Hi, and thanks in advance for any help.

I'm starting to gather parts for a build. I want to do an AR15 with a 20" wylde barrel and a 1:8 twist. The reason for the 20" is, many years ago (may be a factor) in the army with an m16a1, I was hitting pop up silhouettes at 400 yds. Going to the range now with a 16" barrel/magpul pro sights and  I can just hit paper at 150 yds. I like the look of a collapsible stock and also the fact that the pin can be drilled out should I move out of our peoples republic state. Now to the question.

While unsuccessfully looking for a rifle length extension tube that will accept a carbine adjustable stock, I ran across a few threads on other forums that addressed the issue by saying: use a carbine tube setup with an H buffer. My question is.... will this setup reliably cycle and not beat up the moving internals? And two, what would be the best buffer for  20" barrel with a rifle length gas system, H1, H2, H3? And last but not least will the standard carbine buffer spring work or is a heavy carbine spring needed with the heavy buffer?

Thanks again for your advise and wisdom.

Stag used to make a standard length extension that houses a standard buffer and spring that had a fixed M4 stock. 

The buffer tube extension is part of the gas system, if you mess with that, you  can expect problems.  The distance between the chamber and the  gas port determines the timing of the system.  The distance also impacts pressure.  Gas port distance, gas port size, buffer weight, extension tube length (length of buffer travel) have all been thoughtfully calculated to facilitate proper operation.  You can probably get out of spec parts to cycle with some finagling, but it will likely cause reliability problems.

Magpul has some very nice fixed rifle stocks that are adjustable, the USGI A2 stock is actually pretty nice too.  Ace makes a great skeleton stock.  Maybe look at some of those options before you Rube Goldberg a rifle.

Magpul PRS and Ace Skeleton

 

6 hours ago, fslater said:

The reason for the 20" is, many years ago (may be a factor) in the army with an m16a1

I too had the same soft spot and missed my old M16.  That 20"'er was our only "choice" then.  So I got one.  Solid stock and triangle forward grips, fixed sites and carry handle.  Then I realized one thing that blew my fantasy away - How much that 4" can weigh!!  So I built a 16" and she sits next to the one that makes me wonder how the hell I carried that mutha like a third arm everywhere I went.  

2 minutes ago, BobA said:

I too had the same soft spot and missed my old M16.  That 20"'er was our only "choice" then.  So I got one.  Solid stock and triangle forward grips, fixed sites and carry handle.  Then I realized one thing that blew my fantasy away - How much that 4" can weigh!!  So I built a 16" and she sits next to the one that makes me wonder how the hell I carried that mutha like a third arm everywhere I went.  

That’s too funny.

I learned the AR pattern rifle on M4 (14.5”) and shorter (R0933 Commando 11.5”) variants.

I built an M16A1 clone a couple of years ago and can’t get over how light it is compared to my work guns.

3 minutes ago, High Exposure said:

I built an M16A1 clone a couple of years ago and can’t get over how light it is compared to my work guns.

This one is a Bushmaster XM15-E2S.  Accurate as hell but makes you pay the price.  Maybe it's the price of age (mine)   I must admit it is a smoother shoot though.

My go to AR is a 20" heavy barrel with carry handle irons.  Why?  For me it's better for shooting quickly and accurately around the yard. Maybe 25-100 yds or longer.  I could always grab my wife's 16" Bushmaster with illuminated optics but I like something heavy in my hands as long as I don't have to hump it all day in day out.

Though I find the carbines very useful, I have an affinity for the 20" rifles of old. 

9 minutes ago, Old School said:

I like something heavy in my hands as long as I don't have to hump it all day in day out.

That's what she said.

27 minutes ago, BobA said:

This one is a Bushmaster XM15-E2S.  Accurate as hell but makes you pay the price.  Maybe it's the price of age (mine)   I must admit it is a smoother shoot though.

To be fair, my 20” has the original Colt pencil barrel bs the Govt profile barrel, or even heavy barrel, on some of my carbines.

Butt stroke

Rifle length gas systems are less violent and lower pressure at unlock time than mid-length or carbine buffer systems. The carbine has a stouter spring, but not much, and the buffer is lighter than a rifle buffer. 

I've run an 18" rifle length upper on a carbine length lower with a spikes S2 buffer with no problems.  I've also run it  with a full mass BCG and ~3oz rifle length buffer without issues. 

For a not TOO insane price, odin works makes a carbine size buffer with interchangeable weights. The AR-15 heavy combo cna be adjusted from 3.7-5.8 oz. Costs like $50. 

 

 

 

 

 

 

The Canadian Forces have been using a 20" barreled upper with a carbine butt stock for quite a few years (C7A2).  I believe they use an H2 buffer with it.