Muzzle Velocity Question

[arkansashntr]

I don't have a chrono and was wondering if I could determine the muzzle velocity on my rifle by going to a ballistics table in the back of a reloading manual and finding the corresponding bullet drop with a 100yd zero... My rifle drops 2.5'' at 200 yds with a 100yd zero and according to the manual I have a muzzle velocity of 2975 fps with a .308 and 18.5" barrel. This sounds way too fast... Wondering if anyone else has ever tried this?

I'm shooting 155 gr Amaxs with 42.6 grains of Varget.

Thanks
AR

 

[thrusty]

Dunno about how accurate that would be to try to do. I do know that apps like Shooter have the ability for you to input confirmed hits (MOA up from zero) at a specific distance (Yards) and it will give you an estimated velocity.

 

[Bradaus]

42.6gr Varget and 155gr Amax? Yeah that sounds way too fast. I doubt you'd be pushing more than 2500fps with that load.

Minimum recommended load for varget with 155's for a 308 is 44gr...

 

[ChemE1975]

you'd might be able to get an approximate value, but i would not hang my hat on it, not by a long way. there are all sorts of variables which need to be taken into account.

 

[TRTAC]

I dont use the provided BC either. Best thing to do is borrow one. You could try plugging your dope into a calculator with a 100 yard zero and data from say 500 yards..... Might get you in the ballpark, but not an exact number. Once you have your dope for the gun your velocity doesnt really mean much. Its just a nice starting point for collecting data.

 

[TRAAV]

In my experience the chrony is only going to give you a good starting point. You still need to go out and check your actuale drops at distance. You probably need to get out past 500 to really tell what its doing.

 

[roggom]

Here are a few links to the G7 and Vortex's version of the G7 software. You can make adjustments based on drop to get a pretty darn accurate drop chart. It is best if you zero at 100Y and shoot to at least 70% of your max distance, i/e 700Y. If all you will shoot is 500y, then shoot to 300Y. Sure the best best is a chrony, but I do not use one, and tried one a couple of years ago. The G7 method has been working for me.

gseven - Ballistic Program

Vortex Optics - LRBC


You will have to do some searching on the sites for the software tweaking tutorials, but in a couple of range visits you should be good to go.

BTW, it is gonna be pretty darn hard to recognize the full potential of the 155 with a 18.5 bbl. Max charge of Varget is 46 and you may be lucky to get 2800. Not that they wont fly flat, just wont be getting the high BC's.

 

[mikeltee]

The further you take it out and measure your drop, the better. I bet you could get pretty close at 1000. 200 seems a little short. Reloading supply shops rent chronys for $10/day around here. Call around and ask. I bet someone on here would let you borrow one if you asked nice enough.

 

[arkansashntr]

Thanks for all the advice. I've shot out to 600 with this rifle and was just curious what my muzzle velocity for my own FYI. I will check out the sites recommended.

Thanks again and safe shooting

AR

 

[TRAAV]

What was your drop at 600 with a 100 yard 0. Also what was the conditions (DA, Temp, etc.)

 

[JGorski]

Yeah, that works out to this:
Range (yards) Velocity (fps)
Muzzle 3160 3437 -1.5
100 2934 2963 0
200 2720 2546 -2.5
300 2516 2178 -9.8

With a 155AMAX you should be up to about 47grs Varget, of course 47grs RE15 always works better.

 

[JGorski]

I do my trajectory figures like this, zero at 300, then go to 200 & 100 and come home and get on Hornadys ballistic Calculator, this target and the calculator proved to be very accurate when I took my first shot at 600yds on sunday. After I took the 3 shots at 300 I dialed the scope down 1 click so it would be zeroed there. Ive got a chrono on the way to verify this.

 

[arkansashntr]

I like that approach. I will do that on my next range trip.

 

[JGorski]

It worked for me, velocity worked out to 3355, give or take a few fps I sure, had to come up 3 clicks at 600yds. Like I said, I verify it with my new Chrony when it gets here.

 

[arkansashntr]

The max load in my Hornady book for varget is 44.9 wouldn't 47.0 be unsafe??

 

[6brshooter]

I tend to use the powder manufacturers load charts. Hodgdon 's "max" is 47.0 gr varget with 155 Palma. I run from 46.5- 47.2 gr varget in a couple different24" bolt guns, they run 2890-2925. I used to get drops out to 500, then backtrack on jbm to find velocity . I would then take that data out to 1k and use the jbm drops as a starting point to fine tune the drop card from 600-1000.