Gas tube length

[Crawdaddy]

I have a AR 15 in 300 BLK that is very finicky about ammo. About 75% of the loads I try will short cycle up until the point the load development process starts showing signs of pressure.

I can use 19.2 grains of Lil Gun with a130 grain bullet and everything is fine.

When I try H110 there isn't a single load that will cycle properly.

Cast boolits are out with any boolit, Weight or powder.

After playing around with this for a year I noticed the gas tube only goes half way into the key. (about 1 inch) Is that far enough?

Also how big should the gas port opening in the barrel be? Mine is 5/64"

[375RUGER]

I can't help with your questions but I do know that those that know will want to know your barrel length and gas system length. I have read many have problems with altitude and you are at 6500' +\-, and if I recall larger gas port is one cure (something like .100") and another is to attach a suppressor. 300blktalk forum is a good place to get info and I'd bet someone has already experience these same symptoms.

[nhrifle]

I had to open my gas port to .110" (actually .111" as drills seldom ever cut to size) to get it to function correctly with most loads. A suppressor will definitely help with function if you can swing the investment and have the patience for the paperwork.

[sunburn]

A pistol length gas tube functions subsonic and supersonic in short and long barrels. Gas tube length is dependent on gas port location of the barrel.
My stuff works with Lil Gun, H110 and 1680.

[Crawdaddy]

Thanks guys. I will open the port up and see how it works.

375Ruger- Im definitley in the high altitude category. 7200 feet +/-

[Crawdaddy]

Ok, I opened it up to.109 wish me luck.

[woodsxdragon]

good luck! i'm doing some 300blk testing right now too. mainly working on getting my lee die to set back where it needs to. I've got a ar pistol with a pretty tight chamber so thats been real fun.
Anyways...I do know from a ar group i frequent there have been people that end up using adjustable gas blocks especially on 300blk load development to fine tune cycling.

[Nobade]

Hey Crawdaddy! Do you know John Dink? He lives close to you and has done a huge amount of work with the 300BLK, mainly in pistols. You two might want to go over some details.

-Nobade

[Crawdaddy]

Woodsxdragon- ill give that a try if this doesnt work. Thanks

Nobade- I don't know him. Wouldn't mind an introduction though. Sounds like a good resource.

What city does he live in?

[Nobade]

He lives in Tijeras. I'll see if I can get you two in touch. I'll PM when I have info.

-Nobade

[wordsmith]

Crawdaddy - I'm not claiming to be an expert, but I have built at least 8-300 BLK AR's and troubleshot a few more, so I have learned a few things. A couple of things that I've seen with cycling issues: 1) gas block screws backing out, allowing gas to blow out around interface of barrel and gas block. Make sure they're tight, and if not, use at least low strength (some use high strength, not me) threadlocker to prevent backout and tighten them down. 2) gas port too small. This seems like you might have this problem. Google and find appropriate gas port diameter for your setup. There are posts / videos of how to drill out port, pretty easy just take it slow and easy.

H110 works well with lightweight bullets in all setups I've used, from 8" Pistol-Gas to 16" Carbine-Gas, with bullet weights from 110 gr to 155 grain.

[wordsmith]

I've got a ar pistol with a pretty tight chamber so thats been real fun.


I had an SBR with an extremely tight chamber, and ended up having to sand off about 0.001" from the bottom of the Lee resizing die to get adequate shoulder setback.

[1johnlb]

I found in my cmmg that the thicker brass like prvi and s&b causing most of the shoulder problems. The thick brass tries to spring back to its original form. Thus causing the bolt not to close and lock.

[woodsxdragon]

I forgot to ask what barrel length and what gas tube length?

[Jupiter7]

For reference, those with "tight chambers" actually have defective dies. The Lee dies are well documented not to set the shoulder back to spec.

Also, if your gun won't run any load with h110, 99% chance it is a small gas port. Subs with h110 are a fools errand.

For or those who use lil gun in a pistol length gas system with warm to hot supersonics, it WILL eat your gas tube and eventually make the gun into a single shot until a new gas tube is installed, took mine about 8k rounds of the lee 312-155 and 15grs lil gun before it stopped cycling.

[1johnlb]

My lee dies are perfect. I have converted some 1500 pieces of brass and all the brass works perfect except that brass which is extremly thick. The thicker the brass the more they try to spring back making it look like bad dies but in fact its just good brass doing it's job and holding it's form.

If your gun won't work with h110 it not a small gas port but it was designed to run with a CAN. SMALLER GAS PORT BECAUSE OF THE HIGHER PRESSURES WITH A CAN ON THE BARREL. Only increase the size of your gas port if you don't plan on ever running a can.

For those of you who eat your gas tube out with lilgun you have performed the impossible. NO AMOUNT of heat can burn or eat out a stainless steel gas tube but in fact those of you who do not addiquately lube and gas check your lead will clogg it up.

And further more, any man that calls a man a fool, when he opens his mouth begins to show his own ignorance.


THAT'S JUST MY 2 CENTS

[Jupiter7]

My lee dies are perfect. I have converted some 1500 pieces of brass and all the brass works perfect except that brass which is extremly thick. The thicker the brass the more they try to spring back making it look like bad dies but in fact its just good brass doing it's job and holding it's form.

If your gun won't work with h110 it not a small gas port but it was designed to run with a CAN. SMALLER GAS PORT BECAUSE OF THE HIGHER PRESSURES WITH A CAN ON THE BARREL. Only increase the size of your gas port if you don't plan on ever running a can.

For those of you who eat your gas tube out with lilgun you have performed the impossible. NO AMOUNT of heat can burn or eat out a stainless steel gas tube but in fact those of you who do not addiquately lube and gas check your lead will clogg it up.

And further more, any man that calls a man a fool, when he opens his mouth begins to show his own ignorance.


THAT'S JUST MY 2 CENTS
Sir,

I think think you should re-evaluate your statements of opinion. I only related my knowledge of fact. I called no one a fool, it's an expression. Heat will melt a gas tube very quickly, proven in fully-automatic firearms numerous times by others. I believe it's the chemical composition of lil gun that erodes/corrodes. A little google research will reveal the early growing pains with resizing/forming 300blk brass with Lee dies. I would assume they have been made aware and have since fixed the issues. Sorry if you felt offended. I feel you might be mis-informed slightly. Fighting fact with emotion and opinion is a losing battle.

cheers,
J7

[1johnlb]

One mans fact is another mans fiction. I appoligize if I sounded offended but I was not. I do tend to get on the offensive when I hear a man say fool, regardless of who it was intended for. There's only ONE that knows all things and He doesn't post on castboolits but on mans heart. That putting it simple to you means WE don't know it all and at the end of the day, it will be revealed how little we thought we knew. I agree that stainless will melt, thats one reason its so used. I also agree that stainless corrodes, i have seen it many times in many ways. My OPINON IS Crawdaddy is not shooting full-auto but it's possible. My OPINION IS your gas tube didn't eat away from corrosion, but it's possible. JUST MY 2 CENTS

To: crawdaddy, I appoligize for not constructively adding to your post.

one inch is more than enough into your gas key, the ball on the end of the gas tube is the seal maker between tube and key. good luck and remember to clean after lilgun.

[Crawdaddy]

I am taking in all the posts and view yours and all others as constructive. I enjoy the diverse opinions.

Thanks to all.

[Crawdaddy]

I forgot to ask what barrel length and what gas tube length?

Barrel length is 20 inches. I'll have to measure the tube.

Going to the range today to try it out after opening the port. Assuming it quits raining. Been raining all night. Not something you hear often in New Mexico.


As our local weather guy Steve Stucker says, "when you live in the desert there no complainin 'bout the rainin"

[Crawdaddy]

Success!

I shot about ten rounds with no short strokes. Right up until the time my gas block worked loose. Guess I should have used lock tite.

Fixed that a few minutes ago and should be golden.

[1johnlb]

That's great. I ended up filing a flat spot on the bottom of my barrel to stop the gas block from coming loose. I've had no luck with loctite in high heat areas.
Looking forward to getting a accuracy report on that 20inch. I am planning another build, thinking about carbine length.