I've been getting the POI vertical jump/shift with a 77. I've followed the shift threads with great interest.
I have 2x 77s.
I've only really shot one in comps. I haven't really shot the other one at all.
The main comp gun then ...
I bought this years ago second hand and it came in a Venom Vantage Tiger stripe stock. I believe this gun was tuned by Venom themselves but only to a stage 1 tune ( not the Lazaglide ... which is buttons on tube and piston etc ... usually with black port ). The front edges of the the comp tube were also rounded at the front outside edge and there had been some work to the front hole on the end block ( I know Venom used to open this up slightly and face off the front to square up the internals and remove that annoying 'click' as the piston rod went through the start of the end block. They did one like that in front of me at Webley once ). It also came with a tuned trigger unit and a straight brass blade.
77k with Venom silencer catch fitted.
I never shot comps with it in that stock as it just didn't fit right and I didn't want to butcher a beautiful Venom stock. It did shoot excellent groups with AA Field and I never saw a shift.
To use the gun in HFT I made ( well finished ) a custom Walnut thumbhole stock for it. It shot excellent groups with that stock and again Fields and I can't remember seeing a jump over a few years. I had many very good HFT scores with that set up, including a joint top recoil score at Kelmarsh at the Worlds 2 day.
I just seemed to take it out of the bag and it was on zero at 35 yards.
Things now get a little complicated as there are so many variables.
The spring broke on the rifle in 2 places. I ordered a replacement spring from what was now Steve at V Mach but it didn't fit the original guides. So I fitted a complete replacement V-Mach kit ( rear and front guides and spring, green Powerpulse seal and steel sleeve ).
I then fitted a custom FT style stock ( but still to use at HFT ). It's an adjustable fore end/high cheek type thing. Like a Paul Wilson.
We now come to the very cold Winter of a couple of years ago. When the gun was good it was fantastic. Groups right out to 45 yards HFT prone were excellent ( under 5p at 45 yards ... sub 10mm ctc at 35 yard zero ). Scores were coming in regularly at high 50's out of 60. I felt I couldn't miss.
Then ... it all went t1ts up. On the zero range I'd suddenly get a 20mm or so shift vertically. Groups excellent ... but a shift. If it held around a course I still scored well ... if it jumped the scores would dip dramatically. A check on the zero range after the comp showed the shift.
Another problem was I'd run out of my trusted old supply of Fields so I was trying to find a pellet that looked exactly the same as the 'good' ones.
I also wasn't sure if the very cold temps were causing probs. I thought they were.
I shot the Worlds again the next Spring but it was freezing. The gun seemed ok and I got a 53 ish score on day 1 ( pm ). On day 2 ( am and literally freezing ) the vertical shift happened a few targets in and I couldn't hit a thing. I switched to all kneeling second half of the course and only missed a few. So I was then convinced the shift only happened in the prone position.
I then switched to FT and had to start developing a sitting stance. Again, I was convinced that the zero held better in kneeling and sitting mode. I tried pellet testing in my old HFT prone mode ( as I felt that was my most stable position ) but still seemed to get zero shifts. Was that the position ... or the newer pellets ... or this stock ... or the temp ... or me ... ?
There was also a lot of wear on that stock around the 'lug hole' and Paul James had advised me to fill that to make it solid. I still haven't as I basically stopped using the gun.
There is no play at the linkage between underlever and main body on that 77.
I really should try it again in another stock.
I also have another 77k 25mm that I tuned as per Bigtoe's advice on the BBS. I changed the guides ( had new ones made ) and did the end block mod that Bigtoe advised ( basically rear guide fitted into end block ). However I retained the original V Mach spring ( that also had a different V Mach kit in it ). It shoots very fast with a kick but seems to hold the sight picture on firing better than the other 77. I found Prems ( boxed ) best in that and at 35 yards it seemed easy to shoot tight groups.
I had just fitted it into that FT stock to see how that went and my knee fell apart and I have drifted away from shooting.
Interestingly that has lots of play around the underlever/main body point. I was going to get that sorted. It did shoot very tight groups though with that play.
In the short time that I tried it I didn't see any shift. That was in the home made thumbhole stock ... not the FT stock.
As I said ... too many variables going on.
Last edited by skires; 19th June 2015 at 10:35 AM.