Home Forums Hunting & Shooting AR and Tactical Rifles BCG Question.

Might be a bit repetitive here. If so, sorry, but tried the search first...

I have an M4 upper that has seen better days. Probably have 5k rounds through it. The accuracy has fallen off to around 1" to 1 1/2" at 100 yards.

I'll be getting a new upper, but to add a BCG is over $100 extra.

Is there any reason I can't just use the BCG from my old upper?

Thanks!

No reason at all. Ran same BC for years, in fact can't recall ever trashing one. Tended to make sure bolt was headspaced and tended to trash bolts after 2-3 barrels life...

Thanks Jeff!

PS, buttoned tubes can die as early as 3000 ish rounds... AMU changes at 2500 on douglas tubes last I heard years ago to be safe.

Cut rifled I've taken Kriegers to right at or over 12K IIRC. But the accuracy was probably what you are getting now at that point... Still won a LA state leg match with one... but it was tough...

If you don't want to replace just the bolt you could do a new extractor and spring for pretty cheap, just for insurance.

Extractor springs and extractor spring buffers (black, of course) are items I keep around just 'cause Murphy is alive and well...

Ed

I've replaced the rings and the ejector spring already.

(Was walking around Shot Show and an AR company gave me a handful of neat little kits.)

sounds like all you really need is a new barrel

If a good bolt won't last 10,000 rounds, it wasn't a good bolt. Carbines are harder on bolts than rifles.

That said, it's always a good idea to change the bolt when changing the barrel. Reason being the bolts wear into the barrel extension and using an old bolt worn to another extension could cause problems, mostly with accuracy. Keep the old bolt for a spare.

And if you are going to buy a new barrel & a new bolt, get them from the same manufacturer like Faxon & the bolt will be head-spaced correctly to YOUR barrel.

Several other suppliers will do the same.

MM

THIS!!

No need for a new carrier, and while you don't need a new bolt, buying one from the same company you buy your barrel from is very cheap insurance that headspace will be right. Use it and keep your old bolt for a spare, always nice to have a spare bolt. I used to keep a spare bolt in the grip hollow of my AR. A little black electrical tape holds it in place. I see now there's someone who actually makes a grip with a bolt holder, and a firing pin holder, and it snaps into the grip...kind of a cool idea.

You only need to buy the new bolt from them IF its headspaced to the new barrel. If its just pulled out of a bucket, then its not ever needed, well not until you get through a couple of tubes....

Yes, exactly. Just buying the bolt and barrel from the same place doesn't mean squat, unless they specifically say that bolt was headspaced to that barrel.

Personally I wouldn't worry about it, just drop a new barrel in and shoot it.

Thought about going the barrel direction, but uppers are about as cheap as barrels in some cases, and I really want a full length rail on the hand-guard for night vision. My current free float hand guard is slick with no rail.

That makes sense. In that case, to your original question - yes, you can just use your old BCG in the new upper. Have fun!

I've been watching this thread and wondering why they have so many BCG's out there if they are not likely going to be headspaced to your barrel. I'm thinking that more than likely a new BCG will work just fine, but not checking headspace after installing a new BCG would be blatant irresponsibility on the owners part. Because of the other thread bleux started about things that go wrong, made me want to buy an extra BCG for one of my AR's. I chose to buy a nice Nickel boron BCG from black rain ordnance for my left handed AR, for just in case, since the left hand BCG's can be harder to find and not found locally anywhere. I also ordered as set of minimum and maximum gauges for checking headspace. We'll see if it passes the test after I receive the gauges.. Crossing my fingers...

No, not really, if we're talking about 5.56 AR15; I'm not saying "parts are parts", but 5.56 bolt dimensions are pretty well standardized and consistent if you buy a decent bolt. A variation of a couple thousandths is not the big deal some folks online make it out to be; there are too many who read & talk a lot more than they build and shoot.

Of course, with the market's current race to the bottom limits of quality and price, checking headspace may become more important than it has been up till now.

I'm sure someone will want to prove me wrong, so post up if you've ever found a decent bolt and barrel (AR15) with out of spec headspace, and include how far out it was.

First, the BCG has little to do with head space, just the bolt. The bolt locks into the barrel extension and just like on a bolt gun, it needs to fit square with head space set to that bolt.

Now since most bolts are pretty standardized as Yondering stated, it's still easy to find one off a little bit. I haven't seen machined parts measure exactly the same from the start of the run to the finish yet. That said, years ago I bought a few bolts that were pulled out of M16's on PM intervals. I don't remember finding one that let the field gauge chamber. In fact the last time I pulled my field gauge out of the box was to take a picture of how I cut the ejector slot in it.

Besides the bolt, there is also the issue on some "match" type barrels being tight on chamber length that can cause headspace to be short or even below minimum if combined with a tight bolt. HS below min by more than a couple of thou can make finding a broad range of ammo that will chamber an issue.

On a stainless, the chamber can be lengthed; not so with a chromed or nitrided barrel.

I think this case is more likely than excessive headspace.....................unless something is badly wrong.

Never hurts with a high grade barrel with tight tolerances, to get a bolt from the barrel source when possible.

JMHO, YMMV

MM

Now I'm very curious as to how my new BCG [comes with new bolt, as most (if not all) do] headspaces to my barrel. Something that is not being discussed here is what go/no gauge to use. Are they (.223 rem/5.56) all the same? What gauges to use to check head space my be an entirely different thread topic, but is necessary to know for sure. This brings me to the question, do you guys buy go/no go and field gauges for both .223 rem and the 5.56 minimum and maximum chamber dimensions?????? Looks like there are some differences in dimensions between the .223 rem and 5.56 NATO. For example:

.223 rem gauges:
GO= 1.464"
NO GO=1.467"
FIELD= 1.470"

5.56 NATO:
GO=1.4646-1.4648"
NO GO= 1.4704-1.4706"
FIELD= 1.4728-1.4730"

For those of you that have built many rifles and checked head space, is there a simpler approach to checking to ensure proper headspace? Looks like my maximum headspace gauge for the 5.56 NATO I just bought is not the same as a "NO GO" gauge, but closer to a FIELD gauge and probably closer to the colt FIELD headspace dimension @ 1.4736". I think this may have been brought up earlier, but would it be wise to use a .223 rem field gauge as a 5.56 no go, if one has a hard time finding a 5.56 NATO no go gauge?????