Theoben Rapid Forum

Hi all

Been trying to increase the ram pressure in my sub 12 ftlb .22 Evolution (currently running at 10.2 to 10.5 ftlb) but my hand pump seems kaput.

I'm sure I've read that you can charge the ram with an air bottle which I have for my MFR.

Would anybody know a target pressure to get to with a bottle.
I accept this has to be done very gently & accurately, which I feel confident to do. Just need someone in the know to give me a target pressure.

Thanks in advance.


Cheers
Brian  8)

Don't think a bottle would be a great idea, just due to the small volume of the piston. It would be difficult to control unless the bottle was near empty to begin with.

You can use a stirrup pump, but again- for the increase you're looking to achieve it would likely be less than half a pump.

If the pump you have is a slim Jim type, there's only 1 o ring to replace on the piston, and one on the check valve(possibly 2). It's a 5 min job.

Now to the pressure- given the variables of differences between efficiency from one rifle to the next- what achieves 10.5 at a given pressure in one rifle, likely will not in another.

Of the 2 Fenmans I have, both have been .22 at some point during my ownership, the ram pressure sat between 750 psi and 800 psi.

Not intended as a Granny / egg post, but hopefully of some help.

Hi Joe

Thanks for the reply, having looked at the strip down/rebuild guide posted on the forum, i did use my air bottle, using the documented starting point of 700psi - no change to the ftlbs, 800psi ftlbs up by 1/2 ftlb, 900psi ftlbs up to 11 1/4 ftlbs.

So by very careful trial & error I got to a suitable power level, it is doable with an air bottle if you are extremely careful,having a larger than standard glycerin filled gauge is definitely an advantage and make the procedure easier.

Thanks for the input.


Cheers  8)