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Air Arms TX200 Mk3, LH Walnut

Discussion in 'Gun Gallery' started by cloverleaf, Dec 25, 2017.

  1. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    A very slow burner this, having been a constant "work in progress" since it was bought maybe 4-5yrs ago.

    Having got back into the sport I decided I needed a decent springer, the obvious choice being the TX200. I'd resolved to buy a new (LH Walnut) example, however one with a fantastic looking stock came up on the BBQ so I bought that instead.

    After lots of grilling of the seller to ascertain that the gun was truely as mint as he claimed, money was sent and the package arrived. Needless to say, thanks to a combination of my OCD / powers of observation and the seller's failing eyesight / economy with the truth, the gun was a disappointment. There were marks on the action where it'd been stripped previously by someone lacking in the required level of mechanical sympathy, while the stock had a few light dings.. but the grain was fantastic.

    Haggling ensued and the seller agreed to refund me some money. I bought a new replacement, swapped the old action into the new stock and sold it on (with full disclosure of course!) - leaving me with a brand new action in the slightly-dinged but certainly recoverable and beautifully-grained stock. A Panorama was lashed to the top courtesy of a fully-adjustable B-Square mount, bringing us to the point illustrated below:





    Thanks to the woodwork and nearly flawless bluing the rifle looked fantastic. Unfortunately it shot like a bag of sh*te though; courtesy of the Mk3's longer stroke and lower rate spring which I found slow, lazy, unpredictable and unforgiving. Somewhat like it's owner I suppose...

    The purchase of a proper Mk2 some time later in the year and their subsequent comparison really drove home to me how horrible the Mk3 setup is, so the quest was on to short-stroke the rifle.

    I decided to modify a standard Mk3 piston (or rather have a grown-up mod one for me) to allow alteration of its stroke. A piston was sourced, its latch rod annealed before being cut in two with both ends drilled and tapped to take a threaded spacer-piece to increase its length and shorten the stroke. I'm not a fan of the way the rod is retained in the piston body - a plain thread that relies on locking compound rather than any additional mechanical means to prevent bits moving and offers no positive register to promote concentricity once the bits are assembled. In addition the thread was apparently p****d, so it was drilled out and replaced with a properly-aligned thread insert.

    I also had the standard dovetail / wedge-shaped piston seal mount machined off; to be replaced by a separate mount to take an HW-format 25mm piston seal. This yielded two advantages - firstly it got rid of the Air Arms seal, which is crap for a number of reasons. The standard items are usually poorly finished, over-sized and very difficult to re-size on account of their material and geometry - which means they deflect easily and are difficult to prevent spinning on the piston when trying to re-size.

    The second advantage is that the HW piston adaptor screws onto the now-exposed end of the latch rod, tightening down against the piston body and acting as a locking nut - giving a more positive mechanical fitting that holds the rod in better alignment. The modified piston setup and associated bits are shown below:

    The original Mk3 piston and rod - disassembly being fairly straightforward once the retaining compound had been softened with a fair bit of heat:



    Rod after modification, along with threaded insert:


    The sear end was rounded and polished to promote smooth operation:


    The modified piston body with seal mount removed and thread insert fitted:


    The new HW-format seal mount / lock nut fitted to the piston assembly. The piston body was also polished a bit as the original finish was crap with evidence of a lot of tool chatter near the rear..


    The nut / seal mount and Vortek HW-fitment 25mm seal:


    Seals - L-R: Air Arms OEM, Vortek HW fitment, HW OEM (now old-type and obsolete since HW no longer make 25mm seals). Note the different effective lengths / thicknesses at 6.5mm, 9.0mm and 9.5mm respectively. Since the face against which the rear of the seal locates on the piston is in the same place for all three the deeper HW seals reduce piston stroke by a corresponding amount to their increased depth. So, for a standard Mk2 setup the OEM seal will give the usual 82mm stroke, the Vortek seal a 79.5mm stroke and the HW OEM a 79.0mm stroke.


    The complete piston assembly, minus seal and bearings:


    ... and with Vortek seal fitted:


    Unfortunately despite all this shiny goodness, this experiment didn't go at all according to plan for a number of reasons:

    1. I was aiming for an initial stroke of 75mm, however I evidently didn't do my sums right and actually ended up with about 68mm.
    2. The lovely, re-profiled and polished end to the latch rod made sear engagement "late" and safety operation intermittent.
    3. I struggled to re-harden the end of the rod (which I've since found out is probably Nitrided - a surface treatement - rather than through-hardened, which would be why!)
    4. This was before I had a lot of experience with springers and didn't understand the importance of piston seal fit; which retrospectivly was too tight.

    The upshot of all this was that the rifle didn't operate as I'd like (on account of the re-profiled rod) and while probably safe, was a bit of a worry with respect to component wear since I'd failed to re-harden the rod and it was marking slightly where the sear engaged. On top of this the gun was only making around 9.5ftlb (no matter how much spring energy I put in) due to the excessively short stroke and piston seal drag. I did learn a bit about the effect of piston mass and input energy by playing with spacers, however this is only of limited value given the reduced output and less-than-favourable operating conditions.

    The gun was re-assembled with the original piston and put back in the cupboard. In the interim I did score a NOS Mk2 piston from Chambers, however never got around to fitting it due to its less-than-favourable piston seal setup..



    Fast-forward a few years and I found myself in possession of an ISP-manufactured Mk2-spec latch rod, having been left in the lurch by a bloke who wanted me to short-stroke his Mk3 for him :rolleyes:

    Knowing the modified piston was languishing in the goodies-box, unuseable on account of its soft, overly-long and poorly-modified rod, I figured I'd swap in the Mk2-spec rod and have another crack at short-stroking the rifle.

    Below is the modified piston body fitted with ISP Mk2 spec rod and (red) Vortex seal, next to the standard Mk3 piston and (purple/blue) Apex seal that came out of the gun:



    Air Arms springs and guides are usually pretty good so I elected to use new Mk2-spec parts in conjunction with a lightweight custom Acetal front guide from V-mach. This is shown in the image below (bottom) next to the standard longer, lower-rate Mk3 spring and .22 piston weight (which is shorter and lighter than the .177 item but still a right porker):


    As has now been established as par for the course this all went bloody wrong too. Having now learnt the importance of piston seal fit, the Vortek seal was sized down by de-greasing and sellotaping to the piston (no expense spared here!), spinning in a drill and taking back the OD with abrasives and files. The material itself worked beautifully; cleaning up nicely with a coarse-ish file and giving a nice surface finish that was hard to distinguish from original.

    Unfortunately through sizing I discovered that the bore of the compression tube on the gun has a slight taper, opening up towards the front end. This meant that while my sized seal felt pretty much perfect (maybe a touch undersized) at the entrance to the tube, at the front it was pretty slack. The gun was hopefully lashed back together and tested - the first shot yielding 11.5ftlb with plenty of dieselling, but quickly falling to sub-9ftlb on account of the seal's poor fit :eek:

    To add insult to injury I also found that the profile of the Mk2 piston rod didn't work well with the Mk3's trigger assembly - failing to engage the safety upon cocking, as covered in more depth here.

    Continued in next post due to image quantity limits...
    Last edited: Dec 25, 2017
  2. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

    Likes Received:

    In an effort to further understand the issue with the trigger / latch rod / safety, I removed the trigger cassette from the end block - no small feat as the pins were bloody tight. When they eventually relinquished their position I thought I might as well have a go at the sears as the trigger felt pretty gritty and I didn't fancy the hassle / risk of damage in attempting to strip the assy again in future.

    The trigger unit removed from the end block:


    Sadly upon stripping the unit I was less than impressed by what I found inside.. for a start everything was covered in thick, sticky oil:


    The sears appear to be drop-forged and were pretty bloody rough; both in shape and finish. Below is the bottom sear after a bit of a clean; viewed from the underside and showing the pocket for the trigger weight adjustment screw (top of image), as well as the surface engaged by the trigger screws during operation. Finish in this area is rough, which was probably responsible for the gritty feel of the trigger during the first stage pull:


    The same unit viewed from the top, showing significant nicks out of the surfaces / edge that engages the middle sear:


    The middle sear:


    .. the important bits of which were also rough as arseholes :rolleyes: :


    Thankfully the top sear was a bit better - somewhat rough where it engages the middle sear at its rear:


    ..and showing some light damage / wear at the front where it engages the piston rod:


    As we all know "less is more" when it comes to trigger work so I restricted myself to improving surfaces finishes by working the parts on some wet and dry paper atop a flat piece of granite. Damage at the edges of the sears was that significant that removing enough material to properly redress this would have probably rendered the trigger inoperable, so I did the best I could with what I had.

    The underside of the bottom sear polished..


    ..along with its upper mating surface with the middle sear:


    The corresponding surface on the middle sear:


    The front face of the middle sear (that rides over top sear during cocking and firing) was also tidied a bit..


    ..as was the rear face that contacts the safety, in the interest of slicker safety operation:


    The rear of the top sear, that engages the middle sear:


    The finish on the two bosses in the unit was also p**s-poor, so these were tidied as best as possible without removing too much material. Before (L) and after:


    The trigger screws were just about the only bits that had a decent finish out of the box, so at least that was one less job...


    Bits arranged on top of the housing in the cocked position to illustrate operation (Note the trigger weight adjustment screw is not present):


    As per this thread again, I did discover that AA are apparently now manufacturing a Mk3 friendly piston with the 82mm Mk2 stroke so bought one and planned to drop it straight in, in light of the failings of the modified piston.

    I swapped over the Apex seal from the original Mk3 piston and chucked it all in with the Mk2 spring and guide.. while it physically worked I remained unconvinced by the tight piston seal, while the spring was uncharacteristically giving a bit of twang on firing and the cocking stroke was (as it always has been) pretty rough. Upon pulling the gun to bits again, I discovered a lot of roughness inside the main cylinder where some d******d has apparently de-burred the three arrestor stud holes in the cylinder during assembly with the roughest file known to man :rolleyes:

    This had lightly scored the rear of the comp tube, so that was polished to remove the worst. Ideally I'd sort the inside of the tube with a hone, however that won't work due to all the slots in the tube - would no doubt make the rifles a lot nicer if this was done at the factory, however given the state of the rest of the gun I don't think this is ever likely to happen. Looks like a bit of wet and dry on a stick it is, then :down:

    So.. that pretty much brings us to where we are now. I'm legitimately p****d off about the state of the main cylinder, although hopefully this can be overcome. The excessively-sized seal found a new home in an HW77 I was doing for someone, in which it fitted perfectly and gave excellent efficiency figures. I can't tolerate the sh*te standard-format piston seals so current thinking is to rob the latch rod from the new, shorter-stroke AA piston and fit it to the modified one; allowing me to use better, properly-sized HW-spec Vortek seals at 79.5mm stroke.

    For the time being that will all have to wait until the crap finish inside the main cylinder has been addressed, though...

    As nice as it looks and as good as AA products usually are, this one's turned out to be a bit of a dog if I'm honest - granted I'd cocked a few things up along the way, although if the gun ran a decent stroke from the off and wasn't suffering from such glaring QC issues I'd hardly have had to have touched it. Quite frankly it's p**s-poor that a new gun should need so much remedial work to shoot acceptably and unfortunately I think things have only got worse (for everyone, not AA specifically) in the four-plus years since this one was pushed out of the factory door.

    Will update the thread as and when I get the chance to have another go at the b*stard thing - unfortunately I seem be be up to my eyeballs in shagged old AA guns atm :rolleyes:
    Last edited: Dec 25, 2017
  3. Kevin2306

    Kevin2306 Donator

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    Very interesting read. The grain in the stock is stunning.

  4. Farty

    Farty Totty GURU

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    Ace Cloverleaf :up:
    Last edited: Dec 25, 2017
  5. greyskull

    greyskull Busy Member

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    Thanks Cloverleaf,
    Another great thread, and brilliant detailed piccies as usual :thumb:
  6. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Cheers guys :)
  7. The Robin

    The Robin Super Moderator Staff Member Mod/Admin

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    Interesting reading as always Mike, hang in there because I'm sure you will master it and get it running right :up:
  8. Ganton Gunner

    Ganton Gunner Super Moderator Staff Member Mod/Admin

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    Ganton scarborough
    not too bad looking.
    hopefully when you get chance you will take some 1/2 decent pics of it.
  9. Blackmax

    Blackmax Forum Rude Guy

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    As always, interesting read, nice gun and a bit of genius, shame about the crap fish scale stock, why have they done it!
  10. Roundshot

    Roundshot Engaging Member

    Likes Received:
    Much enjoyed as ever, now looking forward to a satisfactory conclusion for you.

    Prettiest looking TX I've ever set eyes upon. Pity the hidden woes.

    I well recall your excellent Mk2 vs Mk3 thread. It was a factor in my sourcing a Mk2 TX and having done so, an averagely good condition 1995 .22", I sold my HC.
  11. mikeyhall1

    mikeyhall1 2018 & 2019 Forum Nice Guy

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    Chelmsford/Upminster - Essex
    Interesting read Mike, thank you.
  12. Black country sniper

    Black country sniper Busy Member

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    What a interesting read im thinking of purchasing one of these rifles in the near future.
  13. AJ Roberts

    AJ Roberts Engaging Member

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    That stock is beautiful :up:

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