Hello,

I was chronographing several loads today, but had to set my chrony up at 40.5 feet because I didn't have enough light closer to the muzzle.

If I was at 2279 fps at that distance, what would you estimate my muzzle velocity to be?

I was shooting a 450 grain North Fork bullet out of my 458 Lott.

If the screens are set at 10 feet, the difference is usually around 8 fps. So, maybe 30 fps.

call it 2300 and call it good

Load From a Disk can calculate it.

2 variables you didn't include but needed are chrono screen spacing and ballistic coefficient.

I plugged in 2' and 1.2 BC for a corrected muzzle velocity of 2288fps.

I was thinking it would probably be around 2300. Not that it makes a difference in hunting performance, but I am trying to compare to some load data I found online.

I'd have to measure the screen spacing on my chronograph, but I'm pretty sure it's under two feet. It's a Chrony F1.

To my knowledge ballistic coefficient isn't available for North Fork bullets.

Nor does LFaD list that brand of bullets in their database. I gave the benefit of the doubt that NF's are as streamlined as a .458" bullet can get. The range of BC's is .1 to 1.2.

I plugged in a 1' screen spacing and came up with these results:

1.2BC=2288fps
1.1BC=2289fps
1.0BC=2290fps
0.9BC=2291fps
0.8BC=2293fps

Onefunzr2:

Thank you for going through all that trouble! That sounds about right and puts me w/in 12 fps of that 2300 mark, worst case scenario.

I'm going to set up at a different range next time, at that one I can put the chrony at 10' from the muzzle.

Be careful with setting your chrono at 10'. That might be too close for a 458 Lott.

The muzzle blast from my 338 Win mag overwhelmed my Oehler chrono, so I had to move to 14' to get reliable readings. Although it might have had something to do with the overhanging branch from an oak tree shading the 3 skyscreens.