We need way more details on the rifle before any type of diagnosis can be made. We don't even know what type of ammunition is being used.
Starting with quality, brass-cased ammunition with anywhere from 150gr-168gr would be a good idea. What do you plan to shoot in it and for what purposes? That will drive your gas system configuration, as port location and diameter is not a once-size fits all matter, though an adjustable gas block can increase the selection of ammunition that you're able to run through it reliably.
After a component and assembly method check, I would start with the single fire test, to see if it will lock back on the bolt catch, driven by the follower of the magazine.
If it is short-stroking, it could be both not enough gas, or too much gas. Too much gas can also run the bolt carrier velocity so fast, that it beats the magazine spring's ability to lift the cartridges in time, which is why you should increase the mag capacity after the single shot lock test, since more weight in the magazine is more difficult to lift.
I would like to know the following before even attempting to make a diagnosis:
Frankengun or complete manufacturer's rifle?
Ammunition used?
Barrel length and gas system length?
Barrel make and chamber used?
Bolt carrier type, was it assembled by a factory or someone at home?
Buffer length, type, and weight?
Recoil spring type/length?
Gas block type, make?
Gas port diameter?
Pics would help. I'm just north of you too, and have been dealing with large-frame AR's for 10 years, AR15's since 1988, so feel free to hit me up if you want.
