My M&P Sport ii (made in 2020) has a standard 16" barrel. I read that 20" barrels provide higher velocity resulting in better terminal ballistics, especially tumbling and yawing, in home defense scenarios.

My ammo is Winchester M193 and M855, Hornady Super Performance Match BTHP, 75 grain, and Winchester Super X Jacketed Soft Point, SPRX in 55 grain.

I don't anticipate doing room clearings, but rather shooting from cover (though I keep in mind Mike Tyson's quote that everyone has a plan until he gets punched in the face).

What are your thoughts about my upgrading to an upper with a 20" barrel?

Thanks!

Make sure you do your research before spending money.

Tumbling of 5.56 rounds is a concept that ONLY applies to 55 grain rounds, fired from barrels with 1:12 or 1:11 twist rate. Heavier M885 and up rounds, fired from barrels with twist rates of 1:9 and higher, will NOT tumble, regardless of the muzzle velocity.

Reducing the barrel from 20 inches to 16 inches DOES reduce the MV, and therefore the range at which tumbling will reliably occur, but we're talking about HUNDREDs of yards. In other words M16 and M16A1s firing M193 ball could reliably cause wounds from tumbling and yawing out to something like 250 yards. Going down to 16 inches decreased the MV and reduced the distance down to something like 200 yards. Going to the XM177 platform reduced the barrel length, MV and therefore tumbling/yawing distance to around 150 yards, give or take.

SO in your case do your home defense scenarios involving a distance over 200 yards? If not then..............

At a range of feet nobody will know the difference.

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Pisgah

I would think that the maneuverability of the 16” barrel is not worth losing. The M4 is very handy and ideal for indoor home defense use. The extra velocity would only generate better penetration, maybe of course over penetration, which is undesirable in this scenario. I would stick with the 16” for a “Personal Defense Rifle” and then if you WANT a 20” barreled AR in .223 you can build one! I think my M&P15 is ideal for home defense. Also, LOTS of police departments have or allow or issue M4 clones, often M&P-15’s so I wouldn’t rush to condemn 16” barrels. They are good for many scenarios.


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20" is good for NRA High Power. 16" offers better maneuverability and lighter weight.

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At those distances, it'll make no difference at all to the recipient. Those couple extra inches will make it harder to maneuver, I would think. A pistol length would be more practical in that kind of scenario.

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For home defense uses I don't think it'll matter much at all, and I'd rather ditch 5.5" of barrel and get down to a 14.5 with a pinned muzzle device.

That said, the original SP1/Colt 604 20" pencil configuration is an absolute joy to shoot in a way that would surprise many modern AR users. Don't need it for home defense but that definitely made me love some 20" goodness.

Thanks. I'm in Kalifornia, so pistol length and, in fact, anything shorter than 16" is a no-no.

I'm a fan of 20" barrels.

YES, if you're going to stretch its legs out every once in a while.

If not, then there is no need to but, there are a lot better choices than an AR for home defense.

builds.jpg

Shorter barrels = increases muzzle blast.
For home defense, any high-powered rifle is far from a good choice. I would not use one for that unless nothing else was available.
Get a handgun or short .410 or 20 gauge shotgun.
Handgun, preferably. May be difficult that is out there in the People’s Republic, but goes with the territory you chose.

Thanks. I recognize the two black rifles. What is the brand and model of the brown rifle on top?

I have two with 16" barrels and one 20". I much prefer the 20". Just has a better balance and feel to me. Weight difference between the two is negligible. Velocity difference is only about 100-125 fps less with the short barrel.

It's sort of like 22" vs. 26" barrels on hunting rifles. I've carried both in brush; virtually no difference as far as getting hung up on limbs and twigs, though the premise of a shorter barrel to avoid brush hangups sounds good on paper even if it actually matters little in the field.

From a ballistics standpoint , you won’t notice a difference. Complete waste of money getting a 20 inch upper for such a small ballistics advantage.

Some of the folks above said that the AR is not a very good home defense platform and tactically speaking they are wrong. Yes it’s noisy . It’s biggest con. But a self loading magazine fed rifle in an intermediate cartridge is the best home defense gun currently available.

Op, the troops overseas have complained about the performance of 5.56 FMJ military rounds and they are trained to shoot the subject down to the ground. Multiple hits and continue shooting the subject down to the ground. No need to modify your gun… just modify your tactics. You are not stuck using military FMJ rounds. You can use soft points/expanding ammo which increases its effectiveness.

It looks like it is some sort of Ruger 10/22, but IDK what caliber, or even it's a Ruger, but it seems to be in that family of rifles.

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For a general purpose rifle, you are better served with the 16" barrel. Especially for home defense.

Now, if you plan on getting into precision matches and target shooting. Then a 20" barrel might make more sense. Perhaps compromising with an 18" might be the answer. But from personal experience, working with a 16" barrel is generally much better than with a 20".

I compromised, 18" barrel. 55 gr bullet FMJ, if it doesn't tumble, is designed to fragment so it's still devastating if significant body mass is hit.

Dr Andreas Grabinsky Lecture on Gunshot Wounds - YouTube

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I wouldn't want to stand before a California jury with some gun hating prosecutor showing them my sooper dooper, military grade, warmongering, 6000 rounds per second assault rifle as what he'll call the murder weapon.

Not to mention that it will blow your ears out (and anybody else in the room) inside a house without ear-pro.

I have to back up and admit that there is one undeniable advantage to a 20" barrel over a 16" barrel: it gets you 4 inches closer to your target.

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Pisgah

For home/self defense purposes the 16" is more than enough, and a 20" barrel gives you no advantage.

As it relates to terminal ballistics a light jacketed 40-55 gr. varmint bullet is best and will offer less penetration than handguns, and the velocity out of the 16" will not suffer at all.

Forget the 20" upper. Neither the increased velocity or sight radius will matter indoors. What will matter is having earplugs

I carried the 20" M16A1 in VN and the 20" M16A2 later in my military service as well as the 14" barreled M4A1 in various nice places overseas.

I never did see a hoot of difference in portability between the three-barrel lengths, but I definitely preferred the 20" barrel out in the desert and even in the tropics or clearing buildings.

Now, why not compromise and consider an 18" barrel with a Wilde chamber and a 1 in 8" twist barrel? a few years ago, I couldn't get a 20" barrel for a new upper that I was building and went with the 18" tube. It has worked out well for the recreational shooting that I now do. It's a good compromise and my chronographed velocities for 69 grain and 75 grain bullets are not that far behind a 20" tube and they remain stable and accurate to way out yonder.

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