Air arms xm100 low power

[barrie36]

Hi,just been asked to repair an xm100,apparently it vented all its air the other day,I filled it to 200 bar and seems fine no leaks but it's real low powered 360 fps,I've been on chambers and they don't have a strip down diagram as I wouldn't mind seeing what I'm up against and what seals to get,any info would be great guys.

[Phil Russell]

Email sent with copy of the users manual. In those days they gave more information than they do today.
If venting air, check the seals but be aware that if air pressure drops too low, maybe around 70bar, then the air will vent naturally as there is not enough air pressure to hold the valve shut. For this reason always cock the rifle when filling from empty.
Cheers, Phil

Just reread your post ... 200 bar is too high a fill pressure ... see manual. My guess is that the very high pressure is stopping the valve opening under the hammer blow. Keep firing to bring pressure down to c. 170bar or less and I bet the velocity will increase. Do not adjust until you have tried this.

[barrie36]

Thanks for the info,I did fill it earlier with the hammer cocked and did wonder if the reason it vented the air was because it was too low a pressure as I had an s410 do it just last week,I'll fire a few shots through it to get the power down and let you know how I get on .thanks again.

[Wibblyb]

If you do not know what you are doing take it to someone who does.

[Phil Russell]

Is the XM100 an unregulated rifle ? .... I think it is just the SM100 in a walnut stock. That being so, it is not difficult to strip and rebuild providing you are patient and methodical. It is a few years since I did one and it was a very straightforward operation once the rifle was empty of all air ... essential if you need to change internal seals but not needed if you are adjusting the hammer spring tension as given in the Users Manual.
The only warning I can give is that the main seals are not simple O rings. I think there is an exploded diagram on the Julian Bond Air Arms web page that shows them and gives information on what type they are .. but when I needed a couple those few years ago, Julian did not have any. But I did find some by googling the part number and spec. If I remember, they were also used in the suspension struts of Lambretta mopeds!
So, I am hoping that you do not have a seal failure in the main cylinder. Let us know how you get on.
Cheers, Phil

[barrie36]

If you do not know what you are doing take it to someone who does.

Yeah ok,and be charged big money for the pleasure,this is one of the simplest pcp air guns to work on,and I've done plenty over the years,I'd already part stripped it before posting on here,it's just nice to have a bit of info. The problem was It had just vented all its air as matey let it get too low as he hadn't had the gun long and was told to fill it to 100 bar ,,the low power was down to someone screwing out the hammer pre load,this is an Allen key on the end cap,matey took it to a local gun dealer who said it would cost £200 to have it sent away and fixed,it was left there for a few days and I suspect he messed with it,anyway I've had it on the chrony and got it shooting at a nice 600 fps with accupells ,thank for your help guys.

[Phil Russell]

Very pleased it has worked out OK. I now recall that the cylinder seals are called 'U' seals or a very similar term and there are 2 of them ... one at each end.
Cheers, Phil

[ianbobo1]

yes the seals in the 100 series are a u shaped o ring which flay out under pressure to create a seal so i have no idea where you would get some if required