Gunsmithing Camming on AR style rifles

[GasLight]

Have an extension here, and was looking it over, and started to wonder how extraction cam and battery cam work on the ARs? Is this why their chambers are typically looser than a bolt? Is there any troubles with a tight chamber AR rifle?

Thanks for any enlightenment!

 

[GasLight]

Re: Camming on AR style rifles

Ok, after thinking on it some more, I think I may have it right, let me know if I am wrong: Initially the bolt carrier is moving and the force rotates the bolt to the correct position, then as the carrier continues to the rear it has some inertia, which once it grabs the bolt, will help force the fired case out of the chamber? And when moving into battery it does the opposite, the charging spring gives enough momentum to chamber the round, and then rotate the bolt into battery?

Is there any way to utilize something similar to this on a bolt gun? Where the force is supplied not by leverage, but by momentum?

 

[Rafael]

Re: Camming on AR style rifles

I thought the extraction is more a function of blowback forcing the cartridge out of the chamber.....which doesn't begin until the bolt is unlocked by the carrier moving rearward, be that by gas pressure or piston.

There are bolt-action designs that utilize a straight pull rearward and push forward....just can't recall the names of them.

 

[Bronco]

Re: Camming on AR style rifles

A tight chamber AR will usually run for a few rounds of rapid fire. 20, maybe more maybe less depends on a lot of variables, ie: dies used to make round, how hot the loads are, headspace etc. The extractor can tear out a piece of rim or just distort the rim.
I'm sure there are guys running tight chambers that have never had any trouble, well I've seen a bunch who have.

 

[HotIce]

Re: Camming on AR style rifles

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DebosDave ©</div><div class="ubbcode-body">
Is there any way to utilize something similar to this on a bolt gun? Where the force is supplied not by leverage, but by momentum?</div></div>
You'd be using more energy, since you'd have to convert a push forward force, into a rotational one, in order to lock the bolt.
In an AR, this is provided by the slanted cut on the carrier, and there is energy that get wasted in the process (friction related).
Also, the leverage of the carrier slant cut over the bolt body, is lower WRT a bolt handle, which means an higher forward force should be supplied, to achieve the same torque on the bolt.
In an AR15, you don't care, since such energy is not provided by you.
But when it'd be the operator to provide the required energy, it is more efficient to just use the higher leverage of the current bolt action handle. Which would also provide a more positive locking feel for the operator, IMO.

 

[J.Boyette]

Re: Camming on AR style rifles

Click on the pic



John

 

[bohem]

Re: Camming on AR style rifles

The Swiss K31 is a rotating bolt, straight pull rifle. It's a 2 lug version of the same mechanism type in the AR rifles.

 

[monteboy84]

Re: Camming on AR style rifles

Several companies offer AR15's as a straight-pull variant for places where semi-auto makes them illegal. They're simply a Regular AR, minus the gas block and tube.

-matt

 

[i_Adam_i18]

Re: Camming on AR style rifles

Blazers are straight pull too.

 

[Massoud]

Re: Camming on AR style rifles

Depending on the timing of the whole system, semi-auto rifles can use residual chamber pressure to help in popping the case out of the chamber. Certain rifles also have a built in mechanical cam, like the AK/Sig/XCR and most machine guns, this is called primary extraction. The AR just uses a little extra power from the propellant gases. On a bolt gun, there's no such power. There are some straight pull bolt action rifles out there, I designed one myself a few years ago. On this type of rifle, no primary extraction was needed (as far as I could tell), this is because by the time you hand cycle a bolt, the brass has already shrunk back down and cooled and comes right out of the chamber easily (unless you are really stretching your brass). The K31 has a pretty stiff pull because you are cocking a heavily springed firing pin on the back stroke. On a regular bolt gun, you have a cam to turn the lift of the bolt knob into rearward motion of the firing pin.
Justin