60fps gain?

[Lucky6547]

Hello,
Conundrum:
Same lot and charge of powder (30.3gr RL-15), measured on the same scale(rcbs 10-10), same box of primers(Cci br-4’s), same box of bullets(Berger 105vlds), and the same brass (lapua blue box), out of the same gun in virtually identical weather...65 degrees last week, 64 today.
Speed at target at 600 yards last week was average 1966fps 11.7sd. Scored 199-6x
This week 2025fps 8.7sd, scored 197-5x
Seems weird to me...any ideas?
Thanks,
Ken

 

[TAJ45]

Total spitballing here - direct sun ammo regimen mgmt?

Pulled trigger faster?

 

[Ranger188]

Barrel plenty broke in?

 

[Lucky6547]

More than 750, less than 1k on the barrel

In the shade/covered the whole time

 

[TAJ45]

More than 750, less than 1k on the barrel

In the shade/covered the whole time

Hmm, noggin scratcher for sure.

 

[Old Navy]

I would be looking at what ever you measured the velocity with.

 

[ben_g]

Are you measuring velocity at the target with an open sensor target system?

If that is the case I would not take much stock from the data the target. The data would be easily skewed by angle of flight, angle of the target, distance between sensors.

What does a magneto-speed or a Lab radar say is happening at the muzzle?

What were your come ups between the two sessions?

 

[1shot]

I've been told that the velocity readings of e-targets are within 50 fps of the actual terminal velocity. If your starting velocity is the same between the two outings, I'd say it's the e-target as others have said. If your muzzle velocity is higher, well that another can of worms.

Lloyd

 

[XTR]

I've read several reports lately of e target velocity numbers that don't make sense, the one thing they all have in common is e-target.

 

[miningshawn]

I use Altitude\Density to produce velocity tables. I have noticed 50fps or even greater change with 1000' of A\D. Were the humidity values relatively close on both days, or was it noticeably different? A\D is adjusted greatly by temperature; but, humidity does play a factor! Other factors to a lesser degree could include difference in Coriolis if the ranges were different, following\leading wind conditions, mirage (visual difference), parallax, etc... And not to forget fouling.

I use a Kestrel Drop and Strelok Pro - the system costs less than $100. The tables become more and more accurate the more I observe and back-calculate velocity by measuring drop at target.

There are tons of great articles right here on AccurateShooter about A\D calculation if you want to go down this rabbit hole.

 

[Lucky6547]

Same range, same elevation, same target even, was raining both days.

 

[Plumsask]

What about wind? Is it possible that it mKes thag much of a difference at 600?

 

[Lucky6547]

60fps is 41mph...winds were only at most 6mph...

 

[Lucky6547]

It is an e-target, I don’t have any muzzle velocities