Buy or build a blackout upper?

[Tim K]

I'm still toying with the idea of a .300 upper. It would be shot primarily, if not exclusively, suppressed with subs. I have no firsthand experience with building .300 uppers. Are they sensitive to gas system specs? Should I just buy one complete or can I reasonably expect to get good performance from something I cobble together? It would not be a SBR.

[MarkCO]

If you buy one from DD, BCM or Noveske, it will run and you will not have any problems. Most of the other companies either don't know what they are doing or have not yet figured out the set-up. You don't want to cobble one together, but you can build one.

With a 16" you choose between carbine or pistol length. Pistol length will be easier to get to run with subs, but it can still be done with a Carbine length. That said, the simplest path is to "copy" the parameters of one that is already set up. To me, one of the big questions is do you want adjustable gas or not. If the answer is yes, then a switchblock system is going to be the simplest and most durable. If you have a 16" set-up for subs and run supers in it, the wear and tear will increase some since you will likely be overgassed. You can swap out for a heavier buffer and an XP spring to tame that.

[Tim K]

I'd like the adjustable gas for the additional benefit of being able to turn it completely off. That means carbine gas is OK, right?

[MarkCO]

I'd like the adjustable gas for the additional benefit of being able to turn it completely off. That means carbine gas is OK, right?

Yes. Just realize that with adjustable gas (as opposed to a switchblock) they are intended to be set and locked. Re-adjust, or don't lock it down, then you will have a failure eventually. Systems like the Syrac (which about 5 others have since copied) are nice, but not as robust, and they leak more.

[Tim K]

Pardon my ignorance, I didn't know the difference between a switchblock and and adjustable gas block. I thought those terms referred to the same item. I'll do some research.

[Hoser]

Pistol length gas on short barrels and 16's. Set it up to run 100% on subs and it will be just fine on supers.

Adjustable gas blocks are the devil.

[joeyshoe]

Hey tim, maybe you can get in touch with Belizejet. We went out and tried to troubleshoot his 300blk build since it was having some issues cycling. The odd thing was that his own reloads seemed to work fine while factory ammo didn't...

[Tim K]

I'd forgotten he has one. I think I put the barrel on it...

[belizejet]

Yep Tim, that the one. I'm going to take off the nut and reinstall it with the old one so I can put my Samson rail on it. I'm also going to make sure the gas block is still aligned. I think it just doesn't like the heavier loads. The 110 and 125grn rounds (reloads) cycle but the 150 grn loads (factory) don't cycle. Another option is to look as the spring and buffer combo.

[belizejet]

Your welcome to play with my upper and see what you think. I could use some expert opinion on what to do next. I'll even give you some ammo. I chronoed all of the different ammo and it all seemed to meet published spec.

[Tim K]

Thinking SBR now that I have a trust in place. Is there a length that's too short to be reliable?

[Hoser]

Thinking SBR now that I have a trust in place. Is there a length that's too short to be reliable?

Shorter than 8 inches you almost have to start using shorter than pistol length gas tubes.

[Tim K]

Is there some compelling reason to go longer than 8"?

[Hoser]

8-10 are easy to get/keep running.

[MarkCO]

I've only tried short barrels between 9 and 10.5. I figured if there were 4 or 5 guys who have been running 300s for a while and are fairly smart that were saying keep them between 8 and 10, that was good enough to not go off the reservation.

I am pretty sure Hoser only has like 50 posts and then just auto-fills them into the right spot. :)