Gamo AF10 improvement

[Iain K D]

Before discussing what I did with this, I should first explain the magazine design on this gun. The transfer port in the valve housing is enlarged to form what is, in effect, a .177” calibre chamber (it’s actually front loading, so perhaps I should use black powder terminology – so that would be about 900 bore!). The magazine tube, for 10 ball shot only, lies above the air cylinder and is pivoted at its forward end; as soon as the gun is opened this is able to pivot up slightly and push a ball back into the chamber, and when the gun is closed the magazine is pushed back down again, leaving the chambered ball in line with the barrel.

This means that the mouth of the magazine moves up and down in a vertical channel on the face of the valve housing, on which there isn’t a breech seal of any kind. This didn’t seem very good to me, and since I was happy to lose the magazine feed (the gun can also be loaded directly into the barrel – in fact, access to the breech to do so is very good) I stuck a fairly simple seal from a cut-down thin rubber washer over the transfer port. The barrel was slid forward slightly to accommodate this (the barrel doesn't locate in one particular place), and then secured while being pressed back to butt against the seal.

This worked, although the seal could work loose very easily, so I recently tried making something a bit more elaborate. A thick rubber seal was cut away, and then sanded (mounted on a Dremel style tool) so as to leave a tubular projection facing backwards. This was to fit inside the transfer port. The remainder of the face was trimmed to fit in the channel on the valve housing face, and the barrel then seals against this as before.

For whatever reason, this seems to be giving a better seal than the original lash-up. A few shots with that gave velocities of around 300 ft/s (with RWS Hobby and Bisley Practice); that is now up to around 370 ft/s instead, which is much closer to the figure that might be expected judging by the size of the air cylinder (comparable in size to the PR45).

Iain

[mickson]

Interesting thread, and a very good idea i wonder if the pr15 (earlier version) is the same ??...mike...

[Iain K D]

I'm pretty sure the PR15, 45 and Compact all share the same air cylinder and valve housing, so that has a proper breech seal.

Although, in the case of the PR15 (ball shot only, so no need to access the barrel), instead of lining up with the breech face of the barrel itself, there's a vertically moving feed block between the valve housing/transfer port and barrel proper.

Iain

[mickson]

I'm pretty sure the PR15, 45 and Compact all share the same air cylinder and valve housing, so that has a proper breech seal.

Although, in the case of the PR15 (ball shot only, so no need to access the barrel), instead of lining up with the breech face of the barrel itself, there's a vertically moving feed block between the valve housing/transfer port and barrel proper.

Iain

Cheers Ian could'nt remember breech layout on the pr15 its donkeys years since i owned one, atb...mike...