S410 Low Power Problem

[Portland_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 springs and all new o-rings. I just can't get the power back up to where it should be. It just won't go above 530fps with JSB's when it should be 580ish.

I phoned Julian last week and he said to clean everything which I've done. The hammer shaft is polished to a mirror finish and the hammer has almost zero friction but I'm lost for ldeas. Anyone got any suggestions please?

Jon

[Portland_Jon]

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

[Roger5]

What's the year ?

[Roger5]

Ok, what did you set the firing valve at ?
Have you inadvertently blocked the transfer port when refitting the seal ?

[Blackbaronfish]

Is the transfer o’ring still in place.

BBF

[Roger5]

Leave the hole in the pot alone
And what pressure are you filling to when you chrono it ?

[Portland_Jon]

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.

[Portland_Jon]

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 don't have the correct transfer port o-ring and am using a set that I have which I think are too thick and may be covering the port when compressed.

Jon

[Roger5]

S427 is the transfer port seal,
My S410 .22 is running at 565fps 11.36ftlb with AADF5.52 16gn
That's at about 130bar, well enough