Hatsan .25 cal AT44S-10 Long Mods

[rsterne]

Here are the shot strings with the 5 holes plugged and the top hole enlarged to 0.180" and streamlined.... It is obviously flowing a lot better, because at 6 turns out on the hammer spring preload, the velocity is back to what it was with all 6 holes open but the efficiency has increased....



There are three strings above with 25.4 gr. JSB Kings at 5, 6, and 7 turns preload.... and then two additional strings shot at 7 turns out with 30.9 gr. H&N Baracudas and 35.3 gr. EunJin Domes.... The 7T Pressure line applies to all three pellets shot at 7 turns out....

A comparison between the shot string at 6T with the JSBs and the first one shot in the "full power" mode with all 6 holes open is very interesting.... The peak velocity (924 fps) and the average (909/911 fps) is nearly identical.... In the original setup, only 17 shots fell within 4% of the maximum, with the first part of the curve "missing".... Now, I'm getting 22 shots, with the curve shifted down about 13 bar at the peak.... The efficiency has increased from 1.03 FPE/CI to 1.21 FPE/CI, so not only am I getting 5 more shots, each shot is using less air.... In fact, I'm only using 6 bar more air for 22 shots than I was originally for 17 shots....

Here is a comparison for the three pellets at 7 turns preload:

25.4 gr. JSB King: 944 fps (50.3 FPE) max.
930 fps (48.8 FPE) average for 17 shots @ 1.19 FPE/CI

30.9 gr. H&N Baracuda: 882 fps (53.4 FPE) max.
870 fps (50.9 FPE) average for 20 shots @ 1.24 FPE/CI

35.3 gr. EunJin Domed: 837 fps (54.9 FPE) max.
825 fps (53.3 FPE) average for 20 shots @ 1.29 FPE/CI

In order to get two full clips with the JSBs I would need to back the preload down just a whisker and lose a few fps.... Although I have achieved a peak of over 50 FPE with the JSBs and nearly 55 FPE with the EunJins, I'm not quite done yet.... When I had the breech off, I noticed that the hole in the breech and the barrel are slightly smaller than the transfer port.... I think that needs correcting....

Bob

[SeanMP]

When I had the breech off, I noticed that the hole in the breech and the barrel are slightly smaller than the transfer port.... I think that needs correcting....

Lol...of course you do

I have one request. Do that correction and the epoxying of the dead space in separate steps. I'm really interesting in seeing the effects of that dead volume

50+ FPE....Astonishing. And simple

All those fellows that are always kibitzing about wanting more power should take note of this thread. Get your PAL and have att'er. There is no complicated machining done here

[rsterne]

Stock 0.171".... now 0.183".... Probably not enough smaller to do what I need, but Dan thinks he might have one so I'll get him to send it when I get a backup complete valve (which he has in stock - $50).... He seems to have a pretty good supply of spares for the Hatsans, which is great to see.... If Fastenal would ever ship my Teflon rod I could probably just make one from that and eliminate the two tiny O-rings.... The stock TP has a 1mm section O-ring riding in a shoulder on each end to seal it.... Nice attention to detail.... I could always duplicate the factory setup with a smaller hole, of course....

Bob

[remtom1200]

sorry to reply to an old thread... but what is your turn measurement on the hammer spring preload screw? Is it a 180 or 360 degree turn?

[SeanMP]

How big is the transfer port?