LMT and Colt BCG Difference...

AR/M4 AR Technical Discussion
1

Guys,
I have noticed only one difference between the standard LMT carriers, and the Colt carriers, and that is the underside rear portion of the carrier, which has the keyway slot milled in it, is much longer on the Colt, then on the LMT.
This is the keyway slot that slides over the buffer retaining post.
Can anyone tell me WHY this is? Is it just a different company with a slightly different design, OR is there some advantage to one over the other?
I would think IF there is an advantage of one over the other, than they would both be made the same, no?
Can anyone tell me why the difference?

Secondly, WHO makes Colt carriers? I think LMT makes their in-house, IIRC, but does Colt make theirs in-house, or get them elsewhere???
Thanks.

2

If both are M16 carriers they’ll be the same length. I think what you’re looking at is a Colt full auto (M16) carrier and a LMT semi (AR) carrier. When given the choice always run a M16 carrier.

3

Here is a good picture showing the two types of carriers side by side. Is that what the two you have look like? One of them looks like the carrier on top (AR-15) and the other looks like the carrier on the bottom (M-16)?

Derek

4

Why is that? Can I just drop the M16 carrier into any semi-auto AR?

5

Yes.

C4

6

my carriers picture…

7

Why?

There’s only 0.3 or 0.4oz difference in weight between a fully shrouded semi-auto carrier and an M16 carrier.
Much more weight can be made up just by using a heavier buffer.

If the choice is between a shrouded M16 carrier and an SP1 carrier, then I certainly recommend the M16 carrier as well, but mostly because of the shrouding, not the weight.

8

Because that’s what it was originally designed. Sure you can make up for it but why not start on equal terms. I’m not advocating replacing all AR15 semi carriers in rifles you may already own, I’m saying if building new use a M16 carrier.

My old 2001 Mustang GT came with 17" wheels. When it needed tires I could have went and installed 16" rims and cheaper taller tires but why?

Weights of carriers I’ve weighed (w/o bolts, cam pins & firing pins):

Colt non shrouded 1/2 circle carrier 8.63oz
Colt shrouded 1/2 circle carrier 8.87oz
Bushmaster non shrouded AR15 carrier 8.92oz.
Bushmaster shrouded AR15 carrier 9.26oz.
CMT M16 carrier 9.46oz
ARES G35 M16 carrier 10.54oz.
Bushmaster gas piston AR15 carrier 10.10oz (w/screwed on solid carrier key like older POF, newest POF ones use integral key like ARES).

HK416 carrier w/bolt, cam pin and firing pin installed. 12.0oz

The only gun I run a non-M16 carrier in is my 3gun rifle. I use a 1/2 circle Colt unshrouded carrier in it. It’s a mid-length and I use a regular CAR buffer spring and an H buffer w/Geissele trigger.

9

Question to Randall rausch and GotM4,
On the M16 style Carrier does the metal covering the end of the firing pin “cock” the hammer? And on the other AR-15 style carriers does the actual end of the firing pin “cock” the hammer?

Thank you gentlemen.
Stay Safe,
Jack

10

Yes the M16 was designed so that the carrier is supposed to cock the hammer, the firing pin isn’t supposed to cock the hammer. When the firing pin cocks the hammer like on unshrouded AR carriers it can cause early failure of the firing pin (it’s gets all chewed up), and bends firing pin retaining pins. Colt makes/made the ‘unshrouded’ carriers from M16 carriers that didn’t pass spec. for whatever reason.

11

That is what I thought. Thank you for verifying.

12

Ok guys
gotm4 and tigerseven are correct.
Thanks for posting the link to that pic tiger!
Apparently, I recently purchased an LMT carrier, and I thought I had requested a full auto carrier, but I guess there was a communication gap, or mistake somewhere.
Regardless, I appreciate the pics!

13

Actually, the firing pins only get chewed up and retaining pins bent when either the hammer/trigger or the receiver is out of spec, allowing the end of the hammer to sit too far UP inside the upper receiver.

You can fix this problem with a little grinding to relieve the tip of the hammer.

Unsrouded carriers are designed to work in unison with a notched hammer and semi-auto firing pin.
Should the disconnector fail and the weapon “run away”, the notch on the hammer will catch on the firing pin spool.
Going with a shrouded type carrier defeats this safety feature.

14

thanks for that bit of info Randall.

:wink: Billy

15

I think it’s more to sell out of spec carriers (that didn’t meet M16 specs), I’m sure Colt won’t admit it. It’s a Colt ‘fix’ on civilian rifles for something that was never broken. It also requires the use of a AR15 firing pin. A M16 carrier (and even a shrouded AR15) can use both a M16 firing pin and an AR15 firing pin.

That’s what they’ve said at Colt armorers classes for years.

If this were a safety design (not a bullsh** explanation from Colt about it) where is this same design in the M16/M16A1/M16A2/M16A3/M16A4 and the M4 and M4A1s? Wouldn’t full auto guns be much more likely to have disconnector failure over most semi auto rifles out it the public?

Colt must have changed its mind about this on all new semi rifles as most of the ones I’ve seen since about 2004 have had full auto (shrouded) carriers or semi auto (shrouded) 1/2 circle and some full circle carriers which leads me to believe the unshrouded design and explanation Colt gives is bullsh** (just my opinion here). Hammers aren’t meant to be ‘fitted’ and IIRC there’s isn’t anything about ‘fitting’ in the M16 TM. Why make it more complicated than it needs to be?

I’m just guessing here but I think there’s probably two reasons why new Colts now have shrouded carriers. One, with modern accurate machining they probably F’up very few carriers in production which would then be made into unshrouded carriers. Two, they probably figured out that making both AR15 and M16 firing pins and machining carriers down to unshrouded in the long run ends up costing much more money than just making all carriers shrouded and making one firing pin (M16 style).

M16s aren’t hard to control if they ‘run away’, the most you have is 28/30 rounds. I’ve fired a M60E3 that ‘ran away’ and that was a little different story. I’ve seen many ARs with disconnector failure and I’ve never seen one fire over 8-9 rounds per time when that happened, most just double and triple.

As I said before if given the choice run a M16 carrier. If you can’t get your tinfoil thick enough, then just run a shrouded AR15 carrier.

Also the use of the ‘notched’ hammer like in your pics limits your lower to rifle calibers in DI & piston guns. It will not work with a 9mm or some other blowback uppers. 9mm requires either a 9mm semi auto hammer, a full auto M16 hammer (if used on a registerd full auto lower) or an unnotched hammer like the DPMS style semi hammer which is essentially a M16 hammer with the sear tail bobbed off. Full auto Colt submachineguns have regular M16 hammers, triggers, disconnectors and sears.

unnotched hammer.

And just so people understand what we’re talking about in carrier shrouding:

unshrouded 1/2 circle Colt carrier.

shrouded 1/2 circle Colt carrier.

16

The notched hammers & exposed firing pins were, of course, Colt’s way of minimizing legal exposure to “manufacturing ready to convert machine guns” … via the disconnector method. With the raised shelf precluding drop in sears & this feature, your average garage tinkerer won’t be producing machineguns.

And, a 17+ lb m60 at 550 rpm is a hell of a lot easier to stop running away, than a 7-1000 rpm, 5lb AR… twist the belt with maybe 5-7rds away vs 30

17

Thats what I always thought.

Bob

18

That’s how I stopped it, it got maybe 12-15 rounds off before I got it to stop by twisting up the belt. That was back many moons ago in 1987-88 at Quantico Range 7 when I was 17 or 18 years old.

Like I said I’ve never seen an AR go ‘auto’ that fired more than 8-9 rounds, 99% of the ones I’ve seen just double or triple, I’m not saying it doesn’t happen. I’ve just never seen it. It’s a possiblity vs. probability thing. It was possible for me to beat Todd Jarrett in Limited this weekend but the probability was pretty f***ing slim! :wink: And thus I ended up shooting 58.31% of what he did (he was the Limited winner).

I’m sure a runaway AR can go through a whole mag if someones been Hack-Fu gunsmithn’ with the trigger/hammer/disconnector. Push the mag release button with your trigger finger on an AR and the mag should fall and the rifle would stop.

19

That would be my immediate action as well. :slight_smile:

20

Is a Colt “Half-Circle” carrier the only one that will work in a gun with the raised metal sear block in the lower? In other words, does the Colt sear block interfere in any way with a standard AR15 or M16 BCG with the “full circle”? Thanks.