6 Vs 8 Rifling Grooves for Sabot Reviews
Ballistics past the Inch conducts the best independent, grass roots ammunition tests. Their process is simple and intensive. They have 18-inch barrels made for various a specific caliber. With the help of a Thompson Center receiver, they test fire different brands of ammunition and calculate the various muzzle velocities. Then they chop an inch off the barrel, recrown it and do it all once again. They cut down the barrels until they accept a little ii-inch nubbin left, and and then publish the results.
After they test their single shot barrels (which allow the highest pressures these rounds are capable of reaching), the team from BBTI tests whatsoever "real world" guns they tin get their hands on (which allows for cylinder gap and blow-black discrepancies) . And they post those results, likewise–just for comparison.
And now they're settling some other fence. Which rifling type is faster: traditional lands and grooves, or the Polygonal rifling made famous past Glock?
An oversimplified look at rifling
The 2 principal types of rifling.
Smoothbore barrels simply throw projectiles in the direction the barrel is pointing. Functional, peculiarly if one barrel is throwing multiple projectiles (like a shotgun). A rifled butt grooves cut inside the barrel. The pb (or copper) of a bullet catches these grooves (which screw downwards the length of the barrel). When the bullet leaves the barrel, it spins. That spin ensures that the projectile holds its trajectory more than effectively. The metaphor most commonly use compares the spinning bullet to a spiraling football.
To complicate this piffling bit of science, you add in various materials in the construction of the bullet. So alter its shape: flat nosed, ball, hollow point, wad-cutter, boat-tail, etc. The length of the barrel matters, and the powder load can change the results.
The results are well accepted. The statement against traditional rifling focuses on the energy that may be lost if the bullet doesn't seal the barrel. If the bullet simply skates along the lands, but doesn't mold itself into the grooves, gas may leak out and reduce bullet speed.
The Lothar Walther barrels used in the test. (Photo past BBTI)
Polygonal Rifling
A barrel with polygonal rifling doesn't take the sharp lands and grooves of traditional rifling. Instead, the within of the circular barrel is shaped more like a polygon. In theory, at that place are no grooves through which gas could escape. The within of the butt has flat segments that spin the bullets, but no true grooves through which gas might leak.
In reality, especially in the barrels of Glocks, there are still lands and grooves. The corners of the polygonal shape are rounded over. And the walls have a very slight hump. Just these barrels are noticeably different.
The thought is that the bullet will seat in them more completely. A better seal volition, in theory, produce a faster projectile. But does it?
The Glock Tests
BBTI performed their usual chop tests, but this time with polygonal barrels. They fire their allotted test rounds (10 rounds from each selected brand, weight), chronograph the results, and so chop an inch off the butt and do it all again. As they utilise long barrel blanks for their testing, BBTI isn't testing true Glock barrels, at least not in the chop tests. They procured both traditionally rifled and polygoanlly rifled from Lothar Walther.
Here are some of the results.
The Federal Hi-Shok meets polygonal expectations. (Graph from BBTI)
As the barrel length decreases, the power diminishes. And in some cases, the polygonal barrels performed exactly as they are supposed to.
Other brands produced mixed results. (Graph from BBTI)
PNW Artillery 115 grain SCHP produced consequent power, merely inconsistent results. Upwardly to four inches, the polygonal rifling is winning the debate. Later that, traditional rifling seems to have the edge.
Corbon'due south results were also harder to interpret. (Graph by BBTI)
In some cases, like that of the Corbon, in that location seems to exist no do good at all from the polygonal barrels.
Terminal thoughts
The conclusions from this case are difficult to swallow for diehard supporters of polygonal barrels. In that location isn't a meaning do good. At most, the polygonal rifling produces but marginally faster shots, fifty-fifty in a real Glock. These results suggest that the polygonal rifling may also slow things downwards, but only marginally.
At all-time, the rifling doesn't seem to hurt. Here are the aforementioned rounds fired through a number of production model guns.
The "real globe guns" tests in feet per 2nd. Only the Glocks on this list have polygonal barrels. (Nautical chart excerpted from BBTI)
Hither are all of the results of the chopped barrels in a easier chart. For more on the Glock Tests, cheque out BBTI's page. And for an interesting look at the loss of velocity from pistol caliber rounds fired through long barrels, check out BBTI'due south blog.
The collected results from all of the testing. (Chart by BBTI)
Source: https://www.guns.com/news/2013/12/07/polygonal-lands-grooves-glock-tests-bbti
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