AR gas/buffer, need help

[Diamondback]

Well guys, I'm about to close on a barrel. Here's the catch: it's a 10.3 with a .070 gas port, intended for suppressed apps.

Question is, since this thing is never going to see a suppressor, how do I need to adjust the buffer to cycle both cheap .223 55grain and Mk 262? I had been thinking go all the way up to H3, but... maybe I need more an H or H2.

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[v0lcom13sn0w]

what gas system? pistol or carbine?

 

[v0lcom13sn0w]

correct me if i am wrong but, a .070 Port is pretty small and restrictive. i would only guess that with a .070 port on a 10.3" barrel you are going to be undergassed at best and want a lighter buffer. i would think with a cabine system it would be even more undergassed due to the lack of dwell time from the port to the end of the barrel. with a pistol length you MIGHT be ok and run a standard carbine buffer.

 

[Diamondback]

Sorry, this is Carbine. This guy: 556 NATO 10.3" FSB (Port Size 0.070) which I've been looking at mainly as a more economical alternate to a $250 Daniel Defense and THEN still having to find my own FSB kit to go on it...

Thanks--so it's either stick with CAR or have somebody open up the port. I know Daniel Defense's 10.3 is considered "overgassed" in some circles at .080.

 

[DirectDrive]

Start with a standard carbine buffer/sprng and your favorite ammo.
If it won't run, then try a reduced power buffer spring from Wolff before opening up the gas port.

If you want to jump back and forth from full power military ammo to low pressure .223 you might have to go to an adjustable gas block.

 

[v0lcom13sn0w]

AR15 Build issue. gas?

some good info here

 

[titsonritz]

correct me if i am wrong but, a .070 Port is pretty small and restrictive. i would only guess that with a .070 port on a 10.3" barrel you are going to be undergassed at best and want a lighter buffer. i would think with a cabine system it would be even more undergassed due to the lack of dwell time from the port to the end of the barrel. with a pistol length you MIGHT be ok and run a standard carbine buffer.

The Crane spec for a 10.3/10.5" MK18 is .071 inches. For comparison, the correct size for an M4 carbine gas system is .063 inches. A 20" rifle is .093.

OP, to answer your question, I would go with an H3 but I only shoot 556 ammo, if you want to shoot cheap 223 like PMC Bronze, I'd go to the lighter H2. If you do not already have a buffer system I'd recommend an A5 setup, it is a more forgiving and has a larger range of operation than the standard carbine system, it is truly what the carbine should have been to start with.

 

[Diamondback]

Thanks, guys. Adjustable block isn't an option unless somebody makes one with an FSB on top--fixed sight was one of the "mission requirements" for this project. Right now what I have in-hand is a standard CAR--will I have to replace the tube and spring with an A5 too, or just the buffer itself?

 

[DirectDrive]

Thanks, guys. Adjustable block isn't an option unless somebody makes one with an FSB on top--fixed sight was one of the "mission requirements" for this project. Right now what I have in-hand is a standard CAR--will I have to replace the tube and spring with an A5 too, or just the buffer itself?

VLTOR A5 is system unto itself.

If you already have a standard carbine RE, buffer and spring, I'd start with that.
The internet really can't tell you what weight buffer is going to work the best.
We can guess.
My method is to start pulling the trigger and changing out buffers (if needed) until I get the rate I want.

 

[HB of CJ]

I have no idea.

hundreds of AR builds.

 

[Diamondback]

If I'm changing blocks I might as well go with either the DD or the Strike 1/8 Wylde...

Ugh, back to piecing things together. So much for thinking there was an easy way...

 

[DirectDrive]

No savvy "blocks" ?

 

[titsonritz]

Thanks, guys. Adjustable block isn't an option unless somebody makes one with an FSB on top--fixed sight was one of the "mission requirements" for this project. Right now what I have in-hand is a standard CAR--will I have to replace the tube and spring with an A5 too, or just the buffer itself?

The A5 uses a RE that 3/4" longer than a standard carbine RE, a proprietary buffer ranging from A5H0 to A5H4, and a standard rifle buffer spring (I use Sprinco Green Springs). A5 RE are offered by Vltor, BCM and Magpul.

VLTOR A5 is system unto itself.

If you already a standard carbine RE, buffer and spring, I'd start with that.
The internet really can't tell you what weight buffer is going to work the best.
We can guess.
My method is to start pulling the trigger and changing out buffers (if needed) until I get the rate I want.

A very educated guess can be made, if certain factors are known, gas port size being number one, length of gas system, barrel length and desired ammo choices.

 

[DirectDrive]

A very educated guess can be made, if certain factors are known, gas port size being number one, length of gas system, barrel length and desired ammo choices.

Yep, that's about it.
And it's free for the guesser....sometimes not so much for the guessee.

 

[Diamondback]

I was hoping that going with a preinstalled barrel/FSB combo would reduce the amount of work I have to outsource for lack of a bench vise... only to find that this project only gets even MORE expensive every step I take.

Starting to think maybe I should just see if somebody can cut down a 10.5... and the added length is a problem on a "compact" build even with a folder. (Guess I better forget about that 40-round PMag I was planning to rack into the side-mount carrier and stick to a 30...)

 

[DirectDrive]

I was hoping that going with a preinstalled barrel/FSB combo would reduce the amount of work I have to outsource for lack of a bench vise... only to find that this project only gets even MORE expensive every step I take.

"preinstalled barrel/FSB combo " will still require a vice to mount to receiver.

 

[Diamondback]

True, but that's that much less work my hired smith has to do.

 

[DirectDrive]

True, but that's that much less work my hired smith has to do.

As intel leaks out i'm getting the picture.
If you want an FSB, by all means get it pre-stalled on the barrel.
From a good supplier.....you don't want any canted crap.

 

[titsonritz]

As intel leaks out i'm getting the picture.
If you want an FSB, by all means get it pre-stalled on the barrel.
From a good supplier.....you don't want any canted crap.

Don't ever attempt to install a FSP yourself, it requires a purpose built jig to do it properly. This is the one part of the AR that is like a finger print, no two are exactly alike. Quality manufacturers will use taper pins not a straight pins. I won't even consider a clamp on style FSB.

 

[DirectDrive]

Clamp on FSB is OK as long as it's not a patrol or self defense rig.

Many, probably majority of national match FSB's are set screwed.