7mm/08 and .308

[Shawnee]

Hey All...


Would one of you fine lads who knows how to calculate recoil happen to know what difference in the ft./lbs. of recoil there is (if much at all) between a good 7mm/08 deer load and a good .308 deer load from same-weight rifles - let's say 8.25 lbs with scope and pinstripes ???


Many thanks !

 

[Schleprok62]

It's not going to be THAT noticeable... I have a 7mm-08, and have fired enough .308 Win to say it's not a lot of dif...

The 7mm-08 is flatter, and carries more down range(energy and velocity)... the .308 ammo is available just about anywhere... They will both drop just about any North American deer...

 

[Vern Humphrey]

The formula is M1 X V1 = M2 X V2. The mass of the ejecta times the velocity of the ejecta = the mass of the gun times the weight of the gun.

The ejecta is everything that comes out the muzzle -- both bullet and gas. The velocity of the ejecta is a bit complex -- some of the gas can be going faster than the bullet as it leaves the muzzle.

But for comparison purposes, you won't go far wrong it you simply ignore the gas velocity problem.

Remember, you must convert grains to pounds (divide by 7,000) and you must convert pounds of weight to mass (divide by 32.2 f/p/s/s.)

 

[Shawnee]

You're right, Schleprok62.

I'm just wondering about the numbers. Would be nice to see the comparison with the 30/30 from a 6.5lb. model 94 and the 7lb. 336, and maybe even the .35 Rem. too.

Maybe someone has some software that spits that sort of thing out without too much trouble.

 

[Vern Humphrey]

Try using Excel. I plug in combined ejecta weight of 196 grains (powder and bullet), muzzle velocity of 2634 fps, and rifle weight of 7 lbs, and get recoil velocity of 10.584 fps.

The formula for Excel is:
=((A2*B2)/(7000*32.2))/(C2/32.2)
where A2 is ejecta weight, B2 is muzzle velocity and C2 is rifle weight.

Remember, this is a simplified calculation, and doesn't take the complex velocity of the gas into effect.

 

[telomerase]

The formula is M1 X V1 = M2 X V2.

All that would tell you is the momentum of the recoiling rifle. Momentum is not energy... if it were, we could just throw bricks and not bother with those teeny tiny bullet things

If you want to calculate the recoil energy of the freely recoiling rifle, you have to take the velocity for the rifle that you get from the M1V1 = M2V2, and then plug that velocity into 1/2 (mass of the rifle) X (velocity of the rifle squared).

And if they didn't teach you to do that in 7th grade, then you have grounds to sue your school. Really

 

[NCsmitty]

RealGuns has a program for recoil in their list. Just plug in the info. Not sure, may have to register to use but it's free to join.

http://www.realguns.com/

NCsmitty

 

[Vern Humphrey]

All that would tell you is the momentum of the recoiling rifle. Momentum is not energy...

Actually, it will tell you the velocity. If you know velocity, you can calculate momentum -- which is what you want, not energy, to measure recoil.

 

[Shawnee]

Cheryl "D-Cup" Davis sat next to me in 7th grade Math so if it doesn't show up on my $9 RadioShack pocket calculator I don't have a clue.

I registered at RealGun but they haven't sent the "activation email" yet.

 

[Art Eatman]

The common load for a .308 is a 150-grain bullet. The common load for a 7mm08 is a 140-grain bullet. They use the same amount of powder, give or take darned little; roughly 45 grains for easy math.

So, 195 grains vs. 185 grains. That's about a 5% difference. I doubt I could feel that, particularly when I'm looking at Bambi.

FWIW, my 6.5 pound Ti in 7mm08 is not at all any recoil problem at the benchrest.

 

[telomerase]

If you know velocity, you can calculate momentum -- which is what you want, not energy, to measure recoil.

Vern, the OP asked for the

ft./lbs. of recoil

Recoil energy can be expressed in foot-pounds, or ergs, or any other energy unit you want.

But it's not momentum.

Anyway, Art's right that the OP won't be able to tell the difference anyway .

 

[Vern Humphrey]

Perfectly true that kinetic energy and momentum are two different things. But recoil is usually expressed in momentum, not kinetic energy.

 

[Float Pilot]

Here are a few recoil calculator links.

You will find that due to the slightly heavier slug listed in most 308 loads, you will have between 2 to 3 extra pounds of recoil. Whoppie-doo...


http://www.handloads.com/calc/recoil.asp

http://kwk.us/recoil.html

http://www.siskguns.com/sisk rifles - recoil calculation.htm

http://www.rfgc.org/reload/recoil_calc.htm

http://10xshooters.com/calculators/Rifle_Recoil_Calculator.htm

 

[telomerase]

But recoil is usually expressed in momentum, not kinetic energy.

If you want to know what kind of bruise you're going to get, momentum is useless. Kinetic energy has some correlation, velocity of recoil has some correlation.

(If anyone knows a good equation to factor in recoil velocity and recoil energy to get a USEFUL answer, please post. I sure don't )

 

[Jim Watson]

I recall reading that when the British were working on the Pattern '13 Enfield in .276 calibre, they used the velocity of recoil as a criterion. The round was carefully designed to give the maximum of range and penetration with manageable recoil. A 165 gr .282" bullet at 2785 fps was the most common of the several loads tried.

Did they use recoil velocity instead of energy or momentum because it was easier to determine, easier to comprehend, or because it had a better correlation with shooter comfort? I dunno.

 

[Shawnee]

Thanks Float Pilot...

Here Ya go...

22/250 55gr bullet 9-lb rifle 4.25 ft./lbs

.243 87gr. 7.5 rifle (Rem. Mod. 7 w/scope) 8.4 ft./lbs.

.257 Roberts 117gr. 8.25 lb rifle (Savage 99 w/scope) 10 ft/lbs.

6.5x55 Swede 129 8.25lb rifle (bolt of your choice) 9.6 ft/lbs.

.270 130gr. 8.25lb rifle Win. 70 w/scope 11.2 ft/lbs.

7mm/08 140gr. 7.5lb. rifle (Rem. model 7 w/scope) 14 ft./lbs.

7mm Rem Mag. 154gr 8.5lb rifle (Rem. 700 w/scope) 21.4 ft/lbs

30/30 150 gr. 6.5 lb rifle (Win. 94) 12.4 ft/lbs.
30/30 150gr 7 lb rifle (Marlin 336) 11.5 ft./lbs

.308 165gr 7.5 lb rifle (Rem. model 7 w/scope) 16.7 ft/lbs

.35 Remington 200gr. 7lb rifle (Marlin 336) 14.4 ft/lbs


* Worth noting: The recoil of the .308 is roughly twice that of the .243, and 150% of the recoil of the .270.



So let's put it in perspective. When someone tells a newbie he/she should buy a 30/06 to hunt deer - they are saying:

"Me and Grampaw and Military Intelligence (?) all agree - to hunt 175lb. deer, a caliber that can drop 800-lb. Grizzley Bears with one shot(.270) is NOT enough - you need a caliber that kicks you more than half-again as hard."


Heeeeeeeeeere's Yer Sign !