BCG

[Shootingfun]

I am sure someone out there in M&P 15 sport land has replace there BCG in there sport rifle at some point, I am just curious at what you used and what worked well and at a good price. Thanks for the replies.

I just want to add looking for a full auto standard BCG nothing fancy just something that will work in the M&P 15 sport rifle, mainly for backup purpose, I like having extra parts for my firearms.

 

[Dfresh15]

Bolt Carrier Group - Spike's Nickel Boron HPT/MPI M16 BCG (5.56) [ST5BG03] - $225.00 : Spikes Tactical

Here's what I bought. But snagged mine on eBay for $148 Brand New in Box............ I got lucky

 

[RDFabsRep]

Used a PSA Premium (FA) in the last upper I built from scratch. No issues at all so far

 

[Shootingfun]

Well really want it for the M&P sport rifle I have now. What will work correctly in a full auto bcg in my M&P 15 sport rifle.
Just a basic good standard BCG, in full auto.

 

[jagular]

Any full auto bolt should work. Do some research on the manufacturers you are looking at for quality and materials. We'll known and quality bolts like BCM are gonna run you $190. A mid tier like PSA will run about $90. You can get a regular phosphate coated bolt or nibx coated. Nibx is more costly. You have to decide if it's worth it. I've never had cycling issues with either but I'm also not going more than 200-300 rounds before I clean it.

Do you really need an entire bolt assembly (including carrier) or can you get by with an extra bolt/extractor, springs, firing pins, etc.? Palmetto state armory, for example, has rebuild kits for around $20-30. Do some research on bolt assembly failures and decide from there. My research has shown that the bolt carrier is not often the part that would need to be replaced in a failure.

I have a sport and the preference for a full auto carrier is over rated. It's not a full auto gun. Yes, the weight of the carrier does come into play for gas system but my brasses ejects at 3 o'clock every time which indicates it's gassed satisfactorily. Be careful of the milspec monkey. He's always looking to spend your money for things that may or may not make a difference.

 

[Shootingfun]

Mainly the reason is also for a new build this next year I want to do. That way I have a BCG already. Now will I have to head space the barrel for the bolt I chose. I have my eyes set on a Anderson build, upper, lower and barrel, with even any other Anderson parts that I can find. Did some research and Anderson's part came out with great reviews and quality parts for a new fresh build.
I have all the parts that I want for this build just have to wait till next tax time for the cash or if I get this new job then here sooner.

 

[Kodiakco]

Mainly the reason is also for a new build this next year I want to do. That way I have a BCG already. Now will I have to head space the barrel for the bolt I chose. I have my eyes set on a Anderson build, upper, lower and barrel, with even any other Anderson parts that I can find. Did some research and Anderson's part came out with great reviews and quality parts for a new fresh build.
I have all the parts that I want for this build just have to wait till next tax time for the cash or if I get this new job then here sooner.

If the head space is off on new components you'd need to check the bolt and/or chamber for out of spec. There is no easy way to adjust head space on an AR. Good quality parts will most likely be in spec from the get go.

 

[WR Moore]

If you're going to do a build, you really should get the barrel & bolt as a matched pair from the same maker to make sure headspace is correct.

Carriers are plug and play, bolts really aren't-unless you're getting a barrel with a short chamber and unplated bore. In that case, you'll need a chamber reamer and headspace gauges.

BTW, judging function by ejection patterns is meaningless unless you KNOW the powder used in the ammo is the same. Changes in gas port pressure will change ejection patterns.

 

[SGT_Lindy]

If you're going to do a build, you really should get the barrel & bolt as a matched pair from the same maker to make sure headspace is correct.

Carriers are plug and play, bolts really aren't-unless you're getting a barrel with a short chamber and unplated bore. In that case, you'll need a chamber reamer and headspace gauges.

BTW, judging function by ejection patterns is meaningless unless you KNOW the powder used in the ammo is the same. Changes in gas port pressure will change ejection patterns.

I am not going to say you are wrong, but I will say I have either replaced bolts and full BCG's in existing AR's and I have built AR's where the upper (barrel) and the bolt where not from the same company. I have never had a problem.

Example my Sport runs a BCM BCG/Bolt. After about 1500 rounds with the original BCG/Bolt, I replaced it with a BCM. I cleaned up the original, coated it in CLP and put it in the zip lock bag the BCM BCG came in. It is my complete BCG/Bolt spare for that rifle.

 

[Magload]

I believe it is called Mil Spec parts. Don

 

[WR Moore]

When the factory assemblers are doing barrel/bolt fitting (and actually, if they're doing it by the manual, they're doing bolt group fitting) it's by a selective parts method:

You have a barrel torqued to the upper, you install a bolt group (minus ejector), slip a go gauge in the chamber and using thumb pressure ensure the end of the carrier is flush with the end of the upper. The go gauge is removed and a no-go gauge is inserted and the end of the carrier should stick out, very slightly, from the end of the upper. If it doesn't, try another carrier group after placing the failed carrier group in the minus tolerance bin.

It's a whole lot easier to sit there with a barrel, gauges and a basket of bolts (w/o ejector) and check fit. Again, minus bolts go in one bin, plus bolts another for trial on other barrels. Now, this is doing it right. It's a whole lot easier (and cheaper) for most of us to order a matched barrel & bolt.

I won't deny that in a great many cases, tolerances will be such that dumb luck can possibly give an acceptable fit. If you want to bet your gun and body parts on it, feel free. My question: have you ever actually gauge checked your fit? There's roughly a 0.003 in headspace difference between a go and no-go gauge. There's another roughly 0.003 in headspace difference between a no-go gauge and a field gauge. The military is happy if used barrels & bolts won't accept a field gauge. That's not the standard you want in a new assembly.

Note: our lead armorer serial numbers the BCG to the rifle. Headspace checks are made per vendor requirements. When bolt replacements are made, the combination is gauge checked.