An update. I discovered that the hammer spring spacer (W263) was missing and I couldn't find it. I made one on the lathe and inserted it and it went up to 560ish. That's in the ball park but before I changed the firing valve it easily made the limit. The only simple thing that I can think of is that...

I took the hole in the pot out to 4.6mm and set it at 57mm protruding. Filled the reservoir to 150bar and still only making 530fps with JSB'S.

I'll have a look in a bit but I remember thinking that the hole in the back of the firing pot was too small. It's smaller than the transfer port so it's likely to be the problem.

Jon

Hi all. I'm tearing what little hair I have left out with this S410. It's a .22 carbine and very well used that my friend asked me to look at as it was leaking on the firing valve. I sorted that out but it was inconsistent so I gave it a full rebuild. It's now had a new firing valve and pin, both sp...