"Blow Back" MV Penalty

[ASbobcat]

Saw a thread about easily converting a 10/22 to single shot, without changing any parts, by using a cord to hold the bolt closed. I used a shoelace and it worked, sort of. When I cycled the action it did not extract/eject the case. I had to pry the case from the chamber (wasn't difficult, but still not a good field solution). This was in a Magnum Research model, which I suspect has a tight chamber. This method might work fine a factory 10/22LR, but I didn't have one to try.
I found the velocity from the closed breech to be 50fps greater than the same barrel in normal blow-back mode. This may or may not be significant to some, depending on intended use, but it was a very consistent result.

 

['Freak]

Clean with a carbon eater and brush the hard carbon ring forming in the chamber about and a bit forward of the case mouth. What’s the ammo and how much less than 50 fps is usual velocity variation tested across a fair number of shot samples …?

 

[boltman223]

Saw a thread about easily converting a 10/22 to single shot, without changing any parts, by using a cord to hold the bolt closed. I used a shoelace and it worked, sort of. When I cycled the action it did not extract/eject the case. I had to pry the case from the chamber (wasn't difficult, but still not a good field solution). This was in a Magnum Research model, which I suspect has a tight chamber. This method might work fine a factory 10/22LR, but I didn't have one to try.
I found the velocity from the closed breech to be 50fps greater than the same barrel in normal blow-back mode. This may or may not be significant to some, depending on intended use, but it was a very consistent result.

They dont produce that much rearward force. I've actually held my 10/22 bolt closed with my hand. I wanted to see how much of a sound difference there was with the bolt staying closed vs open with a silencer.

Interesting to see the difference in velocity though.

 

[ASbobcat]

They dont produce that much rearward force. I've actually held my 10/22 bolt closed with my hand. I wanted to see how much of a sound difference there was with the bolt staying closed vs open with a silencer.

Interesting to see the difference in velocity though.

Interesting and good to know. I was using very high performance ammo (Browning 40gr/1435fps) and didn't want a dislocated finger.

 

[ASbobcat]

Clean with a carbon eater and brush the hard carbon ring forming in the chamber about and a bit forward of the case mouth. What’s the ammo and how much less than 50 fps is usual velocity variation tested across a fair number of shot samples …?

That is certainly possible, although this gun hasn't been shot much, so doubt if much carbon has built up yet. I would like some feedback from someone who has a gun with a looser chamber to see if that is the issue.

Ammo is the new Browning 40gr/1435fps (equivalent to the un-obtainium CCI Velocitor).

This stuff is amazing! I have never found any plinking/hunting rimfire ammo to be this consistent, but I don't use expensive target ammo. I tried it in two different guns. The MR MagnumLite (17in bbl) and a 77/22 with barrel cut to 17in.

Fired 10rds through each in single shot mode and 10 through the ML in semi. ES was 10fps and SD 5. Actual velocity over the 30 shots averaged EXACTLY 1435fps! It is the ONLY rimfire ammo I've ever tried that even came close to advertised velocity. Even CCI, which is more consistent than most, is usually 50fps low with a ES of 50fps or more.