Rotating Bolt Short Blowback Action

Rotating Bolt Short Blowback Action
Light Machine Gun for discuss

[@undertow619]

The locking lugs were always the most confusing part about a weapon to me. I kept asking myself "how do firearm manufacturers cut the chamber lugs into the barrel?" But thanks to this video, I finally figured out that the barrel and the chamber lugs are separate parts and that the barrel is screwed into the rifle breech.

[@danielsteger8456]

seems like you never watched forgotten weapons

[@undertow619]

@@danielsteger8456 I've watched Forgotten Weapons. I just never came across any episodes that explained it.

[@brian.louis107]

Take a look at the CMMG Guard 9mm or 45. The bolt with slanted locking teeth which act to delay the blowback. Still not sure if this would work for higher pressure rounds but the modification is intriguing to say the least.

[@adamchurvis1]

It would not, at least not safely or reliably, and the precision manufacturing and quality control necessary to create such a bolt lugs-barrel locking extension would be unusually expensive due to inaccessibility the required grinding disc and lapper would have to the rear faces of the locking lugs and the front faces with which they mate in the barrel locking extension. I think you (or someone) will find later on that the CMMG's so-called "delayed blowback" is more a negligible artifact of something imagined to be significant than it is an actual operating system -- much like the Blish device in the 1928 Thompson submachine gun.

[@alifr4088]

Just get an HK G3 with roller delayed blowback lol

[@ArcturusOTE]

@@adamchurvis1 I thought the Blish system worked, just as a delayed blowback system and not a heat expansion locked one?

[@adamchurvis1]

@@ArcturusOTE No, it was absolutely ineffective, which made it easy to eliminate entirely with the revised M1 Thompson.

[@funcounting]

@@adamchurvis1 Turns out it's not negligible but actually works.

[@robinpage4323]

This is called "Radial-Delayed Blowback"; basically, angles cut on the rear of each bolt lug cause the bolt head to unscrew from the barrel extension, and the BCG cam lug accelerates the bolt carrier to the rear, exactly like a roller delayed or lever delayed blowback. Same principle, requiring only a slight modification of an existing weapon part. Clever, really.

[@ElijahDecker]

If you already have a locked breech bolt, why not make a locked breech firearm? The primary advantage of blowback and delayed blowback firearms is that they don't require precision machined and heat treated locking surfaces, which makes them substantially easier and cheaper to manufacture.

[@thedeedsmaster7148]

Robin Page would you be able to turn a bolt action into a radial blowback firearm?

[@robinpage4323]

Gas operated rifles are almost always bolt action; the gas performs the work of unlocking the bolt, as opposed to the shooter working it manually. The AR-15 rifle operates this way, and a company a few years ago converted a pistol caliber variant to radial delayed blowback by simply machining 45° angles onto the rear surfaces of the bolt head lugs. It can work for necked cartridges, but not very well, for the same reasons that lever delayed and roller delayed rifles don't work well for necked cartridges: too much pressure deforming the neck, plus the risk of head separation.

[@robinpage4323]

Gas operated rifles are almost always bolt action; the gas performs the work of unlocking the bolt, as opposed to the shooter working it manually. The AR-15 rifle operates this way, and a company a few years ago converted a pistol caliber variant to radial delayed blowback by simply machining 45° angles onto the rear surfaces of the bolt head lugs. It can work for necked cartridges, but not very well, for the same reasons that lever delayed and roller delayed rifles don't work well for necked cartridges: too much pressure deforming the neck, plus the risk of head separation.

[@robinpage4323]

I would personally like to see the Benelli inertia drive system for shotguns applied to rifles. From an engineering perspective, I can see a lot of possibilities for it.

[@criticalfxck13]

I can read description for ages and not 'get it' Big + for this coz it clicked so fast when I watched it :)

[@conorclimo8534]

What if you added a gas delayed blowback mechanism similar to the VG 1-5 but you add a strong spring and you make the bolt cover the gas hole and reinforce the surfaces that the bolt contacts the barrel (so no gas leaks). And (as a Semi-Auto Pistol in say .45/9mm) make it striker fired.

[@jeremyshaw1]

What are the primary differences between this and the Benelli Inertial System? It seems to operate on a very similar principle.

[@tommasomorandini1982]

I don't know what the system shown in the video is (to me it looks like a standard rotating bolt, like what you can find in an AR-15) but I can tell you how Inertial Systems (IS) work. In the Benelli family you have a bolt that locks rotating like a standard bolt. Usually the bolt carrier can't go any further, whereas in the IS it can, but it has to compress a spring. The added forward motion of the bolt carrier doesn't do anything on the bolt. When you fire, the bolt will move back under the recoil generated by the round, whereas the bolt carrier will tend to stay where it is because of inertia. This means that the bolt carrier moves forward relative to the bolt, compressing the aforementioned spring, wich will then accelerate the bolt carrier back enough to unlock the bolt. I suppose that then the residual pressure in the camber and barrel, wich acts on the bolt, cicles the action the rest of the way, as I don't think the spring between bolt and bolt carrier has enough energy to cycle the rifle completely. Hope this helps you

[@edi9892]

Besides being compact and few parts, what´s the point? I mean roller delayed or lever delayed should be easier to produce or?

[@путинГНИДАгориваду]

I guess this one is cheaper,cuz any gun company in US may produce bolts and locking lugs

[@eksbocks9438]

This is kind of like how the late-war Wimmersperg Rifle works. Except it has a short stroke gas position to push the bolt back.

[@ERAUsnow]

Way late on this, but this won't work as you have it. There is nothing acting on the bolt carrier to get it moving. All of the recoil impulse is directed at the bolt face, which is fixed in place by the locking lugs. You need something to get the bolt carrier moving first in this design, which makes it not truly a blowback system. If this is done by allowing the barrel to recoil a bit with the bolt and carrier as a unit, you've recreated the short recoil action with a rotating bolt. Aka what's inside the M1919, M2, and Barret M82/107.

[@david-468]

Couldn’t you also fix this design by just having longer and a less extreme locking lugs? To get it on the right “track” and then the blowback will do the rest after the blowback rotates it

[@ERAUsnow]

@@david-468 nope. The white piston part has to be moved by something in order for the bolt to rotate. Gas, barrel movement, something. Any of which means this isn't blowback anymore.

[@lonesurvivalist3147]

Radial delayed lugs my man

[@ERAUsnow]

@@lonesurvivalist3147 What's acting on the bolt carrier to get it moving, "my man"?

[@sonickunckle]

@@ERAUsnow Bolt head rotates and move a cam pin, which forces the carrier backward at quicker pace and in turn, pull the bolt head out, understand?

[@farhanhashmi2705]

What is driving the bolt carrier? How is it moving?

[@mickeytwister4721]

The pressure of the cartridge firing is what forces the bolt back. That's why it called blowback

[@farhanhashmi2705]

@@mickeytwister4721 thats how a straight blowback works but this animation shows a rotating bolt blowback action. Apparently the pressure of the cartridge is not directly acting on the bolt carrier and the pressure cannot interact with the bolt to rotate it so the question still remains, how's the bolt carrier assembly even moving?

[@farhanhashmi2705]

@@mickeytwister4721 I didn't think about it before but maybe I know the answer now. The rotating bolt could possibly be hollow and cannot be called the bolt. Instead the bolt head could be an integral part of the carrier itself and could ride inside the hollow piece with the locking lugs. This way, the pressure could act directly on the bolt carrier to move it backward and the lugs would simply delay the blowback action.

[@WhenDoesTheVideoActuallyStart]

​@@farhanhashmi2705They're not locking lugs. Angled lugs. The bolt is always free to move. The case acts on the bolt, and the bolt is slowed down by friction+mechanical advantage over bolt carrier.

[@tytly-ro7vt]

Could this function with a rifle caliber?

[@EnderMano67]

I don't think it is blowbaack, the locking lucks prevent from the blowback move the bolt.

[@groupsphera]

Эх... Я эту штуку хотел в 2012 запатентовать. А потом узнал, что давно уже есть похожие системы(

[@wowthtsgood]

how does the bolt carrier magically move backwards with no gas pressure pushing it, and a lock breech preventing it from gaining inertia? cool animation, just wouldn't work.

[@davidjenkins7389]

> how does the bolt carrier magically move backwards with no gas pressure pushing it Pressure in the chamber push cartridge case and bolt backward . Sloping surfaces of the breech interact with bolt forcing it to rotate . Bolt carrier can`t rotate and force to accelerate backwards .

[@wowthtsgood]

+David Jenkins that means it's not locked and doesn't come out of there much slower than a straight blow back action.. have you built this yet?

[@davidjenkins7389]

Clayton Sage Correct - no "locking" . This is sort of delayed blowback action .

[@wowthtsgood]

+David Jenkins for light machine guns? using intermediate or full size cartridges? I would be afraid to test it personally. I hope you follow through with this and post your results. I'm sorry to say, by my logic, I'm doubtful. I don't think it will be delayed enough for all of the pressure of a rifle cartridge to exit forward instead of backward.. but please! Prove me wrong! I'd love to see what you come up with. I'm not sure how experienced you are, or If you've done this before, so I don't mean to undermine you when I say this but, if you fail at first, don't be discouraged. Remember: engineering is all about tweaking, testing, and trying again until you get it right. Good luck!

[@groofromtheup5719]

What am I missing? How can it accelerate backwards with the lugs stopping it? the ramp angle would have to be so slight that it would be basically the same as a direct blowback, but with many more failure points.

[@1415J]

what is the function of rotation.Why not simply maintain a linear motion?

[@davidjenkins7389]

This is a sort of delayed blowback action .

[@neptune3569]

To handle the pressures of a cartridge being fired

[@edi9892]

AFAIK you use leverage to accelerate a mass faster than the bolt and thus you save weight. Normally, this is done with a lever, or rollers as in the G3, but here, they use a compact system that uses a rotating cylinder, where two parts have different rotations akin to gear.

[@PhlexCrafting]

I must ask, why is this in my recommended?

[@ВладимирКулик-щ3н]

My dear David, I'd like to see you in the battle about LPI ( F-35 politforums.). I'm so sorry but I've just copied your article fromTM. With best regards!

[@davidjenkins7389]

Which battle ?

[@dwightlooi]

NOPE. You missed two critical features, so this won't work at all. #1 There is nothing that makes the bolt carrier cycle backwards. Usually this will be a gas tube, piston or at least a manual handle. #2 When the bolt goes forward it will rotate and lugs won't fit. Normally, the cam pin will need to engage a track to prevent that.

[@sonickunckle]

Forgotten Weapons had a video for the CMMG rifle using this system, go watch it.

[@WhenDoesTheVideoActuallyStart]

They're not locking lugs.

[@jackpersales4920]

I doubt it works. Too much friction.

[@l-r1622]

I feel dumb not knowing it actually that's simple

[@hinz1]

If AR15 and HK G3 mate, this is what happens ;-)