oversized gas port with adjustable gas block

[RWBlue]

I am having issues getting my subsonic loads to cycle my AR. I am very tempted to use my standard home drill and open the gas port.

So, what is the down side if I open up my gas port?
I have the adjustable gas block that I can use to regulate the gas.

[320pf]

Before you go too far, please tell us what your set-up is.
Barrel maker
Barrel length
gas port location include in from chamber
gas port diameter
type/brand of powder
bullet weight


I have an Oly arms barrels with the gas port in the pistol position (approximately 4 from the chamber). The gas port os 0.071"

I use AA#9 powder, 7.5 to 8.5 g to push 165-240 gr bullets. Subsonic loads run very well in my set-up and the action cycles very reliably. These loads can be found on the Accurate Arms web site. They list several loads for the 300 whisper. Powders faster than AA#7 will have problems cycling the AR15 action

(Important Notes from JD Jones himself:
I would appreciate it if you would delete the Accurate #2 data and say that in SSK AR-15 and M-16 no powder faster burning than Accurate #9 should be used. The gas system is timed for sub sonic with powders with burning rates from #9 through 1680 [ttp://www.quarterbore.com/300whisper/subsonic.html]).


So I would not try any of the listed loads for AA#2 and AA#5 on the Accurate Arms web site in an AR15.


P.S.

I just came across your post on the other thread.

Try the 2400 powder.

How much W296 did you try? W296 might be a tad too slow. I need a bit more info.

Got the info on the barrel (Noveske 10.5) The gas port info would help (location and port diameter)


320pf

[RWBlue]

I would like to keep the thread specific and not drift off into my issue but use it more as a collection point on knowledge on a specific issue.


Although I don't plan on doing anything radical until I test out a few more things, but I am not seeing the down side of opening up the port.

[pug]

RWBlue it is just that the people who made your barrel are very competent and for them to port it in the pistol position seems like they planned for it to cycle subsonic. I am not saying don't but just make sure all the other things that cause ARs to short stroke are not a problem. I assembled my upper carefully and then shot a broad range of bullet weights and decided I wanted to go lighter subsonics so I opened up my pistol gas port whithout hesistation and I like the way it functions now. However one draw back is if you go large and forget to turn the gas down firing a heavy supersonic round can blow your gun to pieces. See one example below.

[320pf]

I also have a Noveske 16" barrel (0ne of the three 300 fireballs that I have) it shoots very well both subsonic and supper sonic loads. I would bet that your cycling problem is not related to the barrel.

If you are not running your loads over a chrono, I defiantly would not modify the barrel until you know what your load are doing.

I personally have a Pact XP chronograph with the infared detectors. It works both outdoors and indoors. I recommend this chrono... high quality, good price, and the company provides good support.

As far as opening up gas port, too much gas can also cause short stroking. As Pug mentions start with the rings in the bolt/carrier and check the carrier key.

Good Luck

320pf

[RWBlue]

Pug, good example of the down side to opening the port. Is that carrier where you forgot to turn down the gas system or is that a stock photo of what "could" happen?



I will be swapping parts, to understand the issue better, but I think the decision is make. I like the idea of being able to shoot lighter subsonics. So opening the port is sounding better all the time.

BTW, while I am asking questions, is there a good solution to tightening up the adjusting screw? It is fairly loose, and would probably fall out if I went for a day in the woods.

[tp555]

You still haven't told us exactly what size your gas port is.So everything else is: should I ,could I ,yes no maybe.Measure the port size then we can give you some
advice.

[RWBlue]

You still haven't told us exactly what size your gas port is.So everything else is: should I ,could I ,yes no maybe.Measure the port size then we can give you some
advice.

I am not asking you to solve an issue. So my perticular port is of no consequence.

I am asking, what would happen if I opened it up. If you haven't opened up a gas port, or played with an adjustable gas tube or block, you will not be able to answer this question.

[tp555]

I make ar-15 barrels for a living for 15 years or so. Over 100 in a special caliber for one customer.I counted them for kicks.I also make gas blocks custom,which includes adjustable gas blocks. So maybe I might know something,but in your case there is nothing to see here.Good luck using that hand drill.

[RWBlue]

tp555, since you claim knowledge in this. What happens if I make the port larger than what would be considered normal?

It appears that if I open it up I have more flexability. Is there a downside?

BTW, I am sure you have more tools on your tool bench than I do. I don't think I have the correct tools to give an accurate measurement even if I did remove the block to check.

[tp555]

Use calipers to measure the gas port hole.They are cheap $10 or so.Gas port holes vary from .045" to .156" in the ar.At least I 've made them that size.Normal .223 stock 20" bbl.is .062".The 30/221 is usually .085" to .125"
depends on bbl length.Bigger hole throws the brass out father away in high pressure.Too big you will have problems and maybe nasty suprize.In the 30/221 with a pistol gas tube make the port big enough to cycle sub loads about .090"
for 16" bbl.Drops brass at your feet.Using high power throws brass 10 feet out.
Too big a hole shaves copper from the jackets and clogs up the port.

[RWBlue]

The 30/221 is usually .085" to .125"
depends on bbl length.

In the 30/221 with a pistol gas tube make the port big enough to cycle sub loads about .090" for 16" bbl.Drops brass at your feet.Using high power throws brass 10 feet out.

Too big a hole shaves copper from the jackets and clogs up the port.

Now that is useful information (especially last line) and may keep me from drilling.