Recoil - semi-auto gas v inertia auto-loading shotguns

[castor]

I often read that a gas operated auto-loader reduces recoil because it uses propellant gas to operate the loading system. Frequently the reference is in the same paragraph as a description of an inertia operated auto-loader, and nothing is mentioned about the inertia operated auto-loader reducing recoil. The cynic in me thinks that any implied suggestion that inertia auto-loaders do not reduce recoil is just gun manufacturer bs.

Doesn't an inertia operated auto-loader also reduce recoil? It might not push as many moving parts as a gas autoloader, but it uses the same propellant gas to complete the reloading cycle just like a gas operated shotgun. All other things being equal, an inertia auto-loader weighs less than a gas operated gun and weight sucks up recoil, so there is that argument. However humping a heavier shotgun wearies a guy out more by the end of a day, so there are two sides to the weight issue.

I am suggesting that if I was to take a pump shotgun gun and an inertia operated semi-auto of the same weight and shoot the same shells from them, the semi-auto would deliver less felt recoil. What do you guys think?

[myfriendis410]

I agree completely. Energy is being dissipated in the auto, but the other factor--the one between gas and recoil, is the inertia system has to bear more directly on the shooter than the gas system. The gun has to push against the shooter to work the bolt back causing the felt recoil. The gas system bleeds off some of the energy and uses a lighter spring to actuate the bolt assembly, usually a bit later in the recoil pulse than the inertia system. But between a pump gun and an inertia system I would think the inertia system would be softer.

[BelchFire]

Originally Posted by castor

All other things being equal, an inertia auto-loader weighs less than a gas operated gun and weight sucks up recoil, so there is that argument.

When's the last time you hefted a Browning "Light 12"? Nuttin light about it unless you're comparing it to a "standard" 12.

MyFriend is correct on the timing. The autoloader will start the ejection cycle almost immediately (I never understood why this wasn't quick enough to effect shot placement), whereas the shot charge is about 1/2 way down the barrel before the gas-op gun gets a dose of gas through the ports and starts the cycle.

Nothing is perceived on the shooter's end until the gas cycle starts. The autoloader, however, will start to push on you just as quickly as the bolt begins to move (Newton's 3rd law; action/reaction).

[castor]

Originally Posted by BelchFire

The autoloader, however, will start to push on you just as quickly as the bolt begins to move (Newton's 3rd law; action/reaction).

Oh boy, here I am side tracking my own thread.

"When" do recoil and breach block movement occur? My understanding is that felt recoil does not begin on a bolt action weapon (for example, to demonstrate the point) until the bullet exits the muzzle. Until then all movement is inside the bore. It isn't until the bullet leaves the muzzle that there is the relative motion outside the bore that we know as recoil - action / reaction. That is one reason why accuracy is possible with a rifle; recoil does not move the muzzle while the bullet is still in the barrel. That raises interesting questions.

First, the same thing presumably happens in a gas operated weapon. Gas entering the gas port moves the gas piston rearward because the recoil mechanism moves independent of the projectile. Timing is therefore crucial to ensure that the projectile clears the barrel before energy can escape via the recoil movement and disturb aim.

The second question is, when does the breach block start moving in a blow back auto-loader? Logic suggests that it must not occur until the projectile clears the muzzle, or else accuracy would suffer? But why not? The bullet (energy) moves down the barrel because it is the path of least resistance. In a blow back mechanism isn't the breach block supposed to move in reaction to back pressure? Why does the breach block not begin moving backward the moment the shot charge starts moving forward? Does the breach block move in reaction to the increase in internal psi, or is movement a reaction to the relative movement of shot and barrel as the bullet leaves the barrel? Logic suggests the latter, but why don't propellant gases blow the breach block open first?

All this might sound like so many angels dancing on the head of a pin, but I think understanding the physics increases my understanding of the shooting and makes it fun.

[BelchFire]

You are right; the "firearm" (rifle, shotgun, piston, whatever) doesn't move (externally) until the projectile leaves the bore. But we also know that there is nothing to impede the movement of a blowback at the point of ignition except inertia; the mass of the bolt and any attached parts as well as what spring pressure there is holding it closed. Once the projectile starts moving forward, the bolt begins to move rearward and you get an impulse, if only through the spring pressure.

The projectile (shot charge, bullet, what-have-you) is relatively light compared to the mass of the bolt, parts and spring pressure. But it's being accelerated much more quickly, so the action cycles. I've always been amused that there is such a broad range of acceptable velocities that would move the projectile and still cycle the action. One would think that it's a delicate balance but it's not.

[castor]

Cool. Thanks.

[bux-n-dux]

Dude-

Just get a Beretta Extrema with kick-off and you'll never think about recoil again. Me? I'm an 1100 guy, but I shoot 2 3/4 almost exclusively and even when I shoot 3" the recoil doesnt bother me. If I was to get a new gun it would be a Beretta 391, no hesitation.

bux-n-dux

[larrysogla]

"For every action....there is an equal and opposite counter-action(reaction)." That is a universal law of objects being accelerated. In looking at inertia operated action versus gas operated action......the mass of the bolt and the carrier in the inertia operated action is less than the mass of the bolt, carrier, operating push rods/bars and piston/cylinder in the gas operated action. The heavier mass in the operating mechanism as in the gas operated action............the bigger is the counter recoil force that accelerates those gas operated action parts. The greater mass to accelerate in the gas operated action means less recoil than the inertia operated action. My personal choice is gas operated actions for less recoil and inertia operated actions for easier??? cleaning................but it does not really matter as both will bag that turkey, goose, duck, wild boar or deer with the proper shot load/ slug ammo.
'Nuff said
larrysogla