Bullet drop, muzzle velocity and energy

[Zeno~SPARTA~]

This is more of a note to myself to consolidate some info, not an attempt to educate. If there are any errors please feel free to comment.

 

The other day whilst attempting a sniper mission in ArmA the topic of bullet drop came up. As usual I took the M107 for its huge stand off range advantage. It was stated that the bullet drop for the M107 was less than that of the M24. I pedantically pointed out that in fact the M107 had a higher Muzzle velocity. I was not correct. After a bit of research and thought this is what I have determined.

 

Bullet drop

 

If you hold the bullets of a 12.7x99mm (.50 cal) in one hand and a 7.62x51mm in the other, both at the same height above the ground and release them simultaneously, they will hit the ground at the same time. If fired on a level field the two bullets would also hit the ground at the same time, not only as each other but also at the same time as the 2 bullets dropped in the first example. So Bullet drop as a function of time is a constant (this is simplified since I have not taken into account resistance).

 

Muzzle velocity

 

7.62x51mm

 

2,756 ft/s (840 m/s)

 

12.7x99mm Lapua

 

2,618 ft/s (798 m/s)

 

The Muzzle velocities of the 2 rifles are similar (in fact the .50 cal has different ammunition ranging up to 3,029 ft/s). So why is it that the M107 can hit a man at 2,430 metres (the longest verified sniper shot) whereas an M24 is all done at around 800.

 

Muzzle energy

 

7.62x51mm

 

146.6 grain 9.5 grammes 2,472 ft/lb (3,352 J)

 

12.7x99mm Lapua

 

750 grain 49 grammes 11,419 ft/lb (15,482 J)

 

So it is the Muzzle Energy that gives the M107 its exceptional knock down ability at extreme range. If Bobby Lee Swagger is to be believed the .50 cal bullet has the same power after 1 mile as the .44 handgun round has at point blank range. But thats hollywood.

 

Here's a few facts for those of you who like to use a 5.56x45mm assault rifles.

 

62 grain (4.0 grammes) FMJBT 940 m/s (3,100 ft/s) 1,775 J (1,309 ft·lbf)

 

The MK12 SPR has a special 5.56x45mm round, the MK 262, with 77 grain and 5 grammes. It is a more accurate round although its effective range is 550 metres.

 

 

Source is mostly Wikipedia

[Zebb]

Lol, nice post mate, a lot of a weapons effectiveness is dependant on the quality of the ammunition provided, when they first started using the 107's predecessors they were using ammo from WW2 and it showed in the results which put off a lot of snipers from wanting to use the kit, they preferred to stick with their 7.62 M24/M40, but once ammunition was developed by their military specialists who deal with making and checking all the ammo the US forces use then it became the piece of kit it should have been all along.

 

I have been reliably informed that the snipers currently in action are using their M4's with ACOG's but with a higher grain ammunition to get a vast number of kills out to about 600 metres and sometimes further instead of their sniper rifles, especially in the urban environment, obviously once you get above that range and particularly in wide open terrains then that's when the sniper rifles and mainly the 107's come into their own, it is not only the snipers who carry out these shots, a lot of units have what they call a "designated marksman" who is someone who has proven to be an excellent shot on the ranges and goes on to do some extra training, he is then issued with a tweaked weapon with a stronger barrel an ACOG sight and the higher grain ammo, and they are used to engage targets at longer ranges.

 

The bigger round of the 107's gives you more propellant so the range so it's effective range is going to be better than a 7.62, even if by the time the 107 has reached any target it is likely to be sub-sonic by then and the enemy probably won't even know that they are under fire (because you won't hear the characteristic "crack" as the round arrives) until you have made your corrections and hit your intended target.

 

By the way, snipers generally don't try to make headshots at anything over 500 metres and at extreme ranges because the variables are so large, wind, air density etc etc they aim to make the first round either on target or short so that their spotter can see the fall of shot and make the necessary adjustments to ensure the second round is a kill.

 

 

So in conclusion if any weapon has sub standard ammunition it's effectiveness, especially at longer ranges, is going to be reduced.

 

 

Source: mainly off the top of my head so feel free to make any corrections for bits that may be complete cobblers.

 

 

[Zeno~SPARTA~]

Hathcocks record hit at 2,268 metres (1.42 miles) was with a Browning M2 .50 cal machine gun with a scope on a custom made mount of his design. They say it was because of his success with this weapon that .50 cal sniper systems were developed. I dont think I could hit a 2,200 metre target in game, that performance with real world variables is incredible.

[Athlon64~SPARTA~]

Well being a avid shooter and reloader for 35 years, I can say its the bullet weaght and style that makes the big difference

Standard ball round= copper jacketed square bottom

Macth round= Is useally a spiztzer boat tail copper jacket bullet

Sniper macth round= Is a spitzer boat tail balanced copper jacket bullet.

 

The balanced bullet will fly truer, strighter, and go longer distance before tumbuling as it slows down at a greater distance when slowing down thru the sound barrier. Useally a bullet becomes unstable in flight as it hitts turbulence slowing down thru the sound barrier, mostly causeing it to tumble. The heaver balenced bullet resists this condition and also carrys alot more kenetic energy for impact. And of coarse the quality of the barrel and the action of the rifle matters alot also. The amount of twist per inch and the deepness of the rifleing in the barrel, and bullet compression, and the head spaceing of the chamber holding the carterage, Bullet seat depth, and exact measurement of propellent makes the big difference. Even the brass caseing hardness has an effect. Its not 1 bullet being good, Its all the bullets the sniper has being consistant to one anouther and then the gun set or zeroed to that paticular round. The difference of bullet seat depth of .005 of an inch can mean the difference of 1 inch at 500 yards.

 

What I mean buy consistant

Caseing length the same

Powder amount the same

Condition of the caseing the same

Bullet head the same

Bullet seat depth the same.

Primer the same bacth mfger

 

Becouse as a bullet or round is fired. The caseing has to expand to fill the chamber of the rifle to provide a seal, and at the same time it also streaches in length. Now if this round is to be reloaded, it has to be resized to the origanal size and length. Now after this has been done it causes micro fractures in the brass caseing, and causes the caseing to become hardened. After several times of this the caseing will fracture and break unless it is re anealled, but it effects the expansion rate of the brass effecting accuraccy.

Edited August 22, 2008 by Athlon64~SPARTA~

[Zathrus~SPARTA~]

I think this agrees with the above. This is from my current sport shooting.

 

Based on target shooting & hunting I know the following is true.

For very long shots Arma makes it easier to hit the target as it doesn't manifest wind or its effects on projectiles.

Obviously the shorter the shot, the less wind effect as the bullet has to lose energy before it can be deflected.

 

As Zebb said, the quality of the ammunition is also very important. At this time I primarily use these ammunitions as follows:

http://en.wikipedia.org/wiki/.22_WMR

http://en.wikipedia.org/wiki/.22_Long_Rifle

http://en.wikipedia.org/wiki/.218_Bee

 

For these smaller calibers I use only winchester ammo as I am familiar with it and I have found it to be consistent.

I am sure there are better manuf.'s but for the stuff I do, Winchester and Remington are cost effective.

Currently, Winchester is easiest to find in my area.

[Xross]

 

There are many factors involved in the ballistic (internal and external) characteristics of a bullet. Once you start fine tuning things then the sectional density and ballistic coefficent of the projectile becomes more critical.

 

All things must be considered including but not limited to:

 

Case capacity

Primer Speed

Powder burn rate

Head Space and Free Bore (leap)

Barrel twist rate for proper stabilization at a specific bullet weight

Barrel Whip (harmonic vibrations)

Barrel Crowning

Trigger Break

Bullet Style

Bullet Weight

Sectional Density

Ballistic Coefficient

Other things that I've now forgotten ;-)

 

I have heard people say that a bullet rises above the bore line prior to falling below it. This is fundamentally incorrect (not too mention impoossible). It may rise above the line of sight but not above the line of departure (bore axis).

 

Here's a good primer on the subject:

Ballistics for Dummies

 

 

Sidebar.... I'm very close to having my rig back up and running and am in need of an ARMA fix in a bad way

 

[Zeno~SPARTA~]

Look forward to your return.

[Athlon64~SPARTA~]

Todays U.S. snipers all custom load their ammo. Basic ball ammo is not good enough, regaurdless of the mfg. Eather Lake city ordence or any of the outhers.

Edited August 22, 2008 by Athlon64~SPARTA~

[Athlon64~SPARTA~]

Here is a good guide to most of the different .50 or 12.7mm browning maw duce rounds. They made a ton of different rounds.

 

http://www.inetres.com/gp/military/infantry/mg/50_ammo.html

 

Edited August 24, 2008 by Athlon64~SPARTA~