Inherently reliable/unreliable auto pistol cartridges?

[Walt Sherrill]

I Believe freebore is one of the differences between a military arm and a sporting arm. The military arm needs to be more tolerant of debris buildup (a margin of safety) while the sporting arms focus is accuracy, less freebore. Less bullet jump before hitting the rifling means better consistency I believe.

Better consistency in what way?

Many high-end commercial rifles also have freebore, so its not a characteristic of military weapons alone. It seems to be something that is seen in almost every firearm, as it allows for some flexibility in the rounds that may be used in the weapon.

I understand how freebore can affect velocity (increasing it or decreasing it by allowing more or less gas to escape before the bullet is fully engaged in the rifling.) A longer freebore also allows some rounds to be loaded with more powder, also increasing velocity. Bullet jump is simply the distance the bullet must travel before engaging the rifling (or its equivalent) -- it's really another way of describing the consequences of freebore.

I've read virtually nothing, so far, that ties more or less freebore to accuracy. It all, thus far, seems tied to velocity. I'll keep looking.

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[JD0x0]

There's a fairly generalized idea that having the bullet just touching, or right behind the lands can potentially increase accuracy in some platforms. Does this hold true 100% of the time? No.
But many guns will benefit from having the bullet close to the lands, rather than an excessive amount of freebore. (one of the many reasons hand loads can be potentially more accurate than factory ammo)

Revolvers are a decent example of potentially very accurate guns that have a big jump to the rifling.

If a gun has a lot of 'free bore' you can usually increase the OAL of the cartridge and at the very least get some more powder in the case. It's a balancing act, though, too far and you can get yourself into trouble.

As far as feeding, if the OAL is too long, and the slide/bolt is jamming the bullet way into the rifling, you could face not only reliability/feeding issues, but pressure issues. With factory ammo you're usually OK, but I've heard some sub-compact pistols can have issues with heavier bullets, due to their length.

 

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I Believe freebore is one of the differences between a military arm and a sporting arm. The military arm needs to be more tolerant of debris buildup (a margin of safety) while the sporting arms focus is accuracy, less freebore. Less bullet jump before hitting the rifling means better consistency I believe.

While it is generally accepted today that seating bullets just off the rifling provides the greatest accuracy, how much that "accuracy advantage" really is varies a lot, and is often overstated.

I've worked with a number of military rifles, past and current and none of them had what I would consider an "excessive" amount of freebore. Generally where they do have looser tolerances than civilian guns (IF they do, many don't) is in the chamber dimensions.

As to civilian guns having "minimum" freebore for accuracy, some do, but some don't. I suggest you take a look at the original Weatherby rifles, famous for having 1/2" of freebore. Never benchrest guns, but plenty good for hunting.

I don't believe any gas "escapes" around the bullet due to freebore. What does happen is the bullet gets a "running start" and is moving faster when it does hit the rifling. This higher speed when it hits the rifling means that wile the jacket's resistance to the rifling is the same, the effect of that "backpressure" is less and greater velocity is attained for the same pressure.