Theory of Operation Question Regarding AR-15 Bolts
- Thread starter WhyteP38
- Start date
The carrier has a cam cut in it that rotates the bolt. Bolt rotation happens as the carrier is still moving, not after it stops. The cam slot is where the bolt body retainer rides, and the bolt body retainer actually is the camming lever. Take the bolt out and push the bolt body back and forth and you will see how it rotates. Then just imagine how it works as the bolt carrier is blown backwards. It is actually very simple.
Yeah, I see how it works when combustion gases enter through the carrier key and force the bolt back. Actually, that's what got me to wondering how it works when the BCG moves forward to load a round. At that point, there's no gas to push the bolt forward, which must happen to load the round and lock the bolt into place. So what is the force that cams the bolt into a forward movement?
The only force I can think of that works when the bolt carrier and bolt move forward is momentum (from the recoil spring). I'm pretty sure that's the force involved, but I'm curious to know if that is true.
The only force I can think of that works when the bolt carrier and bolt move forward is momentum (from the recoil spring). I'm pretty sure that's the force involved, but I'm curious to know if that is true.
Yes, it's the recoil spring that forces the carrier group forward again. When the carrier is forced backwards, its movement is slowed, stopped and reversed by the recoil spring. Nothing happens by itself. When the bolt carrier moves to the rear, it also cocks the hammer, preparing the action for the next round to be fired.
Okay, I can see where I'm not explaining myself correctly, so maybe I should break it down a little bit.
I know that:
I know that:
- Combustion gases travel through the carrier key.
- These gases force the bolt to cam rearward.
- The bolt then contacts the bolt carrier and drives it rearward against the buffer and recoil spring. This rearward movement also cocks the hammer.
- The recoil spring goes into full compression, at which point the BCG stops in its rearward travel.
- The recoil spring then decompresses, pushing the BCG forward. At this point, the bolt is still cammed back inside the BCG.
- As the BCG moves forward, the bolt picks up a round from the magazine.
- At some point in its forward travel, the bolt carrier stops.
- At this point, the bolt itself continues forward. In fact, it cams forward into the barrel extension, chambers the round, and locks.
HappyGunner
New member
Don't remove the firing pin
If your going to work your bolt&carrier in the AR don't remove the firing pin while working it because if the cam pin turns and it will not having the FP to keep in lined your going to have a locked up bolt&carrier. And a lot of jerking around to get it unlocked.
If your going to work your bolt&carrier in the AR don't remove the firing pin while working it because if the cam pin turns and it will not having the FP to keep in lined your going to have a locked up bolt&carrier. And a lot of jerking around to get it unlocked.
Dfariswheel
New member
You don't quite have it right.
The rifle fires.
Gas travels down the gas tube and enters the bolt carrier, blowing the carrier to the rear.
As the carrier starts to the rear, the cam surface forces the bolt to rotate and unlock.
The bolt and bolt carrier move to the rear, compressing the recoil spring.
The bolt carrier and bolt are forced forward by the recoil spring.
The bolt strips off and chambers a round.
The bolt STOPS against the barrel extension.
The bolt carrier CONTINUES moving forward, and the cam surface forces the bolt to rotate, locking it.
What's happening is, the bolt carrier when moving to the rear drags the bolt with it, forcing it to unlock.
On the forward cycle, the bolt carrier is PUSHING the bolt, and continues to move forward after the bolt stops, forcing it to rotate and lock.
Locking and unlocking are instigated by the bolt carrier, NOT the bolt.
The bolt is pushed and pulled by the carrier.
The rifle fires.
Gas travels down the gas tube and enters the bolt carrier, blowing the carrier to the rear.
As the carrier starts to the rear, the cam surface forces the bolt to rotate and unlock.
The bolt and bolt carrier move to the rear, compressing the recoil spring.
The bolt carrier and bolt are forced forward by the recoil spring.
The bolt strips off and chambers a round.
The bolt STOPS against the barrel extension.
The bolt carrier CONTINUES moving forward, and the cam surface forces the bolt to rotate, locking it.
What's happening is, the bolt carrier when moving to the rear drags the bolt with it, forcing it to unlock.
On the forward cycle, the bolt carrier is PUSHING the bolt, and continues to move forward after the bolt stops, forcing it to rotate and lock.
Locking and unlocking are instigated by the bolt carrier, NOT the bolt.
The bolt is pushed and pulled by the carrier.
Perfect! Thanks!
If momentum alone was the acting force on the bolt, I was going to be a bit concerned, because momentum is affected in different ways than the mechanical action of the bolt carrier on the bolt.
Plus, you cleared up my mistaken understanding of the rearward travel as well.
Thanks again!
If momentum alone was the acting force on the bolt, I was going to be a bit concerned, because momentum is affected in different ways than the mechanical action of the bolt carrier on the bolt.
Plus, you cleared up my mistaken understanding of the rearward travel as well.
Thanks again!