Length of threads barrel extension HW97

[Eidem]

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!

[Skengy]

I had a steel insert turned up to add weight in the space of the moderator. A 19.5 mm od steel 'bush' with an 8mm hole down the middle , i think it was 65 mm ( check if you have one made!) i ordered it off the familiar auction bay as a 'steel spacer' It was held in place by a narrow o ring of 19 mm in compression against the end cap . I think it improved my groups but it might be subjective.Subjectively again it seemed to make little difference to noise . I still have it fitted now . I havnt done the scientific test of taking it out to see if the groups open up again yet .
The weight was much less than you are proposing and its all contained in compression in the void by the end cap so i can't comment on whether the end cap threads would support your proposal, be careful, the walls are not thick and the steel is of unknown hardness. Good luck .

[Rich]

According to my local gunsmith, Weihrauch barrels are quite soft.

I feel that your project will not be successful at noise reduction. What is needed is expansion of the discharging air, which is achieved by expanding from a small aperture (such as 4.5mm) into a larger internal diameter cylinder. In your case, the difference in diameter between the outer tube and the inner sleeve is small.

You may also have problems with concentricity. If the device you are making should droop, the axis may fall below the pellet flight line.