WTF???

[Sumpter Steve]

Once again I'm dumbfounded...

Load #1: Temp=45deg.
168gr AMAX
45.3 Varget
CCI Primers
Lapua Brass
FPS=2639

Load #2: Temp=72deg.
168gr AMAX
43. Varget
CCI Primers
Remington Brass
FPS=2662

I'm fairly new to reloading but this seems strange to me. Can temperature and brass make a load with 2.3 grains less of powder shoot 23 fps faster? I know you fellas will be able to explain it to me. Thanks. Steve.

 

[lanwickum]

Re: WTF???

case capacity would be most probable.
Any know the capacities of rem and lapua brass out of the same chamber?

 

[Sumpter Steve]

Re: WTF???

Could the fact that I used two different chronos make that big of a difference? I would think that they would be pretty close to the same.

 

[CoryT]

Re: WTF???

Sure, no problem. 23 fps could be well within the SD envelope of both loads. Now many rounds did you shoot to even get the average. The reality is, unless it's 40 or more, you probably don't even have a good average, much less a good SD. Any given round has about a 97% chance of being within 3 SD's of the average. If you have an SD of 20 fps, you should have most loads between 2700 and 2580 with the first load, presuming the first average was actually valid.

Bottom line. Not nearly enough data here to reach any reasonable conclusion.

 

[VTi]

Re: WTF???

Unless you fired many rounds to get the average velocity, the data doesn't have any merit. I think most chronographs are only accurate to +/- 1% which means that for a cartridge of this velocity the chrono is only accurate to about a 50fps window. Take just a few individual readings with a grain of salt.

 

[Sumpter Steve]

Re: WTF???

Thanks guys. The velocity was measured by taking the average of 5 rounds fired. It seems like I will need to fire a lot more rounds before I can call it an average.

 

[Two Shoes]

Re: WTF???

Rem has a few grains more capacity than Lapua,so I would say temperature, or did you CHANGE powder lots?.

 

[Sumpter Steve]

Re: WTF???

Thanks TS. I forgot to mention that they are from two different powder lots. Would different lots make that much difference? I appreciate all the info. Steve.

 

[NaHa]

Re: WTF???

Steve, for pete's sake, it sounds like you have WAY too many variables to accurately compare what's what like you want.

Here's my take:

Find your most accurate load. As in which shoots the best group average of five consecutive 5-shot groups. Then take that load, and make sure it's going fast enough to achieve the performance you want at the intended range you'll shoot. If it is, you're done.

If you want to start measuring stuff other than group size and velocity, then you've opened a can of worms that will cause you as much "fun" or frustration as you can hope for.

Right now, you've got two different bullets, two different cases, two different chronographs (!!), two different temperatures, and two different powder lots.

Next, I expect you to mention that you fired these loads out of two different rifles, at two different altitudes.

 

[Sumpter Steve]

Re: WTF???

I hear ya Nate. I swear that I only used one rifle. LOL. It just seems kind of strange to me that a round with 2.3 grains less powder will shoot faster based on powder lots, brass, and temp. I told you guys I'm pretty new to reloading. I WASN'T LYING. LOL. Thanks for the info fellas, hope I didn't stir up your dandruff too much. Steve.

 

[CoCaDoRi]

Re: WTF???

Steve,

A LOT of good info above.

Seeing as you used varget and different brass. Hell yeah those numbers make complete sense. 2 huge variables that are know for big variances.

to get real data that is usable you need to get real picky with details.

you'll need

Same brass from the same lot.
Sorted by case volume.
Same bullets same lot.
Sorted by bearing length.
Same powder same lot.
load all round at the same time at the bench.
same primers, same lot. I know guys that sort by weight ( I think that's horse crap though )
use the same chrony, at the same time of the day, under the same conditions, on the same day.

fire at least 50 rounds. then start to look at the averages.

 

[Sumpter Steve]

Re: WTF???

Thanks for the info Weda'. I appreciate it. Steve.