Thread: Actual drops - speed calc

This past weekend I took the Savage 7mm08 up to Hamilton and shot at known distances at the end of each stage of a FTR compo. I was hoping to be able to work out the muzzle velocity from these actual drops, but I am still none the wiser.

When I zeroed at 100yds, the baro was 29.50 inHg, and temp was 55.7 F

I've used humidity of 50% for all calcs.

Rifle details:
7mm08, 1:9.5, 22 inch
Nosler BT 120gr, using Litz G7 published BC (0.185)
Sight Height 1.75 inch

Results I got:

300 yds
Baro: 30.46
Temp: 86.2
Drop: 4.25 MOA

500 yds
Baro: 30.43
Temp: 82.9
Drop: 9.25 MOA

600 yds
Baro: 30.40
Temp: 74.9
Drop: 12.25 MOA

All these are giving me pretty different MV. Maybe one of the clever monkeys on here can tell me what I am doing wrong...

You're right, something doesn't seem right there..

If you were dialling for those drops, I'd be taking a sideways look at your scope first of all, maybe trying a tall-target test.

Was your zero spot on or close enough?

zero was tripple checked, and I paid good attention to paralax and cant when shooting the longer ranges

i've shot a 20 moa tall target at the same time as zeroing, all good.

only thing I can think of is that the initial dial is not to good because scope is almost bottomed out... the 500 and 600 makes sense at around 3050fps

What Calc are you using ebf?

shooter (android) , with zero barometrics enabled

Yup I am thinking you have it sorted if it is near bottoming out. 3000 fps sounds about right.
Maybe shim or get a rail so your start with your image/reticle central in your tube and go from there.

Any vertical component to the wind?

It may be your scope adjusts differing amounts threw its range of adjustment. Easy enough to check on a tall target with moa spaced lines and a vice.

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Not enough vertical to cause that difference Cam.

Yup, will redo tall target and do up/down 5, up/down 10 and up/down 20

My .260 shoots flatter to 400 than my Calc says it should.
It also catches up at 5 and 600.
Not sure why but it is only by a couple inches and I have my turret pre-set for 3 and 400 opposed to what shooter says it should be anyway.
Velocities are pretty consistant over different days of testing so I am sure that my muzzle velocity is not the main issue.

Does your scope dial accurately? why dont you chrony it to compare speed results or maybe your velocity spread is quite high

Ebf, the North Island forum chrony is here if you would like to use it

Originally Posted by scoped

Does your scope dial accurately? why dont you chrony it to compare speed results or maybe your velocity spread is quite high

it does, well at least for a 20MOA up and down tall target. could be an issue at the bottom end of the dial range..

more likely just the nut behind the butt

i don't trust chrony results for calculating long range drops, prefer to shoot actual drops and calculate back. valid point about using chrony to check quality control of reloads with ES and SD.

A bit rough and rule of thumb but working backwards assuming a BC of .36 for your round and a your drop of 48 in at 500yds the Speer reloading manual gives a MV between 3000 and 3100. It's a guess but may be in the ball park.

Buy a Chrony