Shotgun chamber pressures


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BullpupBen
November 18, 2008, 07:26 PM
I've noticed that shotgun chamber pressures only hit about 15,000, while most handguns are over 30,000 and most rifles are over 50,000. Why exactly does the shotgun require so little pressure, when it gives off so much recoil (as much as a .300 Mag according to charts) and has so much energy?

Also does this mean shotguns should, at least in theory, last longer and have much less internal wear than comparably built rifles or pistols?

and does this mean gas-operated shotguns like the Rem 1100 and Saiga 12 have much wider gas ports than gas-piston operated centerfire rifles like Ak-47s, Mini-14s, etc?

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spyder1911
November 18, 2008, 07:51 PM
I am not a firearms expert or physicist but I did stay at a holiday in express.

And I know that the force that is exerted on the projectile is directly proportional to the pressure and the surface area. Force=Pressure x Surface area. Other than the friction of the air/barrel, the force applied is equal to the kinetic energy of the projectile.

A 12 gauge has diameter of 18.5mm so it's area is ~269 square mm.

The .300 Mag rife on the other hand has a diameter of 7.62mm and an area of 45.6 square mm

So that means the .300 Mag need about 6 times the pressure to apply the same force on the projectile. And then the recoil is simply the reaction to the projectile (i.e. equal and opposite reaction).

BullpupBen
November 18, 2008, 11:31 PM
First off thanks for the answer, that all sounds correct.

However, I was looking at a shotgun pressure chart and the .410 bore Magnums are only 13,500 PSI at maximum pressure. I have heard that .410 slugs are equal in kinetic energy to .44 Magnum bullets, which have about the same diameter, but operate at a much higher pressure. How is this possible?

I'm thinking it has something to do with shotshells having much more volume for the gas to expand in or something.. as that is where they are most visibly different from rifle/pistol centerfire cartridges.

Steve C
November 19, 2008, 01:47 AM
While velocity increases performance of rifle and handgun ammunition the maximum usable velocity for a shotgun shooting lead shot is around 1,400 fps with most ammunition running around 1,200 fps. Push a lead shot load out the end of the barrel much faster and you will "blow" the pattern as the wad is shoved through the shot column yielding a doughnut shaped pattern.

Steel shot being less dense can be pushed at a slightly higher velocity of around 1,500 fps but because of this lower density it looses velocity faster than lead.

Because of the size of the bore, the relative thinness of shotgun barrels and the velocity restriction most shot shells run around 8,000 to 9,000 psi in the 12 ga.

As the gauge gets smaller the pressure of the shells does go up with 20ga ammo running in the 10K to 11K psi. The velocity of the shot does remain the same though at around 1,200 fps being typical.

A typical 1oz rifled slug on the other hand will have a velocity of around 1,700 fps, and the sabot versions will be around 1,800 fps.

I have heard that .410 slugs are equal in kinetic energy to .44 Magnum bullets, which have about the same diameter, but operate at a much higher pressure. How is this possible?

Comparing the .410 1/4oz or 1/5oz slug to the .44 mag or .41 mag may yield similar kinetic energy numbers but remember that the barrel of a shotgun is a lot longer which yields velocities of around 1,700 fps for a .410 slug. The 3" .410 slug at 1/4 oz is only approximately 109 grains, about 1/2 the weight of a typical .44/.41 mag bullet of 240gr/210gr. The equivalent energy come from the way energy is calculated using the square of the velocity. When 1,700 fps is squared it is about 2 times the resultant number of 1,200 fps (the typical .44 mag velocity) squared. The projectile of the .410 being 1/2 the weight of the magnum pistol projectile makes the results come out pretty much equal. If .410 slug was shot from a Taurus Judge with pistol length barrel the resulting velocity would be much slower and the kinetic energy would also be a lot less than a .44/.41 mag pistol.

sixshooterfan
November 19, 2008, 12:40 PM
I am no expert, but it seems to me that if a shotgun barrel were thick enough to withstand pistol or rifle pressures it would be impossible to swing on game due to the weight. Imagine what an O/U would feel like.

BullpupBen
November 20, 2008, 07:27 PM
OK I can see how shotshells only need a comparatively small amount of pressure to fire.

So in recoil-operated shotguns like the A5 is the barrel/bolt much lighter and the springs much weaker then if that system were to be used in center fire rifles?

Matt304
November 22, 2008, 07:16 PM
OK I can see how shotshells only need a comparatively small amount of pressure to fire.

So in recoil-operated shotguns like the A5 is the barrel/bolt much lighter and the springs much weaker then if that system were to be used in center fire rifles?

No. In fact, they are heavier. Remember what was discussed earlier, about such a large surface area of the 12GA projectile requiring much less pressure to achieve high kinetic energy? Well, force works this way in both directions. Pressure doesn't act differently on the bullet as it does the base of the shell. It is trying to expand outward in all directions. Being that a 12GA shell has such a large base at roughly 3/4", the bolt face pressure forces from a modest load are actually as high or even higher than they are in an average rifle cartridge. If you take a look at a modern bolt-action slug gun, they have huge locking lugs, and are able to withstand typically very high bolt face forces. Forces which would shear the lugs right off of a typical 30-06 bolt, in fact. The Browning A-bolt or Savage 210 are good examples of such strong shotgun actions.

BullpupBen
November 27, 2008, 01:46 AM
No. In fact, they are heavier. Remember what was discussed earlier, about such a large surface area of the 12GA projectile requiring much less pressure to achieve high kinetic energy? Well, force works this way in both directions. Pressure doesn't act differently on the bullet as it does the base of the shell. It is trying to expand outward in all directions. Being that a 12GA shell has such a large base at roughly 3/4", the bolt face pressure forces from a modest load are actually as high or even higher than they are in an average rifle cartridge. If you take a look at a modern bolt-action slug gun, they have huge locking lugs, and are able to withstand typically very high bolt face forces. Forces which would shear the lugs right off of a typical 30-06 bolt, in fact. The Browning A-bolt or Savage 210 are good examples of such strong shotgun actions.

That made sense at first, but then I got to thinking about lever actions..

Why is it that older lever actions can take low-pressure and high-power rounds like the 12 gauge and .45-70 but cannot take lower power, higher pressure rounds like modern rifle cartridges? If the bolt face pressure is really higher then a rifle, it seems to me it should just rip off the breech of a levergun.
And happy thanksgiving!!

rcmodel
November 27, 2008, 01:24 PM
The weakest link in the old lever-gun design is not the lock-up.

It is the exposed cartridge case necessary for the extractor, and the strength of the barrel /receiver joint.

They are limited to 40,000 PSI class cartridges because of those two things.

When a Winchester lever-action fails, it almost always results in the barrel being blown out of the foreword receiver ring by gas escape from a failed case.

Not a locking lug failure.

rcmodel

BullpupBen
November 27, 2008, 10:20 PM
Well alright, I do believe you are correct:o

Thanks for the help

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