View Full Version : Drawbacks to semi-auto bolt carriers?
Obviously, we all prefer the full auto version, but are there any reliability issues with using semi-auto bolt carriers? I've been looking for a LMT Enhanced Carrier and I have a line on a semi-auto one. I'm looking to continue with gas-to-the-eye mitigation by using an enhanced carrier with a heavier bolt.
Straight Shooter
09-18-21, 17:40
No probs in the LMT Ive been running for 13 years now. NOT ONE.
Why not just dial the gas down?
I'm looking to continue with gas-to-the-eye mitigation by using an enhanced carrier with a heavier bolt.
Why not just dial the gas down?
Gas is already dialed down a bit via GT being set up for 50/50 supp/unsupp. I'm running the Tubbs FW spring with an A5H3 after finding it has less dot movement than the other spring options. Several other threads have mentioned a Tubbs FW/A5H4/E-carrier combo to help keep gas out of the eye. Since the S/A E-carrier is in a rifle with a BRT 16" Opt barrel, which I believe is unneeded given how well you did on those 16" barrels, I'm going to try pairing the E-carrier with the Tubbs and A5H4 and see if it cuts the gas down a bit. I'd like to know if there are any mechanical reliability issues that a S/A carrier might induce before I start the experiment. I may also add the Radian CH specific to this application down the road.
bamashooter
09-19-21, 07:36
Obviously, we all prefer the full auto version, but are there any reliability issues with using semi-auto bolt carriers? I've been looking for a LMT Enhanced Carrier and I have a line on a semi-auto one. I'm looking to continue with gas-to-the-eye mitigation by using an enhanced carrier with a heavier bolt.
Not really though most of mine are "full". ARs are very simple, reliable, and waay over-exploited for profit and self-worth.
As long as it’s not a Colt type with the half circle back part and the cut out that exposes the firing pin, they’re fine.
As long as it’s not a Colt type with the half circle back part and the cut out that exposes the firing pin, they’re fine.
The carriers with the ramp cut to expose the firing pin are (as far as I know) a total no go when combined with an M16(large head) firing pin and old school AR-15 hammers that have the notch cut in them instead of the M16 rounded profile.
The carriers with the ramp cut to expose the firing pin are (as far as I know) a total no go when combined with an M16(large head) firing pin and old school AR-15 hammers that have the notch cut in them instead of the M16 rounded profile.
Thank you. Which particular notch are you referring to?
Thank you. Which particular notch are you referring to?Far right on top(and bottom) are notched. Rarer and rarer to see them I think, but they are around.
http://www.biggerhammer.net/ar15/hammers/
Usually/by design) that hammer combined with M16 firing pins(that have larger retaining collars) will snag and lock the action up when used with the bolt carriers that have the ramp cut away exposing more of the firing pin.
Was a Colt thing that most everyone else copied till Colt ditched it 15? years ago roughly.
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Far right on top(and bottom) are notched. Rarer and rarer to see them I think, but they are around.
http://www.biggerhammer.net/ar15/hammers/
Usually/by design) that hammer combined with M16 firing pins(that have larger retaining collars) will snag and lock the action up when used with the bolt carriers that have the ramp cut away exposing more of the firing pin.
Was a Colt thing that most everyone else copied till Colt ditched it 15? years ago roughly.
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Much appreciated! I've heard of the notched hammer, but never needed to know what it was until now.
As posted. Avoid the Ramped carriers. The rear relief cut on the carrier isn't too big of a deal, but the ramped colt ones are not worth the trouble.
There is no mechanical function for the material removed on the modern semi carrier except to trip an auto sear.
The weight difference is minimal but the total reciprocating weight can be adjusted with the buffer.
As pointed out already, avoid the old “half moon” and “ramped” carriers and you will be fine.
Usually/by design) that hammer combined with M16 firing pins(that have larger retaining collars) will snag and lock the action up when used with the bolt carriers that have the ramp cut away exposing more of the firing pin.
Not really that simple.
Colt did not 'design' it to ball up simply because someone stuck a large flange firing pin in there. Colt designed it the way they did (notched hammer and unshrouded firing pin) to prevent some bubba from attempting to get their rifle to fire more than a single round with a single pull of the trigger by disabling / modifying their disconnector to intentionally cause the hammer to 'follow' the carrier home.
Look at it like a disconnector fail safe...
You are also a bit off as to why Colt reduced the dia of the FP flange. That was done to blend the flange with the ramp in the carrier and smooth things out as the carrier was moving to the rear. Had nothing to do with clearance issues on properly functioning parts going forward.
If I want to stick an M16 FP in my Colt rifle with the semi-auto carrier I can and it will work but over time the FP flange will take a beating. That beating happens as the carrier moves to the rear and the flange is mostly what is cocking the hammer.
What's the sizing difference between large diameter and small diameter flanged firings pins?
Does the LMT semi-auto E-carrier fit into the category of the firing pin cocking the hammer?
What's the sizing difference between large diameter and small diameter flanged firings pins?
I measured .335" on a new BCM AR15 FP just now and .372 on a Colt M16 FP flange. (.373" on a random M16 FP pulled from a Toolcraft carrier)
That is a whopping .037" difference in dia between the two with the Colt M16 pin extending down .0185" lower than the BCM pin flange.
I can pull the Colt pin from my rifle and measure it but would be a waste of my time as I already know it will measure pretty much the same as the BCM AR15 pin. I also know that after thousands of rounds sent downrange in that particular Colt rifle that the pin and its flange are not beat to hell and in perfectly good working order. Those trigger parts, the semi-auto unshrouded carrier, and its firing pin will easily outlast the barrel so long as I do not attempt to dick around with my disconnector and make a bubba auto wannabe conversion.
If your trigger sear and disconnector are functioning properly (hammer being held back like it is supposed to be) that M16 flange being .0185" lower means nothing as far as the carrier going home is concerned.
Not 'exactly' the same as the parts we are discussing here but still a good visual to you understand how the sear holds the hammer back (and LOWER) than where any FP flange would be:
https://i.imgur.com/5lpSADm.jpg
Look closely at the disconnector and its corresponding hook on the hammer in that picture and you may notice that (in a semi-auto config) if the disconnector was the part holding the hammer back that the hammer would actually sit / be held even lower and have more clearance between it and where the FP flange would be...
Colt M16 on top and somewhat recent Toolcraft M16 FP on bottom:
https://i.imgur.com/YZ7HDvk.jpg
Personally I like the fit and finish on the Colt parts better than the stuff that came with my Toolcraft carriers. Was not too many years ago that Colt dumped barrels of those on the market for dirt cheap. At about a dollar each - THAT was the time to buy good parts cheap and stack deep and I did... :)
I measured .335" on a new BCM AR15 FP just now and .372 on a Colt M16 FP flange. (.373" on a random M16 FP pulled from a Toolcraft carrier)
That is a whopping .037" difference in dia between the two with the Colt M16 pin extending down .0185" lower than the BCM pin flange.
I can pull the Colt pin from my rifle and measure it but would be a waste of my time as I already know it will measure pretty much the same as the BCM AR15 pin. I also know that after thousands of rounds sent downrange in that particular Colt rifle that the pin and its flange are not beat to hell and in perfectly good working order. Those trigger parts, the semi-auto unshrouded carrier, and its firing pin will easily outlast the barrel so long as I do not attempt to dick around with my disconnector and make a bubba auto wannabe conversion.
If your trigger sear and disconnector are functioning properly (hammer being held back like it is supposed to be) that M16 flange being .0185" lower means nothing as far as the carrier going home is concerned.
Not 'exactly' the same as the parts we are discussing here but still a good visual to you understand how the sear holds the hammer back (and LOWER) than where any FP flange would be:
https://i.imgur.com/5lpSADm.jpg
Look closely at the disconnector and its corresponding hook on the hammer in that picture and you may notice that (in a semi-auto config) if the disconnector was the part holding the hammer back that the hammer would actually sit / be held even lower and have more clearance between it and where the FP flange would be...
Colt M16 on top and somewhat recent Toolcraft M16 FP on bottom:
https://i.imgur.com/YZ7HDvk.jpg
Personally I like the fit and finish on the Colt parts better than the stuff that came with my Toolcraft carriers. Was not too many years ago that Colt dumped barrels of those on the market for dirt cheap. At about a dollar each - THAT was the time to buy good parts cheap and stack deep and I did... :)
The small flange firing pin refers to the Colt semiauto firing pin used in the Colt bolt carriers of the 90s to early 2000s.
The small flange firing pin refers to the Colt semiauto firing pin used in the Colt bolt carriers of the 90s to early 2000s.
I know.
What were your measurements on them?
Does the LMT semi-auto E-carrier fit into the category of the firing pin cocking the hammer?
No. All of this is old Colt weirdness and is completely irrelevant to anything on the market today.
You guys rock. Thanks for dropping all this knowledge.
You guys rock. Thanks for dropping all this knowledge.
I have some Dykem, a Colt rifle with the carrier we are discussing and all of the different firing pins.
Will dig out the rifle when I get a chance, paint some pin collars, do some cycling / dry firing and take some pictures for you.
Will be a bit as I am 'supposed' to be working on tax crap right now but pretty sure that should help you weed out the internet BS from the reality about the parts we are discussing.
Northridge
11-05-21, 01:42
There have been third party tests previously posted here showing that a heavier reciprocating mass has reliability benefits for M4 style AR type rifles (e.g. carbine length has system)
Without repeating all the details, the two key benefits are:
a) more mass in the BCG and buffer increase inertia and delay unlocking and extraction which allows a bit more time for chamber pressure to drop and the fired case to shrink thus reducing extraction effort. This reduces failures to extract.
b) more mass in the BCG and buffer increase momentum while stripping and chambering a new round which enables the rifle to overcome fouling and other factors (lack of lube, dirt, carbon fouling, bent rounds, etc)
Stronger recoil spring also helps.
Northridge
11-05-21, 01:50
BCG and buffer mass aids in reliable extraction and chambering.
The difference in mass between LMT style semi and full carriers is inconsequential, much less than the difference between buffer types.
The weight difference is minimal... I've weighed both, it's about 0.3 oz difference.
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