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Old February 23, 2013, 08:22 PM   #1
oldsoonershooter
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M16 Bolt carrier assy

I was at a pretty large gun show it Tulsa today looking for a BCG, apparently like a lot of folks. I found one that the seller said had been an M16 version, but had had the back end modified to be open instead of completely enclosed. I ask why that was done and he responded to make it legal for use in an AR 15. I wasn't aware that there was a legal issue in using an M16 bolt in an AR 15. Does anyone know of this regulation? If so, i had better remove some of my bolts.
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Old February 23, 2013, 08:57 PM   #2
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There is no legal requirement to not use the full auto M16 bolt carrier in a semiauto AR-15. The ATF has ruled that doing such does not even begin to make the rifle fully automatic.

Colt (at least in the past) had gone to great lengths to ensure their carriers couldn't be used in a full auto conversion (cutting out the entire bottom of the back of the carrier, unshrouding the firing pin), but that's by no means required.

If a vendor is cutting the bolt carriers so they cannot be used in a FA gun, I'd be buying from somebody else. I wouldn't pass by a good semiauto carrier if I needed one and found one at a good price, but I wouldn't buy one that somebody dinked with because they don't know the actual rules at work.
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Old February 23, 2013, 09:17 PM   #3
oldsoonershooter
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Well I didn't buy any of his carriers. I felt $400 was just a little too high for run of the mill Carrier assemblies. Then I found some junk for $300 each. That was all I saw at at a fairly large gun show. Very sad situation. Thanks for the clearification.
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Old February 23, 2013, 11:00 PM   #4
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Many people prefer the full auto bolt to the semi. It is a little heavier and slows the action of the bolt, much like putting in a heavy buffer. That is the only type I buy. Why modify it when it is better in it's original form. The guy apparently didn't know what he was talking about.
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Old February 24, 2013, 12:48 AM   #5
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In case you are interested, here is the ATF letter abour FA bolt carriers in AR15s:

http://www.gandrtactical.com/images/...6%20Letter.pdf
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Old February 24, 2013, 07:35 AM   #6
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The FA BC is 11 grams heavier than the SA BC. The extra weight can help with a over gassed carbine. Rifle RE's with the 7+ oz buffer should run fine on either a FA or SA BC. These days finding either one can be challenging.

I anticipated the shortage, same as last election cycle, and bought two BCG's from CORE15 in Nov at the good old prices.
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Old February 24, 2013, 04:56 PM   #7
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I felt $400 was just a little too high for run of the mill Carrier assemblies. Then I found some junk for $300 each.
Wow. That is insane. I know the panic is going, but wow. Over 100% mark up from pre panic? Folks must be desperate with lots of cash.
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Old February 25, 2013, 11:55 PM   #8
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yeah that is nuts pricing. In July 2012 you could by a BCG from BCM or DD for about 250, and that was the max you would pay for any BCG.
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Old February 26, 2013, 02:16 AM   #9
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Actually, I got a BCM BCG for $150 last September. Same price when I got one in July. (I did two builds before the election). Now of course it's a seller's market.
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Old February 26, 2013, 10:28 AM   #10
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It wasn't that long ago when I could find BCM BCGs for no more than $140. I even have a couple Spike's I picked up at less than that.

Those days are just a memory right now.
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Old February 26, 2013, 01:07 PM   #11
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You guys aren't just talking about the bolt, but the entire bolt carrier group?

If so, I guess I am no good as a bargain hunter. It seems I over-pay for gun parts just like I do for cars
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Old February 26, 2013, 01:58 PM   #12
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I remember back in 2011 when PSA had their standard BCGs for ~$100 and their "Premium" BCGs (which were identical, but were HP/MPI tested) for ~$110.

Those days are gone forever.
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Old February 26, 2013, 03:03 PM   #13
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Quote:
You guys aren't just talking about the bolt, but the entire bolt carrier group?
Yup, entire bolt carrier group. Back when I bought those things, bolts could be had for about $80.

The economics right now are different; supply and demand is an unforgiving mistress. I expect one day we will once again see similar prices (accounting for general inflation), but that's going to be a while in coming.
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Old February 26, 2013, 03:10 PM   #14
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Great pictures here.

http://www.m4carbine.net/showthread.php?t=14534

I used the heaviest bolt carrier I could find, I think it is the "enhaunced" and a Tubb's carrier weight. The heavier carrier adds reliablity as the extra weight helps close the bolt.
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Old February 26, 2013, 05:38 PM   #15
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I don't understand the mentality of hoarding BCG's, keep one BCG maintained and it should last the life of the rifle w/ gas ring replacements every few thousand rounds.

Are these SHTF people that are going to run around with 2 ARs slung on their backs and a whole satchel full of BCGs?
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Old February 26, 2013, 09:07 PM   #16
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I don't understand the mentality of hoarding BCG's, keep one BCG maintained and it should last the life of the rifle w/ gas ring replacements every few thousand rounds.
Bolts don't always last the life of the rifle. They can indeed break, and if they do, the quickest way to get the rifle back into action is by slapping in a completely new group.

If somebody is getting upset about somebody else's replacement parts, that tells me more about the upset person's lack of preparation than anything else.
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Old February 26, 2013, 09:25 PM   #17
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I understand a backup bolt, I have a backup in my grip. I just don't know how realistic it is to be carrying around a bunch of complete groups. The way some people act, they expect to be changing out BCGs like mags during a fight.
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Old February 26, 2013, 10:16 PM   #18
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For me, a complete BCG wasn't that much more than a bolt. May as well get the whole thing so you aren't wanting for gas key and screws, firing pin, firing pin retaining pin, etc. When it's a $30 or so price difference, just get it all. Easier to swap out too.

The downside is that if you have spares of the hard to get parts, those tend to work their way into becoming complete rifles. Amazing how these things grow.
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Old February 27, 2013, 08:52 AM   #19
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Back in June 2012, I bought a BCM BCG from Brownells and it was 250, including shipping. Like I said, I have never been a very good bargain hunter.

I put the new BCG into my Rock River AR, and tested it with about 100 rounds, then I put the original Rock River BCG back into it. The Rock River parts are chrome plated, which makes clean-up easier. I keep the BCM as a spare. Some AR expert (forgot who) once said that 90% of the failures in an AR can be fixed by swapping out the BCG.
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Old February 27, 2013, 10:27 AM   #20
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Some AR expert (forgot who) once said that 90% of the failures in an AR can be fixed by swapping out the BCG.
I don't know about that... I'd say 90% of non-magazine related failures can be traced to the BCG, but that's me pulling numbers out of the air. It does seem that if there's function issues that are not magazine related then chances are there's some kind of issue with the bolt or carrier- gas key problems, bad bolt, etc. But magazine problems are a big issue with semis in general.

IMO, the bolt carrier group is probably the most important factor in reliability in the AR platform once magazines are accounted for. Poorly torqued/staked gas key screws, busted bolts, they will stop a gun in a real hurry.
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Old February 28, 2013, 02:55 PM   #21
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Get a good bolt. Don’t choose the cheapest option. If your bolt breaks, your gun goes down. Bolts are subjected to the highest amount of stress in your AR. Carpenter 158 steel is mil-spec should be considered minimal for any service level grade AR. Bolts are relatively cheap. It is only $50 for a good one. Please don’t skimp on this part. MP/HP testing should be a requirement for everyone’s build. Chromed or coated bolts and BCGs are nice but not necessarily needed. Coated units definitely make cleaning easier, but won’t necessarily make your bolt any more reliable than it already is. A regular parkerized bolt will do the job just fine. I would also recommend that you get a spare bolt, extractor, extractor spring and firing pin in your bag of tricks.

BCG (bolt carrier group) is the term for the whole assembly which includes the firing pin, bolt, and housing. The carrier usually doesn’t wear out and can be reused. When deciding between a semi auto (SA) and full auto (FA) carrier for semi automatic applications, either one will do the job. FA carriers are made heavier because more mass is needed to slow the cycling rate of full auto applications. Heavier does not necessarily mean better in this instance though. FA carriers also have a small shroud that protects the firing pin from hitting the hammer when the BCG cycles back and resests the hammer. For SA guns, this difference is negligible and in some cases unwanted. There are applications (mostly for competition guns) where some users actually want the fastest cycling possible and opt for light weight BCGs. My personal opinion is that since most factory guns are overgassed, I would prefer a full auto carrier for the added mass and for the shroud protecting the firing pin. Interestingly enough, having a FA carrier doesn’t make your gun automatic nor is it really necessary for all FA guns.

Insist that the gas key bolts of your BCG are properly staked. It’s added insurance to keep your gas key secure, thusly preventing any stoppages. Some manufacturers insist that staking is not needed (i.e. Young’s) but it’s really not too difficult to do yourself if needed.
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Old February 28, 2013, 04:53 PM   #22
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FA carriers are made heavier because more mass is needed to slow the cycling rate of full auto applications.
Strictly speaking, this is incorrect.

The extra mass of a FA carrier is the byproduct of what it is made to do, not the reason it is FA and not a semi. At the bottom rear of the carrier the full auto carrier has the bottom and top notches cut to the same relative spot (on the top and bottom)... that is so that when the bolt and carrier are all the way back in battery the bottom of that carrier catches the sear when in full auto (or burst) mode, causing the sear to let the hammer go again.

What makes a semi carrier a semi carrier is that the carrier is cut in that spot- usually just cut back a bit, sometimes cut all the way (as is the case with some Colts). Then it is unable to trip the sear if one is present. This prevents someone from just adding parts to a semiauto rifle and making it FA (there's some other tweaks to the lower that are often done to prevent this too).

That extra material back there is what increases the mass. It isn't that it has more mass and that makes it full auto, it's made to be a full auto carrier and that's why it has the extra mass.

As for the firing pin shroud, it's not done on every semiauto bolt carrier. Heck, I don't even have one that's unshrouded... not many are nowadays. What that does is catch the notch on the hammer (if the semiauto hammer is notched) to again prevent the gun from running full auto. It's more a precaution to prevent someone bubba'ing an AR into a full auto than anything else, but it's another thing that keeps the maker from getting into trouble from those who accuse them of selling "easily converted" guns.

FA carriers are often preferred, but in actual use any difference is minimal and I wouldn't set about replacing a semi carrier with a FA one if I already had a quality setup in the rifle.
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Old February 28, 2013, 06:19 PM   #23
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Here's a pic of the two (quick and dirty pic with my phone, and yes, those are .45ACP rounds propping them up behind the gas tube):



Top is a semiauto RRA BCG. Bottom is a FA Spike's.

Note at the bottom rear (left side) of the carriers. The FA (bottom) has the cuts even at the top and bottom. This is so the bottom of the carrier can catch the sear in a FA lower. The semi (top) is cut further to the rear to prevent it from ever being used to trip an auto sear.
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