Gas port dimensions: pistol

[interceptor]

I expect my BATFE forms in soon on my newest SBR project, my M1S .300 Fireball which is currently in the carbine configuration. What I need a little help with is the correct dimensions to give my smith to rebuild my barrel from the present carbine configuration to a pistol length gas system on a 9"-10" OAL. By dimensions, I mean hole diameter and placement from a measurable point from the barrel extension. He is a quality smith and I am impressed with his work, but he is very old school and has never worked on AR's before I started bringing him a few barrels to cut down, reprofile, or thread. I would appreciate info that I can relate to him in a manner he can understand.

Components involved will be my YHM Phantom QD can and TP555's 3 position gas manifold (gotta order one!)

As far as filling in the existing gas hole, I figured either to tap it and install a set screw or weld it up. Observations, tips, insights...?


BTW, this same smith will be building me another .300 Whisper on a Rem700 later, have already ordered a barrel blank with him. As a matter of fact he has already started an exact copy of my project with another shooter. We should end up with identical rifles when finished, only he will have his first (you suck Richie!). We both have YHM Phantom QD cans, and have had the idea to use the QD adapter but have the smith mill off the flash hider portion and leave the threaded end only. I'm anxious to say the least!

At any rate I appreciate any info you could pass along to me for my project.

[tp555]

Try 3.6" from bbl ext to edge of gas block.Hole is .295" from edge of gas block.

[interceptor]

So drill the hole 3.895" from the extension....


Diameter?


BTW, which of your gas blocks will I need (if they are different sizes)? Probably going under a YHM FF tube.

[Scoots]

I determined the diameter of my gas port by fitting the largest drill bit that would fit into the gas tube without getting stuck. This ended up being a 7/64" drill bit ( = .109375"). I have seen others mention opening up their gas port to .110" and .125".

I wouldn't go larger than .125".

I have a low profile, adjustable gas block underneath my handguards:
http://www.jprifles.com/buy.php?item=JPGS-5

[jefflaw45]

I too am doing a pistol length gas system.

please clarify where the hole has to go.. if I have the barrel out of the gun am I measuring from the very rear of the barrel extension or from the front edge?

Please clarify where to measure from and what the measurement would be..

Many thanks

Jeff L.

[tp555]

front edge of ext.