Revisiting the HATSAN AT-44 valve mods .... For a Regulator conversion.



Author Topic: Revisiting the HATSAN AT-44 valve mods .... For a Regulator conversion.  (Read 5444 times)

Offline Motorhead

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Thanks to the previous work by fellow member rsterne, took his info and applied it to .22 Hammerli Pneuma.
See: http://www.gatewaytoairguns.org/GTA/index.php?topic=33903.msg315366#msg315366


Started out plugging 5 of the 6 valve holes ( This valve took 4-40 size grub screws BTW )
JB weld up the space between like Bob had done  ;)

Next having just the valve body in hand screwed it into main tube snug, then drilling down from the transfer passage opening up the remaining 6th hole to .165" being same size as the transfer passage. With a dremel tool slightly flared the hole outward into throat area behind seat.

Having pulled the seat earlier found it's I.D. hole @ .162" which was IMO going to be too small with the bigger passages down stream.
So ... gently held it in the lathe jaws carefully drilling it out to @ .175" which leaves the poppet a sealing margin @ .055 total ( .0275 contact width )

Drilled out the face of body with 3 holes as Bob had done using .125" diameter at the 20* inward angle converging holes just under the spring retention cup.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Reassembling rifle for a few test shots changing nothing in hammer tension from previous strings headed over to the Chrony    ;D

** As spring tension was set from earlier, rifle was shooting CPHP 14.3 pellets @ 835 fps for just a tad over 22 ft lb power.
( @2000# in tube )
** After valve mods with SAME settings, rifle was shooting CPHP 14.3 pellets at 965 FPS for just under 30 ft lb power  8) 8)
( @2000# in tube )
So indeed valve responded to some massaging and flow management 

Now why this is all fine and dandy, quite likely rifles a bigger air hog than it already was  :P which gets to the reason for these mods with no interest in efficiency numbers quite yet  :o :o

REGULATION on the way
... Wanted to get the preliminary mods that would have rifle making the @ 30# power I was after at the @ set point pressure regulator will be used at. ( Actually @ 1800# ) which will have valve opening easier yet ... then allowing less spring pre-load to be used lowering dwell and air use  ;)

** Now we wait for the Huub AT-44 regulator from the Netherlands to arrive so we can finish up and see if concept = reality ???

Stay tuned ..........

Scott
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Offline rsterne

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Re: Revisiting the HATSAN AT-44 valve mods .... For a Regulator conversion.
« Reply #1 on: November 28, 2013, 10:10:17 PM »
Well done.... you should be all set for when you get your regulator....

Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
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.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), .22 BAM B-26, .22 BAM B-51 (50 FPE), .25 Hatsan AT-4410 Long (70 FPE), .22 QB79 HPA (26 FPE), Disco Double .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357; Mk.III is .410 shotgun and .458 cal)

Offline Motorhead

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Re: Revisiting the HATSAN AT-44 valve mods .... For a Regulator conversion.
« Reply #2 on: November 29, 2013, 02:10:26 PM »
Here the body with the additional holes feeding poppet cavity. * Also note flattened sides of spring retention cap allowing you to wedge cap off for future service chores.



Valve discharge area with plugged and JB filled holes with 1 discharge passage at .165"



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Offline Motorhead

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Re: Revisiting the HATSAN AT-44 valve mods .... For a Regulator conversion.
« Reply #3 on: December 10, 2013, 05:44:29 PM »
Hot Dang !!! .... Hubb regulator showed up today for the project  ;D ;D ;D

Got a shipping notice it mailed Monday Dec 2 from Holland .... Received USA west coast Dec 10
WOW !!! .... near 1/2 way around the globe in 8 days  :o .... impressive to say the least.

Results to follow .... But O'baby it's sooooo cold outside  :P
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Offline Motorhead

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Re: Revisiting the HATSAN AT-44 valve mods .... For a Regulator conversion.
« Reply #4 on: December 11, 2013, 12:37:17 AM »
**Went in and changed spring pre-load lowering velocity with 2K in tank to be @ 860fps before installing regulator.

Got it installed .... Changing no settings 875 fps with 14.3 pellets.  *24.3 ft lbs
So velocity about where it was  ;)
Some warmer days and we'll shoot for some string data  ;) and see what shot count does on and off regulation.
« Last Edit: December 11, 2013, 02:00:15 AM by Motorhead »
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Offline GARY T

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Offline bruce32466

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**Went in and changed spring pre-load lowering velocity with 2K in tank to be @ 860fps before installing regulator.

Got it installed .... Changing no settings 875 fps with 14.3 pellets.  *24.3 ft lbs
So velocity about where it was  ;)
Some warmer days and we'll shoot for some string data  ;) and see what shot count does on and off regulation.

New to this forum and just got a Hatsan at44 .22 long. I would like to install a regulator on it, but before going through all this trouble, It would be nice to see how you did on the pellet count. What I'm trying to achieve is as many consistent shots as possible @ 900 - 950 ftps using 21.14 grain beeman kodiak. with your mods and a Robert Lane regulator,  what could I expect in results?

Thanks,
Bruce.
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Offline Bwalton

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Looks like you went from 965 to 875 with the regulator, my mods were a little different...with out the regulator I tuned to 890fps for the AT,44 short....My mods were as follows..I plug two hole because the one did not line up, left 4 open..and went 3 1/2 turns out. With the regulator for 20 shots I got a  ES of 9 and a Avg of 824fps now...a whole lot less work. Same results or better, shooting 18.13gr , with 14gr I think it would be a much higher fps'...But with the 18.13gr you have more ftlb. Also Roy makes a very good regulator local no need to go outside the U.S
The Hatsan is very ez to tune. Bec even without the regulator, and just plugging two holes, I got a avg of 890fps shooting 18.13gr with a ES of only 13.
« Last Edit: June 28, 2014, 01:37:13 PM by Bwalton »
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Offline bruce32466

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bump ;D
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Offline Conrad Smith

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Hi all,
 First off, great forum. It has really given me the confidence to mod up my discovery and now my Hatsan. So a big thank you to the moderators and the posters. I figured I would share my results in hopes that it might help someone else. I am resurrecting this post so as not to start a new post on the same subject. I hope that is ok.
I also followed rsterne's advice (link was already posted) for my .25 at44-qe long and I too am doing it to regulate the gun. I use it to plink with as well and I am unhappy with the quantity of shots. I recall 40 being on airgun depot's website when I purchased it. I just checked and it says 20-25, which is still a stretch. I could get maybe 15, which is just too few for what I use it for.
I just wanted to point out a few things that I noticed when following rsterne's advise.
1. Mine did take the 6-32 set screws. I did have to enlarge my holes a little bit though. I put the tap to the hole and it just looked too small. I tried a #36 drill and it didn't fit, so I drilled them out. The 3/16 set screws were too long for my valve. Either I couldn't get the valve screwed in or the stem would seize up. I would get the next size shorter. I had to sand all of mine down about .03".
2. I had to take off about .005" from the main tube to get a hole to align. This was probably the easiest part.  ;)
3. The delrin piece at the back of the valve is a pain to get out. I used channel locks and buggered it up a bit. I added the flats with a file to make it easy to remove next time.
4. Hole sizes: barrel=.1875" or 3/16; breech=.185" or #13; Transfer port=.182" or #14; Valve hole =.180 or #15.
5. I drilled out the poppet? valve seat? (small delrin thing in the valve with an o-ring around it) to .204" or #6. I wouldn't recommend this. I'll explain why. When I got the valve all assembled. I went to fill...off the gun of course. It leaked (audibly) until about 150 bar. Then the noise went away. I set the valve aside and checked in the morning and it had leaked about 25 bar. By the next day it was empty. I took it apart to see what was wrong. I couldn't really find anything wrong. I cleaned it up and tried again. Still leaking. Took apart again and found that the poppet was nearly impossible to remove. After drilling it out, the ID is about the same size as the piece in the valve that it sits against, so trying to get something on it to push it out from the gun side is impossible. So I approached from the air tube side with a hooked poker thing. I was able to get it out, but not without destroying it. I grabbed the spare and pushed it in there. It no longer leaks. My guess is that the taper on the valve stem only has so much area to contact the poppet. Drilling out the poppet, reduces this contact area. My guess is that .204" is on or close to the limit? I'm also not as good as a machinist as rsterne, but I couldn't see any issues with mine, so not sure why it failed? Turning down the valve stem is probably fine, but it probably has a limit as well. At some point it will be too weak to function properly.
6. Don't lube the o-rings in the valve. I did out of habit. I noticed right away something was wrong when I got it all assembled and pushing in the valve would cause the valve to stick open. It would eventually close, but it wasn't responsive like it was before I lubed them. A little hot soapy water fixed this.

First shot string. No preload. JSB heavys 34 grain with all mods described. Resulted in 9 usable shots. Based on this group, more preload would make it worse? Seems as if I'm starting from the top of the string. Do I need to shave off a few turns of the spring? This hammer spring does seem overly tense. If I ever left the gun with less than 100 bar in it, the hammer spring would overcome the valve spring and drain my tank. It happened a few times. Maybe it was a bad seat to begin with?
Shot #   Velocity
1   890
2   893
3   890
4   881
5   884
6   878
7   873
8   865
9   868
10   852

Not the greatest shot string of all time. Here comes regulation. Now I had some issues with the chrono as the sun was setting, so I had to put a light on it and that only seemed to work sometimes. So I put err for when it wouldn't give me a value.  :P
1   err
2   679
3   682
4   678
5   675
6   672
7   664
8   670
9   err
10   err
11   err
12   664
13   670
14   664
15   667
16   664
17   661
18   err
19   668
20   665
21   err
22   err
23   err
24   err
25   err
26   err
27   664
28   658
29   660
30   661
31   err
32   err
33   637
34   err
35   err
36   609
So, somewhere between 34 and 36 use able shots. However, only mid 30's for energy. I have a feeling I should have purchased the .22 cal. I would have had this right out of the gate.  ::) Oh well, I'm learning. I did get one group at 30 yards before I had to put her away and there was just one hole on the paper, so that's good, but it did that before at 30 yards. It will be interesting to get it out to 70+ to see how she really performs. I am also wondering whether I need to drill a hole in the tank. Roy said I could try it without. The string does seem odd in that it starts high and then decreases, not entirely constant. Maybe I need to wait longer for the plenum to fill? Oh speaking of plenum, it is 3.12" long, OD=1.0", and wall thickness is .055". My tank ID is 1.02".
Big thanks to Milo 74 for the regulator. Install was easy and price was reasonable.
I'm open to any and all feedback or suggestions. Just trying to maximize my fun and take out some starlings and ground squirrels in the process. I'm thinking my plenum is more than the 1:1 ratio I've read about, so maybe back that off and turn out the regulator a half turn. This will free up more space in the tank and increase my velocity. Hopefully to get back into the 40 ftlb region.  ;D
Now I'm just rambling. I'm off to bed. Thanks again everyone!!!

Offline Conrad Smith

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http://www.gatewaytoairguns.org/GTA/index.php?topic=74919.0
I think this answers my question as to what I should do next. Thanks rsterne!! I think my spring is too tight. Looks like I need to shorten it. Now how much to cut off? hmmm

Offline BigTinBoat

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http://www.gatewaytoairguns.org/GTA/index.php?topic=74919.0
I think this answers my question as to what I should do next. Thanks rsterne!! I think my spring is too tight. Looks like I need to shorten it. Now how much to cut off? hmmm

With a 200FPS loos I would say the regulator is set really low
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Offline semad

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Forgive a newb question, but see if I am understanding this correctly.  after regulator install, adjust hammer for max velocity (plateau), then decrease till drop is noticed (knee)?  If velocity is lower than wanted, increase reg setting?   
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Offline Conrad Smith

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@semad My understanding is that you are correct. However, in this case, the hammer spring force combined with the hammer weight is just too large and I am at the limit in reducing the spring force. I think I have a few options. Increase the set point, reduce hammer weight, and/or cut the spring. I am going to begin with increasing the set point (currently at 1700, going to increase to 1900). I'm searching the internet for ways to reduce hammer weight. Seems harder than it looks. Plus I haven't figured out how to get the hammer out yet. LOL

@bigtinboat I agree, I need more power.

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