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Expectations for MV Consistency

16 May 2014
@ 07:44 am (GMT)

Joshua Mayfield

When you guys shoot a batch of handloads through a chronograph, what do you consider a good spread between your high and low muzzle velocities? And how do you go about acquiring that? I have done all of my powder loading by hand measuring volume and checking some loads for weight. My greatest spread in muzzle velocity has been 30 fps or less that way. I've always wondered if that spread would grow were I to switch to some form of powder dispenser. Any thoughts?

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16 May 2014
@ 05:40 pm (GMT)

Quote this

Nathan Foster

Re: Expectations for MV Consistency

Hi Joshua, this is highly relative.

An acceptable ES will depend on the power of the cartridge and range you wish to shoot to and BC etc.

I wrote about this to some extent in the second book within the .338 section.

Going over this again, I like to have my rifle group around 6" at its maximum range. So, lets say the rifle groups .3" at 100 yards, it has the potential to group 3" at 1000 yards (excluding other variables). If we have a low ES, this may account for say 3" vertical dispersion at 1000 yards and give me my potential 6" grouping. If the ES is very high, we may be looking at 1 yard of vertical dispersion which is hopeless.

But as for exact numbers of what is and isn't acceptable, we need to look at the individual cartridge.

Lets say you are shooting .308 with the 168 grain A-Max with a max effective range (wide wounding) of around 800 yards or 1400fps. Now lets plug in two muzzle velocities, 2650fps and 2680fps. Lets see how this looks at 800 yards:

2650fps drop -196.13"
268fps drop -191.1"
Difference = 5"

This basically means that the rifle needs to group into one hole at 100 yards in order to be effective out to 800 yards. Or going the other way (if the rifle groups say .3" at 100 yards), we might have to drop our max range back a bit to say 700 yards which would make for a nice accurate rifle and effective load at this range.