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Posted: 11/21/2011 2:43:58 AM EDT
I am building a Mk18 clone SBR. I am getting ready to order an upper and am wondering if there is any benefit of one over the other when it comes to semi vs full auto bolt carrier. I dont have 15 grand to dump so its going to be a semi auto only SBR, but if the price is exactly the same is there any benefit to the FA carrier as far as function/reliability of the 10.5 in barrel is concerned? or anything else Im not aware of?
Link Posted: 11/21/2011 3:00:19 AM EDT
i have no idea but based on what i hear with SBR's i would think the non FA BCG would be more reliable.

lighterweight combined with not as much gas pressure = better cycling.

any one got a factual answer?
Link Posted: 11/21/2011 3:21:43 AM EDT
[Last Edit: 11/21/2011 3:22:17 AM EDT by Strongbow]
Full auto bolt carriers are very slightly heavier (slowing the action down... usually desirable in an SBR application) and it shrouds the firing pin so the pin isn't the part cocking the hammer.

Generally speaking, you can get more weight by going to a heavier buffer, but the extra weight certainly doesn't hurt, most of the time. The shrouded firing pin is the main reason to use a full auto BCG.
Link Posted: 11/21/2011 4:00:28 AM EDT
If you buy the DD Mk18 upper it comes with the FA BCG.
Link Posted: 11/21/2011 6:52:16 AM EDT
Originally Posted By truculenity:
i have no idea but based on what i hear with SBR's i would think the non FA BCG would be more reliable.

lighterweight combined with not as much gas pressure = better cycling.

any one got a factual answer?


Actually it would be opposite IMO. Most SBRs have higher gas pressure due to shorter gas system, I use the FA BCG and T2 Heavy buffer to slow things down and lessen recoil.

I only use FA BCGs.
Link Posted: 11/21/2011 10:05:36 AM EDT
[Last Edit: 11/21/2011 10:09:10 AM EDT by FMJ]
As far as performance I dont see any difference between SA/FA

Also never any problems with the Older SA carriers with the exposed firing pin

CMT & LMT SA carriers have shrouded firing pin
So no so called problems
Link Posted: 11/21/2011 10:10:30 AM EDT
Originally Posted By Strongbow:
Full auto bolt carriers are very slightly heavier (slowing the action down... usually desirable in an SBR application) and it shrouds the firing pin so the pin isn't the part cocking the hammer.

Generally speaking, you can get more weight by going to a heavier buffer, but the extra weight certainly doesn't hurt, most of the time. The shrouded firing pin is the main reason to use a full auto BCG.


Newish SA carriers have the shrouded firing pin
Link Posted: 11/21/2011 1:12:35 PM EDT
I've used both in a 10.3 & it doesn't matter.
Link Posted: 11/21/2011 5:35:45 PM EDT
Thanks a lot for all the replies. everyone's input was very helpful. I think I will stick with the FA carrier for this build.
Link Posted: 11/21/2011 7:06:08 PM EDT
I wouldn't pay more for FA, but the extra weight is nice on 16" or shorter rifles. Same price, I'd go for FA.
Link Posted: 11/21/2011 8:27:31 PM EDT
The difference in weight is minimal. The shrouding is the more desirable effect to me. Most these days are FA so just stick with that instead of trying to hunt down a quality SA piece.
Link Posted: 11/21/2011 9:16:27 PM EDT
I got the m16 bcg from larue and it has a FTF about every other round when running suppressed.

Mabey FA carriers dont work well when over gassed???
Link Posted: 11/22/2011 3:23:49 AM EDT
[Last Edit: 11/22/2011 3:25:31 AM EDT by Strongbow]
Originally Posted By FMJ:
Originally Posted By Strongbow:
Full auto bolt carriers are very slightly heavier (slowing the action down... usually desirable in an SBR application) and it shrouds the firing pin so the pin isn't the part cocking the hammer.

Generally speaking, you can get more weight by going to a heavier buffer, but the extra weight certainly doesn't hurt, most of the time. The shrouded firing pin is the main reason to use a full auto BCG.


Newish SA carriers have the shrouded firing pin


Yup. But unless you can inspect it, I would go with the FA carrier to be sure. There's no advantage to SA carrier I can think of. Might as well use the carrier the gun was designed with.

I have seen a broken firing pin on an unshrouded carrier (though the source of the pin was unknown, so likely the pin was crap).
Link Posted: 11/22/2011 8:26:15 AM EDT
Who all makes the FA bolt carriers?
Link Posted: 11/22/2011 8:51:54 AM EDT
Does anyone feel that their gun cycles smoother with one or the other? Can you feel the speed and recoil difference by changing from SA to FA weight carriers?
Link Posted: 11/22/2011 11:29:43 AM EDT
[Last Edit: 11/22/2011 11:30:42 AM EDT by FMJ]
Originally Posted By M4-AK:
Does anyone feel that their gun cycles smoother with one or the other? Can you feel the speed and recoil difference by changing from SA to FA weight carriers?


nope
but you could try running different buffers
Link Posted: 11/22/2011 2:28:11 PM EDT
[Last Edit: 11/22/2011 2:32:18 PM EDT by REARSPROCKET]
The shrouded firing is the most important, the extra weight of the FA BCG doesn't hurt either, especially with a short barrel . IMHO the Young Man. BCGs are a no brainer for a top shelf BCG, unless your on a tight budget ?––-> http://www.youngmanufacturing.net/
Link Posted: 11/22/2011 4:53:30 PM EDT
I use nothing but FA carriers and rounded hammers. No problems, no bent firing pin retainer pins. Guns have smooth action and no failures of any kind.
Link Posted: 11/22/2011 7:12:50 PM EDT
I have a Young's NM F/A BCG. Their gggggggggreat! ::points finger up in the air"
Link Posted: 11/23/2011 1:54:23 AM EDT
Originally Posted By tlwest1986:
I have a Young's NM F/A BCG. Their gggggggggreat! ::points finger up in the air"


Me too. My dealer, Bison, staked the carrier key bolts for me with his MOAKS tool.
Not only are the Young's NM carriers chrome, but also slightly oversize on the OD. The differences are detailed on their website.
Link Posted: 11/23/2011 4:22:36 AM EDT
Originally Posted By jough43:
Originally Posted By tlwest1986:
I have a Young's NM F/A BCG. Their gggggggggreat! ::points finger up in the air"


Me too. My dealer, Bison, staked the carrier key bolts for me with his MOAKS tool.
Not only are the Young's NM carriers chrome, but also slightly oversize on the OD. The differences are detailed on their website.


+2...I went to the range yesterday, once I got home, I pulled the BCG, I didnt even bother wiping it off, it looked like it was never fired. I love the hardchromed finish.
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