calcs for muzzle velocity

TimC

TimC

CGN Ultra frequent flyer
Rating - 100%
1   0   0
Location
England
Is there a reliable way of calculating muzzle velocity to within 100 fps without a chrono. Not being lazy or tight but I have spent some time last summer working out a load for my .303.
its 44.3 gns of IMR4895 under a Sierra 125 gn sp bullet.
I got this load by shooting it to compare groups and points of impact with 150gn Norma factory. It suits me and I would like to know what MV it is producing.
I have sieera infinity, will that help?
I have to work a similar load as I have run out of IMR4895 and wont be getting any till much later this year! So the new challenge is to replicate this loading another powder so I think I need the MV to be sure!
Edited to add. I have looked up IMR and they dont give a load for the 125gn bullet, Sierra Infinity shows it to be between 2800 and 2850 fps. Tht is acceptable I suppose. I just need to fingd something similar. I found a new tub of varget that I bought, not sure why, that may hold the answer!

2305 .303 Caliber/7.7mm (.311) 125 gr. SPT OAL 2.900

Powder/Velocity 2600 2700 2800 2850 2900
XMR-2015 38.4 40.0 41.6 42.4 43.2

IMR-3031 39.2 40.8 42.4 43.2


Benchmark 38.3 39.7




AA-2460 37.7 40.1 42.5 43.7 44.9

H4895 41.1 42.5 43.9 44.6 45.3

Viht N135 40.1 41.8 43.5 44.4 45.2

VARGET 42.2 44.0 45.8 46.7 47.6

IMR-4064 42.4 44.0 45.6



AA-2520 41.0 42.6 44.2 45.0


Viht N140 42.9 44.6 46.3



Energy/ft.lbs. 1876 2023 2176 2255 2334
Accuracy Load: XMR-2015/ 41.6grs. 2800fps/ 2176ft. lbs.
Hunting Load: XMR-2015/ 43.2grs. 2900fps/ 2334ft. lbs.
Copyright 2003 Sierra Bullets, LLC.
 
Last edited:
Try this:
Set your rifle for a 100yd. zero.
Shoot it at 100, 200, 300, 400, 500yds, of couse you will need some really long targets to read your groups.
You will also need to shoot at least 3 shots at each distance(5 shots is better) now measure the drop at each distance, and record. When you get home get your loading manual out and track the bullet in question in the trajectory tables. When the numbers get mighty close, there's your MV.
If you aint got a 400 or 500yd range, the chrony is about the next best choice.
 
F-1 here is about £99 for the cheapest deal, thats closer to C$250. It isnt the way I wanted to go. Ihave relooked at the figures and all Ineed now is a Varget, Vhit or Hogden load that will get me close to 2800-2850 fps with a .311 in 125 grain.
I can probably work that out without the chrono. I spent some time matching POI at 100 yards for the factory 150 gn ammo and my 125 grain hand loads. The idea being not to have to change the scope settings if I change mags. I hate to use 150 grain ammo on anything smaller than Fallow and I like to use 125 gn up to that size deer. I may keep the factory mags in reserve and use the handloads exclusively knowing that should I see a deer in the local woods up to 150 yards it is burger press time!
 
That will have to wait until I have a new job. typical is that when I work I dont have the time to spend my money and when I 'm not working I'm usually skint! I may do some research and get ready for the summer. I have enough of every possible calibre loaded now for the remains of the doe cull. I am meeting a landowner next week about his woods and I'm going to need somewhere to chill and hang all this venison.
 
Look up "ballistic pendulum".

In reality, measuring drop is more sensible in some ways than using a chronograph. You will know where the loads impact at real ranges rather than calculating drop tables that approximate real world performance. This is like the people who sight their rifles x cm high at 100 metres then say "It is zeroed for 300m". Ha-Ha.

If you want to sight a rifle for 300m, you can do the x cm at 100m trick, but you must then set a target at 300m and test your assumptions. This is a roundabout way to say that you should try your various loads at different ranges and adjust your sights accordingly. There are lots of good external ballistics calculators free on the Web. with them and a notebook of how your loads perform on the range, you should be able to readily calculate what your optimum point(s) of impact should be set at 100m.
 
Robert11 sorted it out thanks but even as he says the program can be as much as 50-100fps out depending upon case length.
nice chap though has volunteered to do some calcs for me to sort out a suitable similar load from some of my other powders.
IMR is of the buy list for a few weeks if not months!
 
TimC said:
he says the program can be as much as 50-100fps out depending upon case length.
Click to expand...

The way to be sure is a chrony, or various other physical measurements (like 100/200/300 drop as already suggested).

Having said that, "the program" will give you better results than stated if you give it good input data. For example, measuring the capacity of your fired (for high-pressure) or sized (for low pressure) rounds by weighing the amount of water they'll hold. Also, direct measurement of barrel length (as opposed to what the manufacturer says the length is). And so on.

I've confirmed this with .308, .223, and .357magnum and .50AE with several different powder/bullet combinations.

If you just use the defaults, then the numbers may be off as mentioned - so don't use the defaults.
 
You must log in or register to reply here.
Back
Top Bottom