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.