Modified S400 for FT

Discussion in 'Equipment Reviews' started by Dale, Jan 15, 2020 at 7:44 AM.

  1. Dale

    Dale Well-Known Member

    Sep 16, 2009
    This text comes from a review I wrote in 2001 that was published in Shooting Sports Magazine.

    Whilst things have moved on since then, the underlying ability of a rifle to accurately put pellets where you intend them to go remains the same.

    Unfortunately I no longer have the original pictures from the article, so I have added in some other images that I still have of it.

    I really do regret selling this rifle, as I won a number of competitions with it and even cleared a tricky course at Dartmoor Marksmen on one occasion.

    Anyway I hope it is still informative despite its age:

    In the latter part of 2001, I decided to purchase an Air Arms S400 Classic rifle in .177 calibre, which was intended to be used as a general-purpose rifle for informal target shooting and some hunting. The day that I bought this rifle I happened to be going to visit one of the neighbouring FT clubs in South Devon.

    Shortly after I had fitted my Leupold 18-40x40EFR scope on to the rifle and zeroed it for 35 yards, Bob, who is one of the members of South Devon Air Rifle Club asked if he could try the rifle as he was thinking of buying one himself. Happy to oblige his interest I handed him the new rifle, so he set himself up on the bench-rest firing point of the club’s zeroing range and using the 8.4 grain Air Arms Diabolo Field pellets with the 4.52mm head size, proceeded to shoot a five shot group on a target card that was set at a distance of 50-yards.

    After he had shot the group I became aware of his assessment of the rifle in broadest Devonshire accent, exclaiming (expletives deleted) that all the shots had gone through the same hole. When the target was retrieved, sure enough there was one ragged hole of just under ¼ inch in diameter. This turned out to be no fluke as further groups showed the same level of performance.

    This result, which easily equalled the performance of my Pro-Target Mk2, sealed the fate of the rifle, it would not be a general-purpose rifle after all - instead it would be built into a competitive field target rifle. In order to achieve this goal, several changes would be required to give the kind of handling characteristics required in a field target rifle. So in conjunction with my friend Nick Jenkinson, who had already carried out some modifications to the 400 series rifle, the process of transformation began.

    The first modification carried out on the rifle was to the trigger mechanism to bring the release up to a target standard. As the 400 series rifles (and their predecessor the 300 series) all feature a genuine two-stage trigger as standard, there is potential for considerable alteration to the pull characteristics. Nick has developed a modification where an extra sear can be installed into the unit to improve the leverage. With this change the performance of the trigger is now very similar to that provided by the Olympic trigger unit that was offered with the earlier 100 series rifles. Following this modification, the trigger pull on the test rifle now stands at an 8-ounce first stage and 16-ounce release weight, which considerably improves control during the release of the shot.

    While on the subject of triggers, by calling the unit a genuine two-stage I mean that when the rifle is cocked it has a considerable degree of sear engagement. Operating the light first stage actually reduces the sear engagement to a point where, when the second stage stop point is met with, further pressure on the trigger blade will release the shot without any creep. If the shot is not taken and the trigger is released the sears return to their full engagement position. A benefit of this type of trigger is that when cocked, it is not prone to releasing the shot in the event of a knock or the rifle being dropped. Some other triggers, although advertised as two stage units are in fact single stage triggers, with the trigger blade set up to have a lightly sprung movement to simulate a first stage. This type of trigger has got very little sear engagement and if set too light can release the shot if the rifle is knocked.

    Having improved the trigger pull, the next area of attention to concentrate on was the balance of the rifle, as in the standard sporter format I found that it was a little bit too light at the muzzle end for target shooting. To compensate for this, I had a cylinder tube from the high-power 400 series rifle fitted to the action. The classic cylinder is 400mm in length whereas the high-power tube is 520mm in length.

    Apart from the weight contained in the extra 120mm length of steel tube, moving the alloy end plug and valve cover forwards by this extra distance dramatically improved the balance. However, with this cylinder fitted the muzzle of the barrel was now behind the barrel support collar. To compensate for this a support collar from the high-power rifle was fitted, the high-power rifle features a shroud type moderator that runs the entire length of the barrel, so the support collar has a larger diameter to allow for this. With this collar fitted a muzzle weight was turned up from brass bar to bring the barrel assembly flush with the end of the cylinder assembly. The brass also added just the right amount of extra weight to balance the rifle perfectly for me.

    Subsequently Nick is offering a variety of options on this extension piece from a short moderator assembly in blued steel to a ported muzzle flip compensator in brass or aluminium.

    A significant side benefit of using this long cylinder is an increase in the number of available shots per charge. Another modification, which has improved consistency, is radiusing of the firing valve and seat. This allows the valve to function more efficiently at the high-pressure end of the charge while retaining excellent performance across the rest of the charge. The overall effect of this change is to flatten off the power curve that is found with all unregulated pre-charged rifles.

    Following these modifications, chronographing of the test rifle showed some amazing results. Filling the rifle to 180 Bar a series of 135 shots were fired with a power band between 11.3Ft-lbs and 11.7Ft-lbs. An analysis of the velocities obtained showed that 119 of the shots exhibited an extreme spread of 20fps (i.e. the difference between the lowest and the highest recorded velocities across the entire string of shots, not shot to shot variation which was under 10 fps), a figure that I consider acceptable for competitive shooting. With the knowledge of this level of performance I generally fill the rifle to 170Bar, which I know will easily give 100 good competition grade shots, allowing me to avoid the need to carry an air bottle to the competitions that I have attended with this rifle.

    Having got the action built to competition requirements, attention was now turned to the stock. The standard sporting stock, which is available in either beech or walnut, is an excellent design for its primary purpose of hunting and the quality of the walnut ranges from very good to superb in terms of figuring and colour. However, it is not ideal for field target shooting without some modifications.

    When considering the options with the stock I decided to go for the walnut thumbhole stock as fitted to the 400 series, this stock was designed by Nick Jenkinson and features an adjustable butt pad as standard and a more vertical style of thumbhole allowing the shooter’s thumb to sit at a natural angle. As the stock has been designed for this more upright thumb position there is no vertical thumb-rest as found on some stocks. Given that this stock is designed primarily for sporting use the cheek-piece is a little too low for target work.

    Cutting the cheek piece away from the stock and installing riser bars to bring it up to the required height soon cured this. It is possible to make the cheek-piece adjustable by using long bolts set through holes drilled from the underside of the butt screwing into threaded inserts fixed into the cheek-piece, the height can then be controlled by making spacers of the appropriate length.

    If required it is also possible to modify the fore end to give extra depth for over the knee style shooting. This can be achieved by either attaching a shaped block of wood to the underside of the stock using an extended stock bolt, or by making a “shelf” out of wood and securing it to the stock via spacers and long bolts into holes drilled through the fore-end. However, I found the depth of the fore-end was sufficient for my shooting style and did not require any alteration.

    The standard quick fill charging system remained unaltered due to its simplicity and there being no way of improving its design. The actual inlet valve of the rifle is contained within the male section of the quick fill assembly, so in the event of a leak occurring the rifle does not need to be stripped to replace the valve, it is just a matter of removing the old component with a spanner, fit a replacement and refill the rifle with no need to re-zero the outfit.

    Apart from a light polish and re-lubrication no major change was made to the loading bolt assembly, but a small internal O-ring was added to the bolt to prevent the ingress of moisture into the striker housing from the rear end of the pellet loading trough.

    The addition of a set of sling swivels and leather cobra style sling completed the rifle.

    With the construction phase completed it was just a matter of fitting a scope and testing the rifle on the FT range of Cornwall FTC. Given that my intention was to use this rifle for full FT competition, I removed the 32x Leupold Mk4 scope from my Pro-Target and fitted it to the S400FT and zeroed it for 35 yards then established dialling values for ranges between 8 and 55 yards. The first outing on the course returned a score of 38 out of 40, the only misses being due to not reading the wind correctly on a 53-yard target and wobbles on the much-dreaded 43-yard standing target. This score is only one point less than I have achieved with my Pro-Target a dedicated FT rifle that I have owned for over two years. Neither of the two misses could be attributed in any way to the rifle, but, were purely shooter related errors.

    One noticeable aspect of using a rifle such as this is the level of satisfaction at achieving a high score using what is fundamentally a modified sporting rifle. Subsequently during the SWEFTA summer series of shoots this rifle has helped me to maintain an average score of about 95%. The real beauty of a rifle such as this is that it gives the shooter a competitive package at an affordable price.

    The modifications can be undertaken in stages on an existing rifle, or a rifle can be ordered from Nick as a complete unit. The modifications can also be applied to the older 300 series of rifles. The improved efficiency of the rifle also means that you get more shots per fill of your air bottle hence fewer trips to the dive shop for a refill.

    The level of accuracy of the test rifle is in no way unusual; most of the 400’s and 410’s that I have examined show a similar degree of accuracy.

    Should your preference be for a shorter rifle, then a similar package can be created around a carbine barrel and the 400mm classic length cylinder. Due to the shorter cylinder and particularly the shorter barrel this version gives a lower number of shots than the test rifle, but enough shots are still available from a charge to easily complete a 50 shot FT course without the need for refilling.

    The multi-shot S410 variant can also be modified to these specifications if you have a preference for a magazine fed rifle.

    The modified thumbhole stock as first used on the rifle.

    A later view of the rifle following the acquisition of a Hyedua target stock originally intended for the 300 series but not adopted.

    The rifle fitted with a big Nikko 10-50x60.

    A trio of modified S400's.
    Last edited: Jan 15, 2020 at 8:07 AM
    Peter M, Glenn, Adam and 6 others like this.
  2. pbrown

    pbrown Bunghole

    May 27, 2016
    Very interesting read, thank you. :)
    Dazza no7 likes this.

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