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Discussion in 'General Shotgun Discussion' started by Cryptic, Jul 25, 2007.
What is the better and why?
Recoil vs gas
They have their own benefits. Recoil operated shotguns are less prone to malfunctions due to fouling. They are generally simpler to manufacture. The Bennellis do not like light loads. They only work with high brass type stiffer loads.
Gas guns have softer recoil. They "can" be more prone to fouling. The gas systems have to be regulated to work with the load. "Some" have a fairly narrow range of loads that work. The remington 11-87 adjusts its self to a fairly wide range of loads. My Saiga seems to eat whatever I feed it.
recoil vs gas
im not sure i understand. gas operated means that the gas produced by the burnt powder moves a mechanical piston that pulls back the slide (ejecting the spent cartridge) and then the slide by action.reaction moves back front (loading the new cartridge from the mag).
recoil operated means what exactly? recoil is produced by the same expanding gas. so what is the difference?
In a recoil system, inertia is used to cycle the action and load the next round. In a gas system, some of the combustion gas is bled-off to cycle the action.
but isnt that the same?
the inertia that moves the slide back is generated by the expanding gases, isnt it?
The explanations posted are close to explaining the difference between recoil operated and gas operated but I will try clarify the difference a little better. I cannot think of any gas operated gun that the bolt or slide depends just on gas to push it to the rear. Rather the gas is only utilized to unlock the bolt and then inertia and momentum of the recoil takes over completing the cycle just like in a recoil only operated gun, it continues to move the bolt to the rear compressing the recoil spring that sends the bolt back into battery picking up a new cartridge along the way and chambering it. How the gas gets to the unlocking of the bolt in a rifle is via a very small hole that is is drilled through one side of the barrel usually located somewhere in the second half of the barrel toward the muzzle. At this hole location there is usually some type of fixture attached to the barrel that connects to a small steel tube that transports the gas to a piston that is connected to a mechanical part that unlocks the bolt. On most gas operated shotguns there is no steel tube but rather there usually is a sliding piston that is fitted around the magazine tube and the fixture that attaches the barrel to the magazine tube transports the gas to the piston which pushes the charging bar just like on a pump gun unlocking the bolt and then inertia takes over as described above. In most but not all recoil operated guns the inertia of the recoil is what unlocks the bolt or slide. As an example almost all recoil operated semi auto pistols work like a 1911 Colt whereby as the slide starts to move back ever so slightly from recoil the back of the barrel drops down unlocking the barrel from the slide allowing the slide to move all the back. There are recoil operated guns that their bolts or slides do not lock and only depend on the recoil spring and the weight of the bolt to keep it closed long enough to allow the bullet to get out of the barrel before the bolt opens. These type of guns are sometimes referred to as "delayed" blow back guns which is really a bit of a misnomer because without that feature of the bolt remaining closed or "delayed" until the bullet leaves the barrel in either case of a gas or recoil operated gun the brass would blow up outside of the gun because of the pressure of the gas pushing on the bullet would also be pushing against the walls of unsupported brass if the bolt were to open too early. Some guns like a Thompson sub machine gun fire on what is called an open bolt meaning that the gun is in the ready to fire mode when there is no bullet in the chamber and the bolt is pulled to the rear. When the trigger is pulled it releases the bolt allowing it to travel toward the chamber and along the way it picks up a round firing it simultaneously as the round chambered. In this case it is the forward momentum caused by the weight of the bolt that keeps the bolt closed just long enough to allow the bullet to leave the barrel. On the 1921 and the early 1928 Thompsons there was a machined slot on the bolt that accommodates a bronze saddle to fit over it. This bronze saddle caused a friction that locked the bolt for just a millisecond to insure the bullet had left the barrel. That system is called the Blish system named after its inventor. I know of only one other gun that uses a modified version of that principal and that is the very classy and expensive Cosmi shotgun made in Italy. I probably told you all more than you wanted to know, but oh well...
I hope that helps, Ron
I know the post above went into great detail, but let me say the abridged version...
All ammunition releases a gas, but that's not what you should focus on. It matters where the gas goes to answer your question. In a recoil operated system, it's basically a force from the shell directly pushing on the bolt. The gas operated system takes gas from in front of the casing, diverts it from the barrel and into a piston. This piston is then pushed back by the gas. The piston is attached to an operating rod, which is attached to the bolt. You see where the difference is now?
In a gas operated gun a tiny bit of the expanding gases is bled off to operate the action. Because of the way the different components of the gun get in motion at different times and rates, it tends to greatly mitigate felt recoil. The gas does not just unlock the action, it operates it. You can hang a gas gun from a string and it will fully function when you pull the trigger. Because some gas is used to operate the action, and these gases are at best somewhat dirty (Blue Dot gas is downright dirty), a gas action will need to be cleaned. The frequency depends on the design to some extent. I clean my guns anyway so to me it has always been a non-issue.
In a recoil operated gun, the recoil gets the whole gun moving backwards. You must provide resistance to make things work. The easiest to explain is the Browning long recoil action. After firing, You slow the stock and receiver down, and the entire barrel and bolt move all the way to the rear position locked together, compressing the action spring as they go. At that point they unlock, and the barrel moves forward, leaving the bolt to the rear, and ejecting the spent shell casing. When the barrel is in battery, it releases the bolt, which moves forward picking up a new shell, and pushes the shell into the chamber and locks itself to the barrel again. Different recoil actions function a bit differently, with less stuff moving so far, but that's the basic principle. All shotgun recoil operated actions have the barrel and bolt locked together until well past when the peak pressure has occurred, and the charge is gone from the barrel. "Inertia" is a sales tool term, because 'recoil' has some unpleasant connotations. Shoot a Benelli 3-1/2" 12 gauge and you will see that "Inertia" can be worse than plain old recoil ! The recoil actions are "cleaner" because they do not get exposed to anything but residual gasses and residue from the empty shells being flung out, so they do not require cleaning as often. Just when or why not cleaning your guns came into vogue, or why, I am not sure.
Virginian: It never ceases to amaze me how some people think. Go get yourself an AK 47, an SKS or an AR 15 and take a look at how the action works. Once the action is unlocked there is no pressure available to continue to operate the action. Pressure from the gas is only used to unlock the gun then recoil takes over exactly as I said. Then I when went on to say I cannot think of any gas operated gun that actually operates the action doesn't mean there isn't one, it means I can't think of one. Can you? Not to be a smart ass, but did it not occur to you from reading my post that I have a great deal of knowledge and experience with various types of firearms? Did you even know what the Blish system is before reading my post? Have you ever even heard of a Cosmi shotgun? How do you think an HK Squeeze cocker works? It has a gas port and a piston and yet it is not gas operated at all, rather the recoil is retarded by gas as opposed to the recoil spring. If you pull the bolt out of an AR 15 you will see snorkel attached to the bolt that fits over a steel tube that runs to the front sight from where it gets gas. Once that snorkel moves away from that tube is open to the atmosphere meaning all gas pressure is gone and this happens just as the bolt rotates and unlocks all caused by gas but that is where it ends. I am sitting here with an SKS in my hands and the gas piston pnly moves far enough to unlock the action. If you think I am wrong please explain to me and others here how and why you think that the gas operates the action other than your hanging the gun on a string theory. Though I understand what you are trying to portray with your theory it has about as much to with what we are talking about as who won last nights ball game.
Okay, I am not going to be a smart ass, and I can do it without making any snide comments, but I know more than a bit about guns and the physics of motion myself. I regret that I did not clarify that I was talking shotguns only, since this is a shotgun forum, but with that caveat, I stand behind everything that I said. I have heard of the Blish system, but it was long ago and I did not even remember the connotation. It is I take it a purely recoil action?
I take it that you do not agree that in order for an action to be recoil operated, that the mechanism has to be moved to the rear completely by the forces generated by the charge and gases exiting the front of the gun barrel. I think that's where we differ. Because if you take say a Remington 1100, and instaed of hanging it from a string, lets anchor it so it cannot move, it will still function (until the recoil obliterates the stock). Now in my vocabulary, that means the action is totally gas operated. If you are talking about the fact that the gasses unlock the bolt and get the action assembly moving in a short gas cylinder, and then the momentum of the moving parts continues to carry them to the rear, and then the action spring powers the return and reloading operations, and you are calling everything after the initial push from the gasses recoil operation, then we have a simple semantics issue. It might more correctly be called gas/inertia action, but that term has been previously appropriated as already alluded to. I call it gas operated, and so does most of the world. And, all gas operated semi autoloading shotguns that I can think of use some variation of the same sequence.
Virginian: I do not agree with you that this is a shotgun forum only. I did reread the question and the gentleman was in fact asking only about shotguns. Perhaps you meant post and not forum. Additionally I must confess that I had to look no further than my own safe at home to find a gun that gas 100% operates the action as you suggest (that's embarrassing). It is a Franchi 20 gauge that I have never even shot. It has charging bars attached to the gas piston that pushes the bolt completely to the rear. I do have a Remington 1100 but I do not have it at home, when I get to my office I will take a look to satisfy my curiosity but you are probably right about that too. I stand on everything I said about gas only opening the actions on the guns that I mentioned and every rifle that I am familiar. As for the Blish system it is strictly blow back that is retarded by a bronze saddle that fits over the bolt. As the bolt is pushed to the rear it causes the bronze saddle to have a slight interference with the body of the receiver a slows the bolt down to keep it from running away. Don't let it be said that if I am wrong I will not say I am wrong and I apologize for being snide. Now if you will please excuse me I have a nasty old crow to go eat.
I have gotten to where I don't mind the crow so much myself, but damn them feathers.
I think I may have folded my tent a little too soon on this one and those feathers were terrible. I got up this morning and took a look at my Franchi again and while it has charging bars that follow the bolt all the way to the rear, only about 3/4 inch of movement rearward movement can be controlled by gas pressure because after that the gas is released into the atmosphere and that 3/4 inch of movement only unlocks the gun. I then thought perhaps the motion of that part all initially caused only by gas moving it and its momentum (because it is heavy and a body in motion has a tendency to stay in motion) it actually worked the action, but I wasn't sure because it was starting to look more like my rifle examples where the gas only unlocks the gun. I went to my office and dug out an 1100 and it too has charging bars that are pushed initially by only gas for about 3/4 of an inch, which is the same distance required just to unlock the action and even though they follow the bolt all the way to the rear. At this point you are probably thinking pushing and I am thinking following. I then took a look at a High Standard Shadow and in my view that did it. It has everything the 1100 and Franchi has but in addition it has a piston on a 1/2 inch diameter shaft at the end of the magazine that can only move about 3/4 of an inch and it pushes on the charging bars unlocking the action but does not follow them because it is blocked by the much larger diameter magazine tube. Bottom line I think I am right, I cannot think of any gas operated gun that the gas is responsible for doing anything other than unlocking the action, then recoil takes over from there completing the cycle. I am going to call Remington in the morning and crow or no crow I will let you know. You have been a real sport about this and I wish you lived closer so we could go do some shooting.
Many years ago I had the fortunate opportunity to sit next to Wayne Leek on an airplane ride, and I think I may have already asked the questions. I (surprisingly) was enough of a gentleman to make sure I wasn't driving him nuts, but he actually seemed to enjoy the conversation. I doubt he got to sit next to many gun nuts either.
On an 1100, the gas only gets the action sleeve, action bar assembly (which unlocks the bolt), and bolt moving, and then their momentum finishes the job. That's one reason why the balance of parts is so important on an 1100 - a 3" gun has a heavier sleeve and only one gas port, so that a magnum load with a longer peak gas pressure, doesn't get things moving too fast before they have to come to a sudden stop at the rear of the receiver. And they also have enough inertia that they do not unlock the bolt before the gas pressure is well past the peak. And you can tie up an 1100 so the gun does not move at all, and that takes recoil out of the picture in my view, and the action will still cycle. I actually did this years ago, proving that an 1100 really does generate less peak recoil than a pump gun. Fortunately, both stocks survived the experiment.
In thinking further about the situation myself, you may indeed be correct that some actions only have the gas unlock the bolt, and the gun already being in recoil at that point is a very necessary adjunct to their actions cycling. I do not know. I haven't really studied any other gas actions all that seriously, and I have certainly only ever completely restrained one.
I have enjoyed the conversation as well. In spite of all the drivel on the internet, occassionally I actually have the opportunity to meet someone intelligent and learn something. I wish we lived closer as well. If you ever get up this way, give me a heads up. I don't travel much anymore, but my buddies and I are going duck hunting in Canada in October to tick off one big item on our "bucket list". I got diagnosed with cancer back in March, and I think it made us all take another look at our priorities and realize that all of a sudden we may not have plenty of time for everything.
Just my luck, I meet an intelligent and knowledgeable gentlemen that I am sure I could be friends and then he tells me he has cancer. If I might ask... I tell you what I going to try to send you a private message and my email address.
For Virginian & (the other guy)
Taking your brawl a bit further, with a few specific examples:
M-14 rifle gas piston "hits" the operating rod hard, but also pushes it a fair distance- 1/2 inch? That hammer-like hit imparts a high-force impact which both unlocks and drives the bolt back. Recoil effects may be present to some degree, but consider that the gas is bled to the piston just before the bullet leaves the barrel, so recoil by then is....??
M-16 impinges gas pressure on the bolt carrier "key" for a very short distance- maybe less than 1/8 inch? That "chuff" of gas-induced force is very short duration, before the gas bleeds away.
FN-FAL has an adjustable gas pressure regulator, a nice feature, if it works. I am not aware of any other common rifle having this.
geni, welcome to the brawl but the truth of the matter I was the butthead and the Virginian was the calm head. The M14 you speak of I presume is essentially an M1 Garand with a box magazine in 7.62 NATO/308 Winchester. To answer your implied question where is recoil? Recoil started the very instant the bullet started to move and continued long after the bullet was gone. It is that recoil that continues to operate the action. You have to remember, if the rifle recoiled at the same rate of speed as the bullet, it would kill you to shoot it. However, as you know for every action there is an equal and opposite reaction. The mass of rifle absorbs this action/energy for a much longer period of time than the much lighter bullet. This can readily realized in the fact that the bolt does not travel back at the same speed of the bullet, meaning that a bullet could possibly depending on the range reach its target before the action completes its cycle. Your M16 comments I am not sure I understand so I won't comment. The FN-Fal has the feature of being able to shut the gas off to launch grenades and to work the action manually if need be. I think it has one more adjustment for blanks but I am not sure, I will look at one mine tomorrow and report back. The Styer Aug has this same feature as the FN but again I will have to check. I am fortunate enough to own these guns and while I don't have an M14 I do have a BM59 and I think one can adjust the gas on it because it has a grenade launcher. Again I will report back.
genie:Well here I go again looking for another crow to eat and I haven't fully recovered from the last one. The only good thing is don't let it be said that I cannot admit when I am wrong. The M14/ BM59 has a gas piston that runs the full length of and operates the action entirely by gas. Recoil does NOT come in to play as I suggested. The FN FAL works the same way and it actually has two separate adjustments for the gas. One regulates the gas as to what ammo you are shooting and the manual says to adjust it to the proper ammo you fire the gun single shot increasing the volume of gas until the magazine holds the bolt open making it obvious that gas is the only thing operating the action. The other is to shut the gas off to operate a grenade launcher with a third position should the sytem become fouled. The Steyr Aug appears to work the same way but only has one adjuster, that has the same three positions of the FN FAL. What makes the crow even worse is that I own two Augs, one Bm59 and two FN FALs, all different configurations. I haven't even looked at them in the last two or three years and this week end I promised myself I am going to shoot them as well as some H&Ks I have. The AR 15 and SKS are like I said depending on recoil to complete the cycle. Every thing else I said about recoil, where the bullet is at while the action is functioning and time is correct.
This post was so interesting that it compelled me to register.
Close, but not quite. Actions that work from the cartridge directly pushing against the bolt are known as direct blow-back actions. Most .22 LR semi autos and other rimfires fall into this category. Typically, this actions don't have locking lugs in their bolts because the bolt does not actually lock into anything. The mass of the bolt is enough to keep the breech closed temporarily until the pressure falls to safe levels. These actions work by taking advantage of mass to overcome momentum (the momentum imparted on the bolt). This is the simplest type of semi-auto action but it's not suited for high pressure cartridges.
Inertial actions are diferent. In an inertial action, the breech indeed locks and the bolt has locking lugs just like in a gas system or any other high pressure action. Inertial actions work by taking advantage of inertia, rather than just the mass of the bolt. In an inertial action, a part of the action (in the case of the Benelli system, the rear of the bolt) resists the recoil forces because it's sort of detached from the rest of the gun. Following the example of the Benelli system, as the gun moves back, the rear of the bolt wants to stay put, and a spring between the rear and front of the bolt gets compressed momentarily. As this spring loads, it reaches a point where it finally overcomes the inertia from the rear of the bolt and pushes the rear of the bolt back, unlocking the breech. It's quite an ingenious and elegant design that requires very few woking parts yet it's suitable even for high pressure systems.
It's worth mentioning that inertial guns and blow-back guns shouldn't be confused with recoil-operated guns. Recoil operated actions are yet a third and different animal. Recoil guns use recoil forces imparted on certain parts of the gun (usually the barrel and slide) to unlock the breech. Usually, the locking system is set up in such a way to delay this process mechanically by adding mass and friction to the equation (for example, by making the barrel and other parts moveable). Most semi-auto centerfire handguns use this principle, as well as some larger weapons such as the Browning 50-cal. machine gun. These guns operate on the principles of recoil and friction. These designs can be fairly complex, but can handle high pressure relatively well and are usually quite reliable.
So, to sum it up, all three systems operate through forces imparted by the recoil, but they are delayed and/or unlock the breech by the use of three very different methods:
Blow back operated systems use, mainly, mass.
Inertial operated systems use inertia.
Recoil operated systems use, mainly, friction.
Then of course there are the gas systems, which use gas, and which you've explained quite well.
H2o, the M-14 I speak of is as you mentioned, the successor to Garand. The distance of gas piston movement is limited to a fraction of the entire bolt travel, so analysis by "gut instinct" is pretty difficult, but suffice to say that I believe the piston imparts a very rapid impact hit to the operating rod, which develops sufficient peak force during that instant of contact, that inertial forces then keep the rod (and bolt) moving rearward to complete the cycle. Whether any recoil force is involved is rather doubtful, since the bolt is essentially a mechanical part of the chamber until the gas piston moves the op rod, which in turn moves the bolt rearward as the locking roller "cams" upward, relieving the mechanical lock-up to the chamber. That event is happening MUCH later than when the bullet passes over the gas orifice (allowing gas flow to the piston). So, the bolt is locked until the bullet leaves the barrel, with the net result that there are then no longer any gas forces acting on the cartridge (or the bolt, therefore), to provide "equal & opposite reaction".
However, as you mention, lots of crows frequent the pasture across from my house.......