1322MLT update

[K.O.]

I decided I had to many things to do to be able to do the valve mods one at a time and test to see the effect of each so today I thinned the

exhaust poppet shaft, went to a weaker spring(cock before pumping now),coned the exhaust poppet and took off a couple threads to increase

valve volume. well I should have waited on the valve volume it takes me 27 pumps to get what I think I could get at about 20. Live and learn.

The good news is that  with  CPHP 14.3g at 27 pumps I am getting  689 fps and it is seeming to only have about a 10 fps variance throughout.

I will take up some space in the valve until I get another nose but I think I just may have a chance of getting 700 fps at 20 pumps or so once

I do. Experimenting  with volume later this year when I have more time I bet it will do it in 15-20 pumps when I get things just right.

It would be nice to get 725 fps or so by 25 pumps but   I have a feeling it will be as accurate at 30 yards as 20 now but did not have time

to test , I will soon though. For now I am pretty happy  with the  15 fpe  it is getting.  I will fiddle with it as time allows but it does show it was

worth doing IMO.

Just for those who do not know what I am updating   http://www.gatewaytoairguns.org/GTA/index.php?topic=64968.0

[K.O.]

well I took up some volume but then it topped out at 665 fps at 24 pumps.

I stuffed the large end of the piston and got back to 682 at 25 pumps.

 It seems the limit is the cup system and with how it is flow ported.  the max pressure is where I am so in a while I will take the spacer back

out.  I did not have the right Dremel bit when I ported this valve and I think I can make more gains  with a bit more valve work.  I took the

other one further and rounded the side edges a bit  I think that will help  12 pumps on up. Also I have the pump cup shimmed to where it

barely makes contact with the piston. Under high pressure it just might be getting compressed enough to cause just a touch of head space so

I will try shimming another .01 or so. I also may order a couple Disco and 2100 springs  and see if that helps.


I  shoot most of the time 12 pumps  and right now that's ~595 fps.  I cant help thinking hey that's what it used to get as a .177 

I still think I might make 700 fps but think it will be between 20-25 pumps...

[K.O.]

The more I think about it the more I think it is the porting job I did on this valve that is holding it back.

I think I got it just about right on my 14.5' barreled 1322 to get the 640-650 fps at 22 pumps. If I put this 18.75" barrel on it I would/should

get another 40ish fps  (680-690 fps)  from the extra 4.25" at 22 pumps. I still have not stuffed the piston on that one... It got me 20 fps on

this one  so that gets it to 710 fps...

I expect close to the same from this build. Two rifles  with a similar state of tune will perform close to each other not to much different.

What the math says is this one should be hitting 710 fps at  18 pumps instead of  22.  that is what the 4.2" pump stroke

should get me..


At 14.3 for atmospheric pressure the 13xx's 3.5" stroke at 22 pumps  and 60% efficiency  says you get about 1484 psi in the valve

At 14.3 for atmospheric pressure the 664's  4.2" stroke at 18 pumps  and 60% efficiency  says you get about 1457  psi in the valve

assuming they have the same volume .13 ci in this case.


this one has the above differences from last post also.  oh the nose of the valve on the 1322 has not been sleeved and this one has.

so logic says buy another good porting bit to replace the one that got broken and shim just a bit tighter  and 710 at 18 pumps is not

unreasonable.


Oh I found this on the other Crosman forum and it lets me know I am doing ok...  He is got 695 fps at 15 pumps with a flat top set up...

http://www.network54.com/Forum/275684/message/1396371412/1322ish+rifle