Loading help for 240SMK, N110 subsonic

[JimM44]

How do I set the correct bullet seating length on my dies for this barrel, I have read where some folks have powder escaping around the bullet if set too far back and then others having loading problems with it set too far foward not chambering properly.

Ok I now have my barrel, not mounted yet 16" from M1S.

I have the 240SMK bullets in hand 2K plus of them.

Brass, powder(N110) both ordered should ship next week.

I have redding dies and winchester small rifle primers, my Sierra reloading manual recommends 9.7 grains for 1050 velocity.

Is there a way to measure my chamber to get the proper length or is it known for the M1S barrels?

I am also waiting for my Gemtech HVT which I will use on this rifle, so this is not a rush as it will be a while before everything is in place.