Thread: Velocity Loss From Summer to Winter.

Thanks, appreciate it.

Originally Posted by James

Thanks for the idea Sneeze,

I only validated the 'Summer' speed out to 550yds- is that enough??

Last weekend I tested at 400yds, 600yds, 800yds and 1000yds. Only shot 5 rounds per distance. But it held sub 0.75 out to 400, and sub 1.0 beyond that (a lot of good fortune involved at 800 and 1000 though ). So I would've thought that was a pretty good sample?

Keen to hear your thoughts.

Normally Id say a 90fps drop was highish for an ADI powder but a range of things will have an influence.Firstly at 550yds a 90fps difference is less than 4 inches( aprox) which can be hard to determine when all the other anomallies are taken into account. It sounds like you have enough info for your current velocity and BC but the summer speeds might need some more work? It may well end up at a 90fps difference but I dont think you can confirm it yet. Chronys are becomming a pet hate of mine , to many people read the numbers on them and take them as gospel. The shooting chroneys are just not accurate enough and at times can give large variations due to nothing more than a change in light ,if you use them and put enough rounds over them then you start to see a trend ,or just use them as a rough guide .The ohler definatly is a step up but a lot of money and you stil have to validate shoot anyway. The CED 2 is a reasonable comprimise with the IR screens. cheaper, easier to set up and gives good info but the best chrony/balistic programe, quickload etc will always be a poor second to holes in paper at range.

My shooting crony will vary +or- 80fps shooting a known load over it(over an ohler) and this with being pedantic about it being fully open(changes spacings) and inline with bullet path in both planes.If you just slap it down its much worse.
It generally gives slightly faster readings than the ohler did with the same load.(mine anyway)

If youve got huge velocity spread over the temperatures ur using the wrong burnrate for your case/pill combination.......... Period...

Originally Posted by R93

Only one I would ever own after using one for a while James. They are a huge improvement IMHO.

+1 One of the best things I have got so for load development/testing etc

Originally Posted by sneeze

Normally Id say a 90fps drop was highish for an ADI powder but a range of things will have an influence.Firstly at 550yds a 90fps difference is less than 4 inches( aprox) which can be hard to determine when all the other anomallies are taken into account. It sounds like you have enough info for your current velocity and BC but the summer speeds might need some more work? It may well end up at a 90fps difference but I dont think you can confirm it yet. Chronys are becomming a pet hate of mine , to many people read the numbers on them and take them as gospel. The shooting chroneys are just not accurate enough and at times can give large variations due to nothing more than a change in light ,if you use them and put enough rounds over them then you start to see a trend ,or just use them as a rough guide .The ohler definatly is a step up but a lot of money and you stil have to validate shoot anyway. The CED 2 is a reasonable comprimise with the IR screens. cheaper, easier to set up and gives good info but the best chrony/balistic programe, quickload etc will always be a poor second to holes in paper at range.

Good info. Thanks for your help Sneeze.
Yeah, drop was just over 4 inhes at 600 so that fits. The variability of the chrony is becoming obvious- I'll go forward just using it as a guide to get me on the paper, and validate from there.

I hate to say it but hes worth listening to when he taps that keyboard... Geez im gettin the sneezes just writing that ahchew..

Originally Posted by baldbob

If youve got huge velocity spread over the temperatures ur using the wrong burnrate for your case/pill combination.......... Period...

Thanks for the idea Baldbob. It's not the wrong combination- not according to the top benchrest/F-class shooters in the states anyway. But then again, they may not be experiencing the low temperatures we get- I imagine benchrest in the US may well be a summer sport, most discussion seems to revolve around avoiding high temperatures rather than dealing with low ones.

But I take it you are saying that 3% is a big change then?? That's good to know thanks. I wasn't sure, as a 3% shift in some situations is minimal.

My oehler is still affected by light particularly this time of the year with the sun being so low. It went friggin nuts yesterday being triggered Constantly, by goodness knows what. I'm hoping it was just static. Prior to this it has worked flawlessly for two years

Originally Posted by R93

Sounds about right too me. I dont loose as much but do loose some. It works with helicopters as far as density goes well. Higher the air density the better the engine and blades perform. They bite better air causing resistence of sorts. Same with anything flying thru air.
I would look at another powder if your worried about it, but 2810 is still good enough for a 6.5 to 700 odd.

I am interest in this percieved drop off in bullet performance during the winter and I am not sure I have a proper handle on the problem.

I remember the Army lectures in particular the claim that the 'viscosity' of the atmosphere had quite a bearing on the performance of bullet/shell. I expect this is true, especially when you take the flight time of the shell.

Copied from the web...This 'sticky' property of the gas is called the 'viscosity' and it plays a large role in Aerodynamic drag.

Now if I understand it correctly bullets perform better in warm, moist, less dense air of the summer..... than the cold, dry, dense air of the winter.

Remembering the density altitude tables at flight school and when pulling loads out of the hills with under powered machine (for the job we used them for anyway) While the Cold, dry, dense air gave the blades more bite and the engine better performance

Now here comes the questions... Is it the density of this air that bleeds off bullet speed???. Could this cold, dry dense air be described as sticky????. Why are rotor blades so much more efficient in cold dry dense air.... is it because the air sticks to them and makes them more efficient???

Originally Posted by James

Good enough for me

-Now, how many organs will I have to sell to purchase one here in NZ? (trying to stick to a policy of supporting NZ retailers- what goes around comes around).

Listed here, although currently shows as out of stock. Does give you price indication.

Oehler 35P 3 Screen Chronograph w/ Printer - oehler, 35p, screen, chronograph, printer - Serious Shooters

Scribe thats a slightly different question, the issue here is around powder/barrel/chamber temp, the variation between winter and summer and how that affects muzzel velocity. The effect of atmospheric temp and pressure on bullet flight is relevant and needs to allowed for when shooting longer ranges but you need to be pushing past 450-500 yds for it matter in hunting terms.

Originally Posted by sneeze

Scribe thats a slightly different question, the issue here is around powder/barrel/chamber temp, the variation between winter and summer and how that affects muzzel velocity. The effect of atmospheric temp and pressure on bullet flight is relevant and needs to allowed for when shooting longer ranges but you need to be pushing past 450-500 yds for it matter in hunting terms.

Yep I do understand pretty well this part of the equation you are talking about 'Sneeze"... but I think here that 'R 93' is addressing the 2 part of the equation.

Air resistance, loss of bullet speed and and as a consequence a lower bullet strike...He used above, density altitude, rotor blade and engine perfomance to explain it.

Moisture or humidity has very little effect on bullet flight, the density of air is more relevant but I couldn't say its because its " more or less sticky" high pressure cold air is denser and harder to move through, from a shooting perspective they often balance themselves out as high pressure systems can bring warm air so as the pressure increases the density the warmer temps lower it. My memory of the principals of lift are pretty hazy but a wing creates lift by having the air move over the top and bottom surfaces of the wing at different speeds,creating a pressure differential, the denser the air the greater the differential for any given amount of air passing. R93 might correct me here.

Jeez guys we are getting into principles of flight here as far as aerofoil designs and lift. I havnt studied any of that stuff for over a decade. In saying that you are right to the best of my knowledge Sneeze.
The idea is to create high pressure under the aerofoil and low pressure at the top. Therefore creating lift. Most rotor blades are symetrical however and change the angle of attack by applying pitch.
As far as a projectiles resistence thru "air" I am not sure on the measured effects, but do see a difference from a low pressure day to a high pressure day in my calcs for said range. It can be a bit and enough to miss at range if not taken into consideration.