The force of the felt recoil is slowed down, peaks later and is halved by the buffer.
So a M4 buffer generates 1600 lbs of force?
Force is equal to the energy divided by the distance over which the force acts.
You can calculate the energy of free recoil fairly easily, the question is what is the distance over which it acts.
I suspect that graph was generated by firing the rifle in hard mount that minimized the recoil distance of the rifle to almost nothing, so very high forces.
You do not experience anywhere near forces that high from and AR.
What force would be realistic in a milspec M4?
I did not consider the scale or unit of measurement when I first looked at the chart.
It does seem excessive, though lysnaders post helps make some sense of it, to me anyway.
The energy of free recoil for an M4 is around 5.5 to 6.0 ft-lbs of energy. If you restrict the rifle to only move 0.004" (hard mount), the force will be 1,600 pounds.
If you let it move 1/2 inch it will be 12 pounds.
How much does your shoulder move when you shoot?
How does that translate to how many ft lbs of force the BCG and buffer are hitting the barrel extension and the rear of the buffer tube?
Well, what is the energy of the bolt group, and how much compression does the rubber tip of the buffer compress?
That’s where a hydraulic buffer makes its gains, it has a stroke of about 1/2 inch versus a few hundredths of an inch.
What is the approximate force of a BCG and standard buffer in a milspec M4?
How many ft lbs of force does the buffer hit the rear of the buffer tube?
This is a buffer inside an AR’s buffer tube, not recoil pad contacting the shooter’s shoulder. It can’t change the felt recoil force due to the free recoil energy of the rifle. What it helps is the felt recoil force caused by the BCG+buffer slamming on to the end of the buffer tube.
Kinetic energy of BCG/buffer comes from the gas. Part of it is stored in the buffer spring to cycle the action, part of it is to be dissipated by buffer loss and other losses. Whatever left over is to cause discomfort on the shooter’s shoulder. The fancy (probably pricey) hydraulic buffer is just that; higher loss. Well it does it better; higher loss over longer travel.
Cutting the gas has the same effect. If the buffer doesn’t bottom out in the tube, the recoil force is almost zero. Almost because the reaction force to the spring is always there.
-TL
Assuming .02" compression of the rubber bumper, about 275 to 300 lbs plus the spring force at full compression.
EDIT: Revised force figures base on the velocity data given below:
About 175 to 200 pounds
I don’t know. 275lb on my shoulder each time I pull the trigger, I probably don’t have a shoulder left after one mag :). Anyway, what if the rubber bumper never touch the end of tube? It should be much less.
-TL
Would 275-300 lbs be the bolt velocity in ft lbs? I would like to know more.
It only acts on your shoulder for 1.5 to 2.0 milliseconds.
The rubber bumper will always contact the back of the receiver extension. You can see the spring only slows the bolt down about 5 fps. If the buffer was never to contact the rear of the extension, the initial bolt velocity would have to be less than 5 fps, or the travel would have to be three times longer.
No, that is the force exerted on the back of the receiver extension by the bolt carrier and buffer bouncing off it plus the spring.
Thats a lot of force! But much less than the graph. All though the graph does not specify a caliber.
Are you aware of any instrument being used to verify this or just by calculation?
Like I state earlier, the force is dependent on how much motion is allowed. If you put a force gage on the end of a receiver tube and back it up into a massive steel block and fire the rifle the force the gage reads will be much higher than if you placed it against a giant sponge.
The energy of free recoil is the energy developed by just the gun firing the bullet. The energy from the bolt is separate and must be added to the free recoil energy to get the total felt recoil.
And again, how you perceive this energy depends on the time it acts on you and your motion during the delivery. Your wife tackling you at a dead run delivers more energy than a being shot by a .22 LR, but they will feel quite different. (135 pound woman at 9 fps vs 40 grain bullet at 1,200 fps.)
That 1,300 pounds indicates very little motion of the rifle was allowed.
I was joking about the shoulder. The 275lbf force is on the rifle. Because of the rifle’s mass, the force actually lands on the shooter is much less. Short time alone doesn’t really help.
Gas can certainly be adjusted to have the buffer not reaching the buffer tube end. It is kinetic energy of the BCG, which is proportional to square of the its speed. Based on the figures from the graphs, the initial speed of BCG needs to be adjusted down to 11fps or so for the buffer tip barely touching the buffer tube end. The rifle is now running on very thin margin against variations. For mission critical applications, over gassing is the norm for a reason.
-TL
So is it fairly accurate to say that a standard M4 bolt/buffer is generating about 200 lbs of force on the rear of the buffer tube?