I’m under the impression that having a longer barrel not only means reduced muzzle flash and report, but reduced recoil as well. Are longer-barreled rifles always softer-shooting? How much more recoil does a 7.5" barrel have when compared to an 18"? What about 14.5" vs 16"?
If this truly is the case, then why don’t more people go with a longer barrel setup, like an 18 or even a 20? I know they’re heavier, etc. but if you have a quieter, less flashy and softer-shooting gun, that might just be a game-changer for me!
yes and no… Do a search. The shorter the gas tube the harder the recoil because of the gas circulation. 7 inch tube will have a sharper recoil than an 9.
I think generally the tradeoff for a handy short rifle is accepted, given the low recoil of the 5.56 round. middys strike a nice balance as the poster above me said. 9" gas tube=smoove.
the 20" rifle certainly isn’t without merit though. Very smooth shooting plus a longer sight radius and a bit more velocity… i just don’t’ see it taking over for CQB applications or even urban combat. right tool for the job and all that.
There is a difference between perceived (or “felt”) and free recoil. Felt recoil is affected by pressure rise, stock design, action type, recoil pads, muzzle brakes and a myriad of other details that speed up, slow down or vector the recoil impulse absorbed by the shooter.
Free recoil is affected by bullet weight, charge weight, weapon weight, velocity of the bullet and the velocity of the ejecta (gases from the powder charge) which is a constant of 4750 fps if I recall right. The answer is expressed in ft/lbs. Increase bullet weight, charge weight or the velocity of the bullet and there is an increase of free recoil. An increase of weapon weight decreases free recoil. All else being equal, increasing the length of an AR from 14.5 inches to 20 inches increases velocity which, in turn, increases free recoil.
What the increase in barrel length does is reduce muzzle blast, a psychological factor of perceived recoil. The human mind is conditioned to believe that a greater muzzle blast means a more powerful weapon, and vice versa. The extra length of the barrel also has more moment to overcome to be overcome by the energy of the recoil resulting in less muzzle rise at a slower rate, another psychological aspect of perceived recoil.
The shorter gas system of the AR carbine means the gases are tapped at a higher pressure, generally resulting in a sharper recoil impulse. Everything happens quicker. Slow down the recoil impulse and the perceived recoil is reduced as it’s now softer.
So the short scientific answer is, all else being equal, the increased velocity of the longer barrel results in more ft/lbs of free recoil.
When it comes to how a longer barrel affects perceived recoil, the answer is much more complicated
If you mean less perceived recoil, then yes. If you mean less free recoil, then no. Port size doesn’t change how much recoil energy the round will generate
Newton’s Third Law of Motion dictates that the absolute amount of recoil will be constant, but if you spread it out over a longer period of time, the perceived recoil will be less.
As an intellectual exercise, I’d love to see a force vs. time graph of recoil energy using different gas systems and buffer systems. I’d expect the area under the curve to be the same, but with significantly varying graph shapes with different gas/buffer systems. The recoil from these rifles is pretty modest and a lot of its management can no doubt be mitigated by training, but that would be a separate exercise.
I thought at one point rob_s was trying to find a way to quantify recoil; devise a way to measure and graph it.
At the end of the day, longer barrels generally have longer gas systems, which can lead to less recoil. Overall, the actual answer to the OPs question is more complicated as there are numerous factors that go into it.
The greater recoil often felt with shorter gas systems is probably the result of a higher cyclic rate. A higher cyclic rate means the BCG and buffer are moving faster, when they bottom out in the receiver extension how is that extra velocity not turned into more recoil?
My 5.56 rifles, from 10.5" to 16", all feel pretty similar. Cyclic rate seems to make much more of difference to me than barrel length or gas ports, within reason.
I have a way, I just need the range time to properly vet it. It’s actually a redundant method with two methods to be able to compare results to ensure that they are accurate.
Sounds like you both are referring to the same thing. He’s just using the term “spread out” in place of a slower cyclic rate…if I’m interpreting to correctly.
It’s a basic physics concept and pretty immutable. For every action there is an equal and opposite reaction. There can’t be more total recoil energy than there is in the explosion of the cartridge. Same total amount of energy, but the way that energy is felt is all about time, and how that energy is dissipated. If it’s dissipated into the receiver extension all at once by the buffer hitting it, it will be felt more. If it’s dissipated by the spring compression over a longer period of time, or in the extra time it takes to accelerate a heavier buffer, or compression of the gas over a longer period of time in a higher-volume (longer) gas tube, or in some combination of the three things, it will be felt less.
Maybe that’s what you mean by cyclic rate. Longer recoil cycle means energy of cartridge explosion dissipated over a longer period of time. Whatever can be done to lengthen the time of the recoil cycle with springs and buffers and gas tube volume means less felt recoil, even though the total energy is the same.
Recoil isn’t just a linear thing that is either greater or less. Perceived recoil would be something we feel as greater or lesser but recoil itself should be imagined as a hump on a graph plotted over time. Basically it’s an acceleration…you’re plotting how fast the rifle accelerates from a dead stop (into you)
Some recoil is sharper for a shorter period of time while some recoil feels softer over a longer period of time. The total recoil felt would be the area under the hump, but the hump can take many forms and give us a different perceived recoil. All the different components and barrel configurations would play a hand in changing the shape of the hump.
One thing people tend to forget is that longer barrels normally result in increased velocity. The more energy imparted to a bullet, the more energy imparted to the rifle. Longer barreled AR’s have more free recoil. It’s how this energy is managed that the shooter perceives. Longer barreled AR’s tend to have longer (read softer) gas systems. They also tend to have more weight, as the longer barrel requires more steel (if barrel diameter remains the same). The longer barrel also means the bullet dwell time is longer. All this means the recoil impulse is stretched out over a longer period of time, feeling softer. Slower recoil which has more free energy should result in more muzzle rise, but less perceived recoil to the shooter. Conversely, faster recoil should have less muzzle rise, but feel much harsher to the shooter.
This is before we add recoil cancelling (not reducing) features to the rifle. Smaller gas ports, stiffer springs, heavier carriers and buffers, muzzle attachments, etc. For example, a 10.5" AR with a larger than necessary gas port is going to have a lot more felt recoil than a 16" middy, right up until you put an effective compensator on it. Then it will actually have less felt recoil. However, because of the increased blast, the shooter may still struggle with it because of the previously mentioned psychological aspect of perceived recoil.
Long story short, the operator’s environment and specific needs should outweigh recoil factors. There a many methods to combat the recoil effects of a shorter barrel. Use the longest barrel you can effectively and efficiently operate in the environment you face. For some it will be a 10.5", some a 16" and some, even longer. Recoil considerations should be secondary.