This should answer most of your questions.
Lately, I've been surfing guns websites for fun (not enough homework). Time and time again, I've read "rotating bolt." I know roller-delayed Blowback, etc. but not rotating bolt.
Also, What are locking lugs, and a lever-delayed-blowback?
And by the way, What's the difference between recoil- and blowback-operated? And the purpose of a gas piston? Is it a delaying device to keep the bolt in the rearward position? If so, then why don't they just make a weaker spring?
Remember, I'm only 14, and want to go about the world seeking information (not destruction, mayhem, or chaos).
Last edited by sniperdude411; 05 Mar 05, at 03:32.
"We will go through our federal budget – page by page, line by line – eliminating those programs we don’t need, and insisting that those we do operate in a sensible cost-effective way." -President Barack Obama 11/25/2008
OK I'm assuming you know how pistons (the physics part) work , and also a conventional Bolt action rifle works- because this is all that will be needed to figure out the issue.Originally Posted by sniperdude411
Hang on tight this is a long one!
When you load or reload a bolt action rifle, what do you do? You grab the cocking knob and rotate it anti clockwise then pull it rearwards to the limit of its travel and do the same thing in reverse to close the bolt. In the rearward movement you have extracted and ejected an empty case, while in the forward movement you've chambered a fresh round from the magazine and also cocked the firing pin/striker , ready for firing.
An automatic weapon with a rotating bolt achieves exactly what your hand does, but with mechanical means.
Lets work on a hypothetical scenario:
You have a bolt action rifle you want to convert to a self loader (Don't try this though!!)
You need a way to make the rifle do exactly what your hand does to reload the rifle.
The first thing you'll need is some way to cause a movement -preferably in a rearward direction. Physics and it's laws of gas/expansion/volume/pressure etc. comes in. The motive force is there in the rifle itself - in the form of the hot explosive gases that propel the bullet. Most of this energy is wasted when the bullet exits the barrel.
We'll harness this energy.
Ok well drill a small hole perpendicular to the axis of the bore, a short way form the muzzle(I'll get to the positioning later). this will allow a significant amount of the expanding gas to exit the bore before the bullet has left the barrel. We'll tap this gas into a cylinder which is secured parallel to the barrel. We'll have a piston which fits pefectly into the cylinder. The piston's rear will have a longish rod which extends some distance behind.
Now at this point lets see what we have, a tiny holle on he barrel through which the gas is tapped into a cylinder. When you fire what happens?- The expanding gases behind the bullet travel into the cylinder and pushes the piston rearwards- There! You now have your motive force!
The next step is to get the motive force to do what your hand originally did- Reload.
Remember-this is hypothetical so no consideration is given to structural intregrity to the contraption i'm rambling about.
Remember the longish piston rod extending backwards? - lets attach this to a rectangular block with an angled slot which is significantly higher in the fore end.
We've cut the angled slot big enough to accomodate the bolt cocking lever. The position of the slot should be such that, when the bolt is in the closed position, the cocking lever rest on the rearmost and lower most limit of the slot. By the way, the slot will have limits both in the for and rear. Also take it for granted that the piston rod is solidly attached to the block, and that the movement of the piston rod and block is limited to only rearwards and forwards.
Now let's see what happens when we fire a round:
Remember the gases driving the piston/ rod? -This now pushes the block rearwards. When thsi happens the slot forces the cocking lever to move along its
angled path and because the slot's angle becomes progressively higher, the cocking lever is forced to rotate counter clockwise upwards- Exactly what your hand would be doing. We assume that we've calculated the angle and fore limit of the slot to be just enough to rotate the lever/bolt adequately to unlock. Now remember that the slot has a limit in the fore end so when this is reached, the lever instead of rotating, is led backwards in a straight line.
There! You've got the weapon to rotate and unlock the bolt and also extract and eject the spent cartridge.
All you need now is to stick a strong spring behind the block. this will counter the rearward motion of the whole assembly, and provide the motive force for a forward motion. This will simply do the reverse of what happened earlier and in addition collect and chamber a fresh round from the magazine. By the time this has stopped the bolt has been rotated down and locked - ready for the next cycle.
That is in essence, the 'how' of a gas powered rotating bolt action.
Now the 'why'?
A rotating bolt is needed basically to keep the breech closed/locked till the immense pressures produced within the bore has come down to a safe level. Though generally not needed for smaller cartridges, powerful rifle cartridges need this or else newtons third law (every action has an equal and opposite reaction) would kick in and blow an unlocked breech open with unhealthy results for the user. The rotating bolt is designed to provide sufficient delay to allow safe opening of the breech. This is one reason why we have the gas being tapped close to the muzzle- By the time the gas has initiated movement of the piston, the bullet will have already left the barrel and any excess gas is bled harmlessly through the now open muzzle. Momentum drives the piston/block rest of the way to unlock the bolt and open the breech. The gas pressure by now is near zero.
Note: If the gas is tapped too far back from the muzzle, there is a good chance that the piston/unlock movement will be initiated when the bullet is still travelling down the bore, leaving dangerously high pressures during opening of the breech.
So this is the essence of the rotating bolt - and its easy then to relate this to the various rotating bolt designs in use.
In a blowback design all this complication is not needed, provided the ammo is relatively small and weak. This system is prevalent in Submachine guns and small bore pistols. In this case the weight of the breech block and the resistance from the main spring is sufficient to cause a delay in opening of the breech at a safe point of time. Intrestingly in this system, the cartridge case acts as a Piston driving back the breech block.
As regards recoil operated, its basically application of blowback and not gas, to unlock and cycle an action. There are many types. The simplest and most common example would be that which you would find in the Colt M1911 Pistol. I can explain this if you want - let me know. There is a recoil operated rotating bolt as well, and also rotating barrels.
Lever delayed is relatively uncommon and I've seen it used with reasonable success only in the hungarian Danuvia and the French FAMAS (and AAT52 I think) Though entirely different in design, the physics involved in a lever delayed action is the same as roller locked systems- I can elaborate this if you want.
About locking lugs, a rotating bolt is usually cylindrical in shape. Just as in as common bolt action rifle the front end of the bolt has usually at least two angular projections around its axis these projections are sized and shaped to lock into corresponding wedges on the barrel extension when the bolt is rotated- this is what locks the bolt. Maybe I'll explain beter in diagrams next time.
Hope this hasn't been too roundabout for you. There are perhaps better and simpler ways to explain this but this is how I learnt the whole drama.
Take care and let me know if you require more guidance or misguidance.
I've been building and fixing firearms for nearly 20 years now- I guess I'm a part-time gunsmith- and I've been asked this question many times. You provided the most concise, technically accurate, and understandable description I have ever read- you must have a background in teaching. If you don't mind, I'd like to copy this and hand it to folks who inquire! Very nicely done.
Hi , I honestly thought I'd be putting people to sleep Hey no problems - go ahead.Originally Posted by WildLomcevak
well you still can simplify the language and add some "woah"s and other stuff like that
Haha - you're free to publish the "woah'" editionOriginally Posted by Ricola-Ranger
Wow... Very logical, simple, and concise. Thank you very much; you should post that on wikipedia or something. What's your occupation? You must have some extenseful experience with guns.
Now I just read an ad for Benelli's semi-auto guns, and they said it was "inertia driven."
Angain, thak you very much.
Hi 411, gimme a day or two to compose it in the simplest way possible(hopefully) I'll try to get some diagrams up too. Speaking of which I've answered your question about the Lever delay action of the FAMAS on the SA80 thread by truong.Originally Posted by sniperdude411
Wow. Thank you very very much; Keep up the good work!
It's so awesome that people will actually take time off their lives to answer questions like these; People like you make me feel more and more important, and later when I can, I will return the favor.
Oh yeah, Many will notice that I haven't posted in like a month; When I stopped posting, I was (still am, but leaving tomorrow) at my dad's farm in Lancaster, running a farmstand all day. Sometimes we'd get rained-out, or 5 people came in a whole day, but it was a great experience for me (taught me ALOT about working hard; every morning I had to wake up at 6 (or earlier) to pick corn until about 8, then I'd set up the stand, pick tomatoes, etc. Some days I stayed up 'till 11 working on things, and I haven't had ANY time to post). But here I am, $500 bucks richer, and am now a seasoned (slightly) farmer boy.
I can't wait until I get back to suburbia tomorrow, and be bored again!
Last edited by sniperdude411; 11 Aug 05, at 20:50.
Impressive Stuff, thankyou for the info.Originally Posted by cottage cheese
Benelli shotguns are a simple recoil operated design. I had a Berretta 1201FP, it's the same exact mechanism as a Benelli Super 90.
Nice time at the farm eh? You should have checked if there was an old black smithy around- Amazing what you can learn in these shops.Originally Posted by sniperdude411
I'm still trying to put the inertia thing together in a comprehensible way. Hope you'll be patient.
BTW, I took a look at your design on one of the threads, very innovative, looks like an enlarged variation of the Hk type roller delay, only difference being the roller is stationary while the bearing surface moves. You'll have one problem though- cocking the weapon. It's going to take the same amout of effort that the ammo takes to overcome the resistance. Perhaps you can refine that.
Thanks to M21 and ak-dave for the suppliments. Stooger, Benelli, Franchi and Beretta, are all identical in opertation. Sniperdude go through the links ak-dave provided- you'll find it pretty simple to figure out.
The Inertia system is a very innovative application of the simplest laws of physics - Newtons 1st Law. The kind of thing makes one wonder what took us so long to apply it. The Benelli weapons, however, are not the first to apply the Inertia system. There seems to have been an inertia system used many years ago, it used a wedge to effect locking - the present Benelli system uses a "reverse" rotating bolt. I also don't know which weapon or company used the older 'wedge' type lock (Maybe it was an older Benelli?)
I've never handled a Benelli (this is India!!) so my explanations are primarily based on theory and logical mechanical principles.
Let's now figure out how the whole thing works.
Practical physics first:
Newtons 1st Law
Newton's First Law states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.
So what does this mean? Say you're standing in a bus. And the boozy driver, for no reason, throws the bus into reverse- you lurch forward right? But you're actually not moving forward and it's actually the bus that is moving backward. Your moving forward is relative and you are actually in a state of Inertia.
Another example (from Benelli USA's site) illustrates this- Drape a handkerchief on the barrel of a rifle. When you fire the rifle recoils and the handkerchief seems to move forward, which in actuality is that the handkerchief remains essentially in the same spot and its the rifle that moves back.
How does this relate to the weapon? Essentially, in this system the bolt carrier(not the bolt) does what you in the bus and what the handkerchief on the barrel does- that is, remain in a state of inertia.How is this applied to the weapon?
Remember, due to the hypothetical nature of this experiment NO consideration is given to the structural integrity of the contraption in question. The point of this exercise is to illustrate the working of the delay/locking mechanism and not how it interacts with components like trigger/firing/feed mechanisms. It is assumed that these simply work. This is in no way a DIY gunmaking lesson- Don't try this under any circumstances- you'll risk serious injury potentially fatal.
Because the Benelli uses a Rotating Bolt to lock up, lets go back to our famous hypothetical bolt action rifle. This time however, we don't need to play around cross bore drills, pistons, gas and other nasty stuff. We retain only the old rectangular block from our last misadventure. We'll also need to modify it slightly, and add a part or two.
Remember the main spring we simply stuck behind the block in the last experiment?- This time the main spring will be applied a little differently (This is important)- If you consider the mainspring in the M-16 or the FAL- what do you notice?- it is Captive, meaning it is retained within it's housing and has a set limit to it's forward movement.In the Benelli too, the main spring is usually housed within the stock and has a closer resemblance to the FAL because of its link arm. Note that this doesn't always have to be so and there are other ways to limit forward movement of the main spring.
Anyway, for our hypothetical tomfoolery, we will simply house the spring inside a tube with an inner flange on the front end to limit it's travel. We'll also stick a follower in front of the spring, cap the rear end to retain the spring and finally find a way to secure the tube in position, some distance behind the block. Remember, the Tube should not be movable. I'll also later get to why it's important to position it precisely.
Now let's get back to that famous rectangular block of ours. We'll have to slightly modify its structure and also add a few parts. First will be a cylindrical rod a bit longer than the length of the block or a wee-bit longer than the recoil distance... Hell, you can use the piston rod from our earlier experiment- just secure it to the rear of the block. In the Benelli and FAL, this is hinged and angled downwards- this is because the mainspring follows the contour of the stock and is angled. To simplify matters, our experiment will have the spring sitting straight, parallel to the movement of the bolt. We'll stick the rod behind the block so that it looks like a modern art version of a Rat and its tail. Assuming you've got the length of the rod figured out, its rear end should just about rest on the mainspring follower. You must ensure the spring doesn't exert any pressure on the rod when the block/bolt is at rest.
Ok now let's modify the block a little more. After ensuring that the location and position of the block is more or less in the same position as in our eariler experiment, we'll attach a smaller block in the rear of the original block so it roughly resembles a reverse "L". The new piece is positioned to sit, directly but a short distance away behind the rear end of the bolt. Needless to say this little block must be solidly secured. Also you'll have to place a carefully calibrated spring between the rear of the bolt and the small block. This spring is also long enough to maintain a predetermined distance between the rear of the bolt and the small block. By the way this is the Inertia spring.
Now the difference
At this point, I'll illustrate the primary difference. (Assuming you still remember the way the bolt interacted with the rectangular block) You'll now have to position the block back such that the bolt lever is turned half way through- remember the bolt is still 100% locked- only, it has been rotated partially. This is the idle position that the bolt/carrier assembly sits at, in the Benelli. The Inertia spring exerts enough force to keep the assembly in this position/distance, but no more. Also note that in this position the Main Spring does not exert any force.
What happens when you fire?
First it goes "Booom..."
The weapon recoils(Newton's 3rd Law) and the rectangular block due to its weight remains at inertia (Newton's 1st Law) Remember yourself in the bus and the hankerchief on the barrel? The block moves forward relative to the rest of the weapon which is travelling backards.
What happens then?
This "Forward" Movement of the block causes the bolt to actually rotate and lock completely or "tighter", at the same time compressing the inertia spring. Note that the "forward" movement actually is only a few mm, but this is enough 'dwell' time to allow the pressure in the chamber to drop to a safe level.
Now the Inertia spring that was compressed during the "forward" movement now behaves as it should, it begins to expand again, pushing the rectangular block rearwards. The inertia spring having been compressed quite briskly now converts its potential energy to kinetic energy and exerts enough 'recoil' force to cause the whole mechanism to move and unlock as in any rotary bolt action. The residual gas pressure in the chamber is enough to then drive the whole assembly back against the main spring, to cycle the extraction, and rechambering of a new round.
At the end of the forward stroke, the inertia spring again causes the block back to the 'battery' position i.e. partially rotated position.
You're now ready for the next shot.
The Inertia system is brutally simple and only the inertia spring needs some careful consideration. This system is dependent, however, on recoil - the actual external recoil that the shooter feels and not internal recoil like blow back actions, where the shooter feels only the 'transmitted' recoil. Thus the system would probably not work with zero recoil, so muzzle brakes or similar fittings of any type MAY degrade performance.
There is also a remote possibility that shooting the weapon at steep angles (upwards or downwards) may influence optimal functioning of the system because of the effect of gravity on the inertia of the carrier. This is however only academic speculation and in actuality, a non issue.
We'll there she is... I may have confused you more, and if I did I'm sorry and you're welcome to throw questions or abuse
Kinda felt lazy to actually draw pictures, so I hope the explanation is adequate. Let me know if you need pics anyway... I'll try to get some up when I'm not feeling lethargic.
Last edited by cottage cheese; 12 Aug 05, at 14:05.
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