Puzzled by low power
I have a UK spec Stealth in .177 with a 12″ barrel.
I am trying to use Webley Mosquito pellets through it and want to have them fly at about 810fps (abut 11.6fpe).
No matter what I try I can’t get them to go any faster than 695fps!
So far I have:
Increased pre-load on hammer spring with spacers to a point where any more pre-load is going to make the gun hard to cock.
Gradually adjusted top hat out from fully wound in all the way to about a quarter of an inch out.
Taken valve out and have reduced tension on the valve spring by winding the brass spring retainer all the way out until the spring is just holding the valve stem in position with the minimum of pre-load.
I have had a look at the valve spring retainer and the hole through it seems to be about 5mm which surely should not be throttling the air flow @ 200BAR (about 2900 psi)?
I had a spare brass insert and valve stem and have swapped them over.
I am at my wits end with it. My other gun, a Storm with 18″ .177 barrel is fine with the bottle that is on it and swapping the bottles over shows that it is definitely this bottle and valve that is the problem.
Any help/suggestions gratefully received.
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I have a valve you can borrow until you gets yours sorted if it helps
It is a sod when work gets in the way of your hobbies. Alas haven’t had time to try yet.
Not sure my drill stand will be as good as a proper pillar drill either so may chicken out and give it to a mte who is an engineer with all the gear.
Then again, it is useless as it is so may as well have a go, if I break it I will then definitely have to find a replacement!
Odds are that if I tried myself I would make a complete chutney of it!!
How did you get on with the steam and power drill?
By the way, I appreciate that the Brits here use “inches” and “FPS” instead of all that metric hoo-hah. Thankya… I think it’s time for a pint… not a “half-litre”. 😉 😆
Thanks for your reply. Yeah, the barrel length does make a difference but I can sort that with the top hat on one bottle/valve – it obviously don’t have the same anti-tamper stem as the other.
As for good old imperial measurements, I started school before the metric stuff came in and still think in feet and inches.
I have absolutely no idea how long a kilometre is for example! Can’t visualise it at all.
A 12″ barrel vs. an 18 incher has a lot to do with the equation. The 12 has an inherent velocity handicap compared to the 18 and will always shoot slower, assuming the valve performance is equal between the two. Have you factored that in? You didn’t mention your FPS with the 18, but if you’re getting low 800s with the 18 and ~695 with the 12, I’d call that normal/normal.
By the way, I appreciate that the Brits here use “inches” and “FPS” instead of all that metric hoo-hah. Thankya… I think it’s time for a pint… not a “half-litre”. 😉 😆
I haven’t checked them but I have tried the same bottle and valve on 2 different guns with the same result and both guns are fine using my other bottle/valve so I don’t think that can be the problem.
I have spoken to Brutus and it appears there is a restriction inside the actual valve stem – a 0.05″ allen key will pass down through it but a 1/16″ one wont.
Looks like I will need to source a new valve stem as it is restricting the amount of air that will pass through.
Sodding anti-tamper measures we have to put up with here – not because of any law but simply a decision of the cartel of airgun manufacturers.
Have you checked the breech slide o-rings for leaking ?
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Brutus my friend, you are a gentleman, no doubt about it.
You have already been very kind and have helped me a lot.
This kind of spirit is what these forums should be all about.
I will decline your offer (for now anyway!) as I really need to sort out a permanent solution, even if it is buying the CO2 adaptor and valve as you suggested.
I really appreciate your kind offer though.
Oh, Paypal payment has been sent btw.