I reamed out a carrier for a .25 ACP, and was going to bore deep enough to use full length, however the plug does not have enough meat left in the flash hole. I also thought about shortening the cases, it would work but would also make a lot of work. If the flash hole was even just a quarter of an inch further forward in the plug, this mod could be easily done by just drilling the right size hole to the right depth. I have also considered drilling it out and installing a vent liner but this type of mod would be very time consuming and you would still be stuck with the same crappy breech plug.
Be careful with those shortened cases, if you don't have a well for the case to fit into, you will get some serious blowback. The problem with the open cartridge cases, is the space/chamber between the primer and the flash hole. The fire is not channeled directly into the powder charge, and therefore has room to cool off and stray off course. This is especially true with the Huntsman/Sidekick primer carriers and plugs.
I did a #11 conversion that worked well, using the old #11 nipples from the old orange Knight DISC rifle. These nipples slide into the business end of the carriers without any modification. They are easier to prime before sliding into the carriers, the firing pin will set them off, but blowback/carbon would migrate into the firing pin channel. I could only get a few shots before I would have to spray the carbon out to free up the firing pin. This method would work well for a hunting situation where very few shots are taken, but needs to be attended to at the range to keep the pin from locking up. But for states that do not allow 209's, this conversion would work.
Just be careful, you will get some serious gas venting out the tab slot, hope you are not left handed. I have already been down this road and have concluded there are much safer ways to do this. Good luck, and wear your safety glasses!
