P.O.I. shift in old BSA airgun........temperature?????????

[edbear2]

Just had my model D in the garden for the first time in 6 weeks plus........now this gun at 6 yards, put pellet on pellet, and I locked the aperture slide at a dead 6 yards (second zero at 25 yards) with the point of impact being the tip of the foresight plus a gnats airspace.

So tonight.........even after 50-60 shots to settle down, it is constantly shooting 10mm high at 6 yards.....Any ideas please??????

Being an ex 1970's two stoke rider...I know the cold air makes a big difference in power to an engine......(frosty morning + 500 triple kawasaki = pain)........But will it being 10 degrees today whilst shooting, instead of the mid twentys as when it was zero'd make a difference to my old BSA??....Or am I just going bonkers???

Same pellets used (H+N FTT).......and same batch,
Same hold/rest used
Gun was not oiled before storage
Sights still on scribelines.....i.e. have not moved

HELP!

[Josie & John]

My money is on the temperature Ed. Same thing happened at a vintage shoot last Jan, when it took me 3-4 shots to realise I was shooting higher than my intended point of impact every time (failed to use the zero range beforehand like a right muppet!). Admittedly it was -5 but if all else is a constant, as unlikely as it seems, its probably the drop in temperature and air pressure.
Kind regards,
John

[Caddy]

I have experienced the same thing on wednesday night with my lincoln Jefferies. But the other way, definitely shooting lower by quite a margin in the cold? Which might mess up the theory? But each one of these old guns has very different character anyway. I guess we might have to develop a "winter" and "summer" setting on the sights!

[LeeEv2]

HI, your POI at 6 yards shouldnt change with temp! maybe at 25 though! put the gun over a chrono and see if its consistant? I shoot in big comps where we have to chrono guns before shoot and from -5 degC to 25c only about 5 fps change! at 55 yards about 10mm drop! its my scope that shifts more but as your with open sights you dont have my problem!
I say chrono it at different temps and see what happens?
Lee

[trevorj]

Hi Eddie
I have had this same problem with a 45" IMD. After trying all sorts of obvious things like checking tap and trigger guard screws, without result, I finally decided to look at the stock bolt. I couldn't tell it was loose until I put the large screwdriver in the slot. It was only a little but it brought the grouping back to where it was originally sighted. Worth a look?

[Mark D]

Just had my model D in the garden for the first time in 6 weeks plus........now this gun at 6 yards, put pellet on pellet, and I locked the aperture slide at a dead 6 yards (second zero at 25 yards) with the point of impact being the tip of the foresight plus a gnats airspace.

So tonight.........even after 50-60 shots to settle down, it is constantly shooting 10mm high at 6 yards.....Any ideas please??????

Being an ex 1970's two stoke rider...I know the cold air makes a big difference in power to an engine......(frosty morning + 500 triple kawasaki = pain)........But will it being 10 degrees today whilst shooting, instead of the mid twentys as when it was zero'd make a difference to my old BSA??....Or am I just going bonkers???

Same pellets used (H+N FTT).......and same batch,
Same hold/rest used
Gun was not oiled before storage
Sights still on scribelines.....i.e. have not moved

HELP!

500 Kawasaki triple and your still breathing!! My money would be on something coming loose

[edbear2]

500 Kawasaki triple and your still breathing!!

Hi Mark........Breathing but limping, and less a spleen, and 1/2" of femur..........

Thanks guys, for all the suggestions......On the loose fastener idea...I always go over all screws before shooting anything I have, but I double checked the stock bolt, and it was fine.........I tried shooting again indoors last night, and used a 500w builders type light to light up the hall / target, and it seems O.K. now.....I am starting to think it was the awful light I was shooting in as well that was not helping, but am going to take up the idea of an indoor / outdoor chrono to see what I get.........I would be VERY happy with the 5 fps variation mentioned earlier in the thread