Posted: 12/9/2009 8:59:25 AM EDT
|
Hey guys, I'm looking for some info from you guys that use a Chronograph.
I have developed an accurate load for my .308 bolt gun. I shot a .76" 10 shot group yesterday with it so my load development is done. But, I ran them through my new Chrony Beta that I just got and my velocity was only 2495 fps. It was 21 degrees out. When I developed this load it was about 50 degrees and I used a friends Chrono and was right around 2600 fps. My question is. Is there a way to Check the accuracy of the Chrono itself? or is the 30 degree temp difference effecting my velocity? Load data. 168 SMK 42 grains IMR 4895 Fed GMM brass CCI BR primers I think I will go out today and run a few rounds of Federal GMM 168's through the Chrono and see what velocity I get out of them. Should be around 2650 fps if I recall right. TIA for any insight you may have on this. Until that day, Darkop |
|
Well I went back out today and ran 20 rounds of Federal GMM 168g through the Chrony Beta. I got an average of 2718.6 fps. I also tested my 175g SMK load and got an average of 2565.4 fps.
It was colder today, about 12 degrees. But I think my results are honest. I shot at 214 yds and everything was still sub minute. Maybe I should just not worry about it and go shoot more :-) Do you guys see much deviation in velocity when shooting in a colder environment than the load was developed in? I just looked back over my loading notes and it looks like I'm loosing 192 fps due to the cold. Does this sound right? TIA Until that day, Darkop |
Cooler temps will effect your loads quite a bit depending on the powder they will also effect many chronographs (some quite a bit) I tend not to trust chronographs in temps much below 30 degrees. I gave my chronograph the 480 Ruger Impact Test it didn't survive  . one of the best things I ever did  . I used 42 grains of Blc 2 with a 168 match (SMK) it ran just over 2500 fps in 20 degree temps and shot real well. Find what shoots well at around that velocity and throw the chronograph away. 
|
|
Quoted:
Just remember if you work up a load over the winter, it might become an issue for you in the summer This load is nice and accurate summer and winter, well under MOA. It is just is a little slow when colder. Im not to worried about it. I have lots of powder and bullets so I'll just shoot them. Interesting that Federal GMM is supposed to run at about 2650 fps, and I'm getting 2718 fps out of a Remington 700 5R in 12 degree weather. This has me wondering if I'm not pushing there bullets fast enough? This Chrono stuff is new to me and I'm interested in this Velocity stuff! Thanks fora all your input Until that day, Darkop |
|
Darkop,
Dad was a chronograph maniac for years. Although I used to glaze over when he would discuss this with me, he had always said that his pet loads for different rifles would vary quite a bit depending on temperature, humidity and barometric pressure. Altitude was also often an issue –– but if you're chucking bullets from the same spot in Valdez, then that's no much of an issue. I am impressed that you've found a load that will give you 3/4-inch 10-round groups. Think about that –– 10-round consistency. That's hard to get from anyone. |