Air rifle tuning / AT44-10 / fitting a regulator

[TheTurn]

Hi all - I know this is an old thread, but recently got around to tuning an AT44-10 (tac) that landed on my dirty white towel (work area).
Out of the box, the UK spec AT44-10 performed rather poorly, but accuracy wasn't at all bad, so I decided it may be worth a tinker.
See pic 1 for 'out of the box' 200 bar (rifle gauge) to approx 95 bar shot string. https://image.ibb.co/cS7OQp/Screensh...0048_Excel.jpg
As with many air rifles designed to be Fire arms certificate (FAC over 12 ft/lb - 16 joule) rated in U.K., the transfer port was this size of an asthmatics bronchial tube, mid attack - 1.5mm dia as best I could measure it.
I opened this to 2.0mm, since I was 'between lathes' and couldn't readily make another / am too tight to buy them.
I repeated my shot string, initially filling to a (rifle gauge) indicated 200bar I quickly realised the 'sweet spot had shifted, and the rifle could now be filled to an indicated 155ish bar, give more (consistent) shots for less air down to approx 95 bar.
See pic 2, 200 bar rifle gauge fill and 3 (155bar fill - note 40 shots over 11 ft/lb) https://image.ibb.co/ggZ3Qp/Screensh...0142_Excel.jpg https://image.ibb.co/gDCCJ9/Screensh...1607_Excel.jpg
This rifle was begging to be regulated, and I had found a guy on (in Lithuania) who was selling regs for $65 (or best offer) posted. I bid $60 (did I mention I'm tight?) and got one, which incidentally arrived very quickly.
The instructions were sketchy (no pun intended) but anyone with any experience tuning (messing) with air rifles would not struggle. I had asked the reg be set to 95 bar. The only nagging question I had, I had already asked the seller "Are these for FAC rifles?" hit the language barrier, The reason I wanted to know was the plenum chamber (the low pressure chamber side) of the reg seemed cavernous for 12 ft/lb / 16 joule. The seller recommended removing the knock open valve end large o ring to allow the reg to recover (breathe) more on that later - please remind me if I forget!.
See pic 4 of reg. (God, I hope they all upload!) I have to say the reg is well made. https://image.ibb.co/bUFA5p/Screensh...2054_e_Bay.jpg
I fit the reg within minutes, literally by unscrewing the brass cylinder plug (AFTER EMPTYING THE CYLINDER TO NOTHING) sliding the reg in place, making sure reg vent hole is upwards so lubricant isn't all blown out during use, and replaced the brass plug / knock open valve assy. Filled cyl to 50 bar, waited (held air) to 100, waited, then to 150. Reassembled rifle, after taking transfer port to 2.5mm. First shots were well hot, so backed off hammer spring until 777 fps (JSB exact, 8.44 4.52mm) achieved. Filled to 200 bar (indicated on fill bottle this time, rifle gauge indicated approx 210 bar) took rifle to my club, and did a shot string of 120 shots.
See pic 5, 210bar (rifle gauge) to approx 70bar (again, rifle gauge) https://image.ibb.co/jP7q5p/Screensh...4128_Excel.jpg
This string showed me the rifle was getting nearer to it's U.K potential. The rifle was very, very accurate (I compare all tests with my Steyr LG110), repeatedly hitting 20mm spinners at 60 yards (yes, we use metric and imperial as it suits us)
The string showed me the rifle had a reg pressure, and hammer tension a tad high. The transfer [port also needed opening up (to 4mm)
I will post the results of these final mods shortly, when I figure a way of reducing that plenum volume (approx 850mm2 or 1.3 cu inches) without wrecking the reg stand off tube (plenum).
As I suspected earlier this is too big for a sub 12 ft/lb - 16 joule rifle.
More to follow.
Hope I uploaded this O.K. - first try!.

[thisisdonald]

I Tuned one of these a couple years ago, following instructions found on the USA yellow forum. My rifle came to me in a sorry sorry state. Someone had bored out the transfer port and messed with the anti tamper without actually removing the rod. I can't remember exactly what sizes I used, but I made a new transfer port , 3mm I think, tapped and plugged all but one of the breather holes on the brass nut thingy, and JB welded all the plugged holes. I then turned back the shoulder, so that when screwed in, the remaining breather hole lined up perfectly with the transfer port.
The result was loads more shots and a predictable curve, also very consistent with about 6fps spread in the sweet spot. Mine was in .22 and was also really accurate. Lovely gun, but really front heavy. I sold it to a lad that I believe bullpupped it.

[peddy]

Sounds like you had fun, it's great when a plan comes together! As much as I like Turkish guns I gave up with the at 44 after two guns that were too pellet fussy and poorly made. When folk compare them with their Webley cousins they have clearly not owned both.