Most Reliable AR15 for Self Defense?

[OldState]

I'll utilize the powder and bullet speed example provided above to further illustrate the mathematically measurable difference in recoil between carbine and mid length gas systems. The perception of reduced recoil is due to this mathematically measurable reduction in energy directed into the shooter's shoulder.

Published tables of cartridge performance all correspond with the reality that measured energy is a product of velocity and mass. Using just one bullet weight, push the bullet faster and measured energy increases. Slow down the velocity of the same bullet and measured energy decreases.

The bolt carrier group (BCG) is thrust into the buffer tube after a cartridge is discharged. The quantifiable energy of the BCG is directed into the shooter's shoulder. Increased velocity of the BCG increases the measurable amount of energy the shooter receives in the shoulder. Referring back to CRANE's measurement, the BCG moves 22.6% slower in a mid length gas system compared to a carbine length gas system. This significant reduction in BCG speed factually, mathematically and perceptibly reduces recoil energy.

I don’t mean to participate in the derailment of a thread, but you can’t “mathematically” eliminate energy. This is simple physics. The same energy is realeased firing the same cartridge regardless of what it is fired in. The midlength is simply allowing the recoil energy to be distributed over a longer amount of time giving the perception of less recoil....as was said in the post before. So instead of the rifle giving you a quick “punch” you get a shove. You could also achieve the same perception by making the rifle heavier, etc.

Still a good thing no doubt and would theoretically allow the shooter greater control and cause less stress on the rifle.

Like if you were to jump off a 6 foot platform and land with your knees locked vs bending them to deliver the energy slower.

[Buncheong]

You can always just build another. Nothing wrong with the colt as a first rifle. Use what you’ve learned and start stockpiling parts.

KISS mutt

Oh man, does that carbine look NICE!

[Desert Trekker]

I don’t mean to participate in the derailment of a thread, but you can’t “mathematically” eliminate energy. This is simple physics. The same energy is realeased firing the same cartridge regardless of what it is fired in. The midlength is simply allowing the recoil energy to be distributed over a longer amount of time giving the perception of less recoil....as was said in the post before. So instead of the rifle giving you a quick “punch” you get a shove. You could also achieve the same perception by making the rifle heavier, etc.

Still a good thing no doubt and would theoretically allow the shooter greater control and cause less stress on the rifle.

Like if you were to jump off a 6 foot platform and land with your knees locked vs bending them to deliver the energy slower.

Does an immobile bolt carrier group (BCG) exhibit any recoil energy? The answer is no. Does a BCG propelled at a speed of 3.23 feet per second (fps) as a result of the discharge of a cartridge exhibit recoil energy? The answer is yes. CRANE measured a 3.23 fps BCG speed decrease in the mid length gas system compared to a carbine length gas system. Gas pressure decreases with every inch of travel in the barrel. Reducing the amount of pressure applied to the BCG definitively reduces the amount of recoil, both measured and felt. The mid length gas port is further down the barrel from the location of a carbine length gas port, therefore it has less pressure available to send to the BCG. Pressure is what causes the BCG to recoil. Hence, mid length gas systems factually and perceptibly produce less recoil than carbine gas length systems.

The recoil energy of the BCG directed into your shoulder is measurable and tangible. The faster you move the BCG towards your shoulder the greater the amount of very real and measurable recoil transmitted to the shooter. This is neither subjective nor theoretical. BCGs move significantly faster in carbine length gas systems compared to mid length gas systems when firing identical cartridges in each.

Carbine length gas systems in fact produce more recoil than mid length gas systems. Science, math, and shooter perception all confirm this truth.

[OldState]

Does an immobile bolt carrier group (BCG) exhibit any recoil energy? The answer is no. Does a BCG propelled at a speed of 3.23 feet per second (fps) as a result of the discharge of a cartridge exhibit recoil energy? The answer is yes. CRANE measured a 3.23 fps BCG speed decrease in the mid length gas system compared to a carbine length gas system. Gas pressure decreases with every inch of travel in the barrel. Reducing the amount of pressure applied to the BCG definitively reduces the amount of recoil, both measured and felt. The mid length gas port is further down the barrel from the location of a carbine length gas port, therefore it has less pressure available to send to the BCG. Pressure is what causes the BCG to recoil. Hence, mid length gas systems factually and perceptibly produce less recoil than carbine gas length systems.

The recoil energy of the BCG directed into your shoulder is measurable and tangible. The faster you move the BCG towards your shoulder the greater the amount of very real and measurable recoil transmitted to the shooter. This is neither subjective nor theoretical. BCGs move significantly faster in carbine length gas systems compared to mid length gas systems when firing identical cartridges in each.

Carbine length gas systems in fact produce more recoil than mid length gas systems. Science, math, and shooter perception all confirm this truth.

You can not create or destroy energy and every action has an equal and opposite reaction. Physics 101

https://en.m.wikipedia.org/wiki/Conservation_of_energy

[MistWolf]

The bolt carrier group (BCG) is thrust into the buffer tube after a cartridge is discharged. The quantifiable energy of the BCG is directed into the shooter's shoulder. Increased velocity of the BCG increases the measurable amount of energy the shooter receives in the shoulder. Referring back to CRANE's measurement, the BCG moves 22.6% slower in a mid length gas system compared to a carbine length gas system. This significant reduction in BCG speed factually, mathematically and perceptibly reduces recoil energy.

Now were entering the realm of multiple recoil forces. Just as the rifle recoils to the rear from the force of the bullet being shoved forward, the rifle is also pushed forward by the force pushing the carrier to the rear. This transfers a part of the recoil energy to the carrier buffer and spring. When the carrier buffer and spring reach the end of their travel, the energy is once again transferred, back to the rifle and ultimately to the shooter. Moving the carrier faster doesn't create more recoil it just transfers more of the recoil energy to the carrier. If the carrier slowed to a stop over time recoil feels soft and more manageable. If brought to a sudden stop, such as when carrier momentum is more than the spring is designed to handle and slams into the back of the RE, recoil is sharp.

None of that recoil/counter recoil monkey business creates or destroys energy. It just stores and redistributes it.

[MegademiC]

Energy is the same.
Impulse is different.

As I stated in another thread, if you take the recoil in a big spike when the bcg bottoms out, its a higher impulse.
If you spread it out over the entire bolt cycle (extreme example is kac lmg), you get a long, soft impulse with little to no spike and feels like little recoil. Its like a soft butt pad- it doesnt reduce recoil, it lowers the impulse in your shoulder.

[medicman29]

Like most everyone else has said, buy from a reputable company. colt. BCM. Daniel defense. Lube it up. buy lots of good training ammo and mags. go get lots of training, then practice. As much as you can. I've got all three of the above mentioned rifles, and they all run really well. I will say that my BCM rifles are my favorites, and I have several thousand rounds through a couple of them each. One has never had a failure I didnt induce on purpose. The other, the only failures came during a high volume class when the independence ammo I was shooting was blowing the primers out, and caused several failures. Not sure why, because I ran a case of the same ammo through that rifle at a previous class with no problems. My DD and colts don't have enough through them at this point for me to say one way or the other, but they've been reliable up to this point. I will also say that I feel that the midlengths seem to shoot softer, subjectively.

[Desert Trekker]

You can not create or destroy energy and every action has an equal and opposite reaction. Physics 101

https://en.m.wikipedia.org/wiki/Conservation_of_energy

The energy released from discharging identical cartridges will be identical within tiny fractions of differences due to the impossibility of everything being perfectly exact among multiple examples.

If these cartridges were discharged in the open air with a bolt carrier group (BCG) two inches behind the cartridges, how much recoil would you expect the BCG to exhibit under these circumstances? (Never attempt this as it would be unsafe)

Now if these cartridges were discharged in a carbine, would you anticipate more recoil of the BCG under these circumstances? Of course there will be massively more recoil in this scenario. The same amount of energy is present, yet more of that energy is directed to the BCG when fired in the carbine. The mid length gas system transmits less energy to the BCG then does a carbine length gas system. Energy is not recoil. The manner in which energy is directed will increase or decrease recoil.

Unless we are to redefine the universally accepted meaning of recoil, mid length gas systems factually produce less recoil than carbine length gas systems. When discharging a cartridge within a rifle recoil is typically understood to be the force transmitted rearward.

[Desert Trekker]

For the legal CYA, NEVER, repeat, NEVER discharge a cartridge in the open air or in any way other than the manufacturers approve of and/or recommend. The previous post comments were provided to make a mental visual point, NOT to suggest physically attempting any actions.

[Desert Trekker]

Now were entering the realm of multiple recoil forces. Just as the rifle recoils to the rear from the force of the bullet being shoved forward, the rifle is also pushed forward by the force pushing the carrier to the rear. This transfers a part of the recoil energy to the carrier buffer and spring. When the carrier buffer and spring reach the end of their travel, the energy is once again transferred, back to the rifle and ultimately to the shooter. Moving the carrier faster doesn't create more recoil it just transfers more of the recoil energy to the carrier. If the carrier slowed to a stop over time recoil feels soft and more manageable. If brought to a sudden stop, such as when carrier momentum is more than the spring is designed to handle and slams into the back of the RE, recoil is sharp.

None of that recoil/counter recoil monkey business creates or destroys energy. It just stores and redistributes it.

Every action has an equal and opposite reaction. This is an undeniably proven fact.

Recoil in a rifle is rearward thrust. The recoil energy from the thrust of a BCG is transmitted to your shoulder before the opposite reaction occurs. The push and subsequent pull are not simultaneous.

An increase in BCG speed increases recoil energy transmitted directly to the shooter, and Newton's Third Law does not reduce the force received by the shooter because the opposite reaction occurs after the recoil energy impacts the shooter.

Hence, a mid length gas system shown to move the BCG 22.6 % slower than a carbine length gas system will produce a quantifiable and perceptible reduction in recoil.