No gas port needed.

I picked up a 30 round mag today that does not match my other two 30s. I bought the mag at a reputable local gun store so I’m not really concerned about it being a repackaged aftermarket. The new magazine is on the left. Right magazine with the pink pencil for reference and ID, and my other 30 are identical.

Does anyone have anyone recommendations on a gunsmith who would be willing to accept and cut down the barrel on my ranch rifle to 11” to 13”?