View Full Version : RE: Odd M16 Bolt
A friend of mine sent me this pic. It came from an original Colt M16 rifle that his agency acquired from the Government cheese program.
The bolt has an MPC marking on it. Anyone seen a bolt like this before? The rings are also rather odd or maybe it's an illusion.
Broken or manufacturing flaw. Time to get a new bolt.
It appears to have been made that way if you look closely. I admit it could be a defect, but it's curious nonetheless and I have never seen it before.
Broken or manufacturing flaw. Time to get a new bolt.
Interesting. Do all gas rings move freely? Those look like they need replacing no matter. That does look like purposeful machining on the bolt. Maybe some experimental LMG bolt? That would be neat.
That might be THE Bolt that started the wive's tale of "make sure your Gas Ring gaps are never lined up?? :)
I've never seen that but I agree it looks like it was made that way.
I'd put a regular bolt in this gun and set this aside until a definite answer comes.
Scallops appear symmetrical and machined.
The rings are also rather odd or maybe it's an illusion.
Just an observation- the scallops & notch would make the rings easier to remove or install quickly. Slip an end under the tab and screw on. Not that it's needed, just conjecture as to why someone might intentionally scallop and leave the tab.
I'm trying to remember where, but I think I've seen a similar approach used to facilitate installation of split rings in a non-firearms application.
I've been searching, no hits yet. :(
Contact Dean Caputo, I'd bet my paycheck he can help you out with it. I would put my money on some experimental design for an overgassed shorty gun to bleed gas off to slow down the BGC? i say this as those notches should be lined right up with the BC vent holes during extraction, right? The width of the center part looks almost identical to the distance between the gas vent ports in the bolt carrier.
I hadn't even thought to look at the orientation of the cuts to the extractor. :secret:
I sent Dean Caputo a link to this as well as the pics, so we'll see what he has to say about it.
I almost wonder if that didn't come from an M231 port gun? Did they not at one point drop the ROF on the port guns, maybe this bolt was one of the mods to drop the ROF?
Very interesting. Right click, save as.
I'd agree with what has been suggested- looks like a way of dealing with an over-gassed rifle, or reducing the cyclic rate. Those notches would line up with the carrier's vent holes- I'd question how effective they would be, though, since the bolt isn't sealing anything. The gas rings, which are left in place, are what creates the seal.
Still really cool.
...Those notches would line up with the carrier's vent holes
I agree. They don't line up with the 'ports' for a M231 bolt carrier, though. Just an observation.
Any idea what model of rifle this bolt came out of?
Experimental?maybe one slipped through the cracks
I think it's interesting that the unusual machining on the tail of the bolt is indexed on the same clock position as where there is no locking lug on the front of the bolt. Over the years some armorers machined off the locking lug on the opposite side of the bolt from the extractor, so there would be even pressure on the front of the bolt when it is in full battery. This was done to enhance accuracy. Could this be a bolt out of an old division match rifle?
Let us know what you find out. This is a very interesting discovery.
Oddly Enough, I think I have seen a bolt just like that.
I was helping the armorer at the Bozeman MT Nat Guard armory once and the armorer was showing me the M-16s they had in a rackl and I remember him showing me the bolts on a couple of guns and he made a big deal about the bolts being different.
At the time, I had no idea what he was talking about, but it very well could have been this. I remember all of the ones they had were old guns, like a 603 model and most had the 3 prong flash hider.
Which also may explain my love for the original M-16s...
Either that or it was SWAT with Robert Urich.
Personally I would look at reaching out to Reed Knight if you don't find an answer - maybe take the bolt to SHOT show and let him see it at the show; KAC has the world's largest and best AR collection so it would be a natural place to start
The rings are definitely damaged, caused by lack of support in the cut-out areas
I worked this up in Solidworks, a normal bolt partially covers the exhaust vents on the carrier in the unlocked position. The cuts on that bolt spot on to where they would need to be, for the exhaust ports to be unobstructed.
It's broke. If it is parkerized it was broke and they re-finished it.
It ain't for an M16, M16A1, M16A2, M16A3, M16A4, M4/M4A1, or M231.
Note the "Divots" coincide with the vent holes on the right side of the bolt carrier (in the depression to accommodate the ejection port cover plunger and spring).
Shit-can it, replace with a new one, continue with work.
That rearmost ring would deform every time I'd think unless there was a gap locator in there. Which I would not think could be trusted.
How about this-- an experiment to get gas under the rings, pressuring them outward against the carrier bore, to effect a better seal? If so I'd say this is the kind of experiment that eventually gets "failed" added as a prefix.
I don't have the bolt. One of my associates did and he doesn't have access to it now.
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