recoil???

[KenH]

OK, If I've got 2 rifles, one with a 22" barrel and other with 32" barrel, both chambered in 45-70 shooting the same 405 grain with 70 grains FFg black powder. The 32" will have "around" 100 fps more velocity due to extra barrel length - "***-u-ming" the guns weight the same, will the 32" barrel with higher velocity have more perceived recoil? OR - will it be about the same?

Thanks to all for comments and guidance,

Ken H>

[Nueces]

The higher muzzle speed means higher recoil impulse, but the subjective experience (stock design, rifle weight, etc) may cause a shooter to experience things differently. It is recoil velocity that most of us experience as sharpness. Momentum is velocity times mass, so an increase in rifle weight will slow down that recoil velocity and seem to calm things down. Snugging a rifle butt into your shoulder will tend to add your upper body mass to that of the rifle and further slow the recoil velocity. We all know how that works.

Keeping this short, so it is not a dissertation.

[Mk42gunner]

Actual recoil-- Yes.

Perceived recoil-- Maybe.

With equal weight, the rifle with more velocity will recoil more. However, apparent or perceived recoil may ar may not go along with this, do to gun fit, i.e. stock dimensions and just how you hold the gun.

Muzzle blast also adds to how you perceive recoil.

Robert

[country gent]

Alot goes into pervievd recoil and its effects. The shorter barrels blast beibng closer to the shooter will have an effect. Balance will have some effect also. Muzzle velocity is a direct contributor as is bullet weight. Rifle fit is also a direct contributor to percieved recoil. The short barrel is going to be more "compact" and recoil may be diffrent due to this. The 32" barrel will have weight out farther in the hands giving it more leverage to alleviate muzzle rise and a more straight back recoil due to this. Also do they both have the same buttstock? comparing a cresent plate stock to the shotgun style stock or straight grip to pistol grip is kind of like comparing apples to oranges also.

[KenH]

Thank ya'll for the replies - and confirmed MUCH of what I was thinking. The "ideal" situation would be two rifles exactly the same fit, weight, etc so the only variable affecting recoil would be the velocity. I was thinking recoil was an effect of velocity, but then the powder charge got me confused a bit - same powder charge, but more velocity only due to extra barrel length. Simple, each reaction has an equal but opposite reaction - bullet goes forward, gun goes back in perceived recoil.

Now, would the peak pressure be the same, but extra velocity picked up from the pressure acting on bullet for a longer period of time? Per QL program using smokeless powder the peak pressure is the same for a 22" barrel as for a 32" barrel, but the longer barrel picks up velocity due to the pressure acting on bullet for a longer period of time. I guess BP works the same.

Thanks again to all for comments. This is a GREAT forum for learning, and I've learned a LOTS over the last few months.

Ken H>

[country gent]

While it may be the same pressure it may be a slightly diffrent pressure curve with the longer barrel to it being contained longer. I would also be that some of the 100fps increase may also come from powder not burned in the 22" barrel that may be in the 32" one. 10" is quite a bit extra length. After a certain length diminising returns kick in and velocites will start to drop due to lack of pressure and friction build up.

[KenH]

Ahhh, yes I should have included the % powder burnt in each case - you're right there was more powder burnt in 32" barrel than 22" barrel. I should run some numbers and see just how long the barrel would be before the velocity starts dropping.

[Nueces]

The full engineering expression for free recoil includes a term for mass and velocity of the propellant gasses and solids. This term adds a small amount to the projectile term and is often ignored in discussions such as this.

When I first studied physics, I was annoyed that so many approximations were used in calculations. Exactness, darn it! Then I got way beyond that and learned that approximations got more sophisticated, not less numerous. Ah, well. It all got us to the moon and back.

[rfd]

ah, all good stuff ... just gimme the longer barrel and i'll add in some butt stock weight.

[KenH]

OK, just for grins I used QL to setup a 45-70 load using Lee .457-405-F cast bullet with 45 grains of IMR 3031 powder. This gives 100.1% case fill when seated .65" deep in case. This is deep but that gives 100% case fill. Peak chamber pressure is 24,623 psi with all barrel lengths.

22" barrel: % powder burnt=92.3% with 1673 fps
32" barrel: % powder burnt=92.3% with 1801 fps
42" barrel: % powder burnt=94.3% with 1885 fps
52" barrel: % powder burnt=95.6% with 1947 fps
62" barrel: % powder burnt=96.5% with 1994 fps
72" barrel: % powder burnt=97.2% with 2033 fps
172" barrel: % powder burnt=99.4% with 2227 fps
472" barrel: % powder burnt=100% with 2396 fps
572" barrel: % powder burnt=100% with 2423 fps

The pressure at muzzle goes down similar to the % powder burnt, peak chamber pressure didn't really change, only showing from 24,623 or 24,624 psi which I'm sure is a rounding thing. The % powder burnt I rounded to tenths.

I wonder if QL is correct in the fps keeps increasing, OR if actual tests would show at some point the fps would actually fall? I really think internal barrel friction would cause the velocity to drop, but QL supposingly factors barrel friction into the calculations.

QL says 400" is max barrel length, but it took and did calculation with 472 and 572" barrel (with length numbers in red) giving 2423 fps.

Yea, I've got too much time on my hands this morning - should be reloading 'n shooting instead of sitting here playing with QL {g}

Ken H>

[Toymaker]

First, 100 fps isn't going to make that much difference in recoil. Second, shoot over a chrony, then come back to QL, input your load info and adjust the Burn Rate Factor Ba to obtain the actual velocity attained. Don't forget to adjust the ambient temperature first. Then you know what that batch of powder is doing and you can play with the load. Third, no matter how long the barrel or what powder, your highest pressure is the initial pressure before the bullet starts moving. Fourth, these are 100 yards, and I think you'll have better luck with IMR 4759 (hard to find) or Accurate 5744.

[Ballistics in Scotland]

The same momentum is imparted to the rifle and to the bullet. That is mass of the solid and gaseous ejecta times velocity, not times velocity², so you don't have to worry about being hit with all the energy of your elephant gun. A slow .30 will give more momentum than a .22 centrefire. In the OP's example, the higher velocity of the long-barrel bullet and escaping ejecta will impart more momentum to the rifle.

But there is another source of recoil, namely the jet effect produced by the sudden release and acceleration of gases at the muzzle, like a sort of momentary rocket. General Hatcher said that for rifles in the .30-06 class you got a pretty good approximation by doing the momentum calculation but pretending the powder charge was 50% greater than you actually used. For a modern magnum, with a higher terminal pressure, it might be more accurate to assume an extra 75% of imaginary powder.

Terminal pressure will be higher with the 22in. barrel than with the 32in. As the jet effect is smaller than the momentum one, I would expect this to go part-way but only part-way to reducing the difference in recoil.

Even that isn't the whole story, though. I've always thought that a big part of perceived recoil doesn't come through the shoulder at all, but from the impact of the rifle on cheek and head. Even when the weight is the same, the short rifle may have more of a tendency to rise against the cheek.