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Hw97K Tuning

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Hello all, Il start by saying that I have just started a project and would like some opinions. I have owned a Hw97k for a while now but over the last few months I have not been using it as I brought an AAS410F. I decided I could use the 97K as a project to see just how little recoil and noise can be achieved from a springer. Tonight after I finished work I got home and had nothing to do, so the project began! I started off by stripping down the Hw97k, as you do. I then proceeded to clean all of the lube off of the internal parts. I would like to add at this point that my 97K did have the back block glued to the cylinder. However it still came off after a few swift hits onto an old spanner I had lying around which matched the size of where the trigger was ( close enough!)


I then measured all of the parts and this was what I recorded (results are in metric and results may be + - up to 0.02):




Outside diameter 25.57

Inside diameter 22.00

Width of the pistons shaft which moves into the trigger mechanism 9.80

Length of piston 140.56

Length with the shaft included 169.65 (approximately?)

Thickness 1.68

Slot diameter 5.30

Depth inside piston 124.74


Piston seal outside diameter 26.08

Length 10.32


Factory fitted washer 1.06

Rubber O'ring which appears to hold the washer in place 1.48




Wire diameter 3.07 (average)

Length 230.86 (was hard to accurately measure)

Internal diameter 14.04 down to 13.91

Outside diameter 20.21 down to 20.07



Spring Guide


Washer on spring guide outside diameter 29.81

Washer on spring guide inside diameter 13.98

Thickness 3.01


Guide length 99.99

outside diameter 13.74- 13.54

Inside diameter 10.01- 10.05

Thickness 1.75 ( measured from the top of the spring guide)


Compression tube


Outer diameter 29.72

Internal diameter 25.98

Thickness 1.96 (measured from the back of the compression tube)

Length 154.27

Internal length 143.99

Diameter at the end of the tube where the seal sits 11.98


Trigger block


Internal diameter for the piston to slide into 10.02

Length from front of back block to touching the main sear where the piston would engage 22.98





Now I am wondering what the next step could be? I have a old Rekord trigger unit which was made in 1981 which is a lot smoother than the newer one so I am going to be using that instead. I have taken apart the older Rekord Unit and made sure everything is okay inside and gave it a quick polish and put it back together. I have also polished to piston tonight and gave the cocking slot a smoothen.


I am asking what you guys would recommend A) manufacture new parts so that they sit tighter together inside ( still allowing smooth movement) and making as little movement as possible sideways. Or B) Use the standard factory parts and alter a few things I.E place a sleeve inside the piston and button the piston + comp tube.


I would also like to hear from anyone who has used graphite as a lube inside their airguns as I am toying with the idea.



Any opinions very welcome







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Iv recently picked up an old hw97k mk1 25mm piston. My step father owns his own tool room and he's going to have a top hat machined as it doesn't have one at the moment and possibly a spring guild but the current one is nice but the gun is only doing 8 1/2 flbs. Another option is buying a v-Mach spring and making my own derlin top hat and guide

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i did a deal with vislauk off here a good friend of mine and it had a welsh willy trigger fitted and a v,mach kit as well but when i gave it to marksman to do his magic we found out that it did not have the v,mach piston seal on it so i got one and vislauk fitted it for me and after marksman did his magic on it ,it was one of the best 97k,s iv ever owned and very little recoil at all im just gutted i sold her atvbmac

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After I posted that I looked one BAR and purchased a v-Mach spring. It cost about £30 with postage so will be turning spring guild and top hat when that comes next week but I need to know thickness of the end bits of them to determine the power

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