I was looking at a friends AR tonight and saw that he has a half circle bolt carrier in his AR.  I went home and looked at mine and mine was a full circle.  What is the difference between them?  Is either one better then the other?

Your friend has a semi-auto bolt carrier.  You have an M16 bolt carrier, which works fine and protects the firing pin collar (M16 and AR15 firing pins are slightly different).  New designs can have the full circle or more of a ramp that protects the firing pin.


Edited to say, sorry for the half assed answer.  I took an uneducated leap and I am very happy I was schooled and corrected with a wealth of information!  I learned a lot myself.  I need to keep my mouth shut until I know what I am talking about....

A little clarification is in order.  His friend has a Colt blue label semi-auto bolt carrier (half circle) and he has a semi-auto bolt carrier that is like the ones that Colt used in their pre 1989 green label rifles and is the design now used by all the AR15 manufacturers.  Mostly all of the semi carriers made now have the long ramp that protects the firing pin.  Even the new Colt semi carriers now have this feature.

You cannot asert his bolt carrier is full auto just because its full circle.  I run a full auto carrier and had to get it special ordered through an FFL.  Civilian ARs dont often come with full auto carriers.  Even the firing pin ramp can be included on some semi carriers that are full circle.

My bushmaster I bought about a year ago had a unmilled ramp on the semi-auto carrier (fully enclosed firing pin). So about 2 weeks ago I order another bushy carrier for my franken-AR thinking it would be the same. It was not, the carrier was milled to expose the firing pin. [:(] Who still makes enclosed pin carriers?

That's weird, this morning I received a bolt carrier from a COLT dealer, and I was just wondering the VERY SAME thing, I replaced my olyarms bolt carrier that cracked because of a kaboom.

It's the colt design less strong?

Any info REALLY appreciated, thanks

Thanks for the reply's so far guys.  
Just to clarify my Bolt carrier is NOT an M16 carrier.  
Is there one bolt that is better then another?  I am working on a project rifle now so which carrier would you use a full circle or half circle?  Is either stronger then the other?

I run both kinds and have not had a bolt carrier related problem with either. I do like the added weight of the full circle carriers. to me it just seem to give just a little more forward momenton to help lock the bolt. I have nothing to support this, just a feeling.

My favorit bolt is my Smith Enterprise bolt. It is an M16 bolt that has been milled back about a 1/4 inch so that it could never engage the auto sear on a real M16 (I checked with a department M4. It was a no go).

If I had the cash I would replace all my bolt and bolt carriers with the new LMT design.

Actually, it's not a "new" design; it's the very oldest[:D]  The very first Colt AR15s had M16 carriers that had the front of the lower shoulder milled back about 1/4-3/8 inch so they couldn't trip an M16 auto sear.  After a couple of thousand of those went out, some bozo at Colt decided that they needed to mill out under the firing pin, and put a catch notch on the hammer.  The vast majority of the SP1s went out that way.  

After that, it gets kind of fuzzy, for me at least.[:D] I'm told that the full cutaway carriers were originally brought out when Colt went to the steel insert block in the back of the lower, but in between there was another partial cutaway that had more of the shoulder cut back.

For everyone except those who have a Colt w/the steel blocking piece, I strongly recommend taking an M16 carrier, cutting that under shoulder back about 1/4 inch. and getting rid of the others.  The AR15/M16 was designed to use a bolt/carrier assembly of a certain weight.  That's the way it will function best over time, and give the longest service.  Using a lighter assembly may function just fine,(and usually does), but the lighter part puts greater stress on the action each time a round is fired.

That approach has worked on my SP1 carbine for about 30 years now. I ain't about to change a thing[:D]

Here is a pic of a RRA complete bolt (front) I just got from ADCO verses a Bushy complete bolt(rear).

[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=15858[/img]

I think I'm going with RRA carriers from now on.

MM419

shamayim:

You need to reread my post. The LMT bolt is VERY different than any bolt availible and is quite new.

I never claimed that the M16 bolt with 1/4 cut off was something new, its just what I like.

If you are unfamiliare with the LMT bolt and bolt carrier go to the EE and do a search. MSTN is selling them for $300 complete and $180 for just the bolt.

Here is a pic of the LMT bolt next to a Colt.
[img]http://www.hunt101.com/img/054144.jpg[/img]

Sorry for the goof. Yeah, I've seen the thread, but had forgotten the name and just assumed you were talking about an early dup[:D]

I don't know; after 8-9000 rounds out of the SP1 with only an extractor spring change, I'm happy enough w/Stoner's original design to not be overly enthused about this new thing.

I'll get back to you on it in 3 or 4 years[:D]

I hear ya. But its new man ITS NEW!!!

If a heavier carrier is better, why not a heavier buffer?  Any problems with that?  It would be a lot easier to make.

That is exactly what Colt did when they introduced the H buffer on the M4 stock. H = Heavy.

Okay, now I know there are many variants out there, especially these recent days.  I want to know the same original question about which is better - WHO MAKES THE BEST CARRIER OUT THERE?  Yeah, I realize as long as it is mil-spec/government issue there is nothing wrong with it but for those that want the best all purpose, say for an M4 semi auto clone, what brand and model is the shiznit?

what are the advantages of an enclosed-pin carrier vs. the exposed pin carriers?

My Oly's bolt carrier appears to protect the firing pin. The lower part doesn't seem to be milled as far back as in the picture shown above, but it is slightly further back than the top.

crappy pic:

[img]http://www.boneville.net/pix/olybolt.jpg[/img]

Great pictures Troy.  Here are some for sale (not so sneaky sales pitch):

[URL]http://www.ar15.com/forums/topic.html?b=7&f=22&t=176942[/URL]

OAI buys their parts from a multitude of suppliers. Sometimes they get slotted semi carriers and sometimes M16 carriers that require millwork. When the carriers are milled not a lot of attention (they're sometimes modded on a belt sander) is paid to where the face of the bottom shroud ends up.

I know one advantage.

If your rifle begins to go full auto because of a disconector/ hammer related problem... then that allows the hammer to catch the back of the firing pin on its return to chamber a round. When the Firing pin is caught, it can be bent by the violent foreward cycle of the rifle. That colloar protects the firing pin from such an incident. I know this because when my DAEWOO had a disconector related problem, I was out of a firing pin after it got bent by the hammer.

Just put an M16 carrier in your AR15 and be done with it.  It is not illegal.  If you doubt it show me where the ATF has stated a full auto carrier with no other full auto parts is illegal or a law with such wording in it.  It does not exist.  I have a letter into the tech branch and have been waiting over 6weeks for them to put in writing that it is not illegal but I am wondering if they dont want to open a can of worms.  My next leter will be certified and I will have it notarized so they cant say they didnt get my next one...

The difference is whatever you see. There are dozens of ways to make a Carrier, you are looking at two of them. Colt alone has changed their method at least 5 times that I know of.

Only 5?  Yep, you can count on Colt to go changing things, making non standard parts, making things difficult. [flame] Looks like the LMT B/C assy is the way to go for now.  At least the rest are wising up to the benefit of a longer ramp to protect the firing pin.