Which should I choose? BCM 300 blk barrel length upper

[airwolf]

I am ready to buy a sbr 300 blk upper. I tend to like BCM and plan on getting either a 9 inch or 12.5 inch upper they offer. I will be running an Omega suppressor, as that is my only .30 cal can.

I have drove myself crazy doing research on barrel length and its impact on quietness. The overall consensus is that shorter barrels are always louder. Some say they can tell very little difference between a 9 or 10 inch barrel vs a 16 inch barrel in 300blk..... then some will say they can tell a noticeable difference between barrels of only a few inches difference.

I have very damaged ears with severe tinnitus and sound sensitivity and will no longer shoot 5.56. I will only be shooting subsonic 300blk with a suppressor and will be wearing ear plugs and ear muffs (my ears are that bad).

Does anyone have any experience between any difference in loudness with only a few inches of barrel length difference. I always thought that since the 300 is far less pressure than 5.56, barrel length would not be as critical, but sound suppression is my primary concern without having to go as cumbersome as a 16 inch barrel. Is 12.5 inch barrel likely my sweet spot?

[dellet]

Longer will be quieter and noticeably so. The longer the barrel, the less noticeable the difference becomes. The difference between 6-8” will be far more than 9-11”.

The factor most beneficial to noise reduction is powder choice, so commercial ammo will be louder than it needs to be.

What will be more important for you will be port noise, that is more of what you will hear. You can control it some with an adjustable gas block.

If I wanted to put something together for commercial ammo to be as quiet as possible, it would be 10”+ with carbine gas length and adjustable gas block. This will give the powder more time to burn and reduce the internal pressures as much as possible before the bullet exits and the port opens.

If you want something really quiet, it probably won’t be on the shelf as a ready made upper.

[airwolf]

[quote

If I wanted to put something together for commercial ammo to be as quiet as possible, it would be 10”+ with carbine gas length and adjustable gas block. This will give the powder more time to burn and reduce the internal pressures as much as possible before the bullet exits and the port opens.

If you want something really quiet, it probably won’t be on the shelf as a ready made upper.[/quote]

Would a carbine gas system still be reliable for defensive use, I' guess this would reduce port pressure, similar to a carbine vs midlength AR? Am I mistakenly under the impression that even with a suppressor, subs were not overgassed, so I thought there would not be much advantage to a adjustable gas block?

[dellet]

If I wanted to put something together for commercial ammo to be as quiet as possible, it would be 10”+ with carbine gas length and adjustable gas block. This will give the powder more time to burn and reduce the internal pressures as much as possible before the bullet exits and the port opens.

If you want something really quiet, it probably won’t be on the shelf as a ready made upper.

Would a carbine gas system still be reliable for defensive use, I' guess this would reduce port pressure, similar to a carbine vs midlength AR? Am I mistakenly under the impression that even with a suppressor, subs were not overgassed, so I thought there would not be much advantage to a adjustable gas block?

Depends on the barrel manufacturer, the suppressor and the load.

In theory, carbine gas under 16” is not supposed to work. Part of that is based on use without a suppressor. The extra back pressure of the suppressor makes it possible, but becomes a must have.

Subs are just less over gassed than supers. If the port is sized for the ammo, then it will not be over gassed. If the port is sized to work correctly with the absolute worst ammo imaginable, it is likely to be oversized for most of what is on the market. This is the standard barrel makers have to build to. So if you are looking to reduce noise to the absolute minimum, you want to have the least amount of gas possible, with the least pressure at the bolt.

Two ways to get a quieter sub round. Use faster powder, or a longer barrel. Let the powder burn out completely before opening the bolt.

With all that said, using factory ammo, although a limited sample. I prefer the 10.5” carbine gas over the 9” pistol gas. Smoother running, less recoil and has been perfectly reliable with a suppressor with subs.

If handloads are on the table, I might change opinions.