Optimal port size on a 10.5 inch barrel

[philcam]

I'm going to have a Colt 14.5 inch M4 profiled barrel cut to 10.5. Looking to have SAW, ADCO or ar15barrels.com do the work. None of these companies are local to me.

I've read LMT uses .071 in their 10.5 barrel, but have heard of issues with not cycling weaker ammo. DD specs their 10.3 gas port at .082, but almost everyone agrees this is overgassed.

I haven't had any luck finding reliable info on what Colt is using in their 10.3/10.5 barrels.

I do not have a suppressor yet, but hope to be able to purchase one this summer. Upper will be used on a Colt factory 6933 lower with H weight buffer.

What would most consider an "optimal" port size on a 10.5 barrel?

[Iraqgunz]

Your port sizes are a little mixed up. DD ports theirs at around .082. .071 +/- .001 is the spec used by Crane and LMT. That port size was based upon M193/M855 and similar.

Based on what I have seen, if you are concerned about shooting some lower power stuff, I would consider .075.


I'm going to have a Colt 14.5 inch M4 profiled barrel cut to 10.5. Looking to have SAW, ADCO or ar15barrels.com do the work. None of these companies are local to me.

I've read LMT uses .071 in their 10.5 barrel, but have heard of issues with not cycling weaker ammo. DD specs their 10.3 gas port at .075, but almost everyone agrees this is overgassed.

I haven't had any luck finding reliable info on what Colt is using in their 10.3/10.5 barrels.

I do not have a suppressor yet, but hope to be able to purchase one this summer. Upper will be used on a Colt factory 6933 lower with H weight buffer.

What would most consider an "optimal" port size on a 10.5 barrel?

[Jwknutson17]

I've read LMT uses .071 in their 10.5 barrel, but have heard of issues with not cycling weaker ammo. DD specs their 10.3 gas port at .075, but almost everyone agrees this is overgassed.



Been a while since I measured a LMT but mine was in the .070 range. My factory DD Mk18 was .081. For me on my 10.3/5 I opted for the .068 gas port and still runs a H2 buffer and Carbine spring.

[philcam]

IG,

You're right on the DD port size. I double checked the info I have and I should have typed .082. Original post corrected. Thank you.

[Jwknutson17]

Your port sizes are a little mixed up. DD ports theirs at around .082. .071 +/- .001 is the spec used by Crane and LMT. That port size was based upon M193/M855 and similar.

Based on what I have seen, if you are concerned about shooting some lower power stuff, I would consider .075.

+1 What Gunz said. If your concerned about ammo at all and not strictly running M855, M193, etc, I would hover around the larger spec.

[MistWolf]

My 10.5 barrel has a .082 gas port. With a carbine buffer, it was so over-gassed that it sent a stinging slap through the trigger bow with every shot. An H2 buffer tamed it nicely. The pistol RE was replaced with a rifle RE and the shorty ran good. An adjustable gas block was installed soon after and has been useful for fine tuning

[sinlessorrow]

Dd chose .082 for their gas port so people can run TULammo, per an email from them.

The spec is .071+/-.001.

[markm]

Pappabear just got an LMT recently, and it's no where near choking on .223 pressure loads. We had to put an H3 in it to tame it down because it bucked too hard with anything lighter.

[Robb Jensen]

.071" for 5.56mm ammo and .073" for .223 ammo is ideal.

[markm]

I'll be interested to see how my Aeroprecision runs. It's supposed to have a port that's .077". I finally gave up trying to find a correctly gassed 10.5. Since I'm not running a can, I hope I can buffer it into a shootable gun.