S410 firing pot.

[dunc1984]

Good afternoon

I am in the process of putting my s410 carbine back together. I have a longer exhaust vavle supplied by trrobb. Previously I had the firing pot set at 57mm I believe. This made 11.2

I am wanting to know a good starting point for the firing pot with the slightly longer exhaust vavle fitted?

Also would it be a good idea to wind the power adjuster screw out, so the air has less restriction, then adjust the power on the pot, to keep it legal.

Any advise is welcome.

Thanks for looking

Duncan

[Roger5]

How much longer is the firing valve, I would measure against the original, and however much longer it is would add to pot measurement, and yes back the Venturi screw out, hope you have plenty of air, and it can be a bit time consuming getting it right, good luck

[dunc1984]

How much longer is the firing valve, I would measure against the original, and however much longer it is would add to pot measurement, and yes back the Venturi screw out, hope you have plenty of air, and it can be a bit time consuming getting it right, good luck

I have not measured yet. I will measure tomorrow.

Yes I have a full 7ltr dive bottle. And scuba shop isn't far away.

Just to confirm. I assume shortening the pot puts power up, as less air capacity in the pot.

Thanks

[tonyc]

Yes, limiting the power to below 12ft lb by adjusting the pot is the best way. To save on air you can put a solid object in the cylinder to take up volume while you are refilling to make adjustments. Hardwood dowel or broom handle would do it... but be careful you don't let it slide around and bash the pot.

[Roger5]

How much longer is the firing valve, I would measure against the original, and however much longer it is would add to pot measurement, and yes back the Venturi screw out, hope you have plenty of air, and it can be a bit time consuming getting it right, good luck

I have not measured yet. I will measure tomorrow.

Yes I have a full 7ltr dive bottle. And scuba shop isn't far away.

Just to confirm. I assume shortening the pot puts power up, as less air capacity in the pot.

Thanks

Screwing pot in ie reducing the length, will lower the power as it makes it harder for the hammer to open the firing valve. It can take quite a few dismantles to get the power to where it needs to be, the broom handle trick does come in handy whilst doing this, and you only need to fill to about 160/165 not to 190bar

[tonyc]

you only need to fill to about 160/165 not to 190bar

Extravagance!
120 bar is more than enough.

[Roger5]

you only need to fill to about 160/165 not to 190bar

Extravagance!
120 bar is more than enough.

Please excuse me for encouraging wastage of air

[dunc1984]

How much longer is the firing valve, I would measure against the original, and however much longer it is would add to pot measurement, and yes back the Venturi screw out, hope you have plenty of air, and it can be a bit time consuming getting it right, good luck

I have not measured yet. I will measure tomorrow.

Yes I have a full 7ltr dive bottle. And scuba shop isn't far away.

Just to confirm. I assume shortening the pot puts power up, as less air capacity in the pot.

Thanks

Screwing pot in ie reducing the length, will lower the power as it makes it harder for the hammer to open the firing valve. It can take quite a few dismantles to get the power to where it needs to be, the broom handle trick does come in handy whilst doing this, and you only need to fill to about 160/165 not to 190bar

Okay great thats what i thought. Well I'm going to stick with the standard valve. Maybe if I decide to get one regged in the future I will pull it out.

I am going to experiment with the venturi grub screw, screwed all the way out. I will adjust power on the pot, keeping it legal. I will adjust the pot in slowly, and try the pot at 56mm or 56.5 and see what happens. I have polished the hammer rail and hammer to almost a mirror finish. The hammer and valve spring I replaced a few months ago ( these are original standard ones ) and have had no more than 200 pellets through. I Also polished the ends of both springs.

What happens if you stray to far from the reccomened 57mm. Will it affect consistency also. The reason in ask is, there must be a reason the factory don't leave the venturi grub screw right out and adjust the power on the pot?.

Thanks

Duncan

[tonyc]

What happens if you stray to far from the reccomened 57mm. Will it affect consistency also. The reason in ask is, there must be a reason the factory don't leave the venturi grub screw right out and adjust the power on the pot?.

I think the reason is probably the time and consequential cost of fiddling with it. Much easier to tweak a screw and seal it off. Other manufacturers change the pre-load on the hammer spring.

[rob2hook]

Just a few more thoughts on the subject. The extended length of the non-standard firing valve will principally affect the stroke of the striker (hammer). This is principally used as an alternative to making a striker with an extended nose when balancing a (usually) lighter striker and reduced rate striker spring with a regulator fitted.

It might also increase the opening of the valve and duration although judging by Robert Lane's observations for tuning with his regulators, the limiting factor for valve travel is likely to be the point at which the valve spring becomes coil bound.

Rob.