proper pistol gas port diameter

[320pf]

Well I finally had a chance to check the gas port diameters on the two 300-221 Fireball barrels with a set of pin guages. Here are the results.

The Olympic Arms 16", 1:8 twist stainless steel barrel; the action cycles for both sub-sonic loads as light as 165 gr and super sonic all rounds without having to adjust the gas block. The gas port is about 0.5" closer to the chamber than the standard ar15 pistol port. The port diameter is 0.082"

The Noveske 16", 1:7.5 twist stainless steel barrel; the action does not cycle light (165 gr bullets) sub-sonic loads. I have not tried sub-sonic loads with heavier bullets. I have shot super sonic loads in the following bullet weights, 110,125,150,155,165,168,175, and 180. All cycle the action. This barrel will shoot 0.5' groups all day long. The port is in the standard pistol position and the port diameter is 0.071".

So in conclusion, if you are building an upper with the gas port in the pistol postion, you will want a gas port to be 0.082" in diameter

I hope this helps

320pf

[Ron458]

Thanks 320pf! I set the gas port in the pistol location @ .070 on my 16.5 Pacnor poly. I am not concerned about subsonic loads on this brl so I am very happy I went small:grin: This brl is verry accurate also & I will use this blank again. Thanks, Ron

[320pf]

Thanks 320pf! I set the gas port in the pistol location @ .070 on my 16.5 Pacnor poly. I am not concerned about subsonic loads on this brl so I am very happy I went small:grin: This brl is verry accurate also & I will use this blank again. Thanks, Ron

Ron,

Who cut your chamber in your pacnor barrel? I am pretty sure that my noveske barrel was cut from a pacnor barrel and it is all very accurate.

A friend opened up my noveske barrel from 0.071" to 0.0781" and it now cycles my 165 grain loads (165 gr Sierra MK loaded with 8.5 gr of Alliant 2400). So it look like you may not have to go with a full 0.082" gas port to get sub-sonic loads to cycle. There is a caveat. we only test fired it with 8 rounds in his test bullet trap. I still need to take it to the range and give it a real workout.

320pf

[Ron458]

Thanks for the update on the gas port! I did all the work myself. I used a PTG reamer to cut the chamber. I am more than pleased with this brl. 11g of A2400 behind a 180g Rem SP produced 2 small holes about 1/4" apart for 5rnds! I also ran some Win.147g FMJs with 17g LilGun & was suprised that for a less than perfect bullet, I had a group around 1/2-3/4 & well centered. I was only shooting @50yds but still. I havent tried any Sierras yet, still breaking in the brl. My first experence with the 300/221 was a olympic arms brl about 10yrs ago & I gave up trying to get the accuracy I wanted. My bigbore uppers smoked it! Recently I took up turning my own brls & thought I would give it a try. VERY happy I did. Does your noveske look like a 3 groove? I may try one of the 3 groove's next but this poly is sweet! My plan was to get the perfect load or 2 & tune the gas port for them. For subsonics I may run the reduced power spring/light buffer but my SBR will be centered around subsonic use. Thanks, Ron
http://i53.photobucket.com/albums/g61/ron458/mybuild007.jpg

[Ron458]

320pf When you opened up your gas port, have you noticed any loss in accuracy? I always wondered when it is opened up that the timing changes a little causing a loss in accuracy or if it made no diference. Thanks, Ron

[320pf]

320pf When you opened up your gas port, have you noticed any loss in accuracy? I always wondered when it is opened up that the timing changes a little causing a loss in accuracy or if it made no diference. Thanks, Ron

Ron458,

I was at a 3-gun match about three weeks ago running the Noveske barrel. About half way through the match the gun started short cycling. Lucky for me there was a gunsmith at the range where the match was being held and he drilled the port out to 0.083. The gunsmith said that as you run the gun the port will close up a bit because of power and bullet material get deposited in the port.

The gun ran fine for the rest of the match. I have shot about another 200 rounds through the gun without and stoppages. I have not noticed any degradation in the accuracy of the barrel. In fact this weekend I shot several 0.7 in. groups.

320pf

[Ron458]

Thats great news. I always wonderd if it would cause a timing issue. I guess it would have to be way oversized to create problems. It does make sense to give a little extra room for buildup though. Great information! Thanks, Ron