I have a M70 with Boss and was thinking of cutting the barrel to 22".My hope would be to make the gun more useable.Will I lose to much fps?

Thanks

I had a 24, and cut it to 22.5 for portability and it was fine. I doubt you will lose 25 fps per inch per actual barrel you have now under the boss.

Larger calibers are less effected by barrel length due to the expansion ratio. 25 fps is a good estimate but this is not a linear computation. I recommend a 23" barrel if you can cut and crown at that length.