Undoubtedly a little late, but for future reference the full specification is:
'3x1.5 O RING 70 SHURE'

There's a useful exploded parts diagram of the pressure vessel, courtesy of R-Gun Pete of Canadian Airgun Forum at:
https://www.airgunforum.ca/forums/topic90163.html

Thanks for your reply.

You're probably right about flat-headed pellets being used at 25m. The clue's undoubtedly in the name - RWS R 10 Match - clearly designed for 10m!

But that still doesn't explain the poor grouping I now get at 10m, when the power is set to 11.5 ftlb.

Gary Thanks for the reply. According to the Air Arms brochure, in the MPR 10m Precision, 'the firing valve is designed to be self-regulating'. But I believe the S400, on which the rifle is based, is non-regulated. So I'm not sure how they achieve this. It might be reasonable to assume that the 'regu...

Does increasing power improve accuracy? I have an Air Arms MPR 10m Precision (a version of the S400). It comes out of the factory set at 5.15 ftlb. I'd now like to use it at 25m, so I've increased the power to about 11.5 ftlb. But it seems to be less accurate at the increased power (the grouping, ev...

I've got an Air Arms S400 (10m MPR Precision). Normally, when I unscrew the air cylinder, I just get a momentary 'phut' at about the half-way point. But now, when I unscrew it, it 'locks solid' at about the half-way point i.e. I'm unable to unscrew it any further, and it dumps all the air. Only then...

Here's an update to my last post: I've found the leak - It's a pinhole on the air cylinder itself. I'll try to seal it. My initial thoughts are Araldite. Can anyone suggest anything better? Here's a link to an image of the problem: https://i1053.photobucket.com/albums/s468/mainliner1/DSCN0620_LI.jpg...

' I've made sure the cylinder is empty but .........' Keith I suspect that my Alfa pistol is leaking air, just like yours, and I might well need to unscrew the cylinder and check the seals. How, exactly, did you ensure that there was no air left in the cylinder? The manual describes how to empty the...

I have received the following information from Air Arms: 'The technical department has advised that spraying a degreaser of any kind is a bad idea. The fluid may get into the mechanism and cause rust issues. The action should be stripped down, cleaned, and re-assembled with the correct lubrication.'...

Peter Thanks again for your advice. I'll certainly investigate the Napier degreaser suggestion. Your diagnosis of the problem seems correct. The power output has definitely dropped off considerably - I can now see the pellets in flight! I actually used 'Glide' spray to lubricate the cocking mechanis...

Peter

Thanks for your input. I now have to consider how to clean the affected area. I'm thinking about using a solvent spray (e.g. brake cleaner) to 'rinse' the oil away - or will that make things worse?