Best general port size for MK18 build

[GarandShooter]

I settled on a .073" gas port on mine. I wanted to be able to use a Vltor A5H4 with colt spring and have it function test with Federal 55 gr .223. I would start at .070" and not open it up anymore unless you have a problem. The difference in area/volume between .070" and .073" is 9%, that's a pretty big difference. The difference in area/volume between .070" and .082" is 37%, that's huge.

Also, for the build it says use a KAC MK12 gas block. Which are .75. Is that still acceptable for the .70 hole?

[jstalford]

You don't cut the tube. Carbine gas is carbine gas.

Also the .750 gas block is the diameter of the barrel, not the hole. It has nothing to do with the gas port size which will be .070. Emphasis on the .0.


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[GarandShooter]

You don't cut the tube. Carbine gas is carbine gas.

Also the .750 gas block is the diameter of the barrel, not the hole. It has nothing to do with the gas port size which will be .070. Emphasis on the .0.


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Good to know, thank you.
Still learning here, so all this info helps a ton.

[MistWolf]

If my experience is worth anything, you do NOT want a .083" gas port on a 10.5" barrel. It's much too large, even without a silencer. My 10.5" barrel has a .083" port and with a H buffer and it needed an adjustable gas port. Now, with an Omega, the gas block has to be adjusted down even more.

Later, I plan to test an 11.5" barrel suppressed with a smaller gas port. I'll let you know how that turns out

[elephantrider]

I disagree. Starting with a colt offers the end user a known quality from which to build from and opening the port up allows selection to specific desired range of performance.

Plus then it's all colt so win.

Start with a quality barrel, that you will cut/re-thread, then open the port to 'Jenna Jameson' dimensions so that it will work with the lowest quality dirt shooter ammo? Logical.

[jpmuscle]

Start with a quality barrel, that you will cut/re-thread, then open the port to 'Jenna Jameson' dimensions so that it will work with the lowest quality dirt shooter ammo? Logical.

Except that's not what he's doing. But whatever.

And even that were the case I'd still do it since it's Colt and not some off brand crap.

[Iraqgunz]

Not sure why this is so difficult. It's actually been discussed NUMEROUS times should one actually use a search feature. When I finally get around to building my 10.3", I am using a Colt SOCOM barrel (because it was cheap) and I will open it to the Crane spec which makes sense for many reasons.

[GarandShooter]

Not sure why this is so difficult. It's actually been discussed NUMEROUS times should one actually use a search feature. When I finally get around to building my 10.3", I am using a Colt SOCOM barrel (because it was cheap) and I will open it to the Crane spec which makes sense for many reasons.

I used the search feature and found a lot of MK18 threads. Problem is, most of the builders won't discuss any other port size except .70 because otherwise it wouldn't be clone correct. Yet everything I read requires running a hotter than normal load to get the rifle to function as it should. I read where DD uses a .83 and allows for a wider range of ammo.

So I was curious on opinions.


I'll stick to the .70 and open if needed.

[lt1 sport]

When I cut my colt SOCOM barrel down to 10.3 I opened up the port to .070.

[MQ105]

If my experience is worth anything, you do NOT want a .083" gas port on a 10.5" barrel. It's much too large, even without a silencer. My 10.5" barrel has a .083" port and with a H buffer and it needed an adjustable gas port. Now, with an Omega, the gas block has to be adjusted down even more.

Later, I plan to test an 11.5" barrel suppressed with a smaller gas port. I'll let you know how that turns out

I sent you a PM re 11.5" barrels and gas ports. The summary is that you can go small - .05XX small.