I am making a barrel extension for my HW97K.
I am using a 22m od, 18mm id 300mm long steel tube. Also I might be using a 18mm od, 12mm id steel tube.

The idea is is to start with the full length large diameter tube and experiment with different inserts of the smaller
diameter tube to alter the balance of the gun.

The full weight of the two tubes is about 680g. I will most likely not use the whole length of the outer tube, it depends
on balance achieved and how it affects groupings at 50m. Neither do I think I will need to use the whole length of the
smaller diameter tube.
I will make different length baffles ranging from 5mm to 40mm, tapered 45 degrees inside on one side leaving the other
side straight.

I will experiment with the inner tube as baffles to see how it affects balance, groupings and sound.
Ideally the end result would be a "long heavy moderator"

I am however concerned about the short length of threads inside the tip of the barrel of the 97. About 8mm.

Will this be strong enough to take the added weight or should I lengthen the threads inside the barrel tip with a few mm?

I have no experience with moderators, would someone be bothered to share their thoughts on this?

Cheers!