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).

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.

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 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.

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.

+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.

Originally Posted by R93

+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.

Roger that. I only have the upper model in the "Shooting Chrony" range, 'Alpha Master' or some such.

Funny you should bring it up, I was just researching Chronys earlier. I really like the idea of the 3rd "proof" screen on the 'Ohler 35p'. Is that model/brand a significant improvement over the "Shooting Chrony" models?

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

Originally Posted by R93

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

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).

You have too get one from the States unless you can get one second hand. Around $580 US with a 2 foot bar. I dont think anyone in NZ sells them retail but I could be wrong.
Try here and follow your nose. I e-mailed them and they were excellent to deal with. PM me if your serious about buying one. Oehler Research, Inc.--Model 35P