Discussion in 'General Airgun Chat' started by RobF, Feb 2, 2009.
Do you see it, if so, what do you do?
I have found by experience that once the temperature goes below 4 degC then I tend to miss on the low side. I have found that I can usually compensate for this by adding 5yds to the turret marking. Thats what I enjoy about FT/HFT there are some things that make you struggle for a while until you uderstand why.
Speaking to some on Sunday at Bisley they were mentioning that they were missing low. I do have a temp gauge on my scope and all day it never went above 0decC.
I tend to aim high if I know it's happening rather than adding clicks. I know this isn't very precise & was hopeing to start a better, more disciplined approach to temp shift, hence ordering the thermometer strips as was discussed a couple of weeks ago but they never showed up so haven't implimented it yet.
My extra '5yds' are actually noted on the turret so that I can make the decision. I found this when searching for something else and it seems to show the colder the temperature then the denser the air.
Therefore my thoughts of a denser air slowing the pellets down seems to make sense.
Ohh my head now hurts with all this thinking.
Interestingly, humid air, at the same temp is less dense than dry air according to the common thinking.
So, we should start weighing air then...
Lets weigh Holly, and see if he's full of hot or cold air... others have assured me that his density is constant
I don't touch my scope but then again we don't shoot a winter league in the south west and only have one real winter shoot which is south devon next weekend, So I have october to february off from competitive shooting, Plus I think this temp shift is a mith,Leupold optics are so good that they are more prone to shifting in differing light than temp. Thats my therory.
Havent touched gun or scope in 3 1/2 years since i set it up properly. Used all year round, rain, sleet or shine.
Thats what i have been saying for 9 years Chris with Leups, incidently both use same scope.
I did figure around 16 years ago air pressure can drastically affect what happens to trajectory. Worst i seen was a 30 yard 45mm kill correctly dialled and ended up 20mm over the top, write it off as a bad day cant learn anything with that.
When temp drops below 4 degrees i start to loose power, below 0 I loose about 30fps. Less power = more wind taken by pellet. With a crombo in the kit bag I can tweak the power back up again before a shoot. Bit of a faff and the gun (2002) takes a while to stabilise but at least i know I'll hit something! Tempted to shoot springer next year to avoid all this messing about before a shoot.
Rare to find a gun that doesn't loose power in the cold, I hear Walthers are pretty stable?!
I add / subtract clicks. We shot at Hull a few weeks ago and I ended up adding 8 clicks (1/8th MOA). I added 4 to start with and then went back and re-filled the gun. Continued plinking and decided it needed another 4 clicks. When I first arrived on the plinking range the gun shot fine for the first 10 shots but slowly dropped away. The gun needed the clicks removing the next time I shot it and it was fine (no clicks needed) at Woodend and Anston.
I would say that Anston was as cold as Hull.
Shooting is a funny old game - let the gun aclimatise on the day and then see what it needs on the plinking range. People up and down the plinking range put 10 pellets through their guns and announce to everyone that theirs doesn't shift with temp - you see them after the comp cursing they number of targets the hit low / high.
I try as best I cna to leave the rifle out of the car for at least 30minutes preferably an hour before shooting it, in either hot or cold weather. Then 2 or 3 shots at a target to get an idea of what it is doing. adjust as needed.
That's what I do.
Walther sent me some new seals at the start of last season, and she didn't shift a jot all year. But come the cold winter, she jumped. Trying some harder ones soon.
I don't mind a shift, as long as it's constant for the shoot. But before, it would shift a click/degree almost instantly. Hot sunny & cold shaded shoots required constant observation of the temp gauge...
My rifle is very temp sensitive. I have a temp strip on the side of the action and I've measured the velocity and plotted clicks for 22, 18, 15, 12, 9 and 4 degrees so far
What gun is that Adam? PM me if you don't wish to tell everyone...
Sorry missed your reply, didn't have auto-subscription on.
Rifle is an HW100. Not a problem other people knowing; it's a matter of record on other fora.
Using a cotton bud I've now removed most of the excess grease from the trigger, cocking arm and shuttle. It does seem a little more consistent now. Still sensitive but after experimentation I've been using the 9 degree clicks at every NEFTA WL since November in spite of it being a fair bit colder at one or two shoots.
So I suspect instead of being an almost linear relationship as it seemed to be, it now seems to "cluster" around two points.
Now the WL is finished I'm minded to strip it, degrease and run it nearly dry (using dri-slide and a tiny smear of LT2). It will be an interesting exercise.
When it gets hot..
I have always had the gun set close'ish to the legal limit so with any great change in air temp and always chrono the gun to make sure it is legal. As long as the gun is running to the same levels then the aim points are fine. May not be required, may be work I need not do but I do it and i seem to shoot more consistently now.
Check zero,not much change there off to the course,normal as usual.
When I used to shoot my S400 I was always turning it up & down but since having the Mk3 I haven't had to touch it.
My MK3-EB Sniper combo is not sensitive to temperature change. But my MK4 GP-Big Nikko is.
In summer, when the temperature was 35 Celsius, I set to zero, but when the temperature fell below 20 degrees Celsius it had to do 3 clique and when it fell below 10 more 5. A total of eight.
I usually used cheapo scopes as I could rarely afford both a good air gun and a Wish List scope at the same time,
AGS varied a lot in cold weather, lower end BSA did not?
Kept the gun, changed the scope scenario, switched HW77K and BSA Lightning XL to Walther Scopes,
Variations ceased to be more than one or two clicks, 35 metres
Nephews coveted Guns,
Caved in for little money, (Relly's Rool) Bum!
Bought HW 95, dumped moderator onto BSA Ultra, loaded UK Neil Air Splitter (2 part) mounted an Optik 3x9x50 AO IR little temp variation, Webley Venom Lazadomes, (Deadly) 35 metres.
Have .177in FX Typhoon Tactical, Optic 3x32 all the bells and whistles, Little temp variation,
JSB Exact 4.52mm, cloverleaf at 35 Metres.
BSA Ultra, Terrific buy from Air Arms Dave, Hawke Eclipse Scope, Temp adjustments 1 to 5 clicks, JSB Exact 4.52, 5mm hole at 35 Metres.
Brocock Aim X Contour, A Light Fantastic Gun (Ooops!) Hawke Eclipse Scope, Temp adjustments 1 to 5 clicks, JSB Exact 4.52 same hole shooter, 35 metres Amazing.
only did this last year with 2008 nikko now i moved to leup and new gun im trying this at moment and yesturday down the greyhound when i got their -1 at 9am shoot a group when i got the out of the car all bang on the mark then tryed 1 hour later leaving the gun outside (shooting springer whilst waiting)the gun woz very cold to touch and shoot another group and i had no movement at all and it woz done on paper as well,im going to do this all through the winter to see matey,i dont think the leup suffers with temp shift like the nikko did