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Air Gun Home Forum Index » Rifles » Hatsan .22 Cal. AT44-10 PAL Shot Strings Goto page 1, 2  Next
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Hatsan .22 Cal. AT44-10 PAL Shot Strings 
PostPosted: Fri Apr 29, 2011 3:15 pm Reply with quote
rsterne
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I decided to start a new thread for the PAL version as this is the beginning of the "Modification" process.... I have my PAL as does the owner of the gun, so no problem there....

The owner supplied me with a "full power" valve stem along with a spare air reservoir.... I put the slimmer stem in that, and swapped out the two cylinders.... That is the only change from the sub-500 fps non-PAL version at this point.... The restricted stem measured 0.140" in diameter, and the full power one measures 0.100".... This allows more air to pass through the valve.... basically DOUBLING the velocity and providing FOUR TIMES the FPE levels of the non-PAL gun.... The shot count, however, drops from about 180 shots to 30.... Shocked



The first string, shot with RWS 11.9 gr. Hobbies, started at 200 Bar and 30 shots dropped the pressure to about 125 Bar where the velocity was heading south in a hurry.... It was down 10% from the peak reading by shot 35.... I filled to 200 Bar again for the JSB Express 14.3 gr. pellets, but this time the first shot was down over 10% below the eventual peak.... It turns out that with pellets from 14.3-18.1 gr. the optimum fill pressure is 190 Bar (as recommended by Hatsan) and the 30 shots drop the pressure to about 115 Bar.... With the H&N 21.0 gr. Baracudas, the usuable pressure range is 185 Bar down to 110 Bar.... and with the JSB 25.4 gr. Monsters there is no point in filling past 180 Bar but you can shoot down to 105 Bar.... In every case, the usuable pressure range turned out to be 75 Bar for a 30 shot string.... EunJin Pellets are too long to fit in the magazine (as are Predators).... so 25.4 gr. pellets were the heaviest tested....

It turns out that three 10-shot magazines are all that this gun can handle in this form.... and even then, the velocity range between the slowest and fastest shots is 93-94%.... If I apply my usual criteria of 96%, the shot count drops to 23-26 shots depending on pellet choice.... This is about the same shot count as a Discovery, but at significantly higher power levels.... Hatsan's power claim of 31 FPE is achieved with the JSB 18.1 gr. Exact Heavy pellet, and exceeded with the heavier ones.... However, their claimed shot count of 70 shots is pretty much a joke.... You might get that many if you shot the gun to empty.... but even 35 shots will see the velocity down 10% from the peak.... They have a longer barreled version for which they claim another 100 fps, and from what I have heard, that may well be possible.... There is also a longer air tube available, which is 230cc (14 CI) instead of the 180cc (11 CI) version on this gun.... That should translate into nearly four clips (40 shots) per fill.... or less variation over the 30 shots (my preference).... Here is the summary for the various pellets:

Pellet and weight; Average Velocity; Average Energy; Efficiency; Pressure at Peak Velocity

RWS 11.9 gr. Hobby; 986 fps; 25.7 FPE; 0.93 FPE/CI; 165 Bar
JSB 14.3 gr. Express; 926 fps; 27.2 FPE; 0.99 FPE/CI; 155 Bar
JSB 15.9 gr. Exact; 915 fps; 29.5 FPE; 1.07 FPE/CI; 150 Bar
JSB 18.1 gr. Heavy; 876 fps; 30.9 FPE; 1.12 FPE/CI; 145 Bar
H&N 21.0 gr. Baracuda; 830 fps; 32.2 FPE; 1.17 FPE/CI; 140 Bar
JSB 25.4 gr. Monster; 766 fps; 33.1 FPE/CI; 1.20 FPE/CI; 135 Bar

To me, the pellet choice would narrow down to JSB Exact 15.9 gr. or Exact Heavy 18.1 gr.... or the 21.0 gr. Baracuda/Kodiak.... Those weights are the best balance between velocity, FPE, and efficiency.... I think Hatsan are to be congratulated on a well thought out and reasonably priced rifle.... especially considering what you get for the money.... The power levels are on a par with a Marauder, from what I hear, at significantly less money.... Both are a 10 shot repeater, and the weights are similar.... and the Hatsan has a lot of options as to stock choice and length.... with even single shot models available.... Mr. Green

Where next?.... That depends entirely on what you need.... If more power is desired, then the obvious thing required is a heavier hammer strike with the heavier pellets.... This would allow the gun to be filled to 200 Bar without losing velocity.... and the net result should be increased velocity and energy.... with little loss in efficiency.... There is no point in doing this if you want to shoot light pellets as they are already pushing the limits of practical velocity.... This is likely the path I will follow, using 18-21 gr. pellets and trying to get them into the 900-950 fps range....

At this point, I see little advantage to trying to make the gun "breathe" better by slimming the valve stem more or increasing the port sizes.... Anything in that regard (if my prior experience holds true on this gun).... will likely reduce the usuable shot count further by making the shot string even more "peaky" than it is now.... I will have to give some thought to how the "JB Weld" modification to the valve ports seems to have increased the efficiency and whether it (or something similar) is worth exploring.... Another option is a valve stem in between the current two sizes (0.110" to 0.120" has been recommended) to lower the power a bit but increase the shot count.... Flattening the shot string from it's current shape would seem to be desireable, as the gun already has lots of power (IMO).... Remember my "rule of thumb" that at 950 fps the FPE is twice the pellet weight.... For me, that puts the practical limit at 36 FPE with JSB Heavies or 42 FPE with Baracuda/Kodiaks.... 50 FPE might be attainable with the JSB Monsters, but at what price in shot count?.... Rolling Eyes

One thing for sure.... There are lots of alternatives to customize this platform to meet your needs.... whatever they are.... Wink

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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JSB 18.1 gr. Exact Heavy Pellets 
PostPosted: Sat Apr 30, 2011 7:02 pm Reply with quote
rsterne
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Well, today's assignment was to try the three heaviest pellets and adjust the hammer spring setting from Minimum (all the way in, the way it comes stock) to 10 turns out.... shooting either 30 shots or until the velocity dropped 10% below the maximum, whichever came first.... All my comments are based on the current tune of this gun, which is using a 0.100" diameter valve stem but all other items stock.... I will break the information into three posts, starting with the JSB 18.1 gr. Exact Heavy pellets in this post....



The first thing that became apparent was that there is no point in going past about 4 turns out with this pellet as you are already on the peak of the velocity curve at that point.... Adding more tension only give a few shots that are faster, and by the time you are at shot 6, all the heavier hammer spring settings are actually slower.... Shocked

You can see what happens as you increase the hammer spring preload.... You get more velocity, particularly on the first shots, and the peak velocity occurs at higher pressure.... Once I went past 2 turns out on the adjuster, I could no longer get 30 shots before the velocity dropped 10% from the peak at that setting.... With this pellet, there is no point in going past 2 turns out unless you only want about 10 shots.... Below is the summary for each hammer spring setting....



With this pellet, there is really no down side to not cranking the adjuster out 2 turns.... You get more power, the same number of shots, and only a slight loss in efficiency.... This is an excellent combination for the Hatsan AT44-10.... assuming the pellet proves accurate.... You get 24 shots within 4%, averaging 907 fps (33 FPE), filling to 200 Bar and shooting down to 130 Bar.... Mr. Green

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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H&N 21.0 gr. Baracuda Pellets 
PostPosted: Sat Apr 30, 2011 8:27 pm Reply with quote
rsterne
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Next pellet up is the 21.0 gr. H&N Baracuda (aka Beeman Kodiak).... I followed the same procedure as before.... but when I looked at the results, I decided I need an "in between" test so I did an additional test with the hammer spring out 3 turns....



2 turns out produced a decent shot string, but it started out down 5% below the maximum.... The string at 4 turns out was a good string, nice and flat for 14 shots.... but I wanted one in between.... You will notice that all strings with 6 turns and more of hammer spring tension have the highest velocity on the very first shot which means they don't have any curve at all.... Any setting between 2 and 4 turns out can produce a usuable string with these pellets.... while starting from a 200 Bar fill.... You can dial up what you want, choosing more power and fewer shots through to less power but a longer string.... Below is the summary for each hammer spring setting....



I didn't want to take the time (or pellets) to do yet another string.... but I think that about 2.5 turns out might be the sweet spot for this pellet.... delivering about 20 shots within that 4% window I aim for.... As it is, at 3 turns out, you get 17 shots within 4%, averaging 890 fps (37 FPE), filling to 200 Bar and shooting down to 140 Bar.... Mr. Green

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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JSB 25.4 gr. Exact Monster Pellets 
PostPosted: Sat Apr 30, 2011 9:22 pm Reply with quote
rsterne
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The third and final pellet I tested today was the 25.4 gr. JSB Exact Monster.... Once again, I tested each hammer spring setting from full in (stock, minimum setting) to 10 turns out, in increments of 2 turns....



Once in a while you get lucky.... and 4 turns out was obviously the sweet spot with this pellet.... I got 19 shots within 4% of the maximum which was 848 fps (40.6 FPE).... That's a whack of power in a very usuable string.... Here is the summary....



At 4 turns out, you get 19 shots within 4%, averaging 838 fps (40 FPE), filling to 200 Bar and shooting down to 135 Bar.... and it does that while delivering an efficiency of 1.05 FPE/CI.... Mr. Green

So, what did we learn today?.... First off, the Hatsan can be tuned to deliver a whack of power with just a valve stem change and a bit of tweaking on the hammer spring.... With the stock hammer spring setting, heavier pellets require filling to less than 200 Bar or the first few shots are a long way below the maximum velocity.... That (short fill technique) is a perfectly acceptable option, as shown in the first graph in this thread.... Pay attention to the scale on the graphs.... The first graph had a vertical scale of 300 fps.... These last three were only 200 fps.... so although the shot strings look more "curved" that isn't true.... Being as how most of us are power hungry, it's nice to have the ability to tune up the Hatsan to be able to take advantage of the 200 Bar maximum fill.... That's where increasing the hammer spring preload comes in....

You will note that I didn't test any light to medium weight pellets.... I guess I could have tested the 15.9 gr. JSB Exact, and I likely would have found out that 1 turn out on the adjuster would have produced a very usuable string at about 950 fps average (32 FPE).... Given the choice, however, between a 16 gr. pellet at 950 and an 18 gr. pellet at 920... and knowing what I do about what happens to the BC at those velocities.... I think it's pretty much a no-brainer in favour of the heavier pellet.... Incidently, I did throw a couple of Hobbies downrange at 10 turns out on the hammer adjuster.... and it still didn't break Mach 1... about 1080 fps was the best I saw.... It was also pretty obvious to me that turning the hammer spring out more than 4 turns from stock is a waste of time unless you just want to see a few (very few) high velocity shots.... Yes, you can do it, but the first shot is the fastest, and they tank from there.... and BOY do they waste a lot of air.... especially the last 2 turns which shows no gains, just wasted air....

What's next?.... Trying to improve the efficiency and flatten the shot string is about all that is left.... It seems that the way to do that is to restrict the breathing a bit and (likely) lean harder on the hammer spring.... Since others have tried the "JB Weld" or set-screws in the valve ports surrounding the stem.... I'm going to try a bit bigger valve stem and then lean on the hammer spring a bit.... I don't mind giving up a bit of power if I can flatten and lengthen the shot string.... Wink

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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PostPosted: Sun May 01, 2011 11:29 am Reply with quote
AirGunEric
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For anyone not familiar with it, the Hatsan AT-44 is also sold as the "Air Venturi Halestorm" and the "Hammerli Pneuma".

The "PAL" vs. "non-PAL" Bob is referring to is only applicable to Canada, I assume a stock AT-44, Halestorm or Pneuma sold anywhere else comes out of the box as Bob has tested it in this thread (as a "non-PAL").

Can you determine if the valvestem change was the only "detuning" method used on the "non-PAL" version, Bob? If the info here is good for the rifle bought anywhere else, it makes for a nice resource.

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PostPosted: Sun May 01, 2011 11:39 am Reply with quote
rsterne
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If the Halestorm and Pneuma are the same as the full power Hatsan (with the 0.100" valve stem).... then it appears the only change Hatsan made to make the gun "non-PAL" for Canada is to increase the diameter of the stem to 0.140-0.150" (it actually has a step in it).... I understand that the 12 FPE version has a stem of about 0.132" but have not confirmed that....

Since the valve is mounted in the end of the air reservoir (and comes off the gun with it).... it is a simple matter to drastically change the tune of the gun by replacing the reservoir with one set up differently.... The gun I tested was 31 FPE with 18 gr. pellets with the 0.100" stem and NO other modifications.... and it started as a non-PAL (ie <500 fps) gun....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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PostPosted: Sun May 01, 2011 12:23 pm Reply with quote
rsterne
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I have collected what limited data there is for the Hatsan valve stems and plotted the FPE produced against the diameter.... This data used 14.3 gr. pellets in .22 cal.... I measured the non-PAL stem at the larger diameter (0.150") as it has a step in it, and since it doesn't open very far (it can't or the hammer would hit the valve housing) I reckon that the greatest restriction is between the valve seat and the part of the stem inside it.... The "full power" stem is 0.100", and from data posted in another thread, a stem of 0.090" diameter picked up about 50 fps and there was no further advantage to going to 0.080".... I was told that the "17 joule" (ie 12 FPE) stem for England is "about 0.132" IIRC" by another member, so I used 0.130" to keep the increments on the graph equal (0.010") per horizontal division....



What I am interested in, of course, is estimating what diameters are required for intermediate power settings.... These estimates are for the "stock" hammer spring setting and no changes to the porting, of course.... ie the rest of the gun completely stock.... I will be turning one stem down to 0.120" for the next set of experiments.... The graph predicts about 17 FPE, so we'll see what happens.... Mr. Green

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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Results with the 0.120" Valve Stem 
PostPosted: Sun May 01, 2011 10:58 pm Reply with quote
rsterne
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I got a chance to test out the 0.120" valve stem this afternoon.... It produced a LOT more energy than the previous graph predicted.... so I'm guessing that the size of the 12 FPE (17 Joule) stem was actually significantly larger than I was told.... Since I don't have the exact dimensions, I have deleted it and here is the new graph with known data points so far.... Note that the graph is linear for 0.120" to 0.090" stems....



The gun shoots 25 FPE with 14.3 gr. pellets and a 0.120" stem and no other mods.... It did 27 shots within 96%, starting from 180 bar down to 120 bar.... and a total of 46 shots within 90%, from 200 bar down to about 100 bar.... I was mostly interested in this valve stem to develop this gun for scruffie for Grouse busting.... so I switched to 18.1 gr. JSB Exact pellets (which I use with great success on Grouse) and ran three shot strings, one at stock hammer preload, one at 2 turns out and one at 4 turns out.... Here are the results, with only the shots within 96% of the peak velocity shown....



You will note that 4 turns out is too much hammer spring preload unless you want just a few shots.... but the first 10 shots (at 33.6 FPE) are very flat.... The string at 2 turns out is comparable to what I had with the 0.100" stem and 0 turns.... 23 shots within 96%, but it was down a bit on power and efficiency.... However, I was very pleased with the shot string at stock (minimum) hammer spring setting.... The summary of these strings is in the table below....



The baseline string with this stem, with the hammer preload in the stock position, produced 32 shots within 96% of the peak velocity.... It requires only a 180 bar (2600 psi) fill, which means you can fill about 27 times from an 80 CF 3000 psi SCUBA tank, a big advantage.... You get three full magazines of shooting before refilling at 115 bar (1700 psi).... and the efficiency is 1.12 FPE/CI.... Velocity is between 800 and 833 fps.... averaging 820 fps (27 FPE).... and the gun is significantly quieter than it is with the 0.100" stem.... With the gun sighted at 33 yards, and a 1/2" kill zone (ie POI within 1/4" above or below the line of sight), the point blank range is 12 to 37 yards... and the remaining energy at that range is still 21 FPE.... I'm beginning to wish this gun had a scope on it so I could check the accuracy.... Mr. Green

If you compare this with a Disco with the same pellets, the gun set up this way is more powerful (27 FPE vs. 23 FPE), and has more shots (32 vs 25).... Looking at it another way, it shoots 18.1 gr. pellets at the same velocity that a stock Disco shoots 14.3 gr.... Wink

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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PostPosted: Sun May 01, 2011 11:25 pm Reply with quote
AirGunEric
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How is the rifle for overall build quality and such?

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PostPosted: Mon May 02, 2011 12:07 am Reply with quote
rsterne
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It seems pretty decent.... I'm quite impressed for the price.... Have to get a scope on it and find out what the accuracy is like....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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PostPosted: Mon May 02, 2011 11:10 am Reply with quote
packrat
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JEEEEZ..Bob, as usual. you have put my poor brain in information overload Shocked Shocked I just have to say to other members here that I do hope they realize just what an asset you are to this forum as well as airgunning in general...Positively the most in-depth, thorough and understandable review of that particular gun's performance.....nothing short of OUTSTANDING..and I THANK YOU Exclamation Exclamation Exclamation

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0.120" Stem & 3 Holes Plugged 
PostPosted: Mon May 02, 2011 9:38 pm Reply with quote
rsterne
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I drilled and tapped the three lower holes in the valve to 6-32 and inserted 3/16" long set screws just below flush on the outer rim of the valve.... so that not only do they block the hole, but effectively prevent much air from moving around to the bottom side of the groove, decreasing transfer port volume and restricting the flow somewhat.... I tested with 18.1 gr. JSB Exact Heavy pellets with no preload, 1 turn, and 2 turns.... stilll with the 0.120" stem.... recording only those shots within 96% of the peak velocity for each string....



There are two important things to note about these shot strings compared to the unplugged valve with the same 0.120" stem....
1. There was a velocity decrease (at equal hammer spring tension) of about 20 fps.... which can be made up by 1 more turn of preload....
2. The shot strings are flatter and more evenly curved.... with increased air efficiency....

With one turn of hammer spring preload and the plugged holes, the shot string was 6 fps faster and the same length as the best previous string (0 turns and holes open).... With two turns of hammer spring preload and the plugged holes, the shot string was in between in velocity the previous strings at 0 and 2 turns.... but it was 30 shots long whereas the previous strings were 32 and 23 shots.... It was significantly smoother, with less shot to shot variation.... so there is a definite smoothing of the shot string with the added restriction to the airflow and a slight increase (1 turn) of hammer spring tension.... There is also an increase in efficiency at that power level.... This increase is small, but points the way for further testing.... Here is the summary....



The best string from this test was with 2 turns of hammer spring preload.... The velocity range was 823 to 857 fps over 30 shots, with an average of 844 fps (28.7 FPE) and an efficiency of 1.12 FPE/CI.... This was achieved with a fill to 200 Bar shooting down to 130 Bar.... While I really want to test the 0.120" stem with even more restriction in place.... the next test will be with the 0.100" stem installed in the present valve with the 3 plugged holes....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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PostPosted: Mon May 02, 2011 11:06 pm Reply with quote
AirGunEric
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You wouldn't happen to have a picture of the stem(s) used in the AT-44 (and/or the complete valve as well)?

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PostPosted: Mon May 02, 2011 11:18 pm Reply with quote
rsterne
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Here is a photo of the Hatsan valve and stems.... Inside the valve there is a removable seat (an O-ring, I think) that the tapered face of the valve seals on.... The threads on the left in the photo screw directly into the air reservoir.... the threads facing the right screw into the gun....



Top to bottom is the 0.0150" non-PAL stem (the area inside the seat is actually larger than the part where the O-ring on the stem is).... then the 0.120" stem I machined from one of those.... and lastly the 0.100" "full-power" stem....

The white plastic sleeve is a press-fit in the end of the valve and it is difficult to get out the first time.... I milled a couple of small flats on either side so that you can get a screwdriver blade under it to pry it out....

You will note that there is a groove in the valve body with 6 holes.... That is where 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....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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0.100" Stem With 3 to 5 Holes Plugged 
PostPosted: Tue May 03, 2011 9:45 pm Reply with quote
rsterne
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I re-installed the 0.100" stem in the valve with the three bottom holes plugged and shot a couple of strings.... I then pulled the gun apart again and plugged the other two holes with 6-32 screws, leaving only the top hole (that lines up with the transfer port) unplugged.... I DID NOT drill out that hole as I wanted to see what would happen when I really choked up the flow.... I then shot two more strings and got a 40 shot string at nearly 800 fps with 18.1 gr. JSB Heavies with only 4% variation.... That last string I shot through the Chrony using a borrowed scope to check the grouping.... and I'm delighted that the gun does indeed like those pellets.... Below are four 10-shot groups starting at 200 bar and shooting down to 125 bar (L to R) shot indoors at 20'.... The squares on the target are 0.10" so the groups are running 0.32 - 0.4" OD (0.10" to 0.18" C-T-C).... If you superimpose all four groups, the C-T-C is less than 1/4".... I think scruffie's Grouse will be in trouble.... Mr. Green



Here is the graph showing all four strings.... Note that the two higher velocity strings were shot with only 3 holes plugged.... while the two lower strings were shot with 5 holes plugged.... The loss is almost exactly 100 fps when you plug the last 2 holes.... Note that on the 40 shot string, the best 32 shots (from 190 bar down to 130 bar) vary only 20 fps (~2%).... with a low of 772 fps and a high of 792 fps and an average of 783 fps (24.7 FPE)....



I am very pleased with the simple modification of plugging the bottom 3 holes in the valve.... With the 0.100" stem you lose about 15 fps which takes less than 1 turn on the hammer spring preload to get back (1 turn gained about 25 fps).... However, you gain both more shots within the 96% window (ie a flatter string), and also about 10% more efficiency.... With the hammer spring at 3 turns out, I got 26 shots within 4%, averaging 908 fps (33.2 FPE).... That is the best string to date with these pellets.... I notice that there is room for a few more shots at the beginning of the string if I backed the spring tension down a fraction.... Set up for 900 fps, I think 30 shots is within reach.... I think that 900 fps and 32 FPE might just be a sweet spot with these pellets.... Wink



The other setup that pleases me is with all 5 holes plugged and the hammer spring at 2 turns out.... With an average velocity of 780 fps (24.5 FPE) over 40 shots (4 full magazines) and all the shots within 96% of the maximum.... this represents the flattest shot string I have found at these power levels.... The gun is significantly quieter, and delivers nearly 1.20 FPE/CI for efficiency, starting with a 200 bar fill and shooting down to 125 bar.... If scruffie wants to tighten up the string even more and he's happy with "just" 30 shots.... he can back the fill down to 190 bar and refill at 130 bar.... Cool

I'm pretty much finished with the R & D work I wanted to do on this gun.... I've blown more than 1500 pellets downrange just shooting shot strings, and had to top up my SCUBA tank 3 times with my ShoeBox.... It's been a very interesting project, and I learned a lot.... and that, after all (for me) is what it's all about.... Mr. Green

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 22XX PCP 8-shot Carbine, 2260 PCP Rifle (50 FPE), Hayabusa PCP, .22 B-26
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Hatsan .22 Cal. AT44-10 PAL Shot Strings 
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