Couple of AR 15 assembly questions...


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clemsonu0219
June 7, 2009, 09:45 PM
I currently have a Bushmaster A3 set up for varmits...fluted barrel, heavy hand guard, etc.

I am going to buy an additional upper, probably a RRA Tactical 16", and just periodically change out the uppers.

I know that there usually aren't assembly problems going from manufacturer to manufacturer outside of Colt, but should I use my current bolt carrier assembly and charging handle with the new upper? Or should I just buy a new BCA and charging handle along with the upper? I know its probably just personal preference but what would you do, and would I have any problems using my Bushmaster BCA and charging handle with the RRA upper? Thoughts?

Thanks everyone.

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cbrgator
June 7, 2009, 09:51 PM
You should be fine.

kwelz
June 7, 2009, 09:52 PM
I am going to buy an additional upper, probably a RRA Tactical 16", and just periodically change out the uppers.

This is ok Short term but Lowers have come back down in price. I really suggest getting a 2nd Lower. Swapping out is a pain.

I know that there usually aren't assembly problems going from manufacturer to manufacturer outside of Colt,

What gives you the idea there is any problem using Colt Parts with other manufactures parts?

but should I use my current bolt carrier assembly and charging handle with the new upper?

Not just no but Hell no. A bolt and BCG will wear in a pattern specific to an upper. By switching back and forth you can cause all kinds of problems. These range from simple loss of accuracy to possible serious malfunctions.

Or should I just buy a new BCA and charging handle along with the upper?

Spend the extra money on a new Bolt.

I know its probably just personal preference but what would you do, and would I have any problems using my Bushmaster BCA and charging handle with the RRA upper? Thoughts?

While the overall quality of the parts will vary from company to company, they are all pretty much interchangeable.


Thanks everyone.

Hope that helps

clemsonu0219
June 7, 2009, 10:00 PM
Hope that helps

Yes. Helps immensely, thanks a lot! So, basically, buy a new bolt carrier assembly/charging handle and there shouldn't be any issues changing uppers. Thanks a lot, again.

Colt upper to other lower issues... only some.

Basically it will come down to the size of the take down and pivot pins. To my knowledge I believe that Colt is the only company that has a Large Pin configuration ( .176" versus a more standard .153"/.154" ).

So a Bushmaster lower, with small pins, would not accept a stock Colt Upper with the large pins. Well, it would accept it, but it would rattle like all hell & not be worth a damn to shoot.

kwelz
June 7, 2009, 10:18 PM
You are thinking of two different issues. LONG LONG ago some Colts had different take down pins. This has not been the case for a very long time. In fact I am not even sure when this was done and would have to do some digging. But even if you did happen to find a Laqrge pin colt upper you would just need this to fix it.
http://www.m-aparts.com/productsDetail.asp?id=645

The pin size you are talking about (.154/.170 is the FCG pins and those are now standard as well. I have a 6940 less than 5 feet away that is proof of this. This only impacts the installation of some Lower parts kits, or mach triggers. Not the upper to lower fit.


But yes to clarify, get a new bolt and BCG for one of the uppers, and you can just swap out upper.

ugaarguy
June 8, 2009, 12:02 AM
The pin size you are talking about (.154/.170 is the FCG pins and those are now standard as well. I have a 6940 less than 5 feet away that is proof of this. This only impacts the installation of some Lower parts kits, or mach triggers. Not the upper to lower fit.
Actually the bushing linked is for putting a Colt commercial large pivot pin upper on a standard pivot pin lower. Commercial Colts not only had larger FCG pins, but for many years had a larger pivot pin than GI standard. Most (all?) of the current "Commercial Colts" are actually LE marked blue label guns that are legal for private ownership in no ban states.

Texpatriate
June 8, 2009, 01:00 AM
double post

Texpatriate
June 8, 2009, 01:11 AM
You're talking about asking some very high stress/high wear parts to do double duty. Yes, your bushmaster BCG and CH *should* be able to function interchangeably in a Rock River or other upper, but you will need to check the headspace of the old BCG in the new upper just to make sure.

It would be preferable, however, to have a BCG and CH dedicated for each upper. The CH would be less crucial than the BCG, but since you can get a brand new CH for about $22, why not? The BCG, and in particular, the bolt itself, is the single most important part (or group of parts) in the AR platform, AND it is also the THE part that is most prone to failure (assuming everything else is properly assembled). Bolts, extractors, and firing pins can (and eventually do) all break, gas rings and extractor springs wear out, and gas keys can fail- all of those parts are part of the BCG, and represent some of the most common failures in the AR platform.

That said, I'd strongly recommend a second BCG, preferably one that with a properly torqued and properly staked gas key, HPT & MPI tested bolt, and a proper extractor spring and black extractor insert, for your second upper. BCM and LMT in particular put together a good BCG package, if you can find them in stock.

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