Hatsan .22 Cal. AT44-10 PAL Shot Strings

[rsterne]

I realize that a bit of air might pass the 6-32 screws, but they are "just" below flush on the valve so that they don't mar the cylinder in the gun when you screw in the reservoir.... I used a tapered tap so the screws went snug just above the surface and just tightened them down until they are low enough.... Others have used JB weld to fill the holes and the groove leaving just the one hole.... and some have drilled that hole out to 5/32" (I understand the transfer port is 4mm, same thing) and the smoothed the 90* corner inside the valve with a Dremel....

If this was my own gun and I was serious about getting maximum power I might have played more.... However, since it's pretty obvious that more power comes with fewer shots and I already have a regulated 2260 PCP that gets 50 shots at 35 FPE it wasn't an issue for me....

Bob

[rsterne]

Ok so scruffie is hunting monster Grouse and he only need 20 shots (at 900 fps, I think he wants to scare them to death!).... In addition, I wanted to finish the testing by drilling out the remaining hole in the valve to match the transfer port.... I took off the breech, and to my delight, the barrel and transfer ports lined up perfectly.... The port measured 0.170", just over 4mm.... I checked the alignment of the remaining hole in the valve and it was off by half the hole diameter.... but I found a neat trick to adjust for that.... The stock mounting screw threads into a bolt which screws into the brass cylinder that has the port machined in it.... the one that the air reservoir threads into.... It is free to slide back and forth in the outer tube a fraction, and the outer tube is slightly proud of the end of it.... That means that by carefully postioning the cylinder in the outer sleeve before tightening the bolt that the stock screw fits into.... you can vary the orientation of the port in the valve slightly when it tightens against the end of the outer tube.... I did that, double checked it, and tightened up the bolt and now when you tighten the air reservoir hand tight the one remaining valve port lines up perfectly with the transfer port....

I drilled out the remaining valve port to 0.166" and then used a Dremel to round off the front corner the way you would on a 22XX valve to smooth the flow.... interesting that the port ended up the same size!.... I cleaned out all the swarf, lubed the O-rings, and reassembled the gun.... I started at 2 turns out on the hammer spring, then tried 3, went back to 2.5, and ended up at 3 turns in the end.... Here is a graph of the results....



The really interesting thing about these three shot strings is that the 2.5 and 3 turns strings have the same peak velocity (933 fps) .... but at 3 turns, the first part of the curve starts at 200 bar instead of 190 and has more shots at a higher velocity in that portion of the curve.... The slight increase in hammer strike enables the gun to use the area between 190 -200 bar much better.... Here is a summary of the shot strings....



If you compare these results to the same power levels with the stock valve (6 small holes, all open).... it turns out that the hammer spring preload required would have been about the same (3 turns out).... What is different, is that the shot string is flatter and longer with better efficiency.... If you compare todays results to the previous set with the small (and slightly misaligned) hole, however.... you find that the shot string is 1 shot shorter (but just as flat) and the efficiency has dropped slighty (both effects could be due to the increase in power)....

I'm pretty darn happy with the way this gun turned out.... and I hope scruffie is as well.... He can fill the gun to 200 bar and get 25 shots at 34.1 FPE within 4% of the peak velocity shooting down to 120 bar.... Alternately, he can fill to 190 bar, stop shooting at 130 bar, and "cherry pick" the best 20 shots with only a 16 fps variation in velocity (less than 2%).... The average velocity is 926 fps (34.5 FPE) with the fastest shot touching 35 FPE.... Also, if he puts the original reservoir back on the gun, he can get 180 shots at 476 fps on one fill....   :

Bob

[eddielee70]

How is the accuracy shooting crosman hollowpoint premier?  picky about pellets?

[rsterne]

I didn't test any.... I only had the scope on for a brief time with the 18.1 gr. JSB so can't comment on the accuracy with anything else....

Bob

[rsterne]

I have one slight correction to the post about the "final" version.... I stated:

If you compare todays results to the previous set with the small (and slightly misaligned) hole, however....

and that made it sound like I was comparing the final version (with the single, big hole) to the one with 5 holes plugged.... I was comparing it to the one with only 3 holes plugged.... so what I should have said is:

"If you compare todays results to the previous set with the lower three holes plugged, however...."

Bob

[eddielee70]

sorry, off topic, where can I get one of these pumper Hatsan AT44-10? 

http://www.airgunforum.ca/forums/topic39951.html

[eddielee70]

found it.

http://store.airgunforum.ca/index.php?cPath=22&osCsid=6bb641328795038564afe539584ea5ca

[Ratpaker]

Took me ages to find this thread again, I have now bookmarked it for future reference....thanks Bob!

[Bwalton]

Took me ages to find this thread again, I have now bookmarked it for future reference....thanks Bob!

I never knew this thread was here! Just the info I needed for the .30cal I knew that I was going to do some port work but in trying to keep it very consistent I will start with the valve holes hammer spring adjustment and valve stem. then if that is not enough I will open up ports. this info has saved me a lot of time!

[rsterne]

Followup Thread on the .25 cal.... http://www.gatewaytoairguns.org/GTA/index.php?topic=33903.

Bob