stiffer valve spring?

[Whatsquirrel]

Playing with at44 today trying to flatten out the shot string. I want to keep it up 900 fps, so just playing around I install a bstaly buffer. Started with full tension on the hammer & got a decline string starting at 950, took some hammer spring out & still had a declining string starting at 930. Took some more hammer spring out & got a decent first 20 shots, went ahead and did a 40 shot string high 879, low 851(shot 40). Just wondering if a stiffer valve spring would do anything. Maybef flatten it out some or give me few more shots. Strings was with crosman pointed 14.3gr.

[Mod90]

Have you closed off the lower holes in the valves yet?
And what sort shot count, fpe range, & es are you looking for?

A stiffer spring will lower that velocity and change your fill pressure sweet spot. You could just leave the stock spring at the setting at which performs best for your needs, then mod the valve to improve efficiency.

If you wish to flatten out the shot string, I have had some good results from blocking off all the holes but the one that lines up with the tp & adding a small washer to the valve stem.

[Whatsquirrel]

Have you closed off the lower holes in the valves yet?
And what sort shot count, fpe range, & es are you looking for?

A stiffer spring will lower that velocity and change your fill pressure sweet spot. You could just leave the stock spring at the setting at which performs best for your needs, then mod the valve to improve efficiency.

If you wish to flatten out the shot string, I have had some good results from blocking off all the holes but the one that lines up with the tp & adding a small washer to the valve stem.

Sorry forgot to mention the mods I've done.
Plugged 5 holes & jb welded the groove
Drilled the open port to the same size as the tp port

I did install a washer on the valve stem but it's big, after I installed the washer on the stem it only shot 300fps. So I'm gonna remove it in the morning & find a smaller one.

I'm looking for 25-30fpe for at least 40 shots. I got 40 shots today with an es of 33fps. Which was Not to bad I don't think, the string was just a very slow decline.

Thanks for your input.

[Mod90]

Is your gun the long or the short version?  You should be able to achieve 25-30 fpe /shot over 30 shots with .22. 40 shots will be not as easy to get unless you have the long version. To be able to achieve the shot count you're looking for you need to optimize the gun's efficiency .
I almost forgot to ask. What are your start & end pressures?

My advice to improving efficiency would be start by reducing the OD of the sail washer you installed by 1mm increments, testing as you go. A 2-3mm clearance from the valve inner wall should be sufficient to allow enough air to flow past the sail yet still leave enough surface area for it to function the way it should.

Another option is to help the valve to breathe better by changing the white valve spring seat to something that would allow more air into the valve. This would require some machining of the valve body and using a seat similar to that of the valve on the bt65.

Keep us informed of your progress

[Whatsquirrel]

Is your gun the long or the short version?  You should be able to achieve 25-30 fpe /shot over 30 shots with .22. 40 shots will be not as easy to get unless you have the long version. To be able to achieve the shot count you're looking for you need to optimize the gun's efficiency .
I almost forgot to ask. What are your start & end pressures?

My advice to improving efficiency would be start by reducing the OD of the sail washer you installed by 1mm increments, testing as you go. A 2-3mm clearance from the valve inner wall should be sufficient to allow enough air to flow past the sail yet still leave enough surface area for it to function the way it should.

Another option is to help the valve to breathe better by changing the white valve spring seat to something that would allow more air into the valve. This would require some machining of the valve body and using a seat similar to that of the valve on the bt65.

Keep us informed of your progress

It's a long version. I start at 200bar with first shot at 879fps & stopped at around 140bar with the shot being 846fps. I'm gonna play around with the sail tomorrow & let you know what happens

[rkr]

A stiffer spring will lower that velocity and change your fill pressure sweet spot. You could just leave the stock spring at the setting at which performs best for your needs, then mod the valve to improve efficiency.

Will it? I understood that the valve spring tension has little to no effect on most guns as long as it's not uber heavy and coil bind is not there.

[Mod90]

A stiffer valve spring will allow for the valve to close faster after the hammer knocks it open as well as require more force to open the valve, in addition to reducing dwell. By how much would depend on how much difference there is in force between the hammer and hammer spring knocking the valve open & the valve spring and the force of the air trying to escape when the valve gets knocked open.
Its all about finding the balance between how much air gets out the valve, and how fast, and for how long.

[Whatsquirrel]

I installed the sail, it did not add any shots to the count. So thinking about how many shots I was getting from my syn-rod with the bstaley mod I decided to try it on the At44. I removed the hammer and drilled all the way through it. Threaded it, cut head off a bolt & installed it in the new threads I just cut. Now I have a striker that is adjustable. A little adjusting & I got 35 decent shots, still shy of my 40 shots or more goal in the 20-35fpe range. I think if I reduce the hammer spring a little I can pick up the 5 shots.

If I figured it right I think it at 5%. I did the es of 45 divided by the avg of 869. Is that the way you figure it out?

[oldpro]

 I would look at my hammer striker mod with o-ring buffer that will let you tune it super flat. I have pics and discription in post.       http://www.gatewaytoairguns.org/GTA/index.php?topic=92332.20