Just to keep us sane lads ...
I was reading through old posts on the subject.
It's happening to TX's too.
Here's a post from Ivan from Anston ...
Picking up from your last line. I have a TX 200 that does exactly the same thing. Its taken me over a year and four scopes before I've gotten around to considering the gun as being at fault. As an addition to other things that have been touched on in the thread; I have also swapped the spring guide from (relatively) loose fitting metal to tight fitting delrin and back again and also a looser fit delrin, changed the spring and piston seal and for good measure the breach seal. I've ruled out the bad lock up/seal issue and loose barrel too. I have also swapped the piston out of my Prosport for the one in the TX both being short stroke alloy jobs: made no difference. My TX is in a Ginb and that is now the main suspect.
Low temperature seems to be involved in my case too and although I also get a power increase, its nothing like enough to give the POI shift involved. Mine also moves fairly precisely between two zeros. I have recently witnessed the shift occurring, once with my Burris on, once with my Nikko on. In both cases it made the shift to the other zero in something around 20 shots, then stabalised. It usually moves back within a few days. I have always associated this with low temperature but I now have a thermometer on the gun and it has shifted when temperatures have been fairly stable at around 9 - 11C. This was one of the ones that occurred while I was on the zero range. I have only one incidence of this though and although it shifted after I'd been shooting for 20 minutes or so, the gun had been in the car boot overnight so temperature could still be playing a part. Whatever the cause is, in my case it has started happening a lot more often recently.
I recently spoke to Nick Murphy about this and he is familiar with the problem but doesn't know what the cause is but barrel or stock are what he puts in the frame. I was also relieved to know it wasn't me going off me trolley . Though if NM doesn't know the answer, I doubt if I'm ever going to find it. Amusingly, I'm now desperately trying to get my V-glided HW77 in an FT stock and ready for the first GP The TX is now with a mate who also has TX's including an ally piston modded one. I'm hoping that maybe a fresh pair of eyes will see something I have overlooked.
I was also reading posts by Ed from the States, who, as mentioned by Bigtoe, uses O rings and little lube on the springs, and says that his and his brother's poi shifts have massively improved by doing this.
I'm convinced it's seals and lubes. Jim will explain the rest in the mags pretty soon but some on here are already onto it. I reckon you get the guides fitting well. You keep petrol based lubes off the seal ( use dry graphite ). Matt's convinced of that and Tony. As little as possible lube on the spring. Get the seal fitting as loose as possible ... or use O rings. Try and zero at the same rate of fire, and at the same temp, that you want the damn thing to shoot accurately at ... and the shift will be minimal.
Is there one person who has switched to O rings and still got the shift?
Snoops ( John ) who won the HFT Recoilng Champs first up swears it's seals and cured his with an O ring. Bigtoe reckons O rings will cure/improve it ( he's as technically minded re airguns as you get ). Ed in the States says O rings have cured it for him and his brother. Matt says he switched to dry lube ( non petrol ) on the seal and he hasn't seen it since. Jim Tyler is convinced it's seal related.
Last edited by skires; 27th June 2015 at 08:10 AM.