calculate muzzle velocity???

K

kilotanker22

New member
is it possible to closley calculate muzzle velocity using a given bullet weight bc and such using the difference in elevation on the target at varying ranges?

if so could someone help me out?

the rifle is a browning xbolt 300 wsm 23 inch barrel

the ammunition is federal fusion 150 grain not sure of the ballistic coefficient. the advertised velocity is 3250

i sighted 2 inches high at 100 yards when shooting a group at 200 yards i was hitting 1.5 inches low that is a change in point of impact of 3.5 inches from 100 yards to 200 yards.

what kind of estimated velocity am i looking at here?
 
"Sumpn ain't right!"

Two inches high at 100 yards should have you a smidgen high at 200.

Normally, any 150-grain bullet, flat-based or boat-tailed, soft-point or hollow-point, and a muzzle velocity of 2,900 to 3,000 ft/sec will be right at dead on at 200 if sighted in for two inches high at 100.
 
That's what I thought as we'll ART.

However the gun shoots lights out and no noticeable problems with recoil repot and what not.
 
According to federal with the advertised velocity of 3250 sighted at 100 yards the point of impact should be 2.4 inches low at 200. My bullet is dropping 1 inch more than the advertised ballistic report so I just figured with my 23 inch barrel I am likely losing 100 feet per second from the advertised speed
 
It's pretty rare to get the velocity published on the box, even with the same barrel length. I've personally seen two gun/cartridge combinations that do it, 17HMR and 7mm-08. Most tend to be as much as 200fps slow, probably averaging about 150 IME.
 
Just off the cuff, I don't see how a 3% drop in velocitywould cause a 30% drop in trajectory.

This goes into the Damfino file. :)
 
You really need to buy or borrow a chronograph. An inch of barrel isn't costing you 100 fps. Numerous folks have done this experiment and none have lost more than 30-35 fps from 1" shorter barrel with a 300 WSM. I know guys who are only 150 fps below factory specs from the 16" barreled Ruger's in 300 WSM.

A difference of 50 fps or so between barrels of equal length is very common and over 100 fps is not unheard of. I load for 7 different 30-06 rifles. Five have 22" barrels, one is 20" and another is 24". None are the same with over 100 fps difference between the 5 guns with 22" barrels, and they overlap. The 20" gun is faster with the same ammo than the slowest 22" gun, and the fastest 22" gun shoots faster than the 24" gun. All with the same ammo.

I suspect YOUR gun may be shooting a little slower than normal and combined with some ammo shooting slower than advertised.

The only way to know for sure is to chronograph ammo in your gun.
 
I have you at 2900fps to get that drop using a 150gr bullet with a BC of .400 . "IF" they used a 26" barrel and there Velocities are a bit high . I' say your 23" barrel is shooting about what it should . Problem is that's a whole lot of "IF"

@ 200yds your right around 2450fps with about 2000 Ft# of energy
 
no there is a bit more info that maybe could make a difference but i dont know

first off the barrel had around 20 rounds through it today when i shot my group at 200 maybe fouling could cause me being an inch low?

the thing that confuses me is if it were fouling would the rifle still group really well just move the point of impact of the group?

i will retest tomorrow but i feel that maybe my point of aim on the target was a little different than i thought
 
I have yet to see factory ammo come close to advertised speed. I ran test with Winchester 30-06 180 gr. powder point bullets advertised at 2700 FPS. I used three rifles with 22, 24 and 26". velocity with we 22" was 2610 FPS, 24" 2630, The slower 1 in 12" twist may be partly resposible and the 26" Ruger #1B did 2660 FPS. Close but no cigar. I believe factories still don't cheat fair especially with the newer hot shot cartridges, Probably determined their advertised velocity with a minimun dimension 26" barrel to get every foot second of speed possible. Even loading manuals cheat. Nosler uses a 26" barrrel for the 7-08 but a 22" barrel for the 7x57. Just how many 26" 7-08s are there on the market today? None that I can think off offhand so I could be wrong. :eek:
Paul B.
 
Hmmm ,I don't load for either but I checked my manuals and the 30-06 holds 10gr less of powder on average and should be quite a bit slower then the WSM .Now that I'm seing that on paper I'd say there is something else going on there . Not sure what that is though . We are talking about a very small measurement . How large were your groups at 100 and 200yds and at what part of the group did you measure as being 2" high or low ? If you missed the measurements by a 1/3" at each distance , high at 100 and low at 200 . That would change your estimated velocity quite a bit . At a glance that could be as much as a 200fps difference . That could mean your closer to 3100fps .
 
Midway had the bottom feeder chronys on sale for $85 bucks here awhile back & I got one.

Once you shoot over a chrony it's such a relief to be done with all that guesswork.
 
A little bit off topic.................then again maybe not if you're trying to use drop charts to estimate velocity.

I have shot a lot of high power rifle in the last, nearly 40 years. M1's, M14/M1A's, and AR's. Plus CMP Vintage Rifles, M1917s, M1903s, M1s.

HP is 200, 300, & 600 yards. Sometimes 100 yards on reduced targets. And a huge majority of my practice is at 100 yards.

You have to have a zero for 100, 200, 300 & 600 yards.

We know the velocities of the '06, 308 and 223 are different. Having said that, in all my service rifle zeros, and vintage rifles, there is a 2 MOA difference between 100 and 200 yards.

It doesn't seem to matter which bullet, be it 150 or 168/175 match bullets.

Before we say that is me, the same 2 MOA come-ups are listed in Hatcher's Book of the Garand, Cpt Edward Lewis' Book of the Springfield and LTC Brophy's "The Springfield 1903 Rifles". I believe Whelen's books too (have to recheck them to be sure. Hatcher also shows the charts in his "Machine Guns 1917"

So I think a lot of math would be involved in determining velocity from drop charts but I'm not a math wizard.

I do know, that regardless of what chronographs, ballistic programs, trajectory tables say, you need to confirm the results on the range.

Its not just 308 & '06. My AR service rifle also has two MOA change in my zero from 100 - 200 and its faster then the two 30 cal. bullets mentioned.

Of course my 270 hunting rounds throws all this out the window.

Just thought I'd throw this in to confuse the issue.
 
There may well be 2 MOA for service class cartridges but that certainly will not apply to all cartridges. If the same bullet is fired faster it will drop less over the same distance. If a higher BC bullet is fired faster it will drop even less.

As an extreme example, a 32gr .204ruger, MV 4,200fps, only has a tad more than 1/2 MOA drop between 100 and 200 when zeroed at 100.
 
That's why I added that my 270 throws a wrench into the equation.

There a .4 MOA difference between 100 and 200 yards.
 
kraigwy I think I agree with your basic point or at least how I see it . The difference from 100 to 200yds and the trajectory of the same cartridge from gun to gun or bullet manufacture to manufacture is not going to be much . I think the shooter would need to be one heck of a shot as well as the firearm being able to shoot lights out for anyone to be able to get the exact or close to the MV there getting from a given cartridge using a drop chart . Like the OP said . If he had even the slightest change in POA at each distance . That would throw everything off .

I also agree that it does not matter what velocity or what any drop chart says . How the rifle shoots and where the bullet hits in the field is all that matters . If the rifle hits 2" high at one distance and low at another every time . Thats what the gun shoots . I would be a little upset if I was no where near what I should be getting though and would want to understand why .
 
I think the shooter would need to be one heck of a shot as well as the firearm being able to shoot lights out for anyone to be able to get the exact or close to the MV there getting from a given cartridge using a drop chart . Like the OP said . If he had even the slightest change in POA at each distance . That would throw everything off .
Click to expand...

All you need to do is shoot groups. Group center should show the drop. You'd never go by one (or two) shots at each distance.

The ballistics calculators tend to be a bit pessimistic but they give you a reasonable idea. The trajectory differences are pretty small so the error in velocity prediction won't be all that far off.

No matter what, you have to put bullets on target at the distance you plan to shoot. You wouldn't go to a match having never shot 600 any more than you (hopefully wouldn't) shoot an animal at 400, having never shot past 200.
 
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