Change in MV question

[XTR]

I'm working up a 308 load with Varget and 175g SMKs.

I went to the range early this week and shot a series of 5 shot groups looking for an accuracy node and trying to get my optimal load weight.

I'd started at 43gr of Varget, which only gets me to about 2550, not enough for 1000 yds.

I made up some rounds with once fired BH match brass and Winchester primers. The loadings were between 43.9 and 44.7 gr in 2 gr steps.

I wasn't happy with the results, I had a couple of flyers and one of the groups was just inexplicably off so I set it up and went back today.

Today's loads were consistently 100fps slower than the ones earlier in the week.

Variable:

The rounds I fired Friday had been on the shelf for a couple of weeks, the ones I shot this afternoon I loaded this AM.


WHY?

Could the neck tension have increased on the older rounds? I've heard people say it can decrease a little for a few days after brass is re-sized, but this brass was all re-sized weeks ago.

I forgot my tape measure both days. (working around the house all day yesterday and I pulled the one out of my range bag while my wife had the my other) The chrono could have been a little further out today. Will a couple of feet make that much difference in the reading?

Other than that, all full length resized brass, same primers, same rifle, temperature was 10F higher today, but it's the slower results.

I'm seriously wondering about the chrono position now.

 

[MALLARD]

Re: Change in MV question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: XTR</div><div class="ubbcode-body"> Will a couple of feet make that much difference in the reading?
</div></div>

no

what kind of chrono ?

was it bright and sunny both times ? or was it overcast ?

do you think the ammo itself was colder ? or rifle colder ? (probably not im just asking)

perhaps your scale did not maintain the same zero/calibration between loading periods ?

neck tension ? i dont think so but i dont know

mystery...

 

[XTR]

Re: Change in MV question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MALLARD</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: XTR</div><div class="ubbcode-body"> Will a couple of feet make that much difference in the reading?
</div></div>

no

what kind of chrono ?

was it bright and sunny both times ? or was it overcast ?

do you think the ammo itself was colder ? or rifle colder ? (probably not im just asking)

perhaps your scale did not maintain the same zero/calibration between loading periods ?

neck tension ? i dont think so but i dont know

mystery... </div></div>

Yea, I figures out how to make JBM show velocity at one yd intervals starting at one, the Chrony would have to have been close to 100 yds away to make that much difference.

I made the "fast" ammo up a month or more ago so and I don't really remember when I loaded them, all I have are the notes in my reloading log. I'm wondering now if I used RL15 instead of Varget? I was working on a load for another rifle with RL15 and I'm starting to doubt my notes, maybe I didn't change powders, or was thinking about one gun and loading for another and didn't document it correctly. The "fast" loads all look good. The es was in the range of less than 30fps on all the strings.

I do remember thinking to myself that at some point I need to have a load worked up for RL15 so that if I got into a spot where Varget wasn't available I could reload, and the more I think about it the more I think I may have made up a batch of RL15 loads and written Varget in my notes and on the box label. It's really the only thing that makes any sense.

 

[Rovieairto]

Re: Change in MV question

That could do it.
The chrono may have been set up differently.
If you can, shoot at 600 yards or further.
At 600 yards, 100 fps difference would be easily noticeable on the target.
That way if the target agrees with the chrono, you know the data is likely good.

I can usually get better peak accuracy with RL15 but Varget produces a more consistent POI, especially when it gets cold.
Shot placement over group size.