A few years ago, I received, by mistake. a 177 steel breech for a .22 Crosman 1322. I installed it without realizing that it was the wrong caliber. Before Installing the breech, the gun fired pellets at about 430fps. When I added the steel breech, the gun was still shoting at about 430 fps. After a couple of weeks I noticed I was using the wrong breech so I repaced it with the original .22 plastic breech. Last year, just out of curiosity, I installed that .177 breech on a crosman 362 that had the correct .22 steel breech and the rifle kept shooting practically at the same 630ish fps with both breeches. When I used the .177 breech on both .22 cal guns, I did feel a little air coming out of the breech, but the chrony never showed any significative difference. Now that .177 breech is on a crosman 1377
Yes, you're right. As you said, the bolt does change. The diameter of the bolt seal (o ring) is smaller. The funny thing is that even with this smaller .177 seal in a bigger .22 barrel, the muzzle velocity was practically the same as with the other breech with the correct .22 bolt/seal. despite the puff of air coming out from the breech. Cheers!!!@@LowkeyAirgunner