Hatsan .25 cal AT44S-10 Long Mods

Now that I'm starting with a "full power" AT44, I'm moving the thread over to the "PCP" section as that is more appropriate from here on.... Here is the previous thread: http://www.canadianairguns.com/showt...Long-in-25-cal

The first mod is a relatively simple one that allows the hammer spring preload to be adjusted without removing the stock.... I didn't invent this, just repeating it here for convenience.... The hammer spring preload in the AT44 is adjusted by a screw residing inside the hammer.... It is accessed through a hole just below the safety, using a 4mm allen key about 7" long.... Grinding/filing a slot in the top of the stock allows the allen key to enter the hole.... The hammer is free to rotate, so you also need a way to prevent that.... There is a hole in the bottom of the main tube, 1/2" behind the main stock mounting bolt.... If you peer in through that hole, you will see the hammer, which has a matching hole in it.... The gun must be uncocked for the holes to line up.... Inserting a pin through both holes locks the hammer so you can adjust the preload screw.... Unscrewing the adjustment (ie CCW when viewed from the rear) INCREASES the tension.... Here are photos of the mods to the stock....

http://i378.photobucket.com/albums/o...0/IMG_2558.jpg

http://i378.photobucket.com/albums/o...0/IMG_2556.jpg

Once the stock is back on the gun, you can insert a small allen key into the hole in the bottom of the stock until it engages in the hole in the hammer to prevent it from turning.... Grinding a taper on the end allows you to slide it in easier if the alignment of the hole in the hammer isn't perfect.... If it won't drop into the hole in the hammer, then rotate the hammer using the long 4mm allen key until it does.... Note that on the pump action, the hole in the tube is further back, and the hammer must be cocked for the locking holes to line up.... The hole in the stock must be drilled further back as well....

On my rifle, the preload screw moved easily, but I have seen them either loctited or squashed flat to make them tamper resistant.... If the screw rotates too easily, it may be necessary to put a drop of loctite on it once you find the best setting....

Bob

Here is the data for various hammer spring preloads using JSB King 25.4 gr. pellets in the "full power" version of the AT44S-10 Long.... NOTE: pressures on the graph are in bar, not psi....

http://i378.photobucket.com/albums/o...25JSBKings.jpg

As you can see, increasing the preload from 2 turns out to 4 increased not only the power, but also the shot count by a couple.... going another 2 turns was a bit too much to achieve maximum shot count, but set up that way the rifle delivered 16 shots averaging 46.6 FPE at 0.97 FPE/CI, so backing it down just slightly should produce 2 clips (18 shots) at about 45 FPE with a 200 bar (2900 psi) fill and bump the efficiency to just over 1.00 FPE/CI....

One small glitch has surfaced, something I knew I would have to watch for from previous experience with a .22 cal AT44.... The hammer spring preload tends to back itself off as you fire the gun, so it will need either some loctite or a locking device on the screw to prevent that.... I'm thinking a hole in the screw with a plastic plug inserted to create friction will probably work....

Bob

That's what I have done a couple times for loose adjustment screws. After drilling and tpping a hole I dropped a small snip of 095 weed trimmer in the hole followed by a set screw. That gave a nice adjustable friction bushing

Has this gun had the valve mod that you described done to it yet?

I pulled the gun apart tonight and fixed the problem of the hammer preload screw moving.... I drilled a 1/8" hole about half way through and drove in a Delrin pin and then shaved it off flush with the top of the threads and screwed it in.... It was a bit too tight, but a little shaving with a razor blade and now it's nice and snug but you can adjust it when you want to.... Here is a photo of the hammer and the two allen keys to adjust and hold it.... There is a spacer between the screw and the spring, and it and the hammer spring are sitting on the long allen key I made....

http://i378.photobucket.com/albums/o...0/IMG_2560.jpg

I also pulled out the brass sleeve that the valve screws into and checked to see how it lined up with the holes in the valve.... It was just a fraction off lining up with one of the holes, so I machined 0.001" off the end so that when screwed in, one hole lines up perfectly with the transfer port.... The sleeve barely comes flush with the end of the main tube, so if you had to machine off more (0.010" would index the valve about 1 hole) you might also have to machine a small amount off the end of the main tube as well.... I added a punch mark to identify the top hole in the valve.... I also noted that the annular groove in the valve is narrower than the transfer port where the circle is on the photo....

http://i378.photobucket.com/albums/o...0/IMG_2562.jpg

Previous experimenting by others on the AT44 showed that plugging the lower three holes has little affect on velocity and reduces air use, thereby increasing efficiency.... I disassembled the valve, tapped the bottom three holes 6-32 (no drilling needed, they are the right size) and installed 3/16" long SHSSs flush with the outer (and inner) surface of the valve.... This not only blocks the holes, but helps reduce the volume of the groove.... If it proves to be the right thing to do, I will fill the remainder of the groove between the screws with JB weld to further reduce the volume....

http://i378.photobucket.com/albums/o...0/IMG_2563.jpg

I put a slight bevel on the edges of the groove to fair it into the transfer port.... I will likely be drilling out the top hole to the same size as the TP (0.172") once I have tested this stage.... I may also be plugging the remaining two side holes as well.... that proved to be the best, when used in conjuction with the larger top hole in the .22 cal I worked on....

http://i378.photobucket.com/albums/o...0/IMG_2564.jpg

The next step is to reassamble the rifle and test it with the lower 3 holes plugged to check the velocity and efficiency, and what hammer preload adjustment has to be made to compensate....

Note to Sean RE the valve threads.... The OD of the threads is 1.080" and the OD of the main tube in that area is 1.202" so the maximum wall thickness above the threads is 0.061" (and it's probably a whisker smaller than that).... The very end of the tube where the O-ring seals is 1.150" ID, so the wall thickness above the O-ring is only 0.026".... I don't even want to think about that.... I guess it works because it's a very short length at that size?....

Bob

Quote:

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Note to Sean RE the valve threads.... The OD of the threads is 1.080" and the OD of the main tube in that area is 1.202" so the maximum wall thickness above the threads is 0.061" (and it's probably a whisker smaller than that).... The very end of the tube where the O-ring seals is 1.150" ID, so the wall thickness above the O-ring is only 0.026".... I don't even want to think about that.... I guess it works because it's a very short length at that size?....

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Your right that would creep me out big time. I did the calculation though at the low end of CrM and your still looking at 4300psi burst. And if the Oring completely fills this reduced area then more than half the force is being taken by the plug. Hehehe I wouldn't do it but theoretically its fine.

That valve mod makes perfect sense now that I see it in action. With that much void space it would induce those little orifices to instantly hit choked flow because of the sudden pressure drop.

I got some time to shoot some strings last night to test the plugging of the three lower holes.... I really like my "Chrony Connect" program and cables I got from the UK, it saves me having to stop and record every shot.... The velocities are stored in a file that I can copy into Excel.... I shot three strings with the hammer preload adjusted 6, 7, and 8 turns out from full in.... The new plastic locking plug in the adjusting screw works perfectly, NO sign of any creep in the adjustment any more.... Here are the results.... NOTE: pressures on the graph are in bar, not psi....

http://i378.photobucket.com/albums/o...th3Plugged.jpg

The first thing I noticed was how much smoother the curves are.... They don't have the large shot-to-shot jumps I saw previously.... It requires two turns more preload on the spring to get the same average velocities as with all six holes open.... but the peak velocity occurs at a slightly higher pressure than before, making a more even bell-curve rather than one with a long front end and quick fall-off after the peak.... This is typical of what I expect to see on restricting the flow slightly.... I also achieved an increase in the efficiency, ie slightly less air was used to generate the same FPE.... 7 turns out gave me 23 shots with 4% averaging 898 fps (45.5 FPE) filling to 200 bar and shooting down to 140, with an efficiency of 1.20 FPE/CI.... That's already a pretty potent quarter-bore....

I'm happy with these results, as they are consistent with what I saw on the .22 cal I worked on.... The bigger caliber required two turns more preload to get back to the same power, whereas the .22 cal only needed one.... I think all we are seeing there is the need for more airflow in the larger caliber.... The next step is to plug the remaining two holes and drill out the top hole to match the transfer port size....

Bob

This morning I had the opportunity to plug the remaining two side holes and drill and chamfer the top hole.... Here is what the top of the valve looks like now....

http://i378.photobucket.com/albums/o...0/IMG_2581.jpg

I added some black ink around the hole to make it more visible.... I milled the top hole out to 5/32" and then moved the mill each way 0.006" to enlarge the hole to 0.170" (the same size as the transfer port).... I then plugged the two remaining side holes with 6-32 x 3/16" SHSSs, got out the Dremel with a 1/8" ball grinder tip and smoothed off the front corner of the hole, plus the two side screws where they protruded into the (now larger) top hole.... Once I was finished, I could see the white plastic valve seat, which was "around the corner" before.... The total area of the larger single hole is the same as the three smaller holes from the previous test.... If I gain any performance (or efficiency), it will be from improved flow of the single, streamlined corner and/or the lower drag of a single larger "pipe" compared to three smaller ones.... Assuming this mod works as intended, I will add some JB Weld between the 5 set screws in the groove to get rid of the last bit of wasted volume I can....

Bob

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....

http://i378.photobucket.com/albums/o...th5Plugged.jpg

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

Quote:

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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....

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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

It's posts like this that make me buy sh!t and then determine I never have time to actually do the work (I have an AT44 w/extra tank and valvestems collecting dust in a case)...

Somebody stop Bob before I go broke...

Ain't that the truth

Barrrel and breech correction are next on deck.... might have to drill the transfer port a whisker at the same time.... Since the valve ended up at 0.180" after I streamlined it, if there is room I'll take the transfer port and barrel out to the same size.... Epoxy between the valve screws after that (and separate, I'm curious too)....

Pretty amazing what a bit of tweaking can do.... Like you said, nothing serious here, really just "blueprinting" and tuning....

Bob

Well, today was kinda wierd.... I took the rifle all apart and matched up all the ports to smooth and maximize the flow.... I ended up with a 0.180" valve top port, 0.183" transfer port, 0.185" through the breech, and a 0.187" barrel port.... I polished the barrel with some bore paste and stuck everything back together and gained a whopping 6 fps (0.5 FPE) for my trouble.... but at least it didn't use any more air, so the efficiency was a solid 1.20 FPE/CI.... Basically all the ports downstream of the valve are as big and smooth as I can go.... By now I figure the choke point is the valve seat itself.... It looks like this....

http://i378.photobucket.com/albums/o...0/IMG_2553.jpg

There was a spare supplied with the parts that came with the gun, and it measures 0.171" ID, less the area of the 0.100" stem.... so the equivalvent area is the same as a hole measuring 0.139" (the same size as a stock Disco transfer port).... This is obviously a lot smaller than the rest of my ports.... I figured if I ruined the seat I had a backup, so I knocked it out of the valve and measured it.... and found that the hole in it was even smaller than the spare, it only measured 0.163" ID.... I mounted it in the lathe, and using my number drills, one at a time, slowly took it all the way to 0.187".... the same size as the ports (but still less area because of the stem).... The throat area is now the equivalent of a 0.158" hole, 50% larger area than the one I took out.... There is enough meat to drill the hole out to about 0.200", and I can thin the stem down to 0.090", and match the throat area to the area of the rest of my ports if I need to.... However, I know that if I make the valve too big, the hammer may not open it.... so I stopped at 3/16".... stuck the gun back together and shot some more strings....

WOW!.... What a shocker.... I still had the hammer preload at 7 turns out, hoping that it would have enough oomph to knock open the larger valve at 200 bar.... Well, the first shot over the Chrony was 990 fps, then 1010, and it peaked at 1023 fps before falling back to 983 at shot 15.... Drilling out that valve seat gained me 75 fps and 8 FPE.... and the hammer still worked !!! .... I dialed the preload down to 6 turns, and then down to 5, and the gun was still shooting way stronger than before.... I set the preload back to 7 turns out and shot a string with H&N Baracudas and EunJin Domes.... Here are the results....

http://i378.photobucket.com/albums/o...25BigValve.jpg

The dotted black lines on the graph are from the first string today, JSB Kings at 7 turns out, before I drilled out the valve seat.... That was the most power up until today.... The red pressure line can be used for all the pellets at 7 turns preload.... Here is a summary of the results:

25.4 gr. JSB King: 1023 fps (59.0 FPE) max.
1009 fps (57.5 FPE) average for 15 shots @ 1.06 FPE/CI

30.9 gr. H&N Baracuda: 957 fps (62.9 FPE) max.
944 fps (61.1 FPE) average for 15 shots @ 1.13 FPE/CI

35.2 gr. EunJin Domed: 915 fps (65.5 FPE) max.
899 fps (63.2 FPE) average for 15 shots @ 1.17 FPE/CI

That's a 9-10 FPE gain over yesterday.... The shot count is a few short of the 18 (two full clips) that I want.... but my power goal of 50-60 FPE has certainly been achieved.... and by enough margin I am confident that I can get an 18 shot string in the 950 fps range with any pellet from 25-31 gr., and that includes all the ones with a decent BC....

It's been quite a day.... Using JB Weld on the groove in the valve will have to wait, the tubes I have are so old they are hard as a rock.... Tuesday (after the holidays) strangely seems a long way off.... but I'll enjoy the weekend knowing I've accomplished my goal with this rifle....

Bob

WOW! :icon_eek:
Wicked numbers your getting, Bob. That rig is turning into quite the beast indeed. I'm continually amazed at how much power can be obtained from opening things up by such small amounts.

At those velocities in a 1/4 bore, it must be loud as a mother...!

Todd

Holy F***:eek-new:

You've got an off the shelf 25 cal flirting with the transonic barrier. NICE!

And enough power to blow marmots into next week

Quote:

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Originally Posted by SeanMP

Holy F***:eek-new:

You've got an off the shelf 25 cal flirting with the transonic barrier. NICE!

And enough power to blow marmots into next week

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I just cannot put it any better....X2

Bloody well done Bob!

Al

Thanks for the accolades, guys!.... much appreciated.... I'm pretty sure with a lighter pellet it would go supsersonic, but really, who cares.... Baracudas in the mid 900s are plently, and I'll likely have to detune it a bit if it's preferred fodder is the JSB Kings.... I wonder how long it will be before JSB bring out a heavier pellet in .25 cal?.... You know, something I can't figure out.... This gun is NOT that loud compared to others I have at comparable power levels.... maybe the air splitter?... EDIT: Nawwwwwww.... I figured it out.... my other guns are all running lower pressures.... therefore a longer valve opening and a higher residual pressure at the muzzle.... No magic there I guess....

One thing I noticed is that with improving the flow, particularly with opening up the valve throat.... the bell-curves are becoming "peakier".... I've seen that before, but the one that surprised me was the Kings at 5 turns preload.... The fill pressure dropped to 170 bar (normal) but there were still only 15 shots within 4%.... I would have expected more as the gun was "detuned".... I'm thinking that I may have to restrict the transfer port slightly to get to my 18 shots I want.... Maybe just putting a stock transfer port back in will be enough?.... I won't do anything until next week when I fill the groove in the valve with JB Weld though....

Bob

How big is the transfer port?

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

Just a photo of the valve with the groove filled with JB Weld.... The idea is to take up the extra volume in between the valve seat and the pellet to help keep the pressure up in the first part of the pulse....

http://i378.photobucket.com/albums/o...0/IMG_2582.jpg

Testing later tonight, time permitting....

Bob

Got some time this evening to do the testing of the valve with the groove filled in with JB Weld.... As expected, there was a slight gain in performance, but the efficiency has pretty much leveled out.... Here are the results....

http://i378.photobucket.com/albums/o...an25JBWeld.jpg

The interesting thing about this version is that the performance at mid-preload settings continues to improve.... The best shot strings are now happening at less preload than before.... I got 19 shots within 4% with the JSB Kings, 971-1007-968, averaging 992 fps (55.5 FPE) at 1.13 FPE/CI, filling to 200 bar and shooting down to 133 bar at 6 turns of preload.... The best strings with the H&N Baracudas and the EunJin Domes were at 6.5 and 7 turns of preload respectively, and returned 16 shots....

I shot a few pellets at 8 turns of preload, and the velocities were peaked pretty much at 200 bar for the lighter pellets and 180 for the heaviest.... The maximums recorded were:

25.4 gr. JSB Kings - 1046 fps - 61.7 FPE
30.9 gr. H&N Baracudas - 982 fps - 66.2 FPE
35.2 gr. EunJin Domes - 939 fps - 69.1 FPE
41.7 gr. EunJin Pointed - 881 fps - 71.9 FPE

I think there is a bit more in the gun yet, I could enlarge the valve throat a bit more and slim the stem.... and then I might have to make the inlet side of the valve breathe a bit better as well.... If I do that, I will then have to restrict the transfer port to keep the velocity under 1000 fps with the JSB Kings.... so I don't know if it's worth it....

Bob

I decided to finish the job.... I drilled out the valve seat to 0.203" and thinned the stem to 0.090".... That makes the throat of the valve the same area as the valve exhaust port.... In addition, I drilled four 7/64" holes at a 20 degree angle in the inner end of the valve to allow more air to enter the valve.... This has more than doubled the inlet area, so it is now a lot easier for air to enter the valve than leave it....

http://i378.photobucket.com/albums/o...0/IMG_2583.jpg

The extra holes in the inlet side should not be necessary unless the valve seat is drilled out, as the original hole was the same size as the throat, and it didn't have a stem obstructing it.... Hopefully I will find time to test again tonight.... Sorry for the slightly blurry photo....

Bob

Bob, nice work. But you do realize winter doesn't start officially until December, don't you? :courage:
I guess you will just have to find a different winter project......

Well when I bought it, I figured it would be until then before I got any time.... Fortunately, that wasn't the case.... Don't you worry about my lack of projects.... I still have a brand new (never fired) B-51 sitting here.... plus my Hayabusa, which will NEVER be finished (at least I hope not, because that will mean I ran out of ideas).... It's next version will be what Sean and I are working on, a .224 cal firing 41.5 gr. bullets high subsonic.... Then I still have .308, 9mm, .458, and .410 shotgun barrels to go on it.... See what I mean?.... Other projects that need finishing are my reversed tank versions of my 2260 and 2560 regulated HPA rifles, and I still have to fit a .25 cal barrel to my QB deluxe HPA....

Yeah, I don't think I'll run out of projects any time soon....

Bob

Got to run some strings over the Chrony tonight.... can you see the smirk on my face?.... Drilling out the valve throat and slimming the stem, combined with opening up the inlet on the valve.... gave me the highest performance I have yet achieved.... The larger valve seat required an additional turn on the hammer spring preload to overcome the extra force holdind the valve shut.... but even without doing that the performance was up, although it was at a lower pressure.... Once I went from 6 turns preload to 7, the entire 17 shot string of 25.4 gr. JSBs was over 1000 fps, peaking at 1044 (61.5 FPE)....

http://i378.photobucket.com/albums/o...MaxedValve.jpg

I didn't bother adding more hammer preload when I shot the Baracudas and EJ Domes, so the graphs above are a direct comparison of the three pellets at the same power setting.... The 'Cudas peaked at 65.4 FPE and the EunJins at 67.5 FPE, but they would be shooting over 70 FPE had I bothered to add enough preload to bring the start of the string up to 200 bar instead of 175.... I cranked up the preload for a few shots with the EunJin Pointed 41.7 gr. pellets, and at 11 turns of preload and 190 bar I got 78.4 FPE.... I'm thinking with 12 turns, right at 200 bar, I can hit 80 FPE (for one shot)....

This rifle has turned out to be a real beast.... I've likely got too much velocity even for the 'Cudas, but until I get the opportunity to put some lead a lot further downrange I won't know if I can get away with leaving the tune as is, or if I'll have to detune it for accuracy.... Nice problem to have, though !!!

EDIT: I forgot to add that the efficiency for the above strings was 1.11 FPE/CI for the Kings, 1.21 FPE/CI for the 'Cudas, and 1.28 FPE/CI for the Domes.... so not only is the performance up, so is the efficiency....

Bob

70 fpe AND 1.28fpe/ci

Who says there is no gold at the end of a rainbow.....BRAVO!

One thing which has puzzled me about this gun is that when I dial the power back with the hammer spring preload, the shot count doesn't increase.... I decided today to fit the oversized 0.153" non-PAL valve stem into the now very much oversized ports and test it.... After doing that, I turned the stem down to 0.140" in the throat area, which is the size of the main part of the stem, and ran more tests.... Here are the results....

http://i378.photobucket.com/albums/o...veFatStems.jpg

It appears that the best way to tune the Hatsan is to adjust the valve stem size to adjust the power, and then use the hammer spring preload to adjust the operating pressures.... certainly if you want to get the best efficiency.... Using the best strings from the above and previous graphs, and always starting from 200 bar (or as close as possible), here are the choices I have so far with JSB King 25.4 gr. pellets.... In all cases, only those shots within 4% of the maximum velocity in the string are counted, and the average FPE for the string is stated....

17 shots at 59.5 FPE (1027 fps) at 1.11 FPE/CI, refill at 130 bar
19 shots at 55.4 FPE (991 fps) at 1.13 FPE/CI, refill at 133 bar
22 shots at 51.6 FPE (957 fps) at 1.16 FPE/CI, refill at 130 bar
25 shots at 45.6 FPE (899 fps) at 1.22 FPE/CI, refill at 133 bar
31 shots at 43.4 FPE (877 fps) at 1.28 FPE/CI, refill at 122 bar

Other than with the mildest tune, I have a usuable pressure range of 1000 psi, from 2900 down to 1900, and with the 43 FPE tune, that range is extended down to about 1750 psi.... Other tunes in between should be possible with the right combination of valve stem diameter and hammer preload.... Small adjustments can be made with just the preload.... I'm very pleased with the shot count and the efficiency figures I have been able to achieve with this rifle.... and I'm looking forward to doing some accuracy and pellet testing....

Bob

Well, vacation's over, time to open up my AT44 10/22 again! I am surprised of the results from opening the valve seat bore. This is a great write-up bob, and now I will try and find a balanced combination for my shorter version in .22 cal.

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?

No problem.... 1 turn is 360*....

Bob

Hi Have you tested the accuracy down range yet?

Did a bit of shooting at 50 yards in the Spring.... 25.4 gr. JSB Kings at ~960 fps from the bench....

http://i378.photobucket.com/albums/o...san50yd001.jpg

Bob

That's pretty good.. Thanks for doing the work tuning the at44, I plan on copying your work if you don't mind. I started with the valve stem (.090) and valve seat I drilled out a bit more.
Thanks again
Bob

Hey guys. Very nice tutorial.
New here. I just completed this entire tune to my at44-10 .22 long but I don't have a chrony to test with but some day I hope to get one. Not sure what to do as all the tests posted in this thead are for the .25 version of this gun.My questions are:
I'm looking to get about 900 ftps using either beeman kodiak 21.14 gr or crossman premeers 14.3 gr. What is the lowest bar level that will achieve 900 ftps in my situation?
I'm thinking about putting a regulator on it and would like to set it to maximise my shot count. What is the best one at this time to get? I'm leaning towards robert lanes on ebay???
Having done this tune, how many turns should I adjust my hamer spring tension to maintane 900 ftps with regulator set at prescribed bar and likewise how many turns should I decide to forgo the regulator? I would hate to have air continue long after the pellet has left the barrel.
Any help is greatly appreciated.
Thanks,
Bruce

I suggest you get a Chrony.... trying to duplicate somebody else's results is almost impossible....

Bob

Thank you Bob for being so quick.
You're right about the chrony but what do you think of the regulator? do you have a prefrance for any one regulator?
Thanks.

I'm not keen on in-tube regulators, but then I'm not often after low-medium performance, which is where they excel.... By the time you leave a large enough plenum between the regulator and the valve for a powerful gun, your shot count is going to be dismal.... So that the pressure doesn't drop too much during the shot you need a plenum of about 1 cc for each FPE of power you want.... You're seeking 21 gr. @ 900+, so that is 40 FPE, so you need about 40 cc.... That is a chamber about 3" long in an AT44 tube, plus the length of the regulator (maybe 1.5-2") so you are going to lose about 5" of reservoir length, which is a lot....

I don't have any preference RE the different brands of in-tube regs. because I never use them....

Bob

Thank you for taking the time to give me a good argument against the regulator. As I said, I'm new and do respect your opinion. I have noticed some improvement in power after the mod so maybe just backing the hamer down a little will sufice for now, at least till I can save up for the chrony.
Thank you much for you input.
Bruce.

A you tube video of this entire process would be gold literally. Or a video you make and sell I would happily be your first customer .

4 year old post, don't even have the gun any more....

Bob