within the carrier, and the rifle chamber.

Anyplace in Colorado is Paradise. I recently spent a period of exile in Virginia. Now I'm grateful to live in Parker.

[Colorado Osprey]

.... did you mean to say that you would not buy a used upper WITHOUT the BCG? .

Correct, but that's just my opinion.


....Wear seems like it would apply to the upper receiver, the bolt carrier, the bolt within the carrier, and the rifle chamber.

Sure, all the items wear, but the barrel extension and bolt with the locking lugs is what determines head space in these rifles. I'm not real particular about all the other wear...it does not affect accuracy or reliability(some would say)....just parts life.

[skeeterbay]

Colorado Osprey wrote:

"There are many stories of the Military putting all the BCG's and loose parts solvent tanks to clean and then re-assembling rifles from loose parts from many different rifles. I'm not sure if I believe these stories or would want to put my life on the line with these assembled rifles."



For what it's worth, I have personally witnessed this! Twenty to thirty rifles at a time were being field stripped. The BCG parts were placed in screen/wire baskets. The baskets were then placed in solvent tanks for cleaning. The parts were brushed/cleaned and assembled in weapons with no attempt being made to match parts.

I am not saying it was right or that I agree with it. I am just stating that I have personally seen it done on two different occasions.

[bterry]

I have never heard or seen the military mixing BCGs. USMC 87-91, they always told us to keep the same BCG with the rifle. USAF ANG 2001-pres, one set of parts in the solvent to keep them with the same rifle.

I do believe it happens. Just saying not everywhere.

[chrashd]

I remember reading in a military manual that it was not advisable to switch bolts and carriers. Not sure where I read that.