12.5” 5.56 Build Help Needed

[Kwfranklin88]

In the process of ordering parts for my first pistol build. I have some questions about the reciprocating system.

I want to use a lightweight BCG and adjustable gas block. I’m trying to keep the recoil as low as possible since my 9 year old will be shooting it.

My question is what gas length should I use with the 12.5” barrel? Mid or carbine?

What buffer and spring should I use with that barrel, BCG, and adjustable gas block? I wanted to use a captured or hydraulic spring to help further reduce recoil. Would it make a difference?

What are your recommendations for building a 12.5” 5.56 pistol that has the lowest recoil possible while still being very reliable. It will be used for coyote hunting so reliability comes first then recoil reduction.

Thanks for the help! Any information is greatly appreciated!

 

[NukeMan]

There's really no recoil to deal with. My 10 year old daughter probably 60lbs soaking wet can run my 10.5 pistol like a boss. Carbine gas, standard bcg and Geissele super 42 with h1 buffer. Also a standard a2 flash hider.
Personally I think making the ar lighter has allowed her to really step up her game vs when she was running a 16 inch barreled ar.

 

[Kwfranklin88]

There's really no recoil to deal with. My 10 year old daughter probably 60lbs soaking wet can run my 10.5 pistol like a boss. Carbine gas, standard bcg and Geissele super 42 with h1 buffer. Also a standard a2 flash hider.
Personally I think making the ar lighter has allowed her to really step up her game vs when she was running a 16 inch barreled ar.

Yea I agree the recoil is very minimal. That’s why I don’t want to compromise reliability. But if I can get it to shoot a little softer then I figured why not.

 

[Docsherm]

Carbine. No real need for a MID 12.5 unless ypu are doing something really specific.

Carbine Gas for a GP set up.

 

[sea2summit]

I wouldn’t do a light weight BCG, it will be harder to gas correctly IMHO. My 12.5 has standard BCG and for suppressed work I put the H3 buffer in. But it is non-adjustable block so YMMV.

 

[tlsmith22]

I just got 2 11.5” pistols to shoot suppressed. I ended up using BCM lowers and uppers for both that I pieced together here and there. I had overgassing issues and that took a little bit to get worked out. I ended up using the adjustable Bootleg BCG and also doing the RTV mod to the charging handle to tame the gas issue. I also went with a Blue Sprinco spring and an H3 buffer, which helped with the recoil and also the gas issue. Then, a buddy of mine let me try his Vltor A5A2 buffer system and I was blown away! You talk abt cutting the recoil in half or more, it worked fantastic. So I ordered an A5A3 VLtor buffer, AR10 spring(VLtor) and dark hour defense buffer tubes(longer rifle length). This made these pistols really soft and smooth shooting both suppressed and I suppressed. I also added Law tactical folders to both.

 

[Kwfranklin88]

Carbine. No real need for a MID 12.5 unless ypu are doing something really specific.

Carbine Gas for a GP set up.

No nothing specific. It won’t be ran suppressed. I just wont a reliable rifle with as little of recoil as possible without compromising reliability.

 

[Constructor]

In the process of ordering parts for my first pistol build. I have some questions about the reciprocating system.

I want to use a lightweight BCG and adjustable gas block. I’m trying to keep the recoil as low as possible since my 9 year old will be shooting it.

My question is what gas length should I use with the 12.5” barrel? Mid or carbine?

What buffer and spring should I use with that barrel, BCG, and adjustable gas block? I wanted to use a captured or hydraulic spring to help further reduce recoil. Would it make a difference?

What are your recommendations for building a 12.5” 5.56 pistol that has the lowest recoil possible while still being very reliable. It will be used for coyote hunting so reliability comes first then recoil reduction.

Thanks for the help! Any information is greatly appreciated!

EVERYTHING depends on the size of the gas port in the barrel.
If you want to run a spring that has more resistance (captured) you will need a larger port. If you want to use a lightweight carrier you will need a smaller port.

If you get a barrel with a big port in it you will need a stronger spring or heavier buffer or AGB.

A mid gas barrel will be a little smoother.

 

[Kwfranklin88]

EVERYTHING depends on the size of the gas port in the barrel.
If you want to run a spring that has more resistance (captured) you will need a larger port. If you want to use a lightweight carrier you will need a smaller port.

If you get a barrel with a big port in it you will need a stronger spring or heavier buffer or AGB.

A mid gas barrel will be a little smoother.

Yea I’m planning on using lightweight carrier and adjustable gas block. I’m just not sure what buffer and spring to use with them. I would like to run the captured spring if it doesn’t affect reliability. I don’t have any experience with lightweight BCG, agb or captured springs.

 

[Constructor]

Yea I’m planning on using lightweight carrier and adjustable gas block. I’m just not sure what buffer and spring to use with them. I would like to run the captured spring if it doesn’t affect reliability. I don’t have any experience with lightweight BCG, agb or captured springs.

Start with the standard spring and buffer, what you have on hand then buy what ever you need to get the results you want. You don't want any carrier to bottom out in the tube. An AGB will allow you to tune it perfectly. The heavier the carrier and buffer the more movement you will have in the whole rifle.

 

[screaminyz]

I’m in the same boat and in the process of gathering all the parts to build a new 11.5 pistol. I’ve got the Faxon gunner 11.5 barrel with mid length gas system. I have a lightweight bcg, reduced power spring and the Taccom lightweight buffer with adjustable gas block I hope to get together soon. If it doesn’t work I’ll put in all the standard weight stuff and just reduce the gas as much as possible but cycles the bolt reliably. What’s everyone’s thoughts on the lightweight setup above?

 

[Kwfranklin88]

I’m in the same boat and in the process of gathering all the parts to build a new 11.5 pistol. I’ve got the Faxon gunner 11.5 barrel with mid length gas system. I have a lightweight bcg, reduced power spring and the Taccom lightweight buffer with adjustable gas block I hope to get together soon. If it doesn’t work I’ll put in all the standard weight stuff and just reduce the gas as much as possible but cycles the bolt reliably. What’s everyone’s thoughts on the lightweight setup above?

That’s pretty much exactly what I want to run. If it doesn’t compromise reliability. I figured the less reciprocating mass and the least amount of gas will soften the recoil impulses tremendously. Your basically removing 1/2 lb or 3/4 pound that is slamming back and forth.

 

[UpSideDown]

Don't set yourself up with problems to find solutions for. The round is going to create whatever recoil impulse it does. You really cannot reduce the amount of recoil produced for a given round, you can only extend the amount of time the impulse takes place over.

Ditch the lightweight BCG. It costs a lot of money and will worsen recoil. You want a heavier mass that cycles slower. This is also more reliable.

A stiffer spring and a lighter BCG is going to be super snappy. The same recoiling force taking place over less time makes a sharper feel.

The longest gas system you can use is the most reliable and softest shooting, again because it's forcing the BCG back more slowly. 12.5 should have plenty of dwell time with a Mid gas system.

The adjustable gas block might be helpful. You could dial the gas down until you have reliability issues and then go up from there. Adjust your gas with the gas block, not the BCG. If you adjust with the gas block the gas not used for cycling leaves the barrel. If you adjust with the BCG the unused gas exits into the chamber and charging handle, and makes for a more expensive BCG.

 

[Constructor]

Ditch the lightweight BCG. It costs a lot of money and will worsen recoil. You want a heavier mass that cycles slower. This is also more reliable.

A stiffer spring and a lighter BCG is going to be super snappy. The same recoiling force taking place over less time makes a sharper feel.

Most top 3 gun shooters will say that isn't true. Tuning the AGB can make both carriers cycle at the same speed. More mass moving in the buffer tube will shake/move the rifle more.
Reliability depends on some common sense. Don't try to use both light 223 varmint loads and heavy 77gr military spec loads. Choose ammo that creates apx the same amount of pressure and thrust.

 

[UpSideDown]

A comp shooter wants the gun in battery fast. If this is for a kid I’m imagining a slow push is better than a snappy recoil. Comp shooters aren’t shooting hunting rounds. Maybe light is the way to go? I would think more mass is better. Why else would guys praise the upgrade to heavier buffer tubes if they still cycle well in their gun?

 

[Shrubjr]

I've never had a 12.5, but I've done 10.5, 11.5, 14.5, and 16 over the years. I know 556 doesn't really recoil, but I hear what you're saying.

From experience, my 14.5" mid-length with a full-weight bcg is the nicest AR shooting experience I've had. If you build a 14.5 as a pistol you don't have to pin it, and given the SBA3, why not? Yeah, its a little longer, but not much, reliabilty is stellar, and if the .gov ever cracks down on pistols, you could pin it. Just my $0.02.

P.S. The 10.5, and 11.5 I had were MISERABLY loud!

 

[clcustom1911]

I've never had a 12.5, but I've done 10.5, 11.5, 14.5, and 16 over the years. I know 556 doesn't really recoil, but I hear what you're saying.

From experience, my 14.5" mid-length with a full-weight bcg is the nicest AR shooting experience I've had. If you build a 14.5 as a pistol you don't have to pin it, and given the SBA3, why not? Yeah, its a little longer, but not much, reliabilty is stellar, and if the .gov ever cracks down on pistols, you could pin it. Just my $0.02.

P.S. The 10.5, and 11.5 I had were MISERABLY loud!

I have a pencil profile 16" mid-gassed with adjustable gas block, standard bolt carrier, buffer, and spring. Used to run a lightweight BCG to sa ave weight wherever I could. It shot well, but on a whim I switched to the standard weight carrier..... man... smooth'd everything out and it's a real kitten now. I even got a 20-30 FPS increase from the slight increase in lock time compared to the lightweight BCG.

 

[B4forever]

I shot 3 gun pretty heavy for 5 years...that being said I’d ditch the LW carrier and AGB if reliability is a priority. A properly gassed barrel with a good brake provides 95% of your recoil reduction. I’d suggest running an A5 receiver extension with an A5H2 buffer paired with a Springco or JP rifle length spring, standard weight BCG, and a 12.5” barrel from Triarc. I wouldn’t run a pure muzzle brake as the sheer concussion on a SBR will do more to scare a new shooter than the recoil will. I’d suggest something like a Surefire warcomp.

 

[bfoosh006]

Remember... ammo can alter the recoil impulse as well.

PMC Bronze 55gr and Remington 55gr FMJ have been fairly weak shooting for me.

FWIW... I assm'd a 18" 5.56 rifle length gas with a LtWt BCG and an Adj. GB, BCM gunfighter brake... I ran a Tubbs flatwire with a 3oz carbine buffer. FN barrel, and I have no idea of the gas port size.

I was expecting a fairly noticeable difference, recoil wise.... but, not so much was the result. Very anti-climatic.

I still use it quite a bit, and it is a fun gun... but the altered recoil impulse isn't wildly better, IMHO.

It does make it "easier and quicker" to shoot "faster"... but only slightly, IMHO... And even then, it is most noticable with weaker PMC Bronze ammo.

I suggest you buy a variety of stronger recoil springs.

A light weight BCG will want to unlock faster ( potential extraction issues from the extraction at higher chamber pressure ) and possible ejection issues from the faster cyclic speed ) ... and adj. GB will help limit the gas port blast, I would use the adj. gb to limit / alter peak pressure gas flow...
A heavier buffer will defeat the LtWt BCG... that said... you want enough "mass / momentum" to reliably chamber the next round.

I suggest making sure your buffer tube is smooth inside, and lubed well, so there is nothing but smooth function.

Allow a decent break in of the parts.. again smooth.
Make sure the chamber is smooth and clean.

I bet you can get it to run, with tuning... but it might not produce a dramatic felt improvement.

And remember, be sure to try function at a vareity of temps and conditions... what might run in a hot day, might not be 100% reliable in a freezing day.

Also, consider a real recoil pad if you are running a Magpul carbine stock. MUCH softer then a Magpul OEM recoil pad.
https://www.nokick.com/Limbsaver_Recoil_Pad_for_Magpul_SL_Stocks_p/ls-10829.htm
https://www.nokick.com/Limbsaver_Recoil_Pad_for_Magpul_Collapsible_Stocks_p/ls-10025.htm



My Next assembly is going to be a Sionics ERGP 11.5 carbine ( no suppressor ) with every thing LtWt.... LtWt BCG, standard carbine spring, maybe even the LtWt Tubbs flatwire 300BK recoil spring , Ultra LtWt carbine buffers (1.7oz, 2.2oz, 2.6oz) ... and weak ammo.

Strictly a fun experiment gun... but I am curious if it will run. Another guy has had great results, and the lack of firearm movement is amazing to watch.
Not trying to reinvent the AR platform... just trying to see its extreme limits.

FWIW....I have seen AR's run super heavy reciprocating mass weights full mass BCG's , Tubbs CWS ( adds 4.05oz ), heavy buffer weight... but all that typically resulted in all that mass causing muzzle dip when it slams home..... so very smooth extraction... but horribly hard "positive" feeding.. LOL