that’s what I was referring too with the POI shift.
I think if I go the ‘cut down’ route, a 6920 or 6940 is a better choice.
There is no reason to cut a Colt barrel.
Agreed. Buy the Colt upper half/barrel in the length you want, and sell off the other upper.
Not agreed. Milspec gas ports are huge if you’re a suppressor user.
If not, then they’re fine.
Well, then what would be optimal port size for running with and without can?
With: .056’’ (Will cycle full power 5.56mm unsuppressed.)
Without: .071’’ (Even if I prefer .062’')
Both sizes are kind of subjective, and it’s my opinion.
Others are free to chime in.
I disagree. I mean… I run my can on a Bushmaster for Pete’s sake. That is a big port. Just bump up the buffer to H2 or H3.
If he cuts the barrel, the gas port is no longer spec for that length of barrel.
You two are spinning your wheels. I am convinced this cat uses a pair of dice in his decision making process.
Having the gas port sized smaller for a suppressor is a backwards approach.
The gas port should be sized for mil spec ammo unsuppressed. That way it insures reliable functioning when the gun is dirty.
If you understand this and select a muzzle device that will index on the muzzle not the shoulder then it’s not a problem.
Selecting a barrel that is larger at the muzzle end but the same under the handguards to reduce POI shift seems odd to me.
The number of people who shoot suppressed only rifles is very small, that’s why there are no rifles made that way. Rifles with suppressed only gas ports should not be considered reliable without the silencer.
Is there a suppressor manufacturer that advocates this method of indexing for a muzzle device? What cutting tool would you use in the counterbore to ensure that the bottom was square to the bore of the barrel?
Which only matters if you are going to be taking the can on and off. With a fulltime can there is no shift.
I’m working on a carbine now with a 10.3" Daniel Defense 0.625" dia. barrel. If it works out I’ll likely be putting together an identical upper for fulltime suppressor use, and won’t give POI shift a second thought.
AAC does, the length of threads needed to index on the muzzle is in their thread specs. The bottom of the mount is as square to the bore as the threads and back if they are cut in the same op.
I guess I’d have to see one cut in half to fully grasp how it’s finished. It would seem that a boring bar would have to be used to relief cut the corners of the counterbore and in my mind it wouldn’t leave enough purchase between the face of the muzzle and the suppressor mount to rely on square fit. AAC gets the benefit of the doubt though.
It has internal thread relief and the face cut square with a boring bar I assume. It’s not like an A2 with the angle of the drill at the bottom.
Have you run it without lubrication, for extended periods of time?
I have, both suppressed, and unsuppressed. This port size works well for me with 5.56mm pressure ammo.
There is no gas port specification for suppressor use. For unsuppressed use though, I gotcha. But there are middle-grounds. Like for a suppressed gun where the suppressor will NEVER come off it’d be something like .048’’ or .050’’ or something super tiny. The gun wouldn’t even cycle unsuppressed. .056/.060’’ or more, will cycle unsuppressed, and will be reliable.
Agreed. That’s why mine is slightly bigger. I subscribed to Grant’s train of thought, and built my guns based on his theories, and findings. After he did them first. I trusted his decisions, and the overall builds have worked for me.
VLTOR A5 will make the bolt lock back unsuppressed. Just a footnote, btw.
That’s if the gun will be shot primarily unsuppressed. Mine is ported for (close to) milspec ammo suppressed. Actually it’s ported slightly larger than that.
Hope the replies make sense. I was in a hurry.
Was it established that the 6720 and 6933 have different size gas ports, and if so do we know the sizes, or are we just assuming they are different based on the different barrel lengths.
It’s my understanding that 6720 has .062’‘, and 6933 has .071’‘. (or .090’’ that I read from a Robb Jenson post.)
The AAC miter mount indexes off the muzzle face.