Ham/Pneuma: free-float the barrel? and an air efficiency lesson?

[darryl]

There is a full shroud out there for the Pneuma, but I know of one person who cut one down to fit against the barrel band. Anyone ever experiment with completely free-floating the barrel? Just curious (for now).

Anyone want to speak on improving the efficiency of air usage with this rifle? If I reduce power will I see a gain in shots per fill? Still asking. Still learning.
darryl

[Ribbonstone]

Working on it...taking a break in prep. for hunting.

Can certainly set it to shoot at lower pressures by reducing the striker tension....and it will shoot slower...and gain a few good shots, but not a drastic amount of shots.

Have not found a reliable simple way to get a large number of shots per fill.  Certainly know how to slow it down or speed it up, but with the issue valve configuration, the shot count stays at about 25 shots (shots inside of a reasonable FPS range of 25fps).

Will try a little less simple and try a smaller diameter transfer port...will let you know once I test that.
----------
Plan on gray squirrel hunting with this one,  so the 25 shots of the current shot count will work out for me.  Have an 8 a day limit, but in my normal after work quick hunts it is a very rare day that I shoot at more than 4.

[rsterne]

Here is the data I collected on a stock Hatsan AT44-10 which is exactly the same rifle....



Hatswan control the power of this rifle by fitting valve stems of different thicknesses.... Here is the same gun with a much thicker valve stem fitted to meet the Canadian regulations (under 500 fps)....



As you can see, you get about 180 shots per fill at 7 FPE (a total of ~1260 FPE).... and about 30 shots per fill at 30 FPE (a total of 900 FPE).... The lower the power the closer you should be able to get to that 1200 FPE figure.... I would think that if set up for the 12 FPE limit in the UK, you would get close to 100 shots.... At 20 FPE, maybe in the range of 50 shots....

Bob

[Pete]

There is a full shroud out there for the Pneuma, but I know of one person who cut one down to fit against the barrel band. Anyone ever experiment with completely free-floating the barrel? Just curious
darryl

Hi..
The theory behind a free floating barrel is...
As you put pressure "3000psi" in the air tube it moves and the
same as the pressure drops..So if the barrel is connected
to the air tube by means of a barrel band..
As the tube moves so dose the barrel...
You will notice a lot of PCPs have the barrel free floating
in the barrel band... My Career Infinity has about .5mm free play
between barrel & barrel band...

[Stefan]

I have a cylinder thats stock, full power, and I get 30-35 shots out of it, and I have a spare cylinder thats limited to 16J (12fpe) and its shot count is around 60.

[Ribbonstone]

That last sounds about right. Managed about the same shot counts. Some of it depends on how much variation you can stand and still consider it as part of the count, but 25-35 shots is about right. Closer to max. effort gives a bit lower.

Am considering making new valve stems...have the equipment (although that tiny little o-ring on the valve stem shaft might get left off), but have been looking for a more simple way to reduce speed/gain shot count.  Reducing speed isn't a problem...lots of ways to do that...but gaining shot count isn't as easy.

Does seem to me that sleeving the inside of the valve would have the same effect...and as I have a pretty good selection of brass tubing, may try that (rather than making the valve fatter...make the air chamber thinner).

[Stefan]

the only problem that can occur with pneuma/hatsan is that stem doesnt work the same way everytime, and then shift a poi. did someone get a solution for that?

[darryl]

thanks for the replies.
Rib please keep us posted on your work on the transfer port.
Bob, thanks for posting your graphs here too.
Pete thanks for the theory on the free-floating barrel. I understand that now.
Stephan, and all, I think I've resolved to accept the shot count as it comes from the factory (unless there is a proven way to make the rifle provide the same power and yield more shots). My P-rod gives a similar number of shots per fill, and I've been satisfied with it.

I should explain that I'm thinking of using a full shroud because it looks less conspicuous than hanging an LDC off the end of the barrel (though the overall length of the rifle seems about the same with either unit in place). It's just a personal preference, but I wanted to understand about free-floating the barrel.  
In the photos both the LDC and the shroud are made by Neil Clague. The LDC does a very effective job; I'm satisfied with it. But I like the subtle look of the shroud.

[Stefan]

but made like this, stock is connected to the action just by two screws?

[darryl]

I'll ask, to be certain. 

[rsterne]

Another route that has been tried is plugging some of the holes in the valve body.... There are 6 holes in a groove that collects the air and distributes it to the transfer port.... I tried plugging the bottom three holes (drilled and tapped to 6-32 and used setscrews), and the gun lost about 20 fps, but gained 5 shots within the 4% variation.... Then I tried plugging the next two, only leaving the top hole open.... The gun lost an additional 100 fps, but the shot count went to 40 shots within 4%.... These tests were done with 18.1 gr. JSB Heavies and with the hammer spring adjusted 2 turns out from the minimum setting.... Here is a photo of the valve with 3 holes plugged.... The testing below was done with the bottom (full power) valve stem (0.100")....



All holes open: 907 fps (33.1 FPE) avg. over 24 shots - 200 bar down to 130 bar - Efficiency 1.01 FPE/CI
3 holes plugged: 883 fps (31.3 FPE) avg. over 29 shots - 190 bar down to 120 bar - Efficiency 1.18 FPE/CI
5 holes plugged: 780 fps (24.5 FPE) avg. over 40 shots - 200 bar down to 125 bar - Efficiency 1.19 FPE/CI

You will note that the efficiency went UP when the holes were plugged.... I then drilled the remaining (top) hole out to 0.166" (the same as the transfer port).... and I made sure that it was exactly at the top when tightened.... At 3 turns out on the hammer preload I achieved 35.0 FPE with 18.1 gr. JSB Heavies, 35.5 FPE with 21 gr. Baracudas, and 37.1 FPE with 25.4 gr. JSB Monsters.... You could get about 25 shots within 4% of the maximum velocity filling to 200 bar and shooting down to 120 bar.... I could achieve similar power levels without the 5 holes being plugged.... but the shot count and efficiency were much less....

In summary, plugging the lower 3 holes increases the efficiency and flattens the shot string with minimal power loss.... Plugging the next 2 holes reduces the power but further flattens the shot string and increases the shot count.... Drilling out the remaining top hole brings the power back up to the original levels but with slightly greater efficiency, flatter shot string, and shot count.... For the optimum, I would plug the bottom 5 holes, and then drill out the top hole until I achieved the power level (and shot count) I desired....

Bob

[darryl]

Stephan I found out that the rifle in the full shroud did not have any of the cut-down bands in it. By I was told that the stock did  feel a bit flimsy without them. So I will assume that whatever I do with the rifle, I will keep the stock rigidity by using the bands (even if I cut them down, they will be in there for stiffness). Also I think I can get the barrel to be free-floating with the LDC on it. I'd take one band out and set it aside, untouched. The remaining band I would simply dremel some clearance between the band and the barrel. Then of course I'd check the stock for stiffness too.

Tomorrow I will do some field testing to see what sort of accuracy I can get out to 30~50 yards. Earlier today in my secret Man-cave I finally counted useful shots from a full air tank. By useful, I mean accurate as in a relatively small hole. Well, it got bigger, but I got 30 shots that could be covered with a nickel, but it was only 9.5 yards. Nothing to write home about, but I was looking to see when the POI would really start to move. Final pressure was a bit less than 100 bar. Of course out at longer distances the hole size is expected to open up because I still haven't found a better pellet yet, though it needs one. I think it will benefit from a heavier pellet too.

Bob which of the pellets in your graphs are the most accurate in your rifle? Also I've seen a post where someone actually placed an O-ring over the holes in that groove. It seemed a novel and simple idea, and I think there was some success. I don't recall where I saw it, but I think I'll try to search it out. But the work you've done is just fantastic! 40 shots from 200 bar down to 125 bar seems super efficient for this rifle (unless I'm reading it wrong). I'm sure your accuracy was also excellent. I don't think I'm able to reproduce what you've done, but I think some tweaking of the hammer spring might be in order. A little less air wasted can't be a bad thing.  nicely done.
darryl  

darryl

[rsterne]

I had good success with 18.1 gr. JSB Heavies.... I think 21 gr. Baracuda/Kodiaks were quite good as well.... I only had the gun for a short time to experiment on.... Once "tuned" it was returned to it's owner....

Bob

[Ribbonstone]

Did get around to trying a new transfer port, but will have to wait for daylight to chronograph.

Factory transfer port has a great big passageway for air. Best measure is .165”.  Would be a good size for a .22 or .25, not so good for a .177.


Decided to make a replacement from Delrin.  The original is a loose fit in the recesses, relying on o-rings for sealing.  Had good luck doing away with the o-rings on Crosman transfer ports (P-Rod and 1700) so thought I;d give it a try here.  

SIZE CHANGED from the original.  Made this one a tighter fit to the recesses (the hole in the valve and the hole in the breech).  Made it to the length of the original PLUS the o-ring. Not my prettiest job, but it seems to work.


Once you get it made, will cup the ends. That seems to allow for some compression to take the place of the o-rings, which seals the transfer port at the ends.  No leaks I can detect


Night lighting system for the chronograph is hosed, and there isn't time to make a new one tonight. Never did get totally reliable velocity  readings at night, so its a small loss.  

SUBJECTIVE: its a bit quieter, and point of impact at 20 yards is good for 40 serious shots.  Doesn't sound all that much quieter...but am shooting at night when the background noise of the world is at its lowest so that's not a sure-fire indication.

Did manage the following 40 shots with one fill.


Not expecting too much, .11” (7/64ths) is still pretty large for a .177 transfer port, but it is enough smaller than .165” that there should be a difference.


TAKE A GUESS.  Cannot chronograph this eventing, but will do so tomorrow(am on call, but will find out tomorrow AM unless called out to work):

CLUE#1: used as much air getting those 40 shots as it use to use getting 30 18.7 foot pound shots.  So with that proportion of air being “saved”, will the per shot energy decrease in the same proportion?

CLUE #2: (not so good). Am pretty certain the air use has changed...it picked up a "ping" it didn't have before.  In a way, that does indicate that air use has changed...but if this setting works out, will have to go in and make de-pinging.

Did reshoot the 8.4gr. JSB's thinking those groups might have been freaks.  Only 20 yards, and I did set the scope closer to POA:

[Stefan]

I did expect to hear that without bands stock would be flimsy, because the heaviest part of the rifle wouldn't be connected to the stock. If you are up to free floating, what you said - cutting one band in half is the solution - the air cylinder must be tight with the stock, somehow. Maybe a custom made band, also with o ring inside? and shrouded barrel, she'll free float. And if you use LDC, remove the o ring that's placed in front of the front sight, that o ring can cause a problem-LDC won't seat in just right and straight, so it can affect accuracy.
Nice work with that TP, let us know chrony results asap
My drop in regulator for hatsan got shipped two days ago, I am impatiently waiting for it to arrive, I hope I'll get some nice results with it. Its set at 125 bar, Bob can you predict what velocity I might get with that setting, using 14.43 gr pellets?
Speaking of pellets, my at44 seems to love those 18,1 gr JSB, and 13.43 gr JSB as well. And cpum is shooting pretty decent out of it.

[darryl]

Bob, that's excellent work. Will there be a tutorial on how to do this once you're satisfied or met your goals? Those JSBs seem to like your efflrts very much!

Stephan, that's my plan: to modify and use only one band. It will be cut down to only support the air cylinder, but not touch the barrel. I'm assuming I can do this, and have  not taken the rifle apart to be certain. At a glance it seems doable. Looking at Bob's graph may give you a ball park figure on where your velocities might be with your regulator. But I'd like to see the testing results once you get it installed.

[rsterne]

Will there be a tutorial on how to do this once you're satisfied or met your goals?

I was working on a gun for a friend.... it's back in his hands.... The version with the 5 plugged holes and the drilled out top hole, and 3 turns out on the hammer preload, was how I left it for him.... I don't have any plans for an AT44 in the near future.... but if I did, I would buy the AT44-S10.... It's the lightest repeater they make at 7 lbs....

Bob

[rsterne]

Its set at 125 bar, Bob can you predict what velocity I might get with that setting, using 14.43 gr pellets?

Sorry I missed this question.... The stock gun shot about 900 fps with 14.3 gr. pellets at 125 bar, as you can see from the graph.... The inlet side of the valve is relatively restricted, but I'm sure it does get some flow from the air reservoir during the shot cycle.... That would mean that once you install a regulator, the average pressure will likely be a bit lower, dropping the velocity a bit.... Just a WAG of course....

Bob

[Ribbonstone]

Tested the .11" port this AM.  Not looking for power (have several 5mm/.22/and a .25...if looking for power, a .177 isn't the place to look).

 The thing I have  to remember about the transfer port is that the passage is a circle so the area changes quite a bit with a small change in drill size.  The original port was .165”, which works out to something like .0214 square inches.  The new .11” port works out to  .0095 square inches.  A good bit less than ½ the area.

Test #1:  .165” port
11.6gr. Pellets : (still using the crappy shooting pellets for shot strings)
fill to 2300 – 1250psi
831
835
832
835
837
836
842
844
848
848
858
859
860
860
860
863
861
863
865
970
870
869
866
864
861
856
851
844
856
844
841
837
831

30fps = 870-840 = 25 shots
20fps = 870- 850 = 17 shots
Average energy:19 foot pounds
Real world use: fill to 150BAR/2200psi, shoot 20 shots, refill.

TEST #2: .11” port
Same pellets/fill pressure:

750
758
762
760
766
765
763
766
765
768
775
774
773
781
779
778
779
781
786
778
778
783
788
785
789
789
785
780
785
780
780
787
786
787
775
780
776
775
774
771
774
769
772
765
759
755
740
740

789-759 = 30fps = 45shots
789-769 = 20fps = 35shots
 average energy = 15.3 foot pounds
real world use: fill to 150BAR/2200psi, shoot 40 shots, refill.

The BAR/CC air efficiency didn't change all that much (still crappy).  Going to take some changes in the valve cycle to really get that to change (and that may be where shutting off some of those valve ports would pay off).

Using that 150BAR fill, there is lots of room to go up in pressure...go up in striker spring tension...and end up with more energy per shot.  Not really the direction I want to go, but it would probably be the one most owners would want.

One more fill this AM...will do 8 5-shot targets. Looking for POI wandering as well as short range (20yard) grouping.


Needs a touch of left windage, but left the groups forming high so I'd not blow the aim point to *(&^. Think I can live happy at this setting.

[rsterne]

Nice change, it really shows what choking up the transfer port can do for shot count and the flatness of the string.... You went from a "real world" of 20 shots at 19 FPE (380 FPE) to 40 shots at 15 FPE (600 FPE).... It looks to me (using Lloyd's calculator over the whole string) that your efficiency went from 0.79 FPE/CI to 0.98 FPE/CI.... That's a pretty good increase....

It would be interesting to see what plugging 5 holes in the valve would do, without drilling out the top hole.... I have a feeling you might not lose much/any velocity and pick up more shots and an even flatter string and higher efficiency.... With the ports strangled you may find that increasing the hammer hit may not gain much velocity at the peak, but give you more shots at the high pressure end (ie a flatter, longer string again).... Keep us posted....

Bob