Taming a Sheridan

[IanSea]

I’m after some advice about taming the power output of my 1980s vintage model C.
I bought it over 10 years ago from a member on here but haven’t shot it much. Having recently invested in a chronograph I thought I’d give it a test only to find it’s running a bit on the warm side.

I’ve removed the hammer spring for the moment so it can’t be fired but just want to check on the best way to restrict the power. Would cutting down the hammer spring be the way to go?

Currently it’s releasing all of it’s air up to 10 pumps. Using more pumps it retains some air but the power still climbs. I didn’t try any more than 13 pumps as pumping arm was getting tired by then.

I appreciate that modifying the hammer spring will be a bit of a balancing act so any advice on cutting the existing spring or any alternative springs would be welcome. I had a model C years ago which had been restricted by drilling two holes in the valve seat. This only produced about 9fp so I expect that the hammer spring route would be the better and easier way to go.

[T 20]

When I bought my Setra (Spanish copy of a Bluestreak) new in 1983 it had the hammer Spring cut so that it gave two sub 12ftlb shots per pumping.

The first shot was just below 12ftlbs and the second shot was around 10 ftlbs so I had to remember to put a couple of pumps in between the first and second shots to keep the velocity about the same for both shots.

Other than that, member Ped may be able to advise you.




All the best Mick

[--ped--]

rather than cutting the original spring I use either a later c9a spring or a crosman 2200 spring in conjunction with an internal adjuster to get the length just right as the replacement springs are much shorter
with either spring set correctly and with an adjustable piston to eliminate head space you should get 2 shots around 600 fps with the 14.3 heavy pellets but no matter how many pumps you won't go over the limit
another way is to find a UK/Can spec c9a piston as it was a blow off one like the UK sharps

[IanSea]

rather than cutting the original spring I use either a later c9a spring or a crosman 2200 spring in conjunction with an internal adjuster to get the length just right as the replacement springs are much shorter
with either spring set correctly and with an adjustable piston to eliminate head space you should get 2 shots around 600 fps with the 14.3 heavy pellets but no matter how many pumps you won't go over the limit
another way is to find a UK/Can spec c9a piston as it was a blow off one like the UK sharps

Thanks for that. I don’t have access to a lathe so I’ll see if I have anything I can make an adjuster out of. I’ll probably be selling this once sorted so I don’t want to throw too much money at it.

[DT Fletcher]

Certainly not an expert in lowering the power of a pneumatic rifle but some of the tricks done to increase the power, used in reverse, might be of benefit.

One trick is to lower the strength of the exhaust valve return spring. This is the spring inside the air pressure chamber and serves to keep the exhaust valve and check valve in place. If this spring is too strong, it will lower the power output. So, it might be worthwhile to explore the option of increasing the strength of that spring.

[IanSea]

Certainly not an expert in lowering the power of a pneumatic rifle but some of the tricks done to increase the power, used in reverse, might be of benefit.

One trick is to lower the strength of the exhaust valve return spring. This is the spring inside the air pressure chamber and serves to keep the exhaust valve and check valve in place. If this spring is too strong, it will lower the power output. So, it might be worthwhile to explore the option of increasing the strength of that spring.

Thanks, but as the rifle holds air well I don’t really want to disturb the valve assembly. I’ll be pursuing the hammer spring route I think hopefully with an adjuster.

[--ped--]

all you need to do is make a spacer /spring guide
can't tell you how log as it's trial and error to get right
https://i.imgur.com/JeUaCrg.jpg

[Lawrie Amatruda]

My method to reduce the power is to solder a thin walled piece of brass tubing inside the valve guide, to blank off the exhaust holes, this guide has two or four holes drilled round it, then all that is needed now is to drill some new holes smaller than the originals, I have found over the years working on Sheridans that the ones made for Europe with the low power limits, have holes approx 1/16”, the Uk ones are approx. 3/32” and the USA ones approx. 3/16”, this always works for me, sometimes minor adjustments to the holes are necessary, so I always drill slightly smaller than I think may be needed so that I can open them a little at a time to get the balance right, I occasionally, increase the power of the hammer spring so that the valve stays open when firiring so that all the air is expelled in one go, after doing this, you then find that it is almost always necessary to cock the gun before pumping.

Cheers, Lawrie

[IanSea]

My method to reduce the power is to solder a thin walled piece of brass tubing inside the valve guide, to blank off the exhaust holes, this guide has two or four holes drilled round it, then all that is needed now is to drill some new holes smaller than the originals, I have found over the years working on Sheridans that the ones made for Europe with the low power limits, have holes approx 1/16”, the Uk ones are approx. 3/32” and the USA ones approx. 3/16”, this always works for me, sometimes minor adjustments to the holes are necessary, so I always drill slightly smaller than I think may be needed so that I can open them a little at a time to get the balance right, I occasionally, increase the power of the hammer spring so that the valve stays open when firiring so that all the air is expelled in one go, after doing this, you then find that it is almost always necessary to cock the gun before pumping.

Cheers, Lawrie

Thanks Lawrie
That sounds a bit too involved for me so I’ll probably give Ped’s method a go first.
Cheers
Ian