"pistol position" Where is it?

[Ulrik]

Precisely where is the "pistol position" for the gas port drilled?

Ulrik

[pug]

Well putting that "precisely" in there makes it a bit tough but for the collection of various brand parts I am holding in my hand this pistol barrel would have the gas port drilled exactly 3.5" from the barrel extension shoulder. Change the brand of something and that dimension could change. I would never recommend drilling a gas port until you have all the parts in hand.

[WhisperFan]

I second that. my barrel had a 'step' that the gas block sat against. I measured how far from the face of the gas block to the center of the hole, then measured from that 'step' forward the same distance and rrilled there. A different gas block might have a different distance - buy mine works well and I shouldn't need to change it.

[Ulrik]

Thanks,

I don't have any "brand" stuff. I'm going to turn and chamber a barrel blank, and make an adjustable gas block, since nobody is selling exactly what I'm looking for.

I thought I'd just modify a carbine length gas tube, unless someone is selling pistol length ones.

Ulrik

[JFettig]

Everywhere I look I get a different answer, I'm in the process of gathering numbers, I have a nice shilen blank that I'll be turning soon.
The 3d model I have from someone else, the port is at 4.17" and the step is at 3.875, both from the extension. I've heard that the step is at 3.6" from another source, and now 3.5 to the port from that spot.
What brand parts are you measuring that your getting 3.5"?


Thanks,
Jon

[pug]

That is the position off of an Olympic Arms factory upper I have. Since I was using an oly pistol gas tube I used the same dimension for the pistol barrel and it worked out fine. I think m1s and dpms gas tubes are slightly longer.

[320pf]

The standard pistol position gas port is about 1/2 further down the barrel toward the muzzle than the Olympic Arm position.

I suggest that you buy a pistol length gas tube from you favorite website/mail-order supplier. You will need one anyway and you can use the gas tube to get the dimensions for the pistol position gas port.

320pf

[JFettig]

I don't plan on using the standard gas system but I'd like to know where the hole belongs if I decide to go back to the standard system.

Thanks,
Jon

[pug]

There would be a few decisions I would make first. If you are going to shoot subsonic you would want a pistol gas port. Then you would decide between a "oly" or "standard" pistol port. Nothing wrong with oly parts but they do things their own way and their tubes and gas blocks are not standard size. The location of the port will depend on whos parts you aquire. If you don't mind doing a second setup then you can put the extension on and fit the barrel to the receiver. Put the assembled block and tube up next to the barreled upper and where the rear of the bell on the tube falls in the middle of the milled circle in the receiver you are very close and you will know which dimensions are correct. I would not use any dimension gotten off the internet without varifying. Even the location of the gas port drilled in the block varies slightly between some brands. Get all your stuff together and take some measurements and you will be fine.