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S200 issue

Grumpybill

Grumpybill

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Hi my AA S200 turned 20 in January and Ive never had a problem with it. A couple of weeks ago it seemed down on power so I chronoed it and it was sitting at 8ft/lb not good. I increased the power back to the usual 10.50 ft/lb. Sunday at the club all my shots seemed to be going low so I put it over the chrono again, only 9 ft/lb.
Here is where I need help confirming my theory from you guys. I think that the mainspring has grown weak over the last 20 years and is no longer holding a steady pressure on the striking pin hence the dropping power. Am I right or does anyone have any other ideas as to what is happening.

Thanks in advance
Bill
 
It's possible the spring is past it's best,but it is quite unlikely tbh

First up I'd check the probe oring, well I wouldn't check I'd just get a fresh one on

Check the cylinder is tightly screwed up. If there's any signs of wobble I'd look at fitting a cylinder shim

I'd also chrono it out of the stock to check for the hammer binding in the block or against the stock.

Then I'd give it a strip and good clean up before looking at replacing any bits 😉
 
Thanks for that @Tillygti6 the probe on ring is new as in only a couple if weeks old. I'll check the other things and see what happens.

Bill
 
Yeah, never known a spring to degrade like that through age or use. Unless they're really abused in circumstances outside of normal use, they typically scrag during the first few cycles then give steady performance forever more.

Can't think of any immediate causes of this issue tbh; were it mine I'd be inclined to strip it down to nowt, clean, inspect, measure everything, chuck it back together and go from there.. although the cylinders aren't the easiest things to get to bits.
 
In addition to all the good advice above - Is your hammer adjuster locked down with the allen bolt? Is the TP adjuster tight ? You do not mention a regulator, so assume rifle is as it left the factory.
 
CZ034 cap 🤔 Not unknown for it to move, causing power to either increase or lower depending on which way it's turned, somebody wrote about this on here awhile ago, same as power adjusting screw which can also do it
 

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@Jamex yes bog standard no reg
@Rog5 yes checked the power adjuster didn't know about the other one thanks

Bill
 
Sounds like something moving over a spring as others have said. While tuning mine with the hammer spring locking grub off it moved shot to shot. Well worth a look.
 
Are the valves on the s200 similar to the softish AA ? Bsa ? type that extrude down the throat of the valve seat ?

s200 valve.webp
 
Grumpybill said:
Hi my AA S200 turned 20 in January and Ive never had a problem with it. A couple of weeks ago it seemed down on power so I chronoed it and it was sitting at 8ft/lb not good. I increased the power back to the usual 10.50 ft/lb. Sunday at the club all my shots seemed to be going low so I put it over the chrono again, only 9 ft/lb.
Here is where I need help confirming my theory from you guys. I think that the mainspring has grown weak over the last 20 years and is no longer holding a steady pressure on the striking pin hence the dropping power. Am I right or does anyone have any other ideas as to what is happening.

Thanks in advance
Bill
Click to expand...
Don't thinks it has anything to do with hammer spring tension.
Reseal and that will most likely do the trick.
 
After 20 years I'd start by replacing every o-ring which have almost certainly gone rock hard if they're still original and a thorough clean up and very sparing relube as it's possible some dampness has had time to corrode or gum up after such a long time.
You could replace the hammer and firing valve springs while you're in there as I don't suppose they are too pricey...but I very much doubt they are your issue.

I might be inclined to check the firing pot is still tight against the valve cap - if it's come loose its possible the firing cap is slowly unwinding itself and that will back off the power.
 
Sorry, I agree about checking the setting of the exhaust valve cap and pot, but if the adjuster cap is unscrewing away from the exhaust valve it will result in increased , not decreased power.
 
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