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Mitch1352
02-17-11, 19:28
Is there an optimum port size for a 10.5 carbine. and if so, what is it?
Robb Jensen
02-17-11, 19:47
Is there an optimum port size for a 10.5 carbine. and if so, what is it?

I find .071" with an H buffer works well with 5.56mm NATO ammo and .073" with H2 buffers with 5.56mm NATO ammo.
Mitch1352
02-18-11, 11:27
So .080 would be too big for a 10.5 inch carbine? If so, any way to keep it from being overgassed short of replacing the barrel that has a smaller port?
Robb Jensen
02-18-11, 13:17
So .080 would be too big for a 10.5 inch carbine? If so, any way to keep it from being overgassed short of replacing the barrel that has a smaller port?

It'll work but you'll likely need a H3 buffer and/or a stronger extra power spring.
If you go to the VLTOR A5 receiver extension the A5H3 6oz and A5H4 7oz buffers were to address this.
Mitch1352
02-18-11, 15:30
So the extra spring weight, coupled with the heavier buffer, is emough mass to "control" the extra gas? I am fighting between ordering a 10.5 upper for an SBR from Rock River to go on my RR lower or getting an entire rifle from Noveske with his Switchblock. It will be 1/2 suppressed, 1/2 not, hence the quandry. I feel sure that I will get another SBR, but if I only do one, I want it right from the start.
Robb Jensen
02-18-11, 18:36
So the extra spring weight, coupled with the heavier buffer, is emough mass to "control" the extra gas? I am fighting between ordering a 10.5 upper for an SBR from Rock River to go on my RR lower or getting an entire rifle from Noveske with his Switchblock. It will be 1/2 suppressed, 1/2 not, hence the quandry. I feel sure that I will get another SBR, but if I only do one, I want it right from the start.

It's a bandaid fix but it'll run. If using 1/2 suppressed and 1/2 not I'd highly recommend the Noveske with a Switchblock.
After I shot out the 10.5" LMT barrel I used a Colt 14.5" M4 SOCOM and left the port small (.062") for a dedicated 10.5" suppressed only upper. It shoots very soft suppressed.

I may be going to an AAC Mini4 suppressor for shooting 3gun. If I do that I'll be using a switchblock on my BCM midlength barrel and milling an opening at the top of the rail for the gas block to adjust from.
EzGoingKev
02-19-11, 14:48
After I shot out the 10.5" LMT barrel I used a Colt 14.5" M4 SOCOM and left the port small (.062") for a dedicated 10.5" suppressed only upper. It shoots very soft suppressed.

Is .062" the size it left the Colt factory with?
Robb Jensen
02-19-11, 14:56
Is .062" the size it left the Colt factory with?

Yes.

I'm using a BCM bolt with a LMT enhanced carrier. Was using an H3 buffer with standard rate Brownells chrome silicon CAR buffer spring. So now with the A5 I'm going to try the 5oz, 6oz and 7oz buffers and the 'green' Sprinco A2 buffer spring with each as well as a standard rate buffer spring to see how it'll run best.
Dunderway
02-19-11, 15:06
Would it be best to go with the smallest gas port that would run reliably, and then just add buffer weight as the port errodes? Assuming it would see a high round count.
87GN
02-19-11, 16:41
What ammo will you be shooting? My 10.5 is a range toy to me, so it sees a regular diet of whatever crappy ammo I can find, along with whatever crappy ammo other shooters say won't work in it (but does). It's right around .080 IIRC, which is larger than what NSWC uses, but I am not always shooting 5.56...I use H2 or Vltor A5H3 buffers, but it works with other buffers too...
Keesh
02-20-11, 23:48
My 10.5" LMT has a 0.0680" port and runs everything from Wolf to Lake City with an H buffer.
Robb Jensen
02-21-11, 04:49
My 10.5" LMT has a 0.0680" port and runs everything from Wolf to Lake City with an H buffer.

You've got an oddball, every factory 10.5" LMT barrel I've measured was. 071"
cebuboy
10-14-11, 05:57
Anybody here have an idea of the port size for a 16" lightweight profile(.625 gas block seat) middy?
Iraqgunz
10-14-11, 08:11
Have you read and understood anything that has been posted about gas port sizes?

Here's a clue- the manufacturer of said upper/barrel is also important.


Anybody here have an idea of the port size for a 16" lightweight profile(.625 gas block seat) middy?
munch520
10-14-11, 10:15
So .080 would be too big for a 10.5 inch carbine? If so, any way to keep it from being overgassed short of replacing the barrel that has a smaller port?

Are you asking because of PSAs upper? I think I remember reading recently their 10.5 port size was close to .080. They of course wouldn't disclose this over the phone :)

Short of re-barreling, you obviously can't get smaller. You can 'band-aid' the problem with a heavier buffer, A5 setup, enhanced carrier, etc