Air Arms Owners Club

Hi
After my tuning with tinbum dropin kit i found that my TX is shooting pellets at jsb exacts 8.4 grn at 830s whereas before tuning it was at 783s. Now there is a huge difference in velocity & with it recoil is also considerably more. So i thought i should share my thoughts/findings & let gurus help me out. I posted a thread in earlier AAOC version mentioning anomaly in my TX rear guide, it was embedded in trigger block with no flared part on trigger block, so as suggested by members i took it out.

Here is pic of both AA stock kit & tinbum kit

I have a made a diagram of both those kit with dimensions, pardon my drawing skills, did my engineering drawing classes 20 years back, i missed the length of rear guide of AA stock kit Fig.3:oops: its full length is 92.58mm & the part emebedded in trigger block is 0.95mm


Now what i can infer from that drawing is
For TBT KIT
1) Top hat full length= 1044+15.07-8=17.51mm (8mm of sleeve i have reduced as it was not letting safety to engage)
2) Now Top hat + top hat sleeve/thrust bearing= 17.51+1.86=19.37mm
3) Total length=Rear guide + Top hat + top hat sleeve/thrust bearing= 86.44+19.37=105.81mm
4) Presently TBT Kit sleeve in spring(TH+RG)= 7.07+83.5=90.57mm
5) TBT kit preload (Thrust bearer in TH side+TH+RG)= 1.86+2.81+10.44=15.11mm (Without adding any power band at rear guide)

For AA Stock kit
1) Top hat full length= 11.59+6.99=18.58mm
2) Total length= Rear guide + top hat= 92.58+ 18.58= 111.16mm
3) Kit sleeve in spring (TH+RG)= 6.99+91.63=98.62mm
4) Stock kit preload= 11.6+1.6= 13.2mm (1 power washer at rear guide end of 1.6mm)

Now i can conclude that that additional velocity is because of excess collar/head of top hat, rear guide & thrust bearer of TBT kit which is 15.11mm in comparison to that of AA kit which is 13.2mm.Additional thickness of 1.91mm is acting as preload & it is more than thickness of power washers provided in TBT kit. Excess vibration is because of additional power along with lesser amount of total sleeve within spring of TBT kit of 90.57mm compared to stock kit of 98.62mm. I am not sure why the safety was not engaging in precut TBT top hat when both those kit had same sleeve length in spring. Though i cutoff extra 5mm from from top hat sleeve, i think 2/3 mm would have let me engage that safety
My guess will be take out the slip washer/thrust bearer infront of top hat to reduce preload or reduce 2mm by filing from top hat. I would ask pros to help me out, I am getting good groupings at 20 yds but not at all satisfied with that extra recoil.
Thanks Moulindu

to reduce the pre load, you could face off a little from the top hat, or you could heat the spring up and collapse a coil. what spring do you have inside? the mk3 hasno collapsed coils and is 2.9mm guage, mk 2 is 3.1mm gauge and has 3 collapsed coils. those are for sub12ft/lb FAC i dont know.

Reduce preload but also look closely at the piston seal, a well run in seal can often be a bit too slick and cause harshness, fitting a new one can often help soften the shot cycle.