Does anybody have any information on
1 Optimum barrel lenght on springers
2 How to rechoke an airgun barrel
As said above a spring gun can get away with a fairly short barrel, the Theoben Fenman makes 12ft.lbs from a 7 inch barrel. One thing to consider though is if the gun is a break barrel you lose leverage with a short barrel so the addition of a sturdy silencer aids cocking.
Re: choking of barrels, it is one of those wierd quirks of airgunning that for some reason the spring gun can live without a choke at the muzzle, so cutting down an existing barrel is possible provided you recrown it properly. However do that to a PCP losing the choke and the accuracy goes to s**t (observed through experimentation).
Theoben used to offer a re-choking service, but haven't seen it offered for a long time.
I have picked up a Slavia 630 in a pawn shop for peanuts. When I got it was doing 450 fps. I have tuned it and at the moment it is doing average 599 fps (20 shots with ES 14 fps and SD 2). It is a sweet shooting rifle with no vibration or twang and very accurate, however the barrel is 500mm long. For optimum accuracy the barrel crown has to be at the tightest spot in the barrel. I do enjoy working with my hands and if I can figure out how to choke a barrel I might concider shortening the barrel.
For my next project I would like to take one of the chinese springers and see how I can improve the shooting behaviour.
As far as rechoking a barrel if I think about it the most obvious way will be to have a set of dies with a taper machined inside. The barrel goes inside the dies and then put in a press. What I would like to find out is what would be the optimum taper for the choke.
Any suggestions will be welcomed.
I took a B3-1 and did a full tune on the rifle. Replaced the piston seal with weihraug(sp) seals and polished the cylynder and the piston. The spring was also replaced. Took the hacksaw and cut 60mm of the barrel and recrowned it using drill bits. After a polish and a cammo paint job I now have a CHEAP(R 169) springer that is accurate and works perfect for hunting ferral pigeons and shooting HFT.
I would guess you could make a mandrel with a taper and then proceed to press and rotate it.
However you will have a task of making sure that the choke is 100% round as to keep the pellet consistant in flight.
Here's a basic bit on choking and accuracy.
Here's BSA's version:
From what I read on a site, sorry have no link handy at work, they reckoned 0.5 of a degree taper.
Also the choke is not right at the end of the barrel, but say 1-2 inches back.
I asume that Cocke applies the same principle as in Shot Gunning where the diameter/apature is reduced over the last section of the barrel?
why would this improve any thing besides velocity .... in a shottie you have a mass of pellets that are controled and the colume of shot expands depending on the amount of chock.
how does this affect a air rifle?