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Discussion Starter · #1 ·
Noob here. Tom in Conshohocken PA.

I am happily and sadly the new owner of a c93. I will not dwell on that here.

Anyway, i think that the roller delayed blowback system is pretty awesome, and I think i'm hooked, but it seems like not many people on the interwebs understand the finer intracate workings of the system during the milliseconds before and after a bullet is fired. So, I decided to sign up on Hkpro and as the HK head mofos in charge.

I have a few questions but let's start with the first:

Question #1:

When a cartidge is in battery, and the bolt is fully forward, right before the trigger is pulled, Is the bolt face up against the barrel? Or, is there a gap? I assume that there should be a gap so the bolt face is not always slapping the barrel, causing wear. But then again, if it isn't, then there isn't a tight seal for most of the pressure to go in the direction of firing. What's the answer?

(can't upload pictures yet.)
 

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The gap we speak of is between the bolt head and bolt carrier. The head I believe is pretty damn close to flush. The bolt gap keeps the head from beating too hard on the trunion.
 

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C93 + maybe new barrel and trunnion + trip to Ghilliebear = happiness
 

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Discussion Starter · #5 ·
Thanks bros!

I understand how to check 'bolt gap'. I was wondering what keeps the bolt face from being damaged if its constantly hitting the barrel face every time a round is seated. I don't think the bolt ever touches the trunion, it hits the barrel face.

I think it's like this: On the return of the bolt assembly under pressure from the recoil spring, (from back (stock) to front (barrel)) the bolt is fully extended on the locking piece w/ rollers in, and the bolt hits the barrel face, and the locking piece then moves forward, and the rollers are pushed out, locking the bolt in place. Correct?
 

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Thanks bros!

I understand how to check 'bolt gap'. I was wondering what keeps the bolt face from being damaged if its constantly hitting the barrel face every time a round is seated. I don't think the bolt ever touches the trunion, it hits the barrel face.

I think it's like this: On the return of the bolt assembly under pressure from the recoil spring, (from back (stock) to front (barrel)) the bolt is fully extended on the locking piece w/ rollers in, and the bolt hits the barrel face, and the locking piece then moves forward, and the rollers are pushed out, locking the bolt in place. Correct?
It's steel on steel under the force no more than the recoil spring can provide on an empty mag... It'll be OK. You're over-thinking it.
 

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Discussion Starter · #8 ·
ok. That settles that.

Question #2: When the following happens:

-a round is in battery
-the bolt is locked by the rollers and against the barrel face
-the firing pin ignites the round

Does the bolt move backwards immediately any amount? Or is it locked up tight until the bullet leaves the muzzle?

I am wondering if there are any gas pressures in the roller locking/trunnion area, OR are most of the pressures bled off through the muzzle before the bolt moves backwards?
 

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Does the bolt move backwards immediately any amount? Or is it locked up tight until the bullet leaves the muzzle?
Neither.

The rearward movement of the bolt is retarded for a short period of time as the rollers unlock. The locking piece angle and bolt gap all factor in how long of a delay is provided.

The opening will begin with the projectile still somewhere inside the bore.

I am wondering if there are any gas pressures in the roller locking/trunnion area
Yep there is pressure. The pressure works with the fluted chamber to 'push' the case off the chamber walls, and help it extract.
 

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Discussion Starter · #12 · (Edited)
Neither.

The rearward movement of the bolt is retarded for a short period of time as the rollers unlock. The locking piece angle and bolt gap all factor in how long of a delay is provided.

The opening will begin with the projectile still somewhere inside the bore.


Yep there is pressure. The pressure works with the fluted chamber to 'push' the case off the chamber walls, and help it extract.

Yeah but I think the purpose of the flutes is to equalize gas pressure between the inside of the shell case and the outside, so that it isn't exploded and jammed in the bore. If you look at the flutes, they don't run all the way down to the case bottom, they stop 3/4 of the way. I am still not convinced that there is much gas pressure in the bolt area after firing. There is certainly momentum from the case pushing back on the bolt, but not necessarily any gas pressures. (probably some, but not 60,000 psi)

Regarding the C93's and their bad barrel to trunion jobs, i originally thought that gas pressure was pushing the barrel forward. Therefore increasing gap.

BUT, i think it's more like:

bullet is fired,
case pushes back on the bolt
bolt pushes on the rollers
rollers push on the trunnion
the trunnion is moving backwards.

Therefore, its not the barrel moving forwards, its the trunnion 'moving' backwards (i know, its welded in place). If the barrel is not pressed and pinned to the trunnion properly, then the barrel will remain stationary (assuming no friction from the bullet) and the trunnion moves backwards (recoil), pulling them apart, and decreasing 'gap' over time.

friggin Eureka.
 

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Good reading starting with the link in post #4 here: http://www.hkpro.com/forum/hk-refer...y-evaluation-g3-rifles-1969-unclassified.html

For the simpler questions:
When a cartridge is chambered there is a .005"~.009" gap between the bolt face and barrel.
You are correct about the flutes equalizing the pressure around the case.
The angle inside the trunnion is 50 degrees on all non-sw made trunnions (sw uses 45 degrees) as the bolt head moves rearward the front of the bolt head window pushes backwards on the roller forcing it inward at a rate of .0012" per .001 of rearward movement. As the roller advances inward at that rate it acts against the shoulder angle of the locking piece. The locking piece angle will vary by weapon system but for ease of understanding, a G3 uses a 45 degree LP (22.5 degrees per side). As the roller advances inward at .0012" per .001" of bolt opening the 45 degree locking piece is moved rearward at a rate of .0029". When the bolt reaches about .16" of opening movement the rollers are completely free of the trunnion and the bolt is free. This is the "delay"

As all this is happening there is also another force slowing the bolt down, the carrier pawl which extends over the ramp on the left side of the bolt head. I don't remember the exact number for the force the pawl holds back but it is very high. There is a fairly technical study going on in the weaponsguild forum on this subject because of all the builders designing their own components.

There are also a few more things taking place after the unlock but it would be easier for you to search the info out than to type it all.
 

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So it turns out that I was right all along,that bolt gap is HIGHER with a round in the chamber. To me the only bolt gap that matters is when the weapon is loaded anyway. All 3 of mine read higher bolt gaps WHEN LOADED. I knew this ten years ago,but no one wanted to face the facts.
 

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So it turns out that I was right all along,that bolt gap is HIGHER with a round in the chamber. To me the only bolt gap that matters is when the weapon is loaded anyway. All 3 of mine read higher bolt gaps WHEN LOADED. I knew this ten years ago,but no one wanted to face the facts.
Yes your bolt gap will always be higher on a loaded chamber, no way around it. In fact, if your bolt gap doesn't grow between loaded and unloaded conditions, your barrel has slipped so far forward that you are resting on the trunnion and not the barrel.

I see people posting all the time that HK's don't headspace or that it isn't important. What they fail to realize is that headspace is set when the barrel is chambered. The amount of cartridge sticking out the back beyond the barrel face has to be the depth of the bolt face recess plus the .005~.009" to force the shoulder of the cartridge into the chamber where it belongs. I tend to not waste my time with those people.
 

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Very good,I,m glad we both agree. Ghillie had told me awhile back that the HK factory sets their bolt gaps at .024 or higher. I guess full auto can reduce bolt gap extensively,ofcourse it all depends on how tight/perfect the fit of the barrel pin was installed and I,m sure not all builds will experience the same amount of barrel movement. Ralph at RTDs told me he could set my bolt gap with -2 or -4 rollers for future bolt gap loss. is that the proper way to build a clone.Just curious.
 

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Thanks man, that's what I was looking for! Where did the video go?

Full Circle?
Collector Grade Publications - Full Circle - A Treatise on Roller Locking by R Blake Stevens

Full Circle - A Treatise on Roller Locking
by R Blake Stevens
$79.95

Deluxe First Edition 2006
536 pages, 737 illustrations

The thirty chapters in this long awaited book tell the in depth story of the ingenious half-locked roller action, from the curiously simultaneous development of initial prototypes by two German companies during World War II - the Mauser Gerät 06H and the Grossfuss MG42V - right through to the present day.

After the war the roller lock was taken first to France, where several hitherto little-known assault rifle prototypes were developed by ex-Mauser engineers in calibres 7.65x35mm French short and 7.62x33mm (.30 US carbine).

In 1950 the roller lock moved to Spain, where what became the CETME family of roller-locked weapons was developed by ex-Mauser engineer Ludwig Vorgrimler, initially chambered for the unorthodox 7.92x41mm cartridge. By the mid-1950s the roller lock had returned - "Full Circle" - to Germany, and a co-operative manufacturing programme had been established between CETME and the fledgling German armsmaking firm Heckler & Koch GmbH, whose pre-adoption prototypes included the 7.62mm NATO calibre H&K "STG CETME" and the H&K "DM3 (CETME)".

The finalised G3 rifle was adopted by the Bundeswehr in 1959, and nearly two million examples were produced by H&K and Rheinmetall with fixed, folding and retractable buttstocks. The roller lock action then formed the basis for the H&K weapons "family", consisting of numerous models and variations of SMGs, carbines, rifles and machine guns in calibres ranging in power from 9mm Parabellum to - very briefly - .50 Browning! Versions of the G3 and other H&K arms were also sold commercially (we list 25 countries using ready-made H&K product), and manufactured abroad under license. Models made by or for Burma, Denmark, Greece, Iran, Malaysia, Mexico, Norway, Pakistan, Portugal, Saudi Arabia, Sweden, Thailand and Turkey are depicted and described, with clear illustrations of their unique features and markings.

Final chapters include an overview of the burgeoning Aftermarket - H&K and CETME copies and clones produced in Europe, the UK and the USA today for civilian collectors and shooters - and a roundup of G3 accessories, including bayonets, blank firing adapters, the various optical sights and mounts, tools, and training aids.

 

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Discussion Starter · #18 ·
Yes your bolt gap will always be higher on a loaded chamber, no way around it. In fact, if your bolt gap doesn't grow between loaded and unloaded conditions, your barrel has slipped so far forward that you are resting on the trunnion and not the barrel.

I see people posting all the time that HK's don't headspace or that it isn't important. What they fail to realize is that headspace is set when the barrel is chambered. The amount of cartridge sticking out the back beyond the barrel face has to be the depth of the bolt face recess plus the .005~.009" to force the shoulder of the cartridge into the chamber where it belongs. I tend to not waste my time with those people.
that's exactly what i was thinking initially, but then i thought too hard and psyched myself out. i'm going to read the gov't declassified report and come back.

But first: Question #3 :

What forces are really causing 'bolt gap' to shrink in all these problem clone weapons? (i know, they were assembled wrong. but what are the Forces acting on them?)
Is it gas pressure inside the bolt area pushing the barrel forward?
Is it the fired case pushing back on the bolt, then pushing on the rollers, then pushing on the trunnion, pushing the trunnion backwards relative to the barrel?
Is it the slamming of a round into chamber by the recoil spring and bolt assembly?
Or a combination of all the above?
If so, how MUCH force is it?
 

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that's exactly what i was thinking initially, but then i thought too hard and psyched myself out. i'm going to read the gov't declassified report and come back.

But first: Question #3 :

What forces are really causing 'bolt gap' to shrink in all these problem clone weapons? (i know, they were assembled wrong. but what are the Forces acting on them?)
Is it gas pressure inside the bolt area pushing the barrel forward?
Is it the fired case pushing back on the bolt, then pushing on the rollers, then pushing on the trunnion, pushing the trunnion backwards relative to the barrel?
Is it the slamming of a round into chamber by the recoil spring and bolt assembly?
Or a combination of all the above?
If so, how MUCH force is it?
Some of the above. Think "equal and opposite" force. The trunnion does not ever move though, it's the barrel moving forward inside the trunnion typically from a poorly sized barrel pin hole, improperly sized pin, not enough interference in the fit between the barrel and trunnion, trunnion cracking, and probably one or two more issues I can't think of at the moment. We've done quite a detailed study on the trunnion issues complete with measurements and metalurgical testing, it is posted on the militaryfirearm.com and weaponsguild.com sites.
 

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Very good,I,m glad we both agree. Ghillie had told me awhile back that the HK factory sets their bolt gaps at .024 or higher.
This is 100% incorrect.

The factory spec for shipping firearms is .004" min, .020" max with an ideal gap of .014"

HK does not gap their firearms with a round in the chamber. All measurements are done with the firearm unloaded. A properly pinned barrel will exhibit no more than .002" initial gap loss.
 
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