How much does rifling affect velocity?

[MikePGS]

I was looking at buffalobore ammunition at their website and came across the following table


Browning Hi Power MK111, 4.6 inch barrel---------1426 fps
Beretta 92F, 4.9 inch barrel-----------------------------1402 fps
Glock 19, 4.0 inch barrel--------------------------------1389 fps

It was discussing the test results from one of its rounds fired from actual pistols as opposed to test barrels and i was rather surprised to see that a 4.6 inch barrel delivered a higher velocity than a 4.9 They had a few rounds and in every case the results were consistent: The browning kept giving more velocity than the beretta. Why is this? I'm guessing its the rifling in the barrels but i certainly could be wrong. If anyone could help me understand why this is, it would be appreciated. Thanks, see ya later

 

[Owen]

it could be the rifling, a slightly tighter bore, different chamber leade, etc.

Someone here, (probably Clark) did an experiment where he drilled the rifling out of a barrel to see what happened. I don't recall the results.

 

[Lucky]

A guy here did experiments with pistol calibers and barel lengths, and 9mm should keep accelerating for several more inches.

 

[GRIZ22]

Longer barrels giving less velocity is not unusual as Owen said. Velocity can vary significantly on two consecutive serial numbered guns.

 

[AZ Jeff]

The flaw in this type of experiment is very basic--it uses a SINGLE SAMPLE of firearm to perform the test of the ammunition.

If you compare the three pistols, you will see a difference of 39fps between the slowest and fastest measure velocity. That's pretty small.

Now, image we had 10 pistols of the same type/brand, and tested the same ammo in those 10 pistols. We could easily see just as great a variation in average velocity between those 10 pistols, and in fact, I would wager the variation would be GREATER than that.

My point here is that, from a statistical data collection perspective, shooting one brand of ammo out of single samples of different brands of firearms, and from that test, concluding that one brand of firearm produces faster/slower/more accurate results, is fundamentally flawed, and such conclusions should be avoided.

 

[Taurus 617 CCW]

Another thing to keep in mind is that factory loaded ammunition is not match grade consistent. They keep their loads within SAAMI specifications but reserve high quality control for the more expensive offerings ie. Federal Match Grade ammo.

As far as the velocity difference goes, metal hardness can also affect the coefficient of friction in the barrel. The number of grooves in the rifling, length of barrel, type of primer used, bullet weight, wall thickness of case, FMJ versus hollowpoint, and cleanliness of firearm all affect velocity. I can tell you one thing though. If we did a controlled test with two different weapon systems in 9mm, a dirtbag wouldn't be able to distinguish the difference, even if it's a deviation of 150 feet per second. But for the purposes of this thread and from a statistical viewpoint, the more data you add to a sample, the smaller the deviation becomes (ie. 10 shots, 2 guns versus 1500 shots, 30 guns).

 

[win71]

That is correct

Velocity can vary significantly on two consecutive serial numbered guns.

Part of the reason for this is simply that just because the firearm was put together consecutively does not necessarily mean each component used was also manufactured sequentially. Generally at each stage of part production the finished part is put into some type container and latter moved to the final assembly point. The accepted tolerances for every part have a high-low (small-large) maximum size. When the particular cutting tool for a specific part is new, the part, i.e. barrel, chamber, etc. will be the largest. Hence, as the tool wears down each part gets slightly smaller until the minimum acceptable size is reached then the tool is replaced with a new one. These tools don't all wear out at the same time. It's easy to see that the chances of two weapons being exactly the same are worse than winning the lotto.
About the only tests I've heard of that eliminate these variables is to start out with the longest barrel to be tested and shorten it via cutting and finishing an inch at a time. However since there are also variances, i.e. "extreme spread" in any ammunition a large sample would have to be fired.

 

[oneshooter]

The M1 Abrams main gun (125mm?) is a smooth bore. This allows higher velocities with the same breech pressures.

Oneshooter
Livin in Texas

 

[Zoogster]

I have often wondered if a smoothbore full auto firearm is ideal at close range for the roles subguns usualy perform. This is because you can maximimize energy and the flipping of the rounds will actualy cause greater tissue damage, though make them far less accurate at any type of distance. Does anyone know of such a firearm? Especialy such a firearm with rifle round muzzle velocity?

Rifling slows down the round slightly by creating friction. The spinning motion imparted to the bullet by the rifling is done through friction. Obviously friction is going to slow down the round. I think that is why the ideal rifling is the bare minimum twist to stabilize a given round. Additional spin would further slow the round unnecessarily by creating additional unnecessary friction the bullet had to overcome. The more energy imparted to spinning the round, the less imparted directly to pushing it forward.

Pistols at close range could greatly benefit with some rounds at extremely close range by being smoothebore to maximize the already limited energy from them. However federal law dictates they must be rifled. Funny how a technological improvement only widely adopted a little over a century ago is mandated now? I imagine it is to help investigations by allowing unique marks to be imprinted on the round allowing investigators to determine to type of firearm used even without additional information like shell casings. Smoothebores would leave no identifying marks on the bullets and so are outlawed even though they would excel at most home defense distances.

 

[Jim Watson]

Ref the original question, there are so many differences in barrel dimensions that you cannot predict velocity differences by small changes in length. Comparing velocity versus barrel length in different guns even if of the same make is not really telling you much.

I have often thought that a pistol or subgun would do well with a smooth bore firing a round ball. With its short bearing surface, no loss to engraving forces or spin-up, and low sectional density it would get to high velocity and deliver a lot of energy to the target. A lot of people who think that the modern muzzle loader with a jacketed bullet in a plastic sabot is the latest and greatest are surprised at how effective a plain old round ball is on a real critter. I think a precisely made smoothbore barrel and truely round balls would be accurate enough for self defense at pistol ranges. Pity the government does not trust an American Commoner to try it out.