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They work very well. They screw onto a friction fit bush that must be turned out to the o / dia of your barrel approx an inch from the muzzle. Drift the bush on with Loctite and a rubber mallet or similar.

Cut it as big as you can, my Sako Varmint is 18mm as an example.

I have a Remmy 700 Mountain Rifle in 243, shoots great. Trigger has adjusted down to a 2lb pull so no need for aftermarket, they are also one of the few factory rifles with a twist that will stabilise a 100GRN bullet.

I have a 30 inch M/C Perennia with the Kick Off system, great guns. My 4th Beretta and definitely my favourite, very well put together, handles great and very smooth to shoot. Seems to throw blistering patterns as well, not had it on a plate but on Game at the end of the season and Clays very positive kills with 1/4 & 1/2 choke and 32G 6's.