Originally Posted by skires
I'm another that thinks that stock fit is something to do with this.
There's yet another variable I've noticed with my 77 ... and Darrin sort of put me onto this after a comment he made at Fort on the zero range ...
Mine most definitely changes with temp ... mine can go up 30 - 40fps in extreme cold. This is slightly different ...
My main problem over the last winter seems to have been zeroing on the day before the comp ... and checking zero just before the comp ... and then in the comp missing in the following manner ...
All longish shots on or above my 35 yard zero missing high. A quick couple of pellets on the zero range after the comp confirm that the zero has shifted high by anything from about 10 to 20mm. However the 15mm kills at about 25 yards also drove me mad as I would, on normal zero, aim just below the bottom of the kill for these to hit centre kill ( so aiming on the plate just below 6 O'clock ). On the course I would miss low with the poi being at 6 O'clock on the faceplate ( usually splitters ). On a number of courses I would actually give up on my normal aim point on these, after missing a couple, and aim just inside bottom of kill and knock them down. Several days later when practising I would check the poi for these and it would be back to aiming below bottom kill and on faceplate. If I aimed just inside bottom of kill in practice a highish shot would miss at 12 O'clock. Just didn't make sense.
Anyway ... Here's what I found ...
My usual routine when getting to our ground for practice or at a comp is as follows ... gun out of car and out of bag whilst having a brew to let gun climatise ... then ...
I've always had this idea that I need to get me and the gun 'warmed up' before checking anything on paper. So I would kneel and just fire off about 20 or so shots at decent size plinkers at mid ranges. Having fired those 20 shots I would then go HFT prone and check zero at 35 yards on paper ( or a faceplate etc if at a comp zero range and no paper available ). Then, when all ok, it's another brew, a chat and wait for safety brief and start of comp.
Darrin mentioned at Fort something about a difference between shooting the gun quickly at the zero range and shooting it slowly during a comp. So I tried this our club. If I don't do the usual 20 or so rapid fire shots to warm up and just go straight to paper at 35 yards the zero is at one point. If I then start rapid firing ( shot every 30 seconds or so ) ... then after several shots the zero creeps down. If the gun is rested for several minutes ( like in a comp ) the zero goes back up. So I'm now convinced that my 20 shot warm up routine and then check zero gives me a 'Rapid Fire Zero' ... and this RPZ then goes higher when in Competition Fire Mode ( 1 shot every 5 minutes or so = CFM ) ... and I miss long shots high. I tried this on the 15mm 25 yarders. Sure enough, if I've shot off 20 shots or so quickly the poi at 25 yards is just a tad under half a bar ( I'm on 30/30 ret ) which means I have to aim on the plate below 6 O'clock to hit centre kill. If I shoot in slow CFM the poi becomes 1/4 bar and I have to aim just inside 6 O'clock. Hence in the comps I'm splitting at 6 O'clock.
It's as if the whole trajectory curve flattens out when I'm shooting in CPM as opposed to rapid fire.
So I now know that I have to zero the gun in CFM and then when checking zero in rapid fire mode I have to accept that if I want to shoot every 30 seconds or so then I have to accept that the zero at 35 drops and the aim point at 25 yards moves down ... and then just have the b0ll0x to use the CPM aim points on the course when shooting every 5 mins. I tried this at our club comp last Sunday and scored a 56/60. That's the first over 50 score I've had for ages. I've been down as low as 42 whilst twiddling with vertical zero between comps and practice. You tend to know what sort of score you should get on a course depending on the difficulty of the course and the wind etc and I reckon I've been several shots down on where I should have been lately. Admittedly that 56/60 wasn't that tough as there was just a tad of wind ( which cost me a 25mm at 40 yards ) but I nailed all the 15mms, including the 15mms at 20 to 25 yards, by aiming INSIDE the kill. I missed another 25mm at 40yards on the edge and 2 standers because of me ... but I missed no shots high because of changes in poi.
So that may not be the full story regarding the shift ... I still think there is some stock thing going on ... but I now know that temp causes a change ... and I now know that rapid fire in practice gives different poi's from competition fire mode.
Maybe that is not your problems but give it a try.
I guess we need to spend more time drinking tea and less time plinking!
I will try out the RFM and CFM theory today, as long as the wind does not pick up.
I have also modified my custom stock, there were a few tight spots which are no more.