Gotta build spacers to take up the length of the buffer weight you're pulling out, and insert that spacer in place of the weight. Don't forget to account for the thickness of the pad that's between the buffer weights, on either end, when cutting the length of the spacer.
^^^ If you don't do that, your buffer will rip itself apart inside the receiver extension...
I had to turn a rifle buffer into a carbine-weighted buffer for my 300BLK rifle, to get it to cycle properly. NEMO 16" nitrided barrel, carbine gas system.