Roller lock
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Words having meaning and you're missing a crucial one..."delayed".
It is the roller locking delayed bolt operating system or delayed roller locking bolt system.
Unlike simple blowback (think Uzi, MAC, Sten, MP38/40, Grease Gun), which immediately goes into recoil when fired, the delayed roller locking bolt system uses a mechanical advantage to cause a delay between firing and recoil.
After chambering in the eight step cycle of operations, force of the bolt carrier, under pressure of the expanding recoil operating rod, presses the locking piece forward, which forces the rollers out of the confines of the bolt and into the recesses on either side, within the barrel extension. At this point, the weapon is "locked".
When the weapon fires, the bullet moves down the barrel, but the bolt group remains temporarily locked. It is not until the bullet leaves the barrel that the gas pressures equalize and the weapon begins to go into recoil. Force is transmitted to the bolt, then the locking piece and finally the bolt carrier. The bolt carrier begins to move to the rear, moving as far as it can go until it begins to pull the locking piece with it. As the locking piece moves to the rear, it allows the rollers to move back within the bolt and the bolt begins to move to the rear as well.
Additionally, a great advantage of the HK design, the barrel flutes, ensure that the escaping gas is forced, not just within the empty casing, but also in a thin layer around the casing, literally floating the casing out of the chamber and significantly aiding in extraction.
All of this together is what makes the weapon so accurate and controllable, especially in automatic.
Not a short answer, but a thorough one. Merry Christmas.
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40 Posts
No. It's Halbstarrverriegelt. Half-locked. Semi-rigid.
There's no locking.
The bolt head, rollers, trunnion ramps, and locking piece interact producing two effects until the rollers clear the ramps:
1. Much of the force on the bolt head goes into the trunnion with only a fraction acting on the locking piece and therefore bolt carrier
2. The bolt carrier moves a multiple (4X in the full-size G3) of the bolt head distance so there's mechanical disadvantage between bolt head and carrier
with each allowing a reduction in bolt carrier weight and recoil spring strength from a pure blow back design.
Once the rollers clear the ramps it operates as a blow-back system; hence roller-delayed blowback.
It's an evolution of the roller locked mechanism which involves a locking piece with a wide flat section allowing no roller and therefore bolt head movement until a gas system retracts the bolt carrier.
Dr Karl Meir was working on a roller locked prototype at Mauser when he noticed the bolt head moving and realized that with the correct angles they could do away with the gas system which was obviously a great benefit to their project cost-reducing the StG 44.
Unfortunately friction between the cartridge and chamber varied too much with conditions with the resulting differences in bolt velocity problematic. Floating the cartridge on a layer of gas delivered via chamber flutes limited variations in friction without the issues lubricated cartridges would cause in the field.
Correct. But Mauser tried to come up with a 'more cost effective' design to compete with and hopefully replace the already adopted Haenel MP43/MP44/StG44. To convince the german authorities to do so, the new design had to prove substantial improvements performance- or cost-wise. So simplification of design and production process was paramount. The first design, the Geraet 06, featured a roller locked design, similar to the MG 42, but with the stationary barrel and the locking piece actuated by a gas system. Though easier and cheaper to produce, production was still not sufficiently cheaper than that of the StG 44 to justify the adoption of a new rifle, especially in the last months of WW II.
One design 'flaw' of Geraet 06 was its tendency for receiver bounce, leading to premature unlocking. One engineer encountered that when the receiver didn't bounce to full opening, the system still had certain locking capabilities. Figuring that calculating the correct angles for the locking piece might lead to eliminating the gas system and therefore substantial reduction in production effort and cost, Mauser went on to develop the Geraet 06H (H=halbstarr, i. e. semi rigid locking), which gave them the necessary edge to get adopted as StG45.
As the name implies, it was a little late for WW II and only parts for 10 examples were finished before the Mauser works were evacuated.
Before I go into lengthy explanations about the differences between roller locked and roller delayed blowback, there' a video by Forgotten Weapons and VolkSudio called 'Last Ditch Innovations', doing a better job than I could https://youtu.be/WEPwmYcCPFs
Um, now I'm confused; does it lock or not? I was SURE it did even if only , temporarily because the charging handle has to "UNLOCK" the rollers before charging takes place. And the way Marine0303 described it sorta made sense. Even reading the FULL CIRCLE book gets kinda technical, too.
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It doesn't lock. The rollers only delay the opening of the blow back action.
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No.
No. Rifle caliber HK roller guns have a Rücksprallsperre bolt rebound lock which latches the bolt carrier to the bolt head on closing (and therefore rollers into the recesses because the locking piece is forwards) to avoid bolt bounce problems during full-auto firing, although it's also semi-rigid not locking - pull hard enough and the bolt head extends forwards from the carrier. Unfolding the charging handle provides mechanical leverage against the the bolt carrier so it takes less force to overcome that resistance.
There's a lot of neat German engineering in these guns.
Pistol caliber HK rollers like the MP5/HK94 and their clones don't have that piece, accompanying initial resistance, or camming charging handle. Absent a princess's sensitivity to peas beneath her mattress you don't notice where the rollers disengage when pulling the charging handle.
This is all in _Full Circle - A Treatise on Roller Locking_ by R Blake Stevens who also wrote _The Black Rifle: M16 Retrospective_. If you were an annoying kid like me that always wanted to know "Why?" that has answers, along with names and dates I always forgot after history tests. If you studied German like I did because engineering schools required a foreign language and those guys are really technical you'll wish you remembered more.
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