Muzzle Velocity without a Chrono

[jbaker47]

anyone know how to get it? I'm trying to set my handloads up in a ballistic calculator and need to know muzzle velocity.. would a ball park estimate work?

.308
24 inch barrel
1;9 twist
150 grain nosler ballistic tips
39 grains of IMR 3031
federal brass and primers

any info at all would be real helpful

 

[BOLTRIPPER]

Re: Muzzle Velocity without a Chrono

somewhere between 2000 and 3000 florida foots per seconds

 

[jbaker47]

Re: Muzzle Velocity without a Chrono

thank you... i plugged that into my BC and the difference is between 44 clicks of elevation or 112 clicks of elevation...

 

[buffybuster]

Re: Muzzle Velocity without a Chrono

You can get a pretty good estimate of your MV from this:

Get a good 100yd zero. Then shoot at longer known distance (400yds or more), ideally at a large shoot-n-see. Record atmospheric conditions and DOPE required to engage distant target.

Take that data and feed into ballistic calculator (JBM Ballistics), select the bullet from the dropdown menu (Litz preferred). Input an estimated velocity and run the calculator. Adjust the MV, until the calculated trajectory matches to your actual DOPE. That should give you a pretty close estimate of your MV.

 

[Notso]

Re: Muzzle Velocity without a Chrono

I've always wondered if calculating MV from drop numbers at various known ranges wouldn't be more accurate than most chronos. The reason I think that might be the case is because there is no way to calibrate a chronograph. So how do you know the numbers it spits out are accurate? I've chrono'd the exact same loads over three different brands of units on the same day and had variations of 20-50 fps between the three.

I know you can calculate a BC number from drops if you know the MV. My Bulletflight app can do that on my iPhone. So I assume you could do the same if you had an accurate BC (Litz) and solved for MV.

 

[vman]

Re: Muzzle Velocity without a Chrono

Set up a target at 300-400 yards. Put in a guestimation into the ballistic calc. Fire a few off at the distant target using elevation adjustments based on your guestimate.

Work back from this. If the rounds are impacting higher your guestimated MV is too low. If the rounds are impacting lower your estimated MV is too high. Make small adjustments of the MV until your ballistics calc has you hitting target in the horizontal plane.

 

[psmith]

Re: Muzzle Velocity without a Chrono

My Hornady manual lists this combo as

min 40.2 gr 2658 fps

max 43.5 compressed charge 2881 fps

I picked up 100 fps with my Bartlein from my stock rem so that will make a difference too. I'd try a guess around 2600 or so.

Like other said, I don't have a chrono yet but I have had good luck getting a good zero and then using a program like Exbal to match the trjectory. Give me a PM with your dope (500yds or better is best) and we can run the #'s.

 

[RTO]

Re: Muzzle Velocity without a Chrono

+1 on shooting as far out as you can and use your dope to plug into a ballistic software program. Change your muzzle velocity on the program until your dope matches your furthest distance. The closer distances should be right on then. I have found that chrono muzzle velocities plugged into ballistic programs dont match anyway. The number that you use to plug into the software to match your dope will be your new MV that you will use for calculation purposes for the program.
Just another way to skin the cat.

 

[vman]

Re: Muzzle Velocity without a Chrono

RTO, theres usually a variable the shooter has forgotten about.

Dont forget theres more to it than just MV, BC and sight height. These things tend to get you there in short to medium range... going further and Temp, humidity, density etc all come into play with what appears to be greater impact.

 

[jbaker47]

Re: Muzzle Velocity without a Chrono

thanks this is all very helpful.. vman: my ballistic calculator is on my droid. it gps fixes on my phone and inputs all the atmospheric data.. all i have to do is put in the wind direction relative to which way I'm facing