Barrel Length Versus Bullet Velocity For The 5.56mm
BY Herschel Smith
5 years, 12 months ago
Via WRSA, this article is a nice summary of what I take to be the delivered wisdom on the subject. I’ll let the readers peruse the subject material and make comments, but this one graph is worth the work to develop it.
While Pete focuses on the fact that peaks out at about 20″ (and properly so), I’ve usually taken the popularity of 18″ barrels as evidence that there are tradeoffs, and those additional 2″ means added weight to the cantilever for very little increase in meaningful muzzle velocity.
At any rate, take note that your 16″ barrels (or shorter, 14.5″ with a pinned flash hider) are near a flatline in performance, and that the very short barrels on pistol ARs are meant only for CQB.
Each tool in its own shop. They all have a purpose.
On November 25, 2018 at 11:17 pm, Ratus said:
I’m sorry but I’m going to take the information with a giant grain of salt with the glaring mistake of referring to what I can only assume to be M193 55gr ammunition as “SS-109”.
M855 is the US designation for the FN designed and NATO adopted SS-109.
I know that it might seem to be pedantic, but if such a simple error hasn’t been corrected in all this time that I’m wondering what other uncorrected errors are in the article.
On November 26, 2018 at 12:27 am, BRVTVS said:
I see a lot of data about barrel length vs velocity (for instance http://www.ballisticsbytheinch.com/), but very little about loudness vs barrel length. About the only test I could find was for the long barreled CZ lux 22.
On November 26, 2018 at 12:29 am, BRVTVS said:
The test I mentioned concerning the CZ Lux: https://youtu.be/sNZ72ix0GxQ
On November 26, 2018 at 1:21 pm, Bram said:
20″ is sure the sweet spot for M855. I was never a big fan of shorter barrels. If a short weapon is really that important, start testing bullpups.
On November 26, 2018 at 4:57 pm, WiscoDave said:
BRVTVS
I own an Extar 556 and CCW it in a backpack (I also carry a Sig P226). With an 8.25″ barrel, 9.25″ with flash suppressor, I will guarantee you that it puts new meaning into loud. At 100 yrs I can hold minute of paper plate, not near a rifle but I can keep it with me.
On November 26, 2018 at 5:46 pm, Herschel Smith said:
@WiscoDave,
Yep. It’s still a supersonic round, but with a short barrel. That’s one reason I dislike the concept of bullpup guns.
On November 26, 2018 at 9:54 pm, JoeFour said:
How loud is your gun?
https://www.m1911.org/loudness.htm
On November 28, 2018 at 4:53 pm, Badger said:
Some recent testing around by folks, possibly due to the large availability of “pistol” kits being available; 10.5″ being the vanilla length usually chosen. For those so inclined there is with many loads a velocity gain for the 11.5″ out of proportion to just the additional inch. Perhaps sweet-spot for a short-gun, something Colt may have found out a long time ago.
Also, for those to whom it matters, the original article I saw with that graph also included one that depicted pressure at muzzle exit/entry to a suppressor. As many add suppressors to their SBR’s, there is a noticeable drop in pressure (burden) on the can running that 11.5″ bbl, vice the 10.5. This could be nice to know as one tunes those little things to run right, which can be a rabbit hole (or warren) in & of itself. Especially so with a restrictive-type-only adjustable gas block. Not advocating for one or the other but thought that seemed like a break point of some sorts worth mentioning.