Thread: Velocity Loss From Summer to Winter.

Really keen to hear from more experienced shooters:

I'm using AR2213sc in a 6.5-284, 50.5gn pushing 140 Bergers at a lesuirely 2900fps.
-Worked this load up last summer (20-23 degree days), it was pretty consistent velocity wise.

-Based on observed drop at targets last weekend (8-11 degree day) I think I'm seeing about a 90fps drop off. (Worked it back through JBM calculations, will chrony it tomorrow...if the bloody rain stops).

I think AR2213sc is supposed to be pretty stable temperature wise.

So, 90fps loss for a temperature drop of 10-15 degrees???? It's a drop off of only about 3% (which I guess doesn't sound that much), but it makes a good dent in my trajectory beyond 300 yds


So, does this sound right? Or am I getting too much drop off?

Thanks for your help.

Ps. Has occured to me that increased air density/humidity will be a factor too, but I ran the numbers- and it didn't seem significant enough....but then again, I am a real amateur

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.

Thanks R93.
-So do you think the drop in trajectory is more likely due to the change in atmosphere? Rather than a decreased muzzle velocity due to the powder/temperature?

(guess I'll know for sure when I get the chance to chrony it).

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???

Possibly a head wind or downdraft? just throwin it out there.

270 load in 20 7/8" barrel Sako 75

130gn Sierra Gamekings
RP brass neck sized
Fed Match primers
Warmish load of ADI 2213sc 61.5gn
OAL to fit mag (71.90mm)

Chrony results

Summer:
3130
3170
3123

Winter:
2989
2933
2919
2969
2949

So quite a difference.

Originally Posted by dogmatix

270 load in 20 7/8" barrel Sako 75

130gn Sierra Gamekings
RP brass neck sized
Fed Match primers
Warmish load of ADI 2213sc 61.5gn
OAL to fit mag (71.90mm)

Chrony results

Summer:
3130
3170
3123

Winter:
2989
2933
2919
2969
2949

So quite a difference.

Thanks dogmatix,
That was just the kind of stuff I was interested in. (bonus that you use the same powder).

-So about a 5% loss for you too then.

-Do you think 2213sc is as temperature-stable as advertised? Or in fact is this quite good stability, and other stuff might be worse?

Cheers for your help

I was put on to Vit powder by Baldbob and havnt looked back. Try some N560 if it suits your cal and you are going to give another powder a go. I get 3070 during the winter. I havnt tried it in the summer months yet but Baldbob uses the same calibre as me at the same speed and has no significant change thru seasons.

Originally Posted by R93

I was put on to Vit powder by Baldbob and havnt looked back. Try some N560 if it suits your cal and you are going to give another powder a go. I get 3070 during the winter. I havnt tried it in the summer months yet but Baldbob uses the same calibre as me at the same speed and has no significant change thru seasons.

Cheers,
Have heard good things in the past- will give it a go.

+1 on what sneeze posted above as well. Also, unless you use a high quality chrony they can be tempermental with temp and light changes as well.

James did you validate your original velocity at decent ranges? and what distances where you shooting last weekend to determine the velocity loss?

Originally Posted by sneeze

James did you validate your original velocity at decent ranges? and what distances where you shooting last weekend to determine the velocity loss?

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.

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.

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.

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)