Air Gun Home :: View topic - Hatsan .22 Cal. AT44-10 PAL Shot Strings

rsterne · Moderator

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.... Mr. Green

Bob

rsterne · Moderator

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

necrobob · New Member

Thanks for the work you do Bob. With this gun in particular since I have the at44w-10 non-pal but I grinded the stem down with my hillbilly drill lathe lol came out nice. no leaks but I don't know what size it is. I didn't buy a digital calibers crono yet. Again enough about me, thanks for giving me a understanding of my gun...
peace
Bob

Weevil · New Member

I'm in Australia, and we can't get the non-pal version here. I've got 2 x cylinders with my AT44-PA and want to install a non-pal stem in it for shooting inside sheds (and getting 180 shots per fill). In the parts list, the valve stem is listed as; 80-00-312 (air discharge pin), but I assume this is for the PAL version. Is there a part number for the non-pal, or does anyone want to swap their non-pal for my pal version?

Also wanted to know if it's just the valve stem that gets replaced or do I need to get the valve seat as well?

rsterne · Moderator

It's just the stem that gets replaced.... Dan Pusaka (sniper) over on the Canadian Airgun Forum (CAF) sell them....

Bob

apitagan · New Member

rsterne · Moderator

The answer to both is "sniper" Dan on the Canadian Airgun Forum (CAF)....

Bob

apitagan · New Member

rsterne · Moderator

That O-ring is downstream of the 6 ports, so no.... The valve is not seating properly, my guess would be a piece of grit on the seat.... Dan can supply a new one (white Delrin with an O-ring seal on the outside)....

Bob

apitagan · New Member

k2apache6.0 · New Member

rsterne wrote:
"You will note that there is a groove in the valve body with 6 holes.... That is here the air exits the valve into the outer chamber and from there into the transfer port.... I presume they make it like that so that it doesn't matter what the rotation is when the threads bottom.... You can see one of the three 6-32 set-screws I used to plug the bottom three holes.... The hole nearest the top in the photo is the one that lines up with the transfer port.... Others have blocked 5 of the 6 holes and enlarged the one that lines up with the port, which I will try eventually.... They report a flattening of the shot string by doing that.... I have found a slight flattening by plugging the bottom three holes"....

OMG!! What a vast amount of time this thread has saved me. I bought an AT44 QE just a month ago and decided to tinker with it, and then found this online. THANK YOU BOB!! This thread is over 3 years old now so hoping you're still around on the forum.
So I'm shooting the same JSB 18.1gr .22 pellets and from this thread I learned (In a nutshell) 3 turns out on the hammer screw from the stock manufacter setting, and plug the three lower ports on the res fitting. Should I JB weld over the 3 set screws to smooth over the groove too, any added benefit to doing that? Is there anything new to add since the thread was 1st posted? And finally if shooting lighter pellets, say 14.5gr (I'm still experimenting for the best pellets for this gun) would I have to turn the hammer screw back in say a half turn for peak performance. I'm a hunter not a plinker/target shooter so 20 to 25-30 full power shots with a good degree of consistency is what I'm looking for. The rifle is a 2018 AT44-10 QE short in .22 Caliber U.S. model, 180cc non regulated (stock) res. Once again.. Thanks ever so much!!!!!!