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All Springer/NP/PCP Air Gun Discussion General > Engineering- Research & Development

AA S410E mod to get a longer hammer stroke

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scattermaster:
Hey guys,
 This is my 1st post in this section.
  I have a relatively old Air Arms S410E in .22. 
 With a full 3000psi fill it seems like the hammer isn't opening the valve very much.
 I tried making shims/spacers to get more spring compression but quickly found out that the piston won't go far enough to catch on the trigger.   Back to the stock set up, I found that after the piston catches the trigger, there is quite a bit of forward travel on the bolt before the spring tension it released and the hammer stops moving forward.
  After looking at it I think I can turn my own hammer and mill a thicker place on the side that catches the trigger.  It should result with more net travel after release.
   I'll post a sketch of it as soon as I can scan it to pdf.  (my pics on my phone are too big to up load here)
   Question:
   It appears that the piston has some teflon coated bushings in the ID that guide it down that rod.
   I'm not sure where I can buy suitable bushings.  Do you know where?
   As a plan B, would it work as well if I machined brass bushings and pressed them in?  I could bore them out to a slip fit on that rod but I don't know how well they will behave compared to the store bought ones with a coating.
     What say you?
 thx,
 Jim
Edit:   I just remembered that I have some acetal rod that might make good bearings too.  ?

Motorhead:
Bearings are LEAD / TEFLON
AA guns use  a SHOT POT that is a small chamber attached to the intake side of the valve.  Its job is to deliver a specific volume of air for each shot.  Leaning on hammer spring or hammer weight will not change much.
Want to up the power potential ??? .... increase the shot pots internal volume.

** It acts similar to a regulated guns plenum  ;)

scattermaster:
Good morning,
 I finished my prototype hammer. I got in a hurry and didn't wait for my bearings and made them out of acetal. I have the real ones coming.  I took it out for a test drive yesterday using JSB Exact Jumbo's (15.8grn.)
 My 1st shot was only at around 1500 psi.   It was very loud. Like a .22 rimfire going off.
 That tells me I had a lot of unused air leaving  the barrel.  I'm opening the valve too much at lower pressures.
 After that I filled it to just over 3000 psi and shot it 5 times over the chrony. ( I didn't record the 3/4)  The noise went away!
1. error 2
2. 1057 fps.
5. 1043 fps.
   Not sure where that leaves me.   I've proved that I can get more velocity from simply hitting the valve harder. BUT,
 I also proved that it's new sweet spot is @ 3000 psi or possibly higher and I don't really want that.
   I thought I'd go back and mill the hammer back a little bit to get the speed at 3000 psi a little slower, but try to have the sweet spot higher than it was before the mod.  My last chrony test before the mod got:
750 fps @ 3000 psi and topped out at 933 fps after 55 shots.  Years ago it shot much harder than that. I think my hammer spring is probably a little tired and the barrel hasn't been cleaned in years. It groups fine so I leave it alone.
 I have notes from 2009 that show:
 968 fps @ 160 bar and topped out at 989 fps after 11 shots.  I seem to remember it usually topped out at just over 1K.

     All this being said,  I'll do a better test with the existing set up with the same pellets and again with heavier pellets.
 I'm hesitant to modify the pot. Maybe I'll make one with a little more volume.
 

 

 

scattermaster:
Well,
 I shot some with the 15.8 JSB's and some with the 18 grn JSB's.   I liked the velocities better with the heavier pellets but it grouped better with the lighter ones.  Hmmm.
  I think I might just leave it as is for a bit and do some more shooting.  My teflon coated bearings came in. I need to see if I can install them in the hammer.  Maybe they'll slide better?
   Jim

scattermaster:
seems like there is no interest in my hammer design?  Maybe I posted in the wrong section...
I thought it was an interesting project.  I ended up with more power and less fps spread than stock and it seems to group about the same.
   I'll end with this,
 I finally got a new  ProChrono Digital and now I can get some more meaningful numbers.
   I shot 60 times a couple of days ago with my custom hammer and again today with the gun back to stock configuration and a new hammer spring.
same pellets- JSB Exact 15.8 grn.
   stock:--------custom:
 min fps-724---851
max fps-925---995
spread-201----144
avg fps-837---937
SD-68---------44

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