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Cuts next to hammer ramp on ar15 bolt carrier


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M16 profile?  Can you see the firing pin within the BCG looking up through the mag well?  If you can not, then it has the M16 profile.   I think it may be crud, dirt, muck, mud or excessive lube/gas escape routes, but I am still not tracking here.  I dunno yet.  Sorry.  HB

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Exactly right thank you.

 

What I am going by is I have a 300 ossm upper (that I am trying to sell btw) that is diff than 556 carriers in the way I mentioned. The rim on the 300 ossm is the same as the 410 shotgun shell, wink wink hint hint

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So what determines how or why those cuts are on either side of hammer ramp? Lookin at you old coot

How deep they are that is. Mainly cause I wNt a fatter dia bolt

 

It's difficult to get a good read on it because the channel is not perfectly flat, but my calipers measure ~.200" from the flat area the hammer rides to the bottom of the channel on my 5.56 carrier. However, measuring the thickness between the bottom of the channel to the wall closest to the channel which the bolt rides in, I'm reading ~.030". The reason for them being there is unknown to me. Hope this helps.

 

Let me know if you need pictures of what I'm trying to describe and I'll see what I can do.

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Twinkie holders. 

 

Like stated, I'm certain they are "muck channels". I would also think the depth/width would depend on the tooling tolerances of the manufacturer.

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This is how I understand it.

Those grooves separate the Lands* from the hammer ramp & contact surface.

If those grooves were not there the lands would not ride properly within the bottom of the receiver and the BCG would not be aligned properly.

 

*Lands are the flat ridges on the outside of the grooves, and the are two more to either side of the gas key.)

 

About the exterior of the bolt carrier are a series of usually four (4) lands and usually accompanying grooves which extend from the forward end of the bolt carrier (as it is mounted in the firearm) rearwardly for a distance of about one-half the length of the bolt carrier.

A land can be defined as a raised portion on the exterior of the bolt carrier which contacts the interior surface of the upper receiver of the firearm.

Such lands are generally equally spaced from one another about the exterior of the bolt carrier and are generally parallel to each other.

The exterior surface of the lands make contact with the interior surface of the upper receiver of the firearm and serve to align the bolt carrier within the receiver.

Edited by ChileRelleno
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I believe that they give clearance for the magazine feed lips when the bolt is closed. 

 

You are onto something there. I just took my carrier out, unloaded a mag, and fit the feed lips into the channels. Near perfect fit.

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prob a combination of everything, like has been suggested...

 

ya, cuts maybe so the bullets can ride higher in mag, or ride higher into path of bolt that is, for feeding...on the single stacks its not the same so you dont cut as deep....maaaaaaybe?

i will post pics in a bit of my 300 OSSM carrier compared to a 556 carrier

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  • 2 weeks later...

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