Why shorter BBL have more recoil?

[hawk45]

Physics..

 

[brickeyee]

the reduced velocity will be offset somewhat by the reduced weight of the gun.

If you calculate the free recoil you will see this is not correct to any significance.

 

[One_Jackal]

If two guns weigh the same recoil will be the same. If we have two 25oz guns, one with a two inch barrel, the other with a 6 inch barrel. The two inch barrel will have more perceived recoil.

 

[brickeyee]

"If we have two 25oz guns, one with a two inch barrel, the other with a 6 inch barrel."

New weightless barrel material?

That IS the whole issue.

Unless you can extend a barrel with zero additional weight, the longer barreled gun weighs more.

 

[Lost Sheep]

Not necessarily.

"If we have two 25oz guns, one with a two inch barrel, the other with a 6 inch barrel."

New weightless barrel material?

That IS the whole issue.

Unless you can extend a barrel with zero additional weight, the longer barreled gun weighs more.

Not necessarily.

You can have two guns with essentially identical frames, but the 2" barreled one has a massive underlug (and a brick tied to it if necessary). The 6" barreled one has no such extra weight. The two guns wind up weighing the same.

The question is valid.

I think the questioner is asking about the relative effects on recoil) of increased bullet velocity vs the increased "jet effect" of the muzzle blast. (I could be wrong, but that is my interpretation of the question's likely meaning and answer.)

Lost Sheep

 

[brickeyee]

While you are free to construct any hypothesis you want, the main issue is that smaller guns tend to weigh less and free recoil depends on the mass and velocity of the ejecta and the mass of the gun.

Less mass for the gun means more recoil velocity (momentum must be conserved) and since the recoil energy is then (mgun*vgun^2)/2 the increased recoil velocity has a pronounced effect.

Any loss in velocity from the bullet in a shorter barrel reduces the input momentum to the system, but it is not that large a percentage loss in the overall velocity of the ejecta.

While the gas velocity does have some effect, it very low mass (no more than the weight of the propellant charge) greatly limits its effect in typical handgun cartridges.

5 grains of powder even at twice the velocity of a 230 grain bullet is just not a large fraction. At 500 ft/s for the bullet and 1000 ft/s for the gas, less than 5%.

A rifle can easily start to have the free recoil energy significantly affected by the mass of the gas ejected.
The powder weight in smaller bore diameters can easily exceed the mass of the projectile.

 

[HKGuns]

Remember also that handgun recoil is as much rotational (e.g. muzzle rise) as it is linear, and shortening the barrel reduces the moment of rotational inertia much more than it reduces the overall mass of the gun, hence much more muzzle flip with the shorter barrel.

^^This^^

 

[brickeyee]

Remember also that handgun recoil is as much rotational (e.g. muzzle rise) as it is linear

That is felt recoil, not free recoil energy.

You can screw up0 gun design a lot of ways to make the felt recoil worse (or better).
my brother had a rifle with a badly designed stock.

It smacked you in the cheek with every shot.

Wrong angle on the butt plate.