The only sleeve conversion that is shown to work without seperating the barrel and handle is the 22 Long sleeve. Anything larger is known to blow the launcer apart. Various sources for other sleeves I researched say you should not use conventional 12 ga shells in a converted heavy metal flare launcher such as GECO or the Polish launchers. The claim is not that it would damage the gun but that you would likely break your wrist from recoil. The GECO and Polish guns
had clamp on stock extensions although I have only seen them as collectable antiques. This would let you handle recoil but you would be better off buying
a real gun. The 410 shot-shell conversion works in these launchers. The 12 ga conversion lets you launch Dragon's breath and mayby a few of the other low recoil rounds.
There are many YouTube videos showing firing of these devices. Some additional videos can be found on the retailing sites for the sleeves. Before you get an insert, I would discuss with the seller (use a real gun distrubitor with sharp people).
The short of it is that I would not use a sleeve in a plastic launcher - period. If you plan to get an insert then get the heavy built military surplus launcher. I have the Polish one. It is impressivly well built, tight, heavy. I do not have any inserts but I am considering the paper-work necessary to legally posess the parts
. I would use the 12 insert for 12 ga flares only. The 410 insert with buck at close range would be OK for bad guys that don't belong on the boat. The 22L insert is rifled and reasonably acurate to around 30 yards with practice.
I figure if you are nuts enough to sail near Somalia
you should get a (cheap) real gun for the transit and let it be confiscated on port of call or toss it over the side. You could always pass it to a sailor headed the other way. I suggest a 12 ga pump or semi-auto with 00 buck. Get a flame-thrower round for their gas tank. You can also get percussion cap exploding rounds from a class III dealer. In many places, these are sold for scaring birds away from crops. I fired them at appliances
at at tac-training outing. They easily blow the door off a front-loader dryer at 150 yards.
Some poetic license
was taken composing this photo
. I took the bird at 45 yards with a Browning BPS 10/12 with 28" barrel, recoil supressor, full turkey
choke and 3-1/2 inch #4 turkey
magnum. 78# recoil. It makes a delightful boom. The echo off the surrounding hills resonated for several seconds. Don't fire this round in your flare launcher.