Bolt carrier mass of the CETME/G3 and related rifles.


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Payload
June 20, 2013, 06:59 AM
Okay, I've been plucking at the math behind Lever and Roller Delay designs and I've been getting some screwy numbers on bolt carrier mass (way too high.) I've taken a good look at this page http://www.hkpro.com/index.php?Itemid=5&catid=4:special-topics&id=133:technical-engineering-detail-of-the-g3&option=com_content&view=article and it gave me a few ideas on reversing the math and coming at it from the other angle. In a nut shell can someone please tell me the mass (in grams please, not slugs) of a CETME/G3 (or whatever civilian .308 variant you have) bolt carrier? I'm messing up somewhere and I think it has something to do with the transfer of energy to the rifle through the roller.

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45_auto
June 20, 2013, 08:03 AM
can someone please tell me the mass (in grams please, not slugs)

I don't know the mass of an HK bolt offhand, but if you're incapable of doing the conversion from slugs to grams, don't be surprised if the rest of the math gives you difficulties!

(1 slug = 14,594 grams. Ok, 14,593.9029 if you need it that exact!)

Payload
June 20, 2013, 09:50 AM
Wow, someone actually knows what slugs are. Half the time I just get blank looks. The other half the time i keep getting handed slugs because they know i have to look up the conversion and they just want to annoy me. It's also a grossly over sized measurement for the task at hand but Americans still describe things in Ten-thousandths of an inch... Couldn't learn the metric system like the rest of the world?

Ian
June 20, 2013, 10:57 AM
I don't have a G3 to measure, but if you're really interested in the roller locking system, you should pick up a copy of Full Circle (http://www.amazon.com/Full-Circle-Treatise-Roller-Locking/dp/0889354006/ref=sr_1_1?ie=UTF8&qid=1371736587&sr=8-1&keywords=full+circle+roller+locking).

adelbridge
June 20, 2013, 02:38 PM
the transfer of energy comes from the unsprung bolt transferring its energy at full speed to the carrier that is sprung. I am sure the rollers also absorb a little as they compress in and roll back.

Destructo6
June 20, 2013, 04:38 PM
I didn't see a mention of the locking lever on the bolt carrier...

stubbicatt
June 20, 2013, 05:26 PM
the transfer of energy comes from the unsprung bolt transferring its energy at full speed to the carrier that is sprung. I am sure the rollers also absorb a little as they compress in and roll back. saith Adelbridge

Kindof... there is the "antibounce" device, or "locking lever" that is tightly sprung and which pivots in the bolt carrier, and bears on the bolt, retarding its opening a skosh.

Else, the bolt is unsprung... :)

Payload
June 20, 2013, 10:50 PM
I thought the Anti-bounce device was a tungsten powder filled portion of the carrier that acted like a dead-blow hammer to prevent the bolt from bouncing back on closure.

stubbicatt
June 21, 2013, 08:38 AM
I thought the Anti-bounce device was a tungsten powder filled portion of the carrier that acted like a dead-blow hammer to prevent the bolt from bouncing back on closure.
Nah. They do have the tungsten filled bolt carriers to retard opening. I for one cannot imagine making this already heavy rifle heavier.

The anti bounce device is a lever which has its pivot in the bolt carrier, and a notch on the other end which sort of clips over a protrusion on the rear of the bolt at "lockup" --the breech doesn't really ever lock, but... It is this device which drives HK newbies nuts as they first try to reassemble their bolt/bolt carriers after cleaning. I'm pretty sure it is this device which offers the initial resistance to one pulling the cocking handle away from its forward position, you know, that initial camming force?

If you watch the videos at Forgotten Firearms (contributor Ian's site) there is some discussion of this lever and its addition to the prototype STG45 IIRC. It seems to have carried over to the G3 bolts/bolt carrier assemblies which I have seen. I don't know about the CETME.

Trent
June 21, 2013, 12:14 PM
It seems to have carried over to the G3 bolts/bolt carrier assemblies which I have seen. I don't know about the CETME.

It's present. Bolt appears identical between G3/Cetme. I can do a trial interchange, if you want.. have both rifles, but never tried mixing parts.

Payload
June 23, 2013, 06:14 AM
Makes sense that they would be close enough to swap. H&K hates it when you bring up the fact that the better part of their business comes from a weapon they bought from the Spanish. Though I'm not sure if there's any serious connection between the CETME and late WWII German Roller lock/delays.

Ian
June 23, 2013, 09:32 AM
The CETME is definitely the derivative of the German WWII roller-delayed experiments - the key designers worked on both projects.

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