What size gas port should I drill?

[L1A1Rocker]

I have a project in the works and need a little advise. I have a M1S 300 Fireball kit that I've been working on. I've chopped the barrel down to 10 inches and am building an integral suppressor around it out to around 17 inches. The gas port is in the pistol location but I know it is too small. I'm planning on a sub-sonic gun without bothering with an adjustable gas block (no need for strictly sub-sonic duty). What do you folks recomend for a gas port size?


Oh, if it matters, I'm going to try loading 200gr Lapua bullets with AA5744 powder. This is my sub-sonic load I've already worked up for my 308 bolt action and was going to try to stick with common components if possible.

Thanks for any suggestions.

[Spook]

I use .118 which may be a smidge big for use with a can and SS only loads. I'd be you'd get by at around .105

[i8asquirrel]

Mine is .116 no sense going bigger than the ID of the gas tube.

[robrob]

Since I installed an infinitely adjustable gas tube I figured bigger was better so I used a 1/8 inch (.125) drill bit on both the gas port and gas tube inlet. My port is in the carbine position so I wanted to get as much gas as possible for subsonic rounds.

Because the gas has to make a 90 degree turn into the gas tube having a gas tube inlet hole larger than the inside diameter of the gas tube is beneficial.

[markpurifoy]

What do you do to clean the inside of the barrel. Where you drilled into the barrel. Before shooting your gun. Is there any metal tabs hanging down at bottom of inside of barrel.

[Spook]

Originally Posted by markpurifoy

What do you do to clean the inside of the barrel. Where you drilled into the barrel. Before shooting your gun. Is there any metal tabs hanging down at bottom of inside of barrel.

If you gain diameter in small increments the burrs have a tendency to be small...I always run a tight patch or two through the bore for any big boogers that might be clinging.

[markpurifoy]

Originally Posted by Spook

If you gain diameter in small increments the burrs have a tendency to be small...I always run a tight patch or two through the bore for any big boogers that might be clinging.

Thanks Spook you always have good info.And you always answer back.Will do slowly.I'm going to wait first Model1 sales sending me their recoil kit for sub loads only going to try that first before opening port up.Well change to a1680 power also insted of h110.I like the 240hpbt but will try 220 maybe cheaper..

[markpurifoy]

Originally Posted by markpurifoy

Thanks Spook you always have good info.And you always answer back.Will do slowly.I'm going to wait first Model1 sales sending me their recoil kit for sub loads only going to try that first before opening port up.Well change to a1680 power also insted of h110.I like the 240hpbt but will try 220 maybe cheaper..

Update I have taken the front site off and can stick a 1/8 drill bit but first into carbine gas hole.So I would say I sould not be having cycling problems.Still waiting on the mail for Model1's sub sonic only hammer & springs,buffer and buffer spring.Then see what happens.You would think 10.8 gn. h110 pushing a 240 gn Sierra HPBT would cycle but no.%$&$%&(. You know want I'm saying.Don't know still working on whats wrong.Have loaded some 15.0 gn. h110 with a 150 gn ballistic tip. See if this cycles. Anything else to check ?

[markpurifoy]

Originally Posted by Spook

I use .118 which may be a smidge big for use with a can and SS only loads. I'd be you'd get by at around .105

Hey I checked and i can put the tail end of a 1/8 drill bit into gas port. So now what.

[robrob]

Did you check the gas block's port size and the alignment of the barrel port with the gas block port?