I was wondering if anyone here could help me with some questions Ive always had about the AR-15 system.
Why does the AR-15 suffer from bolt carrier bounce when other systems do not seem to.
Why does it require a buffer when other systems do not
And why does it require a dust cover while square carrier systems do not?
Jut a few questions I cannot find answers for.
Almost all the weapons I have used have a buffer assembly of some kind; G3, MG3, MP-5, Minimi, FN MAG, AK. It’s just the design that varies from system to system.
The difference is that for most of these systems, the action spring is inside the upper receiver itself. In some, it is attached to an action spring rod. The buffer acts as a stop after the action spring is compressed.
As for bolt bounce, that is most likely a result of the design of the bolt and bolt carrer; the bolt telescopes and rotates in the carrier. With the roller lock system HK used, for example, bounce could not happen.
As to the dust cover, most machineguns have them. I find it to be a good feature to have on a rifle.
The carrier bounces because there is nothing that mechanically locks it into place and because it hits the barrel extension. It probably means that it’s hitting and rebounding before the buffer weights can move enough to damp it out
Why does it require a buffer when other systems do not
The buffer assembly adds the necessary mass to the reciprocating parts while providing damping. It is separate from the carrier to keep the BCG from being so big as to complicate field stripping. All self-loading systems have to have some kind of buffering in one form or another
And why does it require a dust cover while square carrier systems do not?
The AR does not need a dust cover. It’s like the stripper clip guide on an M14- nice to have under certain circumstances but necessary to the function of the rifle
Also, separating the out the weight of the carrier to the buffer is quite a clever bit of engineering in that you can use the same carrier regardless of barrel length and/or cartridge (and more or less caliber) - you only need to swap out the buffer to compensate. Imagine trying to compensate for reciprocating mass using only the carrier…
Even JMB designed firearms with a buffer system of sorts. The 1911 (and pretty much all semi-automatic pistols) just have the buffer spring towards the front, and the slide itself acts as the buffer. Both serve the same purpose: to return the bolt back into battery after removing the spent case and stripping the next out of the magazine.
This.
And, the internal design of the buffer acts like a dead blow hammer. If the carrier were to bounce off the extension, it would unlock, even if only partially. Every auto loader needs some mechanism to ensure that the bolt locks reliably.
The design of the AR pattern bolt carrier has raised rails with a reduced diameter body. This provides clearance at the ejection port for foreign matter to enter. The square bolt designs typically have less clearance for debris to enter. But, as pointed out above, a lot of other designs have some type of cover.
I appreciate all the replys and that does make sense about the dust cover, I had not thought about the fact that it has raised rails.
Here is what I am talking about with the buffer, or lack there of. We all know the AR-15 system
things like the AK, SCAR, ACR do not have an actual buffer(they do have a rubber stopper to keep the bolt carrier from bottoming out against the receiver, so does the buffer on the AR-15) As you can see everyone just has a spring to counter the speed of the BCG as well as send it back home.
ACR
AK47
Bolt Carrier bounce is also still very interesting to me as seeing how these systems do not suffer from it. Is bolt carrier bounce a symptom of a round carrier or something else?
I understand what you’re asking, but think about the above for a moment.
Yes, the AR-15 system has both a spring and a buffer system to help counter it.
This has been covered in a good bit of detail here.
http://m4carbine.net/showthread.php?t=102496
That’s awesome, thanks for the link:dance3:
If you’re concerned that perhaps it’s another component which could fail, granted to some extent. But what about the the wear disbursement factor?
I think you are a bit too wrapped around the design of the AR-15 buffer and action spring system, to clearly see how the other systems work.
First, let’s define what a recoil buffer is:
A component that reduces the velocity and/or cushions the impact of the recoiling parts of a firearm.
The AR system is just one take on a buffer system.
Like I said previously, other systems have buffers, they are just designed differently. In the AR, the buffer system is located in the receiver extension; it houses the buffer and action spring.
In other systems, the action sping is located in the upper itself, sometimes combined with a guide rod, and the buffer is mounted on the receiver end plate, or stock, and cushions the impact of the reciprocating bolt.
A few examples:
G3:
Showing different HK buffers:
Fixed stock and action spring/action spring rod:
Collapsible stock, part of buffer visible above latch
Cutaway view:
MG 3:
Buffer:
Recoil Spring:
Stock:
Removal of stock and recoil spring:
Removal of buffer:
FN MAG:
Stock, number 6 is buffer:
Showing recoil spring and rod attached:
Recoil spring and rod removed:
Now, I have not handled a SCAR or ACR, but from what I can see from the pics you posted, the action spring assembly works as the buffering mechanism, and there is probably something on either the stock or on the action spring rod that cushions the impact (vertical bar on the SCAR rod, and white rubber knob on ACR rod I think).
Again, a buffering system is just that, a system; execution can vary from weapon design to weapon design.
Great post Arctic1. As was explained to me by someone we would all know at SHOT a few years ago, the design may be somewhat unique in regard to the tube but is in no way inferior. The only time issues arise on a practical level is when full concealment is desired.
AK does not have a buffer. BCG stops by slamming into the end of the receiver.
Most weapons I have worked with do not have a buffer.
There is an after-market buffer available. Anyways, the action spring is a buffer system, it just doesn’t have anything to cushion the impact of the reciprocating parts.
What weapons have you worked with that don’t have a buffer?
To be honest I can’t think of a single weapon in the FDF arsenal that has a buffer. Sako/Valmet, PKM etc. don’t have one.
There are aftermarket buffers for the AK, but they will cause problems. Depending on the design they may cause the bolt to short stroke and regardless of the design the have ability to break down. I broke an US made buffer only after few hundred rounds, and the best ones in few thousand (at least the ones I have shot). When they break the parts will drop into the fire control group and cause problems. They do alter the felt recoil and IMHO make the gun a bit nicer to shoot, but also IMHO they definately are not worth the hassle.
A good analogy for the firearm action spring and buffer is the spring and bump stop system used on automotive suspensions.
In the simple case of a leaf spring truck axle, there will be the leaf spring (action spring) and a bump stop (buffer).
The bump stop is most often a rubber on steel contact point, but can be steel on steel in the case of overload springs like used on a dump truck.
One other key defining feature is:
the action spring is active during the full action stroke,
while the buffer is active only during a short distance at the end of the recoil stroke.
The AK’s bump stop is generally the rear trunion, steel on steel.
Other firearms use a very heavy spring, or an rubber/urethane bumper as the bump stop.
The original M1918 BAR has a heavy “buffer spring” surrounding the “actuator spring” (action spring) .
