.300 Blackout Buffer Choice

[JayZee]

Hey everyone, hope you have all been well.

Builiding a "Micro" .300 Blackout Upper and trying to make sure my buffer weight/spring combo is best out the gate.

I plan to run mostly supers until I can get my hands on a can but shooting both is in the agenda.

I do have a basic adjustable gas block, but didn't think it should be the only variable I should use to tweak the gun.
CORRECT me if I am wrong, but I figured both sides of the system should be tuned if possible.


Its a 5" .300 BO barrel, micro length gas tube and will sport a Midwest Flashhider.
I am thinking an H2 or H3?

I have run Carbine buffer/spring on most 5.56 I have. 8.5" which was a little rough, needed tweaking or heavier buffer to mitigate that but ran. 10.5", 11.5", 12.5" 14.5" and 16" all run fine on the Carbine Buffer/Spring combo.

Once this .300 is done, I am going to look towards a getting a can for all the AR's.
It's my last build for a long time.

TLDR;

Whats the best buffer/spring combo for a 5" .300 Blackout build?
Which combo for Supersonic?
Which combo for Subsonic?

 

[Zak Smith]

JP SCS. You can add or remove weight

 

[JayZee]

JP SCS. You can add or remove weight

If I didn't want to have a proprietary option, what would you suggest??

 

[Zak Smith]

Before I used SCS's in everything (and got rid of all "buffer/spring" related tuning), I would have used a regular carbine buffer and spring.

If you tune a 300BO to run optimally on full power, you may not have enough gas to run subs.

 

[wesmonster]

What he said.
My 8” .300bo fixed gas block came very undergassed and out of the box would not cycle subs unsuppressed. Had to go to a lightweight bolt carrier & Sprinco yellow buffer spring to run reliably. I swap in an H3 buffer for supers. So I’d advise to start with a std. buffer and just dial it in how you like it. Assuming you’ve got enough adjustability, the only noticeable difference in light vs heavy buffer is the cycling time.
For variant calibers, I like to run on the heavy side, slow things down and give the mag a few extra microseconds to bring up the next round. Some prefer the feel of a light buffer.

 

[bfoosh006]

For me, It would be hard to recommend a buffer and spring for such a short gas system.

That said... If you end up needing a Lt Wt setup for subsonics... KAK makes very LtWt buffers "NOT FOR USE WITH FULL POWER LOADS"

https://www.kakindustry.com/kak-lightweight-ar15-carbine-buffer-kit

And Tubbs sells a Lt Wt 300BK recoil spring.

https://www.davidtubb.com/tubb-springs/ar15-buffer-spring-stainless

 

[mcb]

If the barrel is ported correctly a standard carbine buffer and spring should work fine. Start their, they are cheap. Add a heavier buffer and/or stiffer springs only if needed. Since you are already planning on using an adjustable gas block that should be all you need to tune the system, adjusting gas (assuming the port in the barrel is large enough or larger) is significantly more effective than messing with springs and buffers.

My 5-inch 300 blackout, running with a standard carbine buffer and spring. Runs fine with subs, suppressed or not, have not bothered trying supers in such a short barrel not much point IMHO. This is a dedicated subsonic gun for me.

 

[jonnyc]

I have a 16 in. BLK shooting Supers and a 10.5 incher shooting Subs. Both function 100% with standard-weight carbine buffers.

 

[citizenconn]

I have used a standard buffer and spring on all the .300 BLK AR pistols I've built: 7.5", 8.5", 10.5", 12.5". They work fine suppressed/unsuppressed and super/sub sonic, but I have started using an adjustable gas block on the last few and that has helped me be able to tune them tremendously.
As far as one as short as 5", good luck. I'd shoot my fat sausage fingers off.

 

[N555]

I recommend a cheap carbine buffer, a 5/32 punch (I think) hammer and 3 tungsten buffer weights.
I say start with an H3, if it short strokes make it an H2 or H1.
Chose the buffer for the subsonic ammo and turn down the gas for the supper sonic ammo. Assuming the gas block adjustment is easier to do than swapping out buffers on your gas block.

 

[JayZee]

I recommend a cheap carbine buffer, a 5/32 punch (I think) hammer and 3 tungsten buffer weights.
I say start with an H3, if it short strokes make it an H2 or H1.
Chose the buffer for the subsonic ammo and turn down the gas for the supper sonic ammo. Assuming the gas block adjustment is easier to do than swapping out buffers on your gas block.

I actually bought the weights prior to this thread. I have them ready to tune if needed. I have a bunch of spare carbine spring/buffers so I will definetly be able to make it work.

Does anyone have experience with the LWRC UICW compact stock?
(I own a registered SBR lower)
I was thinking of going with that to make it even shorter.
If I go that route though, their buffer is a "micro" or smaller than carbine I think? I know its smaller/shorter but not sure on weight.

 

[JayZee]

If the barrel is ported correctly a standard carbine buffer and spring should work fine. Start their, they are cheap. Add a heavier buffer and/or stiffer springs only if needed. Since you are already planning on using an adjustable gas block that should be all you need to tune the system, adjusting gas (assuming the port in the barrel is large enough or larger) is significantly more effective than messing with springs and buffers.

My 5-inch 300 blackout, running with a standard carbine buffer and spring. Runs fine with subs, suppressed or not, have not bothered trying supers in such a short barrel not much point IMHO. This is a dedicated subsonic gun for me.

My idea is to get a Form 4 and grab a nice can for it. Dedicated sub gun, actually doing a 10.5" for supersonic hunting.
How do you like the 5"?
I saw a few videos, but not much on anything less than 7.5" when it came to velocity and performance.

 

[JayZee]

I have used a standard buffer and spring on all the .300 BLK AR pistols I've built: 7.5", 8.5", 10.5", 12.5". They work fine suppressed/unsuppressed and super/sub sonic, but I have started using an adjustable gas block on the last few and that has helped me be able to tune them tremendously.
As far as one as short as 5", good luck. I'd shoot my fat sausage fingers off.

Actually have had a HARD time finding a handstop. I found one and can only mount it on the first MLOK slot on the bottom because the gasblock blocks any amounting going behind the rail. Finally found one that only uses one mounting slot/point of contact. I'll link anyone if they need a SMALL handstop.

Now I'm trying to figure a weapon light that is small enough. Thinking of getting a pic rail adapter for the 45° left hand side and attaching a flashlight from a handgun.

 

[mcb]

My idea is to get a Form 4 and grab a nice can for it. Dedicated sub gun, actually doing a 10.5" for supersonic hunting.
How do you like the 5"?
I saw a few videos, but not much on anything less than 7.5" when it came to velocity and performance.

I would do a SBR as I would rather have a stock than a brace but as current NFA law stands I would have to fill out forms to take it out of state. Given I live in Alabama and have hunting land in Tennessee that would be a pain.

The 5-inch gun is fun but for me the 9-inch barrel seems close to the sweet spot for me. Nice compromise between compact and quiet. The 5-inch gun is noticable louder and I have not even worked up a load specific to it yet and it will no doubt get louder when I get the velocity back up close

 

[berettaprofessor]

Actually have had a HARD time finding a handstop. I found one and can only mount it on the first MLOK slot on the bottom because the gasblock blocks any amounting going behind the rail.

Most of my preferred handstops are MLOK angled foregrips; sometimes I have to grind a screw shorter to keep it from touching the barrel.