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I am thinking about getting a shorter barreled upper on an ar 15 I acquired. I am being told that I can use my existing bcg. I do not understand how this can be. I would not swap bolts on a bolt action rifle. It must be based on how ar 15s head space
Could some one who knows alot more about ar 15s than I do weigh in on this.

Seems like with most things there is always more to learn.

Respectfully
James
 
AR's are totally different than a bolt gun. Most AR's are mill spec so you can switch parts out from one to another. You could use your upper and BCG and just switch out the barrel if you wanted to. If you buy a completed upper then yes you could just take the BCG and put it in the new upper.

I hope that explains it. I am not the best at explaining things like that. @Kruejl could probably explain it a little better.
 
AR's are totally different than a bolt gun. Most AR's are mill spec so you can switch parts out from one to another. You could use your upper and BCG and just switch out the barrel if you wanted to. If you buy a completed upper then yes you could just take the BCG and put it in the new upper.

I hope that explains it. I am not the best at explaining things like that. @Kruejl could probably explain it a little better.
Thank you.
 
Your BCG will be just fine with a shorter barrel providing it's a mil-specish type BCG and not some wonky one-off commercial type AR configuration.
BCG and barrel should mesh just fine. Where you're going to have problems, if any, is in the gas system and buffer system creating timing issues. Make sure you're not over gassing and that your running a heavier buffer to slow down the recoil on the buffer spring.
 
Your BCG will be just fine with a shorter barrel providing it's a mil-specish type BCG and not some wonky one-off commercial type AR configuration.
BCG and barrel should mesh just fine. Where you're going to have problems, if any, is in the gas system and buffer system creating timing issues. Make sure you're not over gassing and that your running a heavier buffer to slow down the recoil on the buffer spring.
Thanks for that info. Kind of made my decision for me.
 
Depending on how much wear the existing bolt has, it should be kept with the existing barrel, because they wear together. Putting an old worn bolt in a new crisply cut chamber could cause premature wear in the new barrel and potential accuracy issues IMO.

Or who knows, maybe it's just all hocus pocus and makes zero real world difference. Just something I'm anal retentive about.
 
Thanks
I think I will just buy a new shorter barreled rifle. Never can have too many and should be no issues that way.
 
Sorry, I missed this one. As stated the BCG doesn't care how long the barrel is. The upper receiver that the carrier slides into is the same (headspacing left off the table here) and as long as the barrel is assembled and torqued properly you can use any off the shelf BCG you want as long as it's made for the caliber.

Use a carbine length buffer and spring and you will be fine for any shorter barrel pistol configurations. I've ran down to 7" with a carbine buffer/spring and it worked just fine.

I've swapped old and new BCG's among various AR's with ease.
 
Last Edited:
Thanks
I think I will just buy a new shorter barreled rifle. Never can have too many and should be no issues that way.


Addressing the original question about headspacing, the "magic" is in the steel barrel extension that the steel barrel is screwed too. The steel barrel extension is the part that inserts into the upper aluminum receiver.

The beauty of the AR design (by design) is if the headspace is set properly in the barrel extension you can swap it between different uppers (ad finem) w/o worrying about the headspacing. As was mentioned, the interlocking lugs of the bolt and the chamber of the barrel extension develop a "signature wear" to each other over time, but it isn't a deal breaker as far as headspacing is concerned. You could just purchase a new bolt and swap out the one for the other barrel into the existing carrier.

But like you said, one can NEVER have enough AR rifles!
 
Sorry, I missed this one. As stated the BCG doesn't care how long the barrel is. The upper receiver that the carrier slides into is the same (headspacing left of the table here) and as long as the barrel is assembled and torqued properly you can use any off the shelf BCG you want as long as it's made for the caliber.

Use a carbine length buffer and spring and you will be fine for any shorter barrel pistol configurations. I've ran down to 7" with a carbine buffer/spring and it worked just fine.

I've swapped old and new BCG's among various AR's with ease.

A .750 gas block properly aligned and the appropriate length tube hasn't let me down yet.

Agreed. And you only need to monkey around with it if you're having timing issues, otherwise carry on...
 
I've only had to once, and it was a loose block that wasn't properly pinned. Easy fix. Although it turned my AR pistol into a single shot that day. :p
 
I've only had to once, and it was a loose block that wasn't properly pinned. Easy fix. Although it turned my AR pistol into a single shot that day. :p

Had that same issue on a rifle length. only the gas hole just needed a little reaming out... I guess not all specs are created equal.
 
Addressing the original question about headspacing, the "magic" is in the steel barrel extension that the steel barrel is screwed too. The steel barrel extension is the part that inserts into the upper aluminum receiver.

The beauty of the AR design (by design) is if the headspace is set properly in the barrel extension you can swap it between different uppers (ad finem) w/o worrying about the headspacing. As was mentioned, the interlocking lugs of the bolt and the chamber of the barrel extension develop a "signature wear" to each other over time, but it isn't a deal breaker as far as headspacing is concerned. You could just purchase a new bolt and swap out the one for the other barrel into the existing carrier.

But like you said, one can NEVER have enough AR rifles!

Buy a quality made barrel and headspacing shouldn't be a worry. If it's aligned properly during the install (pretty darned hard not to) you should be able to swap out BCG's as you see fit. AR headspacing issues are so far and few between. Grab a decent barrel, torque the barrel nut to 50 ft/lbs and enjoy!
 
Thank you all for the information. I feel I have the information I was looking for
ARs are still new to me.

Cool thing about ARs is they are a lot like Legos. They are so modular that most, mass produced parts, fit together so you can build a plethora of configurations...
 
Buy a quality made barrel and headspacing shouldn't be a worry. If it's aligned properly during the install (pretty darned hard not to) you should be able to swap out BCG's as you see fit. AR headspacing issues are so far and few between. Grab a decent barrel, torque the barrel nut to 50 ft/lbs and enjoy!

Agreed. This is paramount to an AR build just like the drive train on a car. A good BCG, bolt, and barrel. Everything else is just rollmarks...
 
Glad you got the info that you were looking for @JRuby and by people that know way more than me. These guys have got me addicted again after a long time out of the military and now there is so much more to learn especially when you are building them yourself.

But damn its fun. :D
 
Glad you got the info that you were looking for @JRuby and by people that know way more than me. These guys have got me addicted again after a long time out of the military and now there is so much more to learn especially when you are building them yourself.

But damn its fun. :D

"Guns is funs" is my motto. Especially with ARs. Pick your favorite roll mark and make it your own. They're are so many aftermarket parts for ARs. What other gun can you do that with? SBR, SPR, truck gun, Varmint slayer, bench shooter... The list goes on. And being able to have one lower and so many different uppers... 5.56, .223, .223 Wylde, 6.5 creedmoor, 6.5 grendel, 50 Beowolf... Stoner was a friggin' genius.
 

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