MOVING the gas port?

[Foxfire]

How has moved the gas port, from carbine to pistol position?
How did you plug it?
How successful is it?
What is the new port size?
Adjustable gas block?

Mine is 16" barrel. Although I may cut it down to around 10" when my SBR comes back.
What are your opinion on this too? If you have one.

TIA, Fox

[320pf]

I have moved the gas port from the pistol to the carbine position. A machinist friend did the actual work but it was fairly easy. One of the frequent posters here suggested this method and it seems to work very well.
(I think it was either tp55 or pug).

I have three 16 in, 300-221 Fireball barrels. Two are Olympic Arms 16 in. barrel with the original gas port in the "Olympic Arm" pistol position. (NOTE: The Olympic Arms barrels have the gas port approximately 0.5 in. closer to the chamber than the "standard" pistol position). The third is a 16 in. Noveske with the gas port in the standard pistol position.

The original gas port was 0.070 in. This is the same port size as the Noveske barrel. Both barrels shot subsonic load very well and super sonic loads as well.

I suggest that you start out with a 0.070 in port in the standard pistol position. It will be much easier to find a gas tube. You might also have to turn the barrel down to a standard size like 0.75 to find a gas block that you can use.


I moved the port on one of the Olympic Arms 16 in. barrels. You should be able to do the same ting that I did but in reverse.

As I said above, the original gas port was 0.070 in. we partially drilled the original gas port part way out with a #47 drill. Do not drill all the way through... we left about 0.130 in of the original gas port intact. Then we tapped the hole with a 8-32 tap to the bottom. We tried a bottom tap but it did not go in too smoothly and were afraid that it would break the tap so we started with a regular tap and went as far as it would go... then ground it down a bit and went deeper. We repeated this until we got a pretty good bottom tap.

We then used an 8-32 hex-set-screw with red lock tight to plug the hole. I then used a port-less low profile gas block to cover the set screw just incase the set screw comes lose. The advantage of this is that I have some hex-set-screws drilled out to 0.070 in so I could go back to using this port if I want to.

As far as gas blocks... I had the to have the barrel turned down a bit so I could use a 0.075 in gas block. I am using a JP Enterprise low-profile adjustable block.

I hope this helps. I you have any other questions just ask.


320pf

[WhisperFan]

How has moved the gas port, from carbine to pistol position?
How did you plug it?
How successful is it?
What is the new port size?
Adjustable gas block?

Mine is 16" barrel. Although I may cut it down to around 10" when my SBR comes back.
What are your opinion on this too? If you have one.

TIA, Fox

Hi Fox

I have an AR upper that I did the exact job you speak of.

It started as a Model 1 Sales 16" 300/221 1-in-8 twist with an A2 style upper.
I wanted to cut the barrel down to just in front of the front sight tower. 10" worked out to be right about where Model 1 Sales ends their letting on the barrel, so that's where the shoulder for the threads is located. It has about 1/2" of 1/2-28 threads beyond that. The total length is a smidge over 10.5"

Like 320pf, I too, used an 8-32 tap, lock-tighted and plugged the hole with a set screw. Since it is an A2 style upper, and was putting back on the sight tower (to use as a front sight only) I was forced to contour the set screw to match the barrel profile .... by doing this, and putting the tower back on, it can never loosen.

My new port size for the 300/221 is .110" and it puts the brass about 5 feet to my left shooting 220gr SMK's pushed by 8.5 gr of AA #9. I could have gone a bit larger, but I wouldn't go much smaller. I am using a non-adustable low-profile gas block beneath a standard carbine length free float tube.

So what I really have is a SBR whose barrel is about 10.5" long - but uses a standard carbine length handguard. My rifle is dedicated up to shoot 220 gr SMK's subsonic only. If I were planning on shooting supersonic loads as well, I would have a smaller gas port, or an adjustable block (or tube)

Hope that helps you.

[Foxfire]

Thanks guys for the info it helps a bunch.

Mine is a 16” model “1” ported at the carbine position. It cycled fine with supersonic handloads, but even after opening up the port to 0.125 and installing a JP adjustable gas block I still can’t get it to lock open with subsonic loads. (For me if it won’t lock the bolt open then it’s not cycling completely.) Even tried slower burning powders. AA#7, H110, IMR 4227, Win 680. My conclusion was that my port was just in the wrong place for subsonic loads.

320pf,
I was very surprised to read that you moved your port from pistol to carbine position. Is that upper dedicated Supersonic? Why did you move it out?

Fox

[320pf]

Foxfire,

I am interested in the super sonic capabilities of the 300-221 fireball. As I mention in my original post, I have three 16 in, 300-221 Fireball barrels. Two Olympic Arms and a Noveske. The two uppers with the gas port in the pistol position work well with subsonic loads. I have found that the best powder for sub-bonic loads for my barrels is 7.5 to 8.5 gr. of AA#-9 depending on the ambient temp. The powder burn rates and the speed of sound change with temp so if you want to have your loads running just sub-sonic you have to tune them for the time of year. On cold days the speed of sound is a slower but the powder also burns slower and usually requires a bit more powder than on hot days. So I have my sub-sonic load pretty much worked out.

Both barrels with the pistol gas port are 0.070 in. and work very well with the sub-sonci loads. The super-sonic loads work mostly pretty well but if I really start working the gun in rapid fire... sometimes the action cycles too fast and tears the rim off the brass and leaves the shell in the chamber. It seems that the pressures are too high when the action cycles. Moving the gas port to the carbine position will delay the cycling of the action allowing the bullet to move further down the barrel and lowering the pressure. I am hoping that this will improve the super-sonic performance of the 300-221 fireball.

Do you have any data on the super-sonic capabilities of your barrel? Loads velocities etc...

thanks,

320pf

[Foxfire]

Sorry, no data yet. I want to work out the kinks in subsonic first, sense that will what I'll primarily shoot.