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Air Arms S400 Ultimate Lashup Mk2

Discussion in 'Gun Gallery' started by cloverleaf, Jan 30, 2018.

  1. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    This one's been a long time in the pipeline, being made up mostly of bits I've slowly been acquiring over the years.

    It's basically just an S400 MPR action in an Ultimate Sporter stock; built mostly from new parts, some used bits as well as a few items scavenged from a tatty donor rifle.

    Building the gun up in this way has brought several advantages, including:

    Pre-AT spec:
    Few if any MPRs were made in true pre-AT spec, i.e. with all six action bolts M3 size and passing downward through the action block. I much prefer the pre-AT setup as it's nicer from an engineering perspective, easier to work on and looks better.

    Ability to mix and match parts: I've selected the best bits from those that have been fitted over the lifetime of the 400 series; without having to replace / duplicate any parts.

    Fewer nasty surprises: The fact that most of the parts haven't already been assembled by someone else means far less likelihood that they've f*cked something up for you -meaning no over-tightened fixings, poorly-fitted parts, damage, anti-tamper to remove or ridiculous amounts of loctite :)

    Known quality and less chance of damage:
    Since the base rifle for this build (S400 MPR FT) is no longer made, going used would be the only option - meaning all the usual potential pitfalls of buying second hand. Sadly sometimes spares aren't right either - but in this case they can go back for replacement!


    I suppose the next question to answer is "why build it when you can buy it?" Echoing the above, an MPR would be AT-spec, a used purchase only and would include a stock I had no use for. Alternatively an HFT500 could be bought new, however it's not available in true-left-hand format and again has the dreaded anti-tamper, so (otherwise nice as it is) no thanks, tbqfh.

    Anyway, on to the assembly. I've documented the process in the hope that some might find the thread a bit more interesting than had I just slung up an image or two of the finished rifle. Assembling the gun from bits would probably have taken 2-3hrs, but was more like double that with the camera work factored in.. not to mention the editing; but I digress!


    The first job was to assemble the exhaust valve and pressure gauge assemblies - the parts of which can be seen below. Please forgive the location of the port adjuster grub screw and cover bolt above the exhaust valve housing - they're not in the correct place for an exploded view, but I'd run out of space underneath. The exhaust valve's stem was polished prior to fitting.

    [​IMG]


    I made a half-arsed effort to polish the ends of the exhaust valve return spring by chucking it in a drill and pressing it against some wet and dry on a flat plate. Tbh I'm dubious of the benefits of such work, got bored and gave up before the ends were perfectly polished and any remaining will to live had finally ebbed away:

    [​IMG]


    The exhaust valve return spring seat was a late-ish revision to the 400 series, as is the larger diameter hole in the valve pot to accommodate it. This gives more clearance around the return spring's OD and prevents its oscillations abrading the inside of the pot over time. Evidence of this can often be seen on earlier guns in the form of brass particles embedded in the sealing face of the exhaust valve..

    [​IMG]


    Valve pot retaining grub screw and nylon ball - again another revision to the original design. Earlier S400 series guns used a plain M3 grub screw that impinged directly on the thread of the valve pot to hold it in position; which often led to damage - especially if the screw was over-tightened. The nylon ball used in the later setup acts to separate the M4 grub screw from the pot's threads; preventing damage.

    [​IMG]


    The transfer port adjuster grub screw and correct M3x4mm socket cap cover bolt. Note the blue locking compound on the grub screw; which serves to prevent both screw movement and air leakage during firing:

    [​IMG]


    Pressure gauge mount ("dogleg") and gauge. Several gauges were tried to find that which tightened to the most appropriate orientation (upright with the rifle held muzzle-up) - this one tightened to maybe 15 degrees past the ideal position, but it seals with no issues once backed off a touch and won't be going anywhere once the gun is pressurised:

    [​IMG]


    The built exhaust valve and pressure gauge assemblies - I should have fitted the (absent) fat cylinder O-ring before the gauge mount; which had to be removed after the photo to allow the O-ring to be added..

    [​IMG]


    The current-spec inlet valve assy was bought as a complete "upgrade kit" - which at around £46 costs about 35-40% less than buying the included parts separately..

    [​IMG]


    The kit contains a complete inlet valve assembly including the housing, valve pintle and spring, valve body, end cap and all O-rings. The O-rings came fitted and I wasn't going to risk damaging anything by removing them for the photos, so they're mostly shown in-situ:

    [​IMG]


    The fill adaptor was also included in the kit:

    [​IMG]


    The completed inlet valve assembly:

    [​IMG]


    Valve assemblies and cylinder, which is a scratched item I had kicking about that was included in a re-blue job I sent to Colin Malloy ages ago..

    [​IMG]


    Valve assemblies fitted:

    [​IMG]


    System pressurised to 100bar - no leaks :)

    [​IMG]


    On to the striker setup - the bare striker body after a bit of a cleanup.. the finish on these seems to vary a lot; some tidy, some not.. some media-blasted, some apparently straight out of the machine as this one seems to be:

    [​IMG]


    Two PTFE-impregnated plain striker bearings - these are a standard, off-the-shelf universal part:

    [​IMG]


    Striker after bearings had been pressed in using a vice (with padded jaws) and a light smear of oil. The fit was a bit tighter than expected but no big deal..

    [​IMG]


    (continued in next post ;) )
     
    Last edited: Feb 19, 2018
  2. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    (...continued)

    An adjustable MPR trigger blade assy was sourced..

    full.jpg


    ..and fitted to the existing trigger assembly - which is a "middling" three-sear unit. This is significantly better than the earlier two-sear units as it gives more definition between first and second stages - meaning more positive operation and much less chance of accidentally pulling straight through the 2nd stage.

    The later trigger assembly (as fitted to F-spec guns) is superior in that the housing contains bosses which space the sears away from its back face, while the cover plate has similar, deeper bosses to control side-float in place of the O-rings used on earlier models. These mods reduce drag in operation; making the trigger a touch more slick and consistent, while also reducing the minimum pull weight at which it will reliably function. Unfortunately the later F-spec unit won't fit the earlier pre-AT striker housing as the rads on its top corners foul the un-radiussed edges on the underside of the housing.

    The function of the bosses in the later unit can be replicated by adding shims beneath the sears on the earlier trigger and replacing the O-rings on the sears with solid spacers. Also, the hemispherical ends of the adjustment screws in the trigger blade were left as-received as their finish wasn't bad and I couldn't be arsed to take them out and polish them. These mods might happen in future but is a bit of a pain to sort out and the trigger feels pretty good as it is, so can stay stock for now.

    Aesthetically I don't really like the angle of the blade / post, but it does the job and looks better with the gun assembled. The assembly below is shown in the cocked position; the grey stuff is powdered graphite for lubrication:

    full.jpg


    Trigger housing side plate fitted - note the button head retaining bolts. These are the same size as that used as a cover bolt at the transfer port and much preferred to the standard BZP slot / cheese head offerings that are fitted as standard - both on aesthetic and functional grounds:

    full.jpg


    The striker housing in isolation, with the loading bolt orientation bias pin in the correct place to allow left-handed operation. This pin should be 15.8mm long but was replaced with an 11.8mm long alternative in the interest of potential future removal as they can sometimes be a sod to get out and the pin's fit in the hole gives sufficient friction to stop it going anywhere..

    full.jpg


    Elements of the striker housing and trigger group ready to go together:

    full.jpg


    This point is where another b*llock was dropped. I'd ordered a later (but pre-F-spec) trigger guard for this project, however it was out of stock so I elected to use an earlier one I had kicking about. While they might outwardly look similar (earlier model top, later bottom)...

    full.jpg


    ... the later unit has a longer slot in its upper surface to accommodate the longer, later trigger blades, as well as a cutout for the much-hated trigger safety button. Unfortunately the slot in the earlier guard (top) is too short to work with the MPR blade assy. Note also the additional hole in the top of the newer guard to take a location pin; which may or may not be added in the future as they can make the guard a bit of a swine to remove.

    full.jpg


    In addition the trigger shoe in the MPR blade assembly is too wide to fit through the slot (its clamp-bolt fouls the slot) so a bit of contortion is required to fit the blade to the post while the guard is being fitted to the gun. Because I wanted the project built, a correctly-specced guard was pinched off another rifle for the time being. All the bits assembled:

    full.jpg


    A new polished striker guide rod was fitted to the rear of the exhaust valve housing with a sparing application of retaining compound (sorry no pics of this specifically as they came out crap). The image below shows the assembled trigger / striker sub-assembly, striker components (spring seat, spring, pre-load spacer, striker) and exhaust valve housing / guide rail assy; ready to go together. Like a tit I forgot to include the bolt in shot that holds the striker housing onto the end of the guide rod..

    full.jpg


    Everything assembled:

    full.jpg


    The last sub-assembly to go together was the breech block / barrel; again the exploded arrangement below isn't strictly accurate, however positioning the bolt assy in the correct place behind the block would have meant they didn't fit in shot so well.

    Prior to fitting the loading bolt handle was heated with a propane torch to allow its handle to be rotated by 180 degrees inside its boss for correct left-handed operation. Also the loading bolt shank was polished - the visible tip is the only bit that gets close to mirror-finished with Autosol; everything else I polish (bolt shank, valve stem, striker rod) with 600 grit wet and dry as it's less hassle and gives no discernible difference in operation. Yes, I'm aware that the two barrel retaining grub screws have a different tip profile (they were supplied like this) - they'll be getting replaced in due course.

    full.jpg


    As always the finish on the loading bolt cocking dog spacer was crap, so it was polished (the head of the bolt is already reduced in diameter and polished out of the box):

    full.jpg


    The breech block assy finished:

    full.jpg


    I'd planned to fit an over-sized FAC barrel band to this rifle to allow the barrel to float (as on my other MPR-based rifle), however unfortunately as the barrel has a noticeable amount of "droop" (causing the gap between it and the cylinder to taper along the length of the gun) there was insufficient clearance with the band.. so it was replaced with a blanking piece from an HFT500 (without the rubber buffer) - allowing the barrel to float correctly:

    full.jpg


    By this point it was getting late so I didn't get any shots of the fitting of the block to the action; which was just a case of fitting the transfer port seal and bolting the block on with 6xM3 bolts. The stock and scope were then added (which had previously been fitted to my right-handed, standard S400-based "Lashup Mk1"), leaving the more-or-less finished product:

    full.jpg

    full.jpg

    full.jpg


    The gun has been set up to produce around 11.3ftlb at 150bar with 8.44gn Exacts, so should be nicely legal with anything else put through it.

    So there we go. I'm generally happy with it so far, although it's not perfect and some things still need addressing. I still need to sort the trigger guard and might do a few tweaks to the trigger setup in future. The finish on the cylinder isn't perfect either so this might get replaced in future; however this means a lottery with where the etching ends up with respect to the gun - which could potentially make it look more untidy.

    I'm not particularly happy about the minimal / tapering clearance between the barrel and cylinder although there's not a lot I can do about this - other than adding some shim beneath the front of the breech block perhaps. I'd like to add a mod as I hate the farty muzzle report of these rifles, however nothing (that I consider acceptable) off the shelf fits the 14mm MPR barrel.

    In addition I need to be careful given the lack of barrel band (in case the mod gets tw*tted on something) and already minimal clearance at the front - which might disappear completely if I hang something heavy off the front. I'd also considered fitting a longer HFT500 cylinder in the past, but I think this is now probably off the menu on clearance grounds.

    Finally the loading bolt handle jumps a little on firing - I suspect because I've polished the bolt dog spacer - it's reduced diameter and better finish meaning it isn't retained in position by friction.. I'll see if there's any end-float in the bolt and if not might consider fitting a heavier brass bolt handle to combat this issue - tbh the existing one is a little tatty and lets the gun down somewhat IMO.

    That's all for now - it'll be going up the club later for a shakedown and I'll update the thread as and when, if anyone's interested :)
     
    Last edited: Feb 19, 2018
  3. The Robin

    The Robin Super Moderator Staff Member Mod/Admin

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    I'm loving this thread, very interesting reading and the pics are always mega :up:
     
  4. TrickyDicky

    TrickyDicky Life in the slow lane

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    Thanks for the write-up, it has given me an insight into the way the hammer and valve are orientated, never owned an Air arms, and I was curious as a friend has asked me about making and fitting an SSG for him.
     
  5. mikeyhall1

    mikeyhall1 2018 & 2019 Forum Nice Guy

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    A great read and amazing pics as always Mike! I’m
     
  6. PumpnGun

    PumpnGun Donator

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    Always enjoy reading your posts Mike, you have great skills and I admire them, can I ask what an F spec rifle is please...

    Ray
     
  7. mikeyhall1

    mikeyhall1 2018 & 2019 Forum Nice Guy

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    i believe it means full spec performance Ray
     
  8. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Cheers guys :)

    I don't think anyone really knows for sure what the "F" suffix applied to later 400 series guns denotes (although I can suggest something on account of how much fun the AT can be to remove :rolleyes:) however the S400F and S410F appeared after serial number 100000 or threabouts; these later guns differing from earlier ones in a number of ways - namely:

    - A revised aesthetic to many parts including fluting on the filler cap, loading bolt handle, barrel support and breech block
    - An extended, circular-section barrel support at the front of the breech block where the barrel is fitted
    - Revised method of attaching the breech block, with all bolts now fitted from underneath rather than four from above and two from underneath, bolts now hidden
    - A revised trigger assy with internal bosses upon which the sears run, different housing and guard geometries with the weight adj. spring and screw in the housing
    - Revised etching / branding on the block
    - Improved surface finish on many parts

    There might be a few more but this is it in a nutshell :)
     
    Last edited: Jan 31, 2018
  9. PumpnGun

    PumpnGun Donator

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    Thanks Mike, tremendous knowledge :cool:

    Ray
     
  10. FerreT985

    FerreT985 Engaging Member

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    Brilliant write up.
    I'm glad there are pictures or I wouldn't have been able to follow most of it. Encourages me to fit my own regulator
     
  11. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    I'd advise that you tread very carefully with a reg. Many are happy with their retro-regged 400s, although personally I don't think these guns take them very well and in the absence of options superior to what's currently available I wouldn't fit one to any of mine. Make sure you're fully informed before taking the plunge ;)


    Again thanks to everyone for your support - it makes the process worthwhile. Documenting everything has turned what would otherwise have been maybe a 3hr job into one that's perhaps 9+hrs.. which of course is all good if I know people like it and it's not all a self-indulgent waste of time :p
     
    Gary Jones likes this.
  12. FerreT985

    FerreT985 Engaging Member

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    It's not for a 400
    It's for my phox, I want a consistent shot and a nice side effect getting rid of the comical echo in the cylinder when fired
     
    cloverleaf likes this.
  13. mikeyhall1

    mikeyhall1 2018 & 2019 Forum Nice Guy

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    I would be careful not to spend too much money on the Phox. Great rifle for the money and reasonably accurate as they are within its sweet spot.

    Thump a reg in it and start tuning you’ll never get the money back that’s been spent. My advice would be if you wished to tinker about you may wish to start with a better and more sought after platform.

    To resolve the cylinder noise, you just need a depinger which would be worth your while
     
    cloverleaf likes this.
  14. FerreT985

    FerreT985 Engaging Member

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    I'll most likely keep it and if my nephew or one day have children of my own it'll be a gun they can use with no worries about damage to an expensive rifle
     
  15. Jagdwaffen

    Jagdwaffen Suns up guns up

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    Excellent write up CL :up:
     
  16. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Cheers guys :)

    The gun went up the range with me on Wednesday and had 50 rounds put through it off the bench to see what it could do. Unfortunately, just as with the R10 before it the three hours spent developing a stiff neck in the freezing cold range were rewarded with less than stellar groups.

    I only tried AADEs (my other MPR-based rifle loves these) and over 10 five-shot groups the gun managed a mean group size of 4.3mm c-c:

    [​IMG]


    While the groups were generally very consistant from one to the next, I'd have hoped for them to have been smaller (3.0-3.5mm being typical of my other rifle).

    Once home it did occur to me that I'd forgotten to clean the barrel before fitting it. Subsequently the first cleaning patch came out black with lead, those following it showed decreasing amounts of red deposits - consistant with the remnants of the bluing process. The red staining on the second patch was pretty prominent; the sixth patch showing a lot less. Finger's crossed this was enough to improve the groups when I get it up the club next week!

    In other news the gun was generally very pleasant to use thanks to the excellent ergonomics and adjustability of the Ultimate Sporter stock; however the minimal clearance between the barrel and cylinder will definitely need looking at though. Every time the heavy-handed gentleman on the point next to me seemingly dropped his rifle onto the deck after each shot, not only did the subsequent shockwave sent through the firing points disrupt my POA, but also made the barrel contact the inlet valve housing with an audible "ting" transmitted along the action and stock to my ear via my cheekbone.. :mad:

    Since I can't do a lot about the orientation of the barrel I'll need to look into installing some sort of buffer to cushion the barrel and prevent it from impacting anything metallic. One option is to shave down the rubber buffer used on the HFT500, although I'm not sure how good-a-job I can do of this. The second is to look at installing something else into the blanking piece around the inlet valve housing - the obvious choice being a nylon-tipped grub screw fitted from beneath; however the shortest I've found is 5mm OAL and I'm not sure if the blanking piece would accomodate this.

    Anyway, that's all for now - as usual I'll update when / if anything arguably interesting happens :)
     
    Last edited: Feb 19, 2018
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  17. PumpnGun

    PumpnGun Donator

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    Thanks for the update Mike, hopefully the clean will make a difference :up:

    Ray
     
  18. mikey

    mikey Pro Poster

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    The f stands for fluted
     
  19. Tadpole

    Tadpole Super Moderator Staff Member Mod/Admin

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    Unable to view pics .. :(
     
  20. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Embedded image links need updating to point to the new forum.. will sort it when I get time!
     
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