My latest project is in pieces in MN. It will be a 14" suppressed Thompson Center G2 SBR chambered in 5.7x28, with a 1-7 twist, for shooting subsonic 70 grain (or similar) bullets. The 5.7x28 is the smallest capacity commercial center fire cartridge that I know of; about 20% less than the 22 Hornet. I have a gallon of the brass I picked up at the range over the last decade. I'm hoping the required powder charge will be between two to three grains of Bullseye. This would allow me to use it with my homemade 22 cal silencer, maybe.
The barrel from Match Grade Machine; $500.
It will look something like my 7mm TCU G2 when finished, but with a scope and a smaller silencer.
It should be significantly more accurate and more powerful than my 22lr rifles at ranges out to 200 yards. I should get about 170 ft-lbs of KE with a 70 grain bullet compared to only 98 ft-lbs with the 22lr. The 70 grain Speer bullet has a BC of .214 whereas the 40 grain bullet in a 22lr is typically about .17, I think.
At subsonic speeds it will not make much of a difference in bullet trajectory out to 200 yards, but the 70 grain bullet will be 20% more powerful at 200 yards than the 40 grain bullet is at the muzzle.
I have a 18" Contender barrel in 22 K-hornet, but it has a 1-12 twist and I normally use 35 grain bullets (300 fps) in it.
