cockercas Posted February 24, 2013 Report Share Posted February 24, 2013 Back in spring/summer i got my hands on a new .243. I loaded some ammo and set out targets at diffrent distances. 100/150/200/250/300meters 100m zero set the marker on the scope so i have a reference point. 1 click on the scope =1cm @ 100m. 100m = 0clicks (zero) 150m = 1click 200m = 2clicks 250m = 3clicks 300m = 5clicks All from my 100m marker on the scope, all strike bull. When i shot these it was hot. I remeber burning my arm on the car bonnet. Allways have the scope set 3 clicks high and point and shoot to 300m. Now today it was cold,1°c i think + wind chill. I had the ammo on the floor and the lid open. Targets 265m away, dialed in 4 clicks of elevation,4 clicks of windage (to much). Waited for the dog walkers to pass, laid down shut the bolt, took aim, fired 4 shots. Drove down to the target and POI is 4inch low of the bull. Group is tight (1.040in) but why so low?. Can the temperature affect it this much? Quote Link to comment Share on other sites More sharing options...
TIGHTCHOKE Posted February 24, 2013 Report Share Posted February 24, 2013 Simply put - YES! Quote Link to comment Share on other sites More sharing options...
cockercas Posted February 25, 2013 Author Report Share Posted February 25, 2013 So i can put low POI down to the temp then. Or is there anything else that will effect it that much?. Quote Link to comment Share on other sites More sharing options...
JonathanL Posted February 25, 2013 Report Share Posted February 25, 2013 Temperature definitely affects ammo performance. A lot of the old dangerous game ammo made by the likes of Kynock and ICI was reckoned to produce 20% less pressure when shot in this country than it did in Africa or India where it was designed to be used. J. Quote Link to comment Share on other sites More sharing options...
wymberley Posted February 25, 2013 Report Share Posted February 25, 2013 Nowhere near that amount. Wind is more likely the problem out of numerous other variables. Quote Link to comment Share on other sites More sharing options...
Dougy Posted February 25, 2013 Report Share Posted February 25, 2013 Check out different powders also, there are those that are more sensitive than others. Quote Link to comment Share on other sites More sharing options...
cockercas Posted February 25, 2013 Author Report Share Posted February 25, 2013 Il add some detail. Shooting prone. Bipod on front, coat under the rear. Scope elevation +4clicks (as i found out in summer) 58gr vmax 43.1gr varget Cci BR primer Cases trimmed to same length. Light wind @ -138° Over compensated for wind. Shot 2in right (no problem, my fault) 4 shots, group 1.040in. 4in low. Wind isnt my issue. I want to know why before 4 clicks hit bull, this time it was 4inch low. Quote Link to comment Share on other sites More sharing options...
Vince Green Posted February 25, 2013 Report Share Posted February 25, 2013 (edited) Its not the temperature as such but everything expand as it gets warmer and air is no exception. So at colder temperatures the air is thicker and has more resistance. apparantly. By that logic you should be 4" high on the hottest day of the year, which I doubt. however, I think its more complicated than just that Edited February 25, 2013 by Vince Green Quote Link to comment Share on other sites More sharing options...
Dougy Posted February 25, 2013 Report Share Posted February 25, 2013 Ive just had a play with strelok and its giving me,using my loads just over 1 inch low with a change in temp from 74c (origanal zero) to 1c at 300yds, wind will also shift poi .whatever the angle,unless of course its constant from muzzle to target which is ni-on impossible Bearing in mind i am using 50 nosler shifting 3870fps Quote Link to comment Share on other sites More sharing options...
JonathanL Posted February 25, 2013 Report Share Posted February 25, 2013 Its not the temperature as such but everything expand as it gets warmer and air is no exception. So at colder temperatures the air is thicker and has more resistance. apparantly. By that logic you should be 4" high on the hottest day of the year, which I doubt. however, I think its more complicated than just that Air is less dense at colder temperatures, surely? J. Quote Link to comment Share on other sites More sharing options...
ajb403 Posted February 25, 2013 Report Share Posted February 25, 2013 Air is less dense at colder temperatures, surely? J. Nope, other way round which is why hot air rises, it's less dense than cold air. To the OP: When target shooting .308s on cold days at Bisley (about -3°C) everyones first shot or 2 would be about 3/4 of a minute lower than the rest of the shots as the diametre of the barrel changes with temperature. Higher temperatures cause the metal to expand which makes the bore smaller and so higher pressure and higher POI. Were your four shots taken at a leisurely pace or were they shot quickly? ie did the barrel get hot? Quote Link to comment Share on other sites More sharing options...
cockercas Posted February 25, 2013 Author Report Share Posted February 25, 2013 I shoot quickly. Probaly under 40sec. But i had checked zero @100m first with 1 shot. Then moved the target to the end of the field. Quote Link to comment Share on other sites More sharing options...
cockercas Posted February 25, 2013 Author Report Share Posted February 25, 2013 I did get a ring come loose from a base. So i took the scope off and tightend it up and rezeroed. Quote Link to comment Share on other sites More sharing options...
Dekers Posted February 25, 2013 Report Share Posted February 25, 2013 Its not the temperature as such but everything expand as it gets warmer and air is no exception. So at colder temperatures the air is thicker and has more resistance. apparantly. By that logic you should be 4" high on the hottest day of the year, which I doubt. however, I think its more complicated than just that It is for sure because temperature is not Generally "simply" temperature, if we take cold in this country it is often accompanied by damp in the air, sometimes very damp, hot too can sometimes be humid or dry, try shooting in dense fog or rolling mist, you can sometimes actually hear a vrooom type of noise, as the bullet cuts through the moisture. Any and all these things, and more effect bullet performance...and altitude of course, I certainly don't know all the variables, but there are a lot! Quote Link to comment Share on other sites More sharing options...
seeker Posted February 25, 2013 Report Share Posted February 25, 2013 (edited) As Deckers says there are more issues and numerous variables ... Just assuming all from the same batch of reloads .. external balistics - changes in alt/pressure: temperature: humidity affect the bullets BC one way or the other. internally a hefty temperature drop can cut your m/v and on a cold day I prefer a shotgun cos I don't like frozen nuts on the buttplate... Ifcyou want a long read Try Sierras site. .... www.exteriorballistics.com/ebexplained/index.cfm . Theres a section on temp etc Just reread your post ... When replacing your scope rings did you torque them and fit to the same as before cos there's another possible variable .... Its a good thing that shooting and checking zero is fun. Edited February 25, 2013 by seeker Quote Link to comment Share on other sites More sharing options...
cockercas Posted February 25, 2013 Author Report Share Posted February 25, 2013 Yes same batch of reloads. Quote Link to comment Share on other sites More sharing options...
activeviii Posted February 26, 2013 Report Share Posted February 26, 2013 its not just the barrel that shrinks in the clod but the bullet does as well. after you have fires a few shots you barrel will get to running temp but your bullets will stay the same. everything moves a little slower in the cold. you might even have a parallax error and not noticing it as you might have good eyes, then in winter your wearing thicker clothing, with a collar no doubt and his will change you POI. People laugh at me because i re zero all my rifles once a month. every time i do a re zero you can just about guarantee there is a shift somewhere, normally on the windage with me. Quote Link to comment Share on other sites More sharing options...
kent Posted February 26, 2013 Report Share Posted February 26, 2013 Have you not considered what happens to wooden doors in summer and winter, or dark upvc ones. It is here I should look first if your gun isn't pillar bedded in a stable stock or the mounts and or scope. Ali tube scopes especially have been known to shift in temperature. I develop all my hotter loads on hotter days for safety but 4" not very likely but still possible its low v high temps I had it occur due to cold ammo once. Stock bedding changes is my first guess though if you have a walnut stock unbedded Quote Link to comment Share on other sites More sharing options...
cockercas Posted February 26, 2013 Author Report Share Posted February 26, 2013 (edited) Laminate stocked T3. Dyralyt scope. Its not pillar beded. But if that was the issue why the good group? What ever the change is, its consitant. The first shot i fired (@100m) landed were it should. Just the next 4 shots are 4inch low of the bull. Edited February 26, 2013 by cockercas Quote Link to comment Share on other sites More sharing options...
cockercas Posted February 26, 2013 Author Report Share Posted February 26, 2013 Just reread your post ... When replacing your scope rings did you torque them and fit to the same as before cos there's another possible variable .... Its a good thing that shooting and checking zero is fun. Yes went back on in the same position. Quote Link to comment Share on other sites More sharing options...
GingerCat Posted February 26, 2013 Report Share Posted February 26, 2013 Apparenently 1.c makes 10 inches difference att a mile, the hotter the temp the higher the poi. Wouldn't have thought a chilly day would make that much difference over 300m though Quote Link to comment Share on other sites More sharing options...
al4x Posted February 27, 2013 Report Share Posted February 27, 2013 Powder wise hogdon do seem to suggest it should give the same performance and meter the same in most temperatures. Other factors could come in but that's a large difference Quote Link to comment Share on other sites More sharing options...
kent Posted February 27, 2013 Report Share Posted February 27, 2013 sorry, I didn't realise you took the scope off and replaced it- there is the answer end of re-zero it! I have seen expensive swing off mounts go wrong on return to zero let alone std type ones you got to remember 1 moa = 1/60th of a degree at the shooters end. Bedding can effect POI as well as groups though in a good laminate provided nothing is loose and its still on the lug, pine needles under the barrel between the stock has put more than the odd gun off zero- impossible to diagnose such things but if the scope has been off................ Quote Link to comment Share on other sites More sharing options...
cockercas Posted February 27, 2013 Author Report Share Posted February 27, 2013 It is zeroed kent. I checked first at 100m. Quote Link to comment Share on other sites More sharing options...
CharlieT Posted February 27, 2013 Report Share Posted February 27, 2013 Ive just had a play with strelok and its giving me,using my loads just over 1 inch low with a change in temp from 74c (origanal zero) to 1c at 300yds, wind will also shift poi .whatever the angle,unless of course its constant from muzzle to target which is ni-on impossible Bearing in mind i am using 50 nosler shifting 3870fps I've just done exactly the same using the details for my .243 using 75 gr Nosler between 80F and 32F and it shows a drop of 1 inch at 300 yds. Quote Link to comment Share on other sites More sharing options...
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