Recently, a video popped up in my feed showing an “influencer” mounting a bayonet on an AR-15 rifle and then engaging what appeared to be 8-inch steel plates from a distance that looked to be around 100 yards. The first view showed the shooter at the bench and the second view was down range with the “clang, clang, clang” of bullets hitting steel.
Far be it from me to cast aspersions, but I wondered just how realistic such a display was?
Many years ago, my friend and gun writing mentor, Wiley Clapp, told me, “You can destroy the accuracy of a rifle platoon by saying two words: Fix bayonets!” Wiley was a major fixture in the gun writing world for about forty years, but many don’t know that he was also a Marine Company Commander during Vietnam.
Barrel Harmonics
Any person with knowledge and experience shooting precision rifles — or just shooting rifles precisely — knows that when a shot is fired, the barrel flexes and then returns to its original state in a fraction of a second. That’s called “barrel harmonics.” There are plenty of super slo-mo videos online that demonstrate this.
During a precision rifle course our instructor had us deliberately take shots with our bolt-action precision rifles and then stick them through a section of chainlink fence with the barrels purposely resting on the fence to see if our point of impact changed. Spoiler alert, the impacts were off dramatically. Our ½-size steel silhouette targets were around 200 yards away if memory serves.
There is a very good reason why custom rifle builders, and even factory-made precision rifles, have “free-floating” barrels. The idea is to allow the barrel to flex, free of anything touching it or putting pressure on it. Naturally, with fixed barrels — those that aren’t free-floating — you can get repeatable accuracy because the barrel is always being “touched” in the same place(s) and the harmonics are repeatable and predictable.
Skilled marksmen know not to allow the barrel itself to rest on cover material because it affects the barrel harmonics. But what about introducing an object, like a bayonet, that alters the flex or harmonics of the barrel? Is it really a big deal?
Testing
To find out, I decided to go with two rifles that are set up to accept bayonets; a Springfield Armory SA-16, a near perfect semi-auto clone of the M16A2 and a Century Arms BFT-556. The BFT-556 is a 5.56mm Kalashnikov semi-automatic.
I chose the BFT-556 so I could use identical ammunition, the hyper-accurate Black Hills Ammunition 77 grain OTM. There would be variables, but I didn’t want ammo to be one of them.
As for the sharp, pointy things, I used the Marine Corps’ new OKC-3s bayonet, a fantastic tool. For the Kalashnikov, I used an AKM Type 2 with the bakelite handle. The OKC-3s weighs 1.25 pounds and is 13.25 inches long. The AKM Type 2 weighs 1.1 pounds and is 10.6 inches long.
Step one was easy…rest the rifles, sans bayonet, and shoot five-shot groups from the bench. I figured a 25 meter BZO distance would be enough to demonstrate any shift in impact.
The SA-16 printed a respectable 0.68 inch 5-shot group at 25 meters. The BFT-556 printed a 2.36 inch 5-shot group at that same distance.
For comparison, the SA-16 has a 20-inch bbl and the BFT-556 has a 16-inch bbl and a 1/7 twist.
Step two was to fix bayonets. The first up was the SA-16 with the current Marine Corp bayonet. The 5-shot group strung out a good bit and measured 2.3 inches at 25 meters.
Also, the group with the bayonet affixed printed about 3 inches above point of aim.
With the AKM Type 2 bayonet on the BFT-556, I slow-fired five more shots at 25 meters. The results were a bit surprising.
The shot groups with the bayonet and without it were essentially the same size; they measured within 0.5 inches of each other. Also, the group impact of shots fired with the AKM bayonet was only 1.5 inches higher than without.
I had some data to consider, but I wanted a bit more. So, I put up a paper target at 50 yards and went back to the bench with the SA-16 rifle. Another five-round group minus bayonet posted a very nice, consistent group that measured 0.78 inches.
With the bayonet in place, I managed to get five more shots into a 2 inch group which was again, just a bit over 3 inches above point of aim. The bayonet group was strung out more so than without it.
Things to Ponder
It was no surprise that the Springfield SA-16 posted consistently tight shot groups. Say what you will about the M16A2 rifles, a lack of inherent accuracy was never a problem. The BFT-556 wasn’t as tight as the SA-16, but the size of the shot groups with and without a bayonet were nearly identical.
When considering the mounting setup, the BFT-556 uses an AK-74 muzzle brake and the bayonet lug is on the front sight housing. The bayonet ring is all the way out front at the end of the muzzle brake. Therefore, the AKM bayonet isn’t actually touching the barrel.
All M16-style bayonets mount to a lug on the front sight housing. However, the bayonet ring actually comes to rest on the back edge of the A2 muzzle brake, right where the brake and barrel come together.
When we do our rifle ballistics math and extrapolate how a one-inch group at 100 yards translates to 2 inches at 200, etc., a 3-inch rise in impact between 25 and 50 yards translates to 6 inches of rise at 100 and a full 12 inches at 200. Being 12 inches off at 200 yards could definitely translate to missed targets.
To be fair, we wouldn’t likely fix bayonets if we knew we were engaging targets beyond 100 yards. The cold steel of a bayonet is intended for up close and personal work. In a close quarters battle environment like the jungle or a MOUT situation, we expect targets to easily be inside of 100 yards.
It’s safe to say that adding bayonets to fighting rifles negatively affects accuracy in longer distance shooting. However, for CQB situations, having a chunk of lethal steel affixed to the end of your barrel wouldn’t have such a negative effect on accuracy as to preclude its use. Just be sure to take it off — or take it into account — before engaging anything at greater distances.
Paul G. Markel is a combat decorated United States Marine veteran. He is also the founder of Student of the Gun University and has been teaching Small Arms & Tactics to military personnel, police officers, and citizens for over three decades.
I love fixed bayonets. A great psychological weapon. No they are not obsolete. Just as a flamethrower is not obsolete. Both can stop a riot and not hurt anyone. Just like two guys who open carry their long guns. They stopped the Ferguson Mo riot. And they didn’t even point guns at anyone.
You talked about whether the mounted bayonet would affect barrel harmonics, but then you tested two rifles with non-free-floated barrels, and you rested them both on your range bag. Your test setup itself introduces variability in the very influence you’re testing.
My M16A2 clone set up for CMP Service Rifle competition uses a correct round plastic handguard (with heat shields) that looks just like this, but it isn’t mounted on the gas block / front sight post. Instead I use a White Oak Armament free-float kit. I can rest the handguard on a support, or attach a taut sling and cuff, and nothing touches the barrel. That means repeatable consistency whether I’m standing, seated, prone, on a bench, bracing on a barrier, or whatever.