Yea, I know, another gas port question...

[too_many_hobbies]

The 300 Fireball in the picture below now has a 16" Olympic Arms barrel. I am going to SBR this weapon with a new 10.5" Shilen barrel. I have read through many posts and still do not know which gas port position and size to specify. I will only shoot 220 Sierra Match Kings at subsonic velocities through this weapon with a sound suppressor always installed.

The weapon functions perfectly with subsonics now with the standard Olympic Arms position and size. Should I ask the gunsmith to duplicate the Olympic Arms barrel relative to the gas port or should I specify the standard AR-15 pistol position and another specific size?

What is the optimum gas port location and size for a 10.5" barrel shooting subsonics through a sound suppressor?

http://i30.tinypic.com/2925jf8.jpg

[jarhead1086]

This is what Steezo757 posted a couple down in the 'charges seating depth' post:

AR with a 10.5" barrel and .100" gas port in the pistol position

I would go pistol position for sure and this port size won't hurt if you don't shoot supers. You can always get an adjustable block from TP555 (Paladine Machine) if you want to try supers later. My 12" works with a ~.090" port, but every barrel is different.
PS- Good work on the kitty

[320pf]

Go with the standard pistol gas port position. My Olympic Arm barrel has a gas port of about -.08. I had to open up my Noveske barrel from 0.071 (which has a pistol gas port in the standard position) to about 0.08 to get it to work with 165 gr bullets.

Heavier bullets generally will run with a smaller diameter gas port. And with shortening the barrel etc... This will change the dwell time, so I would start with a port diameter of about 0.071 and work up in steps.


Good Luck

320pf

[steezo757]

I love my 10.5" Noveske barrel BUUUUUUUUT if I had to do it again, I would probably try to get Marty at Teppo Jutsu (http://teppojutsu.com/welcome.htm) to make me a barrel from a Pac-Nor blank.

The biggest draw back is the 0.875" barrel diameter of the gas block. Not to mention the shorter than normal "contact area" for the gas block. Noveske's gas blocks are shorter than others.

Although I think I hit bingo with my certain barrel config and load, I would of rather have an adjustable gas block to tune my barrel to the loads. Instead of tuning the loads to the barrel.

I contacted tp555 and he said he could make an adjustable gas block for me, but the dimension of the GB would not fit underneath my FF handguards. I've considered having the barrel reprofiled, but damn. It's a pricey barrel and could not force myself to invest more into it. I was even hesitant to have a gunsmith put a drill to the gas port.

So to answer your question: Pistol gas system with the gas port drilled out to .110" and use an adjustable gas port. You'll have a lot more versatility.

[pug]

Since you have an oly barrel there are a couple of things to watch out for. First oly pistol gas tubes are a different length than the other pistol tubes the oly is shorter. Second oly gas blocks are a different size than other gas blocks oly is larger diameter. If you were going to use the parts off the oly you could copy the dimensions and you would be fine but unless you need to save the money I would go the other way. I would acquire the gas block I want to use and then get a "standard" pistol gas tube and send both with the barrel when it is profiled. By getting a standard .750 gas block any of the others will fit if you decide to change it out. As far as the port diameter it doesn't take a large one in the pistol position to get 220s to cycle and you can still shoot supersonics without trouble. If you plan to shoot the light bullets you will need at least a .1" port.

[jarhead1086]

I had my TP555 blocks made to .750 ID before I got my Noveske's which surprised me being fat. I ended up rough machining the barrels to a little over .750 and then low stress grinding to exact size to my blocks which I had honed straight and round. Very nice fit, but not economical for most people who can't get G-jobs at work. The TP555 blocks are the perfect size to fit underneath YHM handguards which it looks like you have, Too many hobbies. Steezo, I'm sure he would machine them a little shorter if you wanted to keep your current handguard. His 2 position push button block looks a little shorter too. The SSK 2 position block is very low pro, but I don't like machining flats and tapping four holes in my barrel to attach it.

[tp555]

As a little note of interest. I make custom gas blocks for a lot of people.I know Marty from Teppo .He wants some really strange gas blocks at times.regards.

[steezo757]

As a little note of interest. I make custom gas blocks for a lot of people.I know Marty from Teppo .He wants some really strange gas blocks at times.regards.


OH REEALLY? I apoligize. I didn't know you were that flexible. This would of saved me a lot of headaches and fustration. I may have to get in touch with you shortly. :wink: