Discussion in 'Piston & Spring' started by cars68, Apr 10, 2018.
Thanks guys. Lots of things to think through. Lots of positive thoughts.
I agree with this 100%.
The effect you describe with the rest of your post sounds like it could be a big factor, but not the only one. The OP is talking about HFT which as Jim says demands huge variation in position from shot to shot. Using Occam’s Razor, that’s the prime suspect right there.
Combining this kind of shooter variation with Jim’s suggestion that the seal friction is causing variation in pellet exit time (as opposed to MV), leads me to think that we’re actually both right. You’ve eliminated the other variables and the effect you describe remains. But consider if the recoil movement was straight line down the axis of the cylinder, variation in pellet exit time would have no effect.
Using the kit Andras used to measure lock time a while back, it should be straightforward to correlate the zero shift with pellet exit time and prove or disprove the hypothesis.
Yes it would be interesting to get to the bottom of it.
For the first time in years I completed a springer competition without zero shift. I've since put it over the chrono and seen it stay at 760 with exacts. So I'm going to see what happens with that. I need to make the stock fit me now.
But yes I think you need everything to be consistent with springers. I think though that the idea that they always behave themselves and it's the shooter is perhaps exaggerated. And I think that these days, even with PCP's, it's the tendency, dare I say it, fashion for shooters to blame themselves or question whats going wrong without looking at the kit. It's easily done, I've done it myself.
HFT with them is difficult. When I dabbled I shot them all kneeling and standing. In days gone by that was good enough for a gold. These days not so. I don't think i'd fair well against those minis that way.
Have you tried shooting the course with freshly painted targets Graeme, you might be able to see if there is a pattern to your misses.
Fit a spirit level to you gun (make sure it's actually level - most aren't!) then use it to check how much cant you're getting when you think you're level. You can always remove it / cover it with some tape during a competition.
What method are you using to counter parallax error? quite a few of the methods the PCP lads use are either not possible or impractical with a springer.
Cant and Parallax error are probably the two main causes for missing in HFT.
My mum used to say theres no such word as cant.
What gun/scope etc and is it tuned?
I've only been shooting a year but probably shot around 30 or more competitions with my TX and I've only had zero shift once, and that turned out to be loose scope mounts.
I hear a lot of people with HW97's talking about zero shift. Is this a problem seen on some guns but not others (i.e manufacturer dependant)?
That might be narrowing down to a seal issue Dan .
Hw and AA seals are very different . Both material and design .
I spent a few months investigating parallax error and how to avoid it with my scope/gun combo. Once I came up with a solution that works for me, my HFT scores pretty quickly went from consistent low/mid 40's to high 40's/low 50's.
Seal or rotating/non-rotating piston. Not sure how much effect the rotating piston would have. I've not shot a weihrauch anywhere near enough to make an informed judgement on that.
OP is shooting a TX. Unless it is highly tuned or running a different seal, I'm going to assume the rifle isn't at fault here
Ahh it's them sneaky hft course setters messing wit ya head .
...........they put you in a funny position without you realising it ...............sneaky lot ........
Take any permutation of a hint of rifle cant (easily done when shooting from sloping ground, or if the peg isn’t quite upright), add in a smidge of parallax image shift, a slight variation in rifle hold and/or muscle tension, sometimes a tiny shift in pellet exit, which might be caused by minor variations in pellet weight.
Sometimes these factors can partially or wholly cancel each other out, and the target obligingly falls; on other occasions, the bias can be all in the same direction, and the effect can be cumulative, so the pellet lands a mile off. If you look for a single explanation for that shot, you’ll never find it.
I think the only solution is to practice good technique; keeping the rifle vertical, paying attention to eye/scope position, keeping rifle hold consistent and relaxing muscles, and to practice until all this becomes second nature.
My main TX had been shooting badly of late. I had checked everything I could imagine. It would group in 2 different places and usually high and low out at 55 yards. I was certain it's not the gun, because this is a very good one even in factory tune. It's now running the LGU piston and shortened transfer port, so it's very near stock. I read above, in one of RobF's posts, about having the trigger finger position down to the mm. I've always had best results from having the finger up in the top of the curve, of the blade, on all my TX's since anything lower gave me the results I was now getting with this TX. A while back I had changed the angle of the trigger adjustment screws, made a nice difference in the feel, so I started trying a different finger position. Put the finger down to just slightly lower than center of the curve and the gun is cured. It's taken me weeks to figure this out. My point is, a very small change can make a major difference. These are spring guns, after all.
Sorry late to this thread, just a thought ( I’m a springer novice )
Rob do you think firing a shot off before every lane would give some consistency - on the temperature issue.
Good question. I guess it depends on the heat soak nature of the materials. Some materials take a while to warm up but then hold that heat, some take a lot less but change temperature more rapidly.
I think if you're seeing issues then you need to be consistent in simulating what you're doing on a course and trying to be consistent on a course as well. ie leaving it in the sun then putting in shade might not be the best route.
Maybe a good idea to,
minimise your exposure to frictional losses especially in parts that can change size with temp .
Letting off shots between targets- is that allowed in FT/HFT?
Into the ground or wide of the target?
Not between no but once in position you cab tell your partner you’re firing one off and the shot won’t be treated as an attempt.
Looks you were spot on Rob; I experienced it today. This has to be the seal 100%. Recently mildly fettled LGU, standard, bar 3mm TP. Doing a bit of practice for GP1. Warm day, on the course. Been knocking em down bar a couple for tricky wind. Suddenly pellets start going low and I double dink the lane. Next lane, on cocking I notice on returning the lever to latch, it it seems much freer, especially in the forward part of the stroke. Pellet hits at 6 o’clock. I cock it again and test it’s still sealing by blocking TP with my finger; it is. Then I move lever back and forth vigorously for 15-20 secs, and it frees up even more, especially on the back part of the stroke. As POI was so low I start using the top of the bottom thick post of the 30/30 as my aim point and targets start going down again.
Trajectory seemed more or less unaffected, just the zero, so I’m with Jim that it’s not changing velocity much but rather the timing of pellet exit. At home just now and the rifle has cooled down a fair bit so it seems to be the same friction it had before so I’d be willing to bet it’s back on zero. Why is it less friction rather than more? Not sure there; if it’s seal expansion it should be tightening up in the heat?
I’m speculating the seal had less friction on the forward part of its stroke because the cylinder is warming most there. Both from higher pressure and the part exposed to the sun through the loading port. If the back part of the tube is narrower I’d have felt this before but I haven’t. This was marked.
I’m even starting to think in terms of temp strip on the comp tube! It should clear on the LGU with its bearings, but not the 97.
Only one way to find out... see if she's back on.
Might be lube changing the friction?
Dunno, it's a path full of questions.
But that temp strip on the comp tube is a super idea! Like that. We can make a recess. Wonder how hot they get. Phil has a laser interferometer so we can see if that gives us a clue.