m249 saw question (maybe a military person can help) - DFWstangs Forums
 
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post #1 of 23 (permalink) Old 09-15-2010, 10:01 AM Thread Starter
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m249 saw question (maybe a military person can help)

First of all, no I do not have a saw, cannot afford a saw, and have never even shot a saw

Anyways, I was curious about them none the less and have a question for any folks who may have shot one or handled one in the military.

How do they work? I know they fire from an open bolt like most machineguns (in the traditional definition of the word) do, but how do they lock/seal the round into the breech? Do they operate via roller delayed blowback like an MG42, or perhaps operate with a rotating bolt like an AR15 variant? If the latter, how does it fire from an open bolt? Surely its not just a blowback type gun, as I am fairly certain that is not feasible for the cartridge.


Thanks
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post #2 of 23 (permalink) Old 09-15-2010, 10:36 AM
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http://en.wikipedia.org/wiki/M249_light_machine_gun

Quote:
It fires from an open bolt and is gas operated. When the trigger is pulled, the bolt and bolt carrier move forward under the power of the recoil spring. A cartridge is stripped from the belt, chambered, and discharged, sending a bullet down the bore. Expanding propellant gases are diverted through a hole in the barrel into a chamber. This pressure moves a piston providing the energy to extract and eject the spent casing as well as advance the belt and compress the recoil spring, thus preparing for subsequent shots.

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post #3 of 23 (permalink) Old 09-15-2010, 10:37 AM Thread Starter
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That does not explain how the bolt locks, surely the gun is not a blowback firearm.
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post #4 of 23 (permalink) Old 09-15-2010, 10:41 AM
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It's the exact same way an mg42 functions.

Instead of rollers on the bcg locking into grooves of the barrel extension, it uses locking lugs like an m60 and a rotation bolt.
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post #5 of 23 (permalink) Old 09-15-2010, 10:43 AM Thread Starter
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Originally Posted by David View Post
It's the exact same way an mg42 functions.
But an MG42 doesnt have a piston if I am not mistaken. Its purely recoil operated with a nielson device to boost recoil.

So the m249 uses a bolt on rollers like the mg42, but a piston system to propel the bolt carrier?
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post #6 of 23 (permalink) Old 09-15-2010, 10:46 AM
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Originally Posted by DOHCTR View Post
But an MG42 doesnt have a piston if I am not mistaken. Its purely recoil operated with a nielson device to boost recoil.

So the m249 uses a bolt on rollers like the mg42, but a piston system to propel the bolt carrier?
See my edit. I'm not use to typing on this iPhone yet.
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post #7 of 23 (permalink) Old 09-15-2010, 10:49 AM Thread Starter
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See my edit. I'm not use to typing on this iPhone yet.
Ah thanks. Well then it must be hammer fired as well correct? It would seem like a fixed firing pin would set off the round before the bolt had a chance to lock into place and rotate fully in to battery.
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post #8 of 23 (permalink) Old 09-15-2010, 10:56 AM
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Ah thanks. Well then it must be hammer fired as well correct? It would seem like a fixed firing pin would set off the round before the bolt had a chance to lock into place and rotate fully in to battery.
No. The bolt when it rotates to the rear locking position hides the firing pin inside the bolt face. The bolt has notches in the bottom as a sear catch. When he trigger is pulled the sear lowers, the bolt moves forward and rotates the locking lugs into the barrel extension grooves all the while the firing pin within the bolt protrudes forward out of the bolt head thus igniting the cartridge.
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post #9 of 23 (permalink) Old 09-15-2010, 11:00 AM Thread Starter
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No. The bolt when it rotates to the rear locking position hides the firing pin inside the bolt face. The bolt has notches in the bottom as a sear catch. When he trigger is pulled the sear lowers, the bolt moves forward and rotates the locking lugs into the barrel extension grooves all the while the firing pin within the bolt protrudes forward out of the bolt head thus igniting the cartridge.
Very interesting, thanks for clearing this up.
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post #10 of 23 (permalink) Old 09-15-2010, 03:38 PM
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Quote:
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No. The bolt when it rotates to the rear locking position hides the firing pin inside the bolt face. The bolt has notches in the bottom as a sear catch. When he trigger is pulled the sear lowers, the bolt moves forward and rotates the locking lugs into the barrel extension grooves all the while the firing pin within the bolt protrudes forward out of the bolt head thus igniting the cartridge.
yep.

From my experience, vary reliable.

Also, the 240 series (240B, 240, etc) operate nearly the exact same, just on a little larger scale.

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post #11 of 23 (permalink) Old 09-15-2010, 04:42 PM
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I should make a correction, the op-rod has the notch for the sear to catch on not the bolt. The bolt and op-rod are connected together.
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post #12 of 23 (permalink) Old 09-15-2010, 07:40 PM Thread Starter
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I should make a correction, the op-rod has the notch for the sear to catch on not the bolt. The bolt and op-rod are connected together.
Ah, that makes sense.
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post #13 of 23 (permalink) Old 09-15-2010, 07:51 PM
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Maybe someone from the Mansfield PD will chime in?
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post #14 of 23 (permalink) Old 09-15-2010, 08:08 PM Thread Starter
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Maybe someone from the Mansfield PD will chime in?
Do they have m249s
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post #15 of 23 (permalink) Old 09-16-2010, 08:19 AM
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Do they have m249s
Affirmative.
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post #16 of 23 (permalink) Old 09-17-2010, 11:00 AM
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The mg42 was absolutely revolutionary for machineguns. So many weapons use its basic design.
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post #17 of 23 (permalink) Old 09-17-2010, 12:02 PM
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The mg42 was absolutely revolutionary for machineguns. So many weapons use its basic design.
And in typical US government fashion they break something that isnt broke.
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post #18 of 23 (permalink) Old 09-17-2010, 12:36 PM Thread Starter
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And in typical Belgian fashion they break something that isnt broke.
Fixed
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post #19 of 23 (permalink) Old 09-17-2010, 03:00 PM
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Fixed
We did it with the m60.
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post #20 of 23 (permalink) Old 09-30-2010, 10:18 PM
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If you still care, a great 60s video. LOL

http://www.youtube.com/watch?v=VXzkHxwaoV4
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post #21 of 23 (permalink) Old 09-30-2010, 11:15 PM Thread Starter
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If you still care, a great 60s video. LOL

http://www.youtube.com/watch?v=VXzkHxwaoV4
Seems to be a combination of mg42 and lewis gun. I did not know that barrel changes were so easy on an m60.
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post #22 of 23 (permalink) Old 09-30-2010, 11:58 PM
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Seems to be a combination of mg42 and lewis gun. I did not know that barrel changes were so easy on an m60.
It's a variety of mg42, fg42, and Lewis guns.

Barrel changes are easy. Problem is most forget to use the barrel glove or bipod when the barrel is hot. Thus on the e3 and e4 variants they attach the carry handle directly to the barrel to aid in safely removing it when hot. I've met many a 60 gunner who were in nam with scarred palms from changing barrels in shtf situations.
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post #23 of 23 (permalink) Old 10-01-2010, 02:41 PM
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SAW = POS unless you keep that gun clean and use LSA and the 240B is probbally my favorite machine gun of all time...well right next to the M2 .50 cal

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