This bolt thing ...
On that FT Paul Wilson style stock the 'hole' where the lug fits is quite worn. So it's not a tight fit when the lug is in place. If you don't tighten that main trigger bolt ( there is only one on this stock ) you can wiggle the lug around due to the wear in that area ( you can move the action backwards a tad ).
So I was convinved this was the cause of my shifts ( I've been convinced it's many things ).
Also, at the very back of the action there is a small gap ( maybe 1mm ) between the very end of the end block ( back of action ) and the very rear of the recess machined in the stock.
So I was also convinced that there could be movement there.
So I became quite paranoid about that for a time. Paul had told me to fill all the gaps with car filler etc.
I tightened up that main trigger bolt into the lug and the lug was tightened in the action. I used feeler gauges to measure the gap between the rear of the action and the stock.
I shot loads of pellets. I kept checking the main pin to see if it had loosened. Not one bit. I kept checking the gap at the rear with the feeler gauges. Not changed at all.
The shift happened. The main bolt hadn't budged and the gap at the rear hadn't altered at all. The action was solid as a rock in the stock.
This pellet thing ... JSB etc ...
Last night I took the dogs up the fields at the back of the house and up to my thinking pool. Lovely evening last night and I've solved all the world's problems sitting on the bank next to that pool.
I used to think, as some on here have posted, that a small increase/decrease in MV ( 30 or 40fps ) can't account for 25mm poi shift at 35 yards. On chairgun it can't and it probably can't with a pcp. However, I've now been educated that very small changes in pellet fit etc and piston behaviour can lead to big enough differences in the behaviour of the rifle that a 25mm poi change is probable. So I totally buy into the fact that those things could be the issue here.
However, re pellets ... if I was just dipping into a tin of JSB and randomly picking out pellets of different weights and sizes ( breech fit ), then I'd expect to see poi jumping all over the place and giving shotgun groups. If I spent time measuring and weighing and selecting different 'groups' of pellets out of a tin I'd expect to shoot the different groups individually and see different poi. I basically did that with the sh1te batch 18 AA Field. I bought tins of them from the Midlands Game Fair. Groups out of the tin were dreadful. I'd get 3 out of 5 cloverleaf and then 2 moons. I closely inpsected the tins. There were obviously pellets that had either deformed tails or little bits of extra blobs of lead ( tiny ) on the edges of the tails. I put these in one pile and the good ones in another. The garbage ones gave dreadful groups. The good ones gave very good groups. So that is all understandable.
This poi shift isn't like that. It's virtually all pellets in a very good group on zero ... then the poi moves vertically by 20mm or so. I reclick the scope ( I think it can be as much as 20 clicks or so [ 9x ] ) to rezero and all my aim points are bang on again and the groups are excellent.
So I can't see how that can be random pellets out of a tin being different???
I'm trying to think of a process to start eliminating things. I can try ...
Put the main 77k in a different stock.
Trying slow mode and fast mode over the chrono to test for MV difference ( I did do that ages ago and saw the 30 to 40fps difference ). Try slow and fast mode at a target and see if the poi moves ( whilst shooting over the chrono ). Maybe even have the chrono just in front of the target ( I'm sure I'm still good enough to miss the damn thing at 35 yards ).
Keep using the Prems and see if the jump happens in this other 77. Maybe try the JSB in that one and see if the jump happens.
Could a tiny amount of lube sneak in front of the seal and it diesels for a while and that causes the poi shift? As that lube burns off it stops dieselling and the poi shifts back? Hence dry lube helps?
Surely that would happen in the TX's too?
So are we saying that there is no one out there with a TX and maybe a Venom seal/kit that gets a poi jump? Confess you b@5tards and put us out of our misery.
Are there people out there that are not using Venom internals and are still getting the jump with 77/97s?
Last edited by skires; 26th June 2015 at 07:30 AM.