Muzzle velocity & bullet drop

[fishnbeer]

I recently started tinkering with these mil dot scopes for a bit and next week i will be reloading .308 for my first time.

So i have gotten good with using 'mildot master' slide ruler for estimating range, thus far only out to 100 yards to get familiar with it. Now my next step is knowing bullet drop at various distances with the hand loads i will be shooting.

Now .... how do i determine bullet drop? Can you use a Chronograph to measure muzzle velocity and make a calculation based on that? Meaning bullet drop is directly related to muzzle velocity? Or do you actually have to shoot at set distances with rifle on a sled and measure bullet drop?

[Rbutler]

to determine bullet drop you would typically get your velocity and plug all the metrics into a ballistics app on your phone or here

then once you have that data it is preferred that you shoot at each distance and confirm the drops/make your custom table. remember to check zero and drop in different temp ranges as well.

[fishnbeer]

Do any ranges rent out chronos? Some ranges they rent out spotting scopes but i would imagine a chronograph being a bit more pricy and delicate

[dskit]

Very little mystery about 308 loads. A chronograph is preferred, but give the barrel length and using your well researched, published load data, an estimate of muzzle velocity should not be too hard.

With that, and JBM, you should be pretty close, and can fine tune to speed input if you can get out to 500 or 600 yards.

[CSACANNONEER]

Bullet drop has many factors, distance and MV are probably the two biggest. But, you should know the BC of the bullet too. Also, wind can play a big factor in drop. After that, there are other things to think about like air density, shooting angle, etc.

[Rbutler]

Bullet drop has many factors, distance and MV are probably the two biggest. But, you should know the BC of the bullet too. Also, wind can play a big factor in drop. After that, there are other things to think about like air density, shooting angle, etc.

shooting angle does not not change drop. you just need actual distance to target (as the crow flies) NOT your line of site.

[shooterfpga]

shooting angle does not not change drop. you just need actual distance to target (as the crow flies) NOT your line of site.

Wouldnt that be part of the formula....

[fishnbeer]

this morning i went out and picked up some bullets powder and primers. a mid range load for what i selected gives me about 2600fps. hornadys site lists the BC at .349. so now i have a good estimation of my bullet drop

that calculator is pretty sweet. its interesting to tinker with that numbers and see how it affects the output data

so i guess at this point i just load up some rounds and see what happens. i purchased enough to load 100 rnds so that should get me started. i plan on doing 25 rounds of each powder load, take notes and save my brass again

[thospb]

Look up Optimum Charge Weight, you will find it a very helpful method for finding your ideal load. Also, even if you Chrono the round, the Ballistic Tables are only a starting point. You will find everything changes with temperature and humidity, taking notes and learning how your rifle performs under different conditions is what counts. Have fun.

[FMJBT]

I typically shoot at a known distance target after getting a 100 yard zero. I measure the drop of the bullet to hit center to the known distance target, then adjust the velocity in the ballistics calculator until the drop I physically see matches the number listed in the drop chart. I'll then shoot a few more rounds at another known distance target at a different range and check that drop against the calculators drop chart to verify my velocity. After that, you should be really close across the board for the drops listed in the ballistic calculator, provided your other info like BC and altitude density are correct.

[shooterfpga]

I typically shoot at a known distance target after getting a 100 yard zero. I measure the drop of the bullet to hit center to the known distance target, then adjust the velocity in the ballistics calculator until the drop I physically see matches the number listed in the drop chart. I'll then shoot a few more rounds at another known distance target at a different range and check that drop against the calculators drop chart to verify my velocity. After that, you should be really close across the board for the drops listed in the ballistic calculator, provided your other info like BC and altitude density are correct.

How often do you have to true your velocity? Seems like you would have to do this every trip unless youre using mv variation and powder temp as well.

[postal]

How often do you have to true your velocity? Seems like you would have to do this every trip unless youre using mv variation and powder temp as well.

For 308, the most common powder is varget which is very temp stable. I used it for years. Dont leave your ammo in the sun. Otherwise from winter to hot summer the Vel change is rather small.

Once you have known data, the real issue is 'density altitude' or DA changes. This will be the biggest factor. Barometric pressure- How thick the air is.

This changes with air temp, storm fronts, altitude changes- (sea level- 3000ft- top of a mountain 6000 ft..) and humidity.

With an online program like JBM, if you have a kestrel that measures DA- plug it in. With a phone app like shooter, you can enter a new DA in your phone and have it spit out the info on the fly while at the range.

If you enter the right info in JBM it's surprisingly accurate- not perfect, but really close- Then fine tune it by changing elevation or MV to match your real world results.

Or buy the "shooter" app for your phone and a kestrel.

_______________________
OP... you bought the wrong bullets man.... you want hornady 177g AMAX or Sierra 175g SMK They have MUCH higher BC- .495 hornady, and .505 SMK... Use Varget.

[shooterfpga]

I use DA just recently and it matches very well especially with g7 & litz. I myself am experimenting with mv and powder temp to wring out the very last bits of correct dope among the entire scale. I understand stability of non temp sensitive powder but my reasoning is i dont think the dope chart will be AS accurate without mv variance and powder temp enabled. Maybe its .2 mil difference throughout but i want that preciseness.


Am i thinking incorrectly? Using DA my dope is pretty well on assuming a corrrect fps input. But is it doing the same thing as mv and powder temp when only talking about fps no other features? I entered my values using a baseline temp taken at the same time as zero. Then i looked at what my avg fps was at two other temps and calculated the difference per degree. and it showed me th corrected fps per my current conditions.

My comparison says no?

[kcstott]

My experience DA can contribute but if you break down all the variables that effect DA you'll see one variable that has more effect than they rest. and that is humidity.

Relative humidity variation effect muzzle velocity more then BP or Temp, if you plug in your variables and change one parameter at a time and watch how your muzzle velocity changes and how your bullet drop is effected it will be an eye opener.

[NorCalFocus]

I typically shoot at a known distance target after getting a 100 yard zero. I measure the drop of the bullet to hit center to the known distance target, then adjust the velocity in the ballistics calculator until the drop I physically see matches the number listed in the drop chart. I'll then shoot a few more rounds at another known distance target at a different range and check that drop against the calculators drop chart to verify my velocity. After that, you should be really close across the board for the drops listed in the ballistic calculator, provided your other info like BC and altitude density are correct.

You can do it a little easier and more accuartaly by using the validation option on Vortex's LRBC.

So you guess your speed and get a general chart. Then you shoot at the range to see what you really got. Go back into the program and plug in you max range shot, and the drop you really got, and if the weather was different. Then you will get a true velocity for your chart.