Does "overbore" apply to handgun cartridges?
- Thread starter jski
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gotboostvr
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Maybe.
The 357 maximum had a reputation for eroding top straps in the Ruger Blackhawks. To my understanding, the 357max was mostly designed for 158gr and heavier bullets, but the cylinder of the Blackhawks was too short to accommodate the super heavies and allot of people wanted to see how fast they could push 110gr-125gr bullets and just ate those guns up. Out of a Contender, it might be a neat experiment but it was just too hard on the Ruger's forcing cones and top straps causing them to discontinue the 357max.
If you're unfamiliar, the Max has not only more case capacity than the Magnum, but runs at an even higher max pressure. It'll get similar weight bullets going at near 35 Remington velocities out of similar length barrels without nearly as much case capacity.
The 357 maximum had a reputation for eroding top straps in the Ruger Blackhawks. To my understanding, the 357max was mostly designed for 158gr and heavier bullets, but the cylinder of the Blackhawks was too short to accommodate the super heavies and allot of people wanted to see how fast they could push 110gr-125gr bullets and just ate those guns up. Out of a Contender, it might be a neat experiment but it was just too hard on the Ruger's forcing cones and top straps causing them to discontinue the 357max.
If you're unfamiliar, the Max has not only more case capacity than the Magnum, but runs at an even higher max pressure. It'll get similar weight bullets going at near 35 Remington velocities out of similar length barrels without nearly as much case capacity.
There is no universally accepted definition for overbore but some define overbore as being when the ratio of case volume to bore area is 0.9 or greater. Based on that definition it would be pretty hard to find a production pistol for an overbore cartridge. I'm sure that there are wildcats that fit this definition.
.308 Norma
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Interesting question jski, but why did you write "revolvers cartridges are the only handgun cartridges this could possibly apply to"? Did you mean you're only asking about possible overbore revolver cartridges?
I'm asking because I can think of several cartridges that might be considered "overbore" that Remington XP-100s and TC Contenders have been chambered for. For instance, my own XP-100 7mm IHMSA might be considered "overbore," and it's a bolt action, single-shot, handgun.
It seems like those old, enclosed breach, Ruger Hawkeye handguns might be considered overbore too. They were chambered for the 256 Winchester Magnum.
As macgrumpy wrote, I'm sure there is "no universally accepted definition of overbore." But it seems to me that if you're applying the term "overbore" to handguns, it could be applied to a lot more single-shot handguns than revolvers.
After looking at my post I realized that I made a huge mistake, the value that would determine overbore would be any number over 900 not .9.
Overbore is simply the volume of the case (in grains of water weight) divided by the area of the bore. You've already got the volume of the case and to find the area of the bore you can use the area of a circle using the diameter of the bore as the diameter of the circle and the formula A = π r².
A = area
π = 3.142
r² = 0.023716 (r = .308/2 = 154)
A = 3.14 x 0.023716 = 0.0745 sq. in.
For the .30 carbine
21.050 / 0.0745 = 282.6
So the 30 carbine isn't even close to being an overbore cartridge.
The .327 Fed. Mag. isn't an overbore either.
19 / 0.074261 = 255.9
It takes a lot of case capacity for a .30 caliber to be an overbore cartridge. The 30-06 is about the smallest overbore rifle cartridge that I know of but that gives you an idea of the kind of physical sizes the bullet diameter must be to case volume.
barnbwt
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In handgun cartridges, heck yes; in revolver cartridges, not as much. Overbore relates to the ratio of powder to barrel volume, or put another way, the ratio of gas generated to the volume it can expand in to drive a bullet. So of course, since there are large revolver rounds, and revolvers can have extremely short barrels (or even no barrel), naturally they can be overbore.
The term is most important in rifles as far as the effect on throat erosion, since this effects accuracy, and rifles tend to attract accuracy-nerds. The real physical phenomena is that short barrels firing voluminous cases throw high-velocity still-burning powder granules across the delicate throat and leade area of the chamber, burning it away much faster than for more leisurely cartridges. Naturally it gets worse the more extreme the constriction from a necked cartridge, and of course for large magnum cartridges with lots of slow burning powder to spray down the bore.
In a revolver, you typically have a much smaller volume of powder and a straight wall case, but the same kind of steel. So apart from cylinder-gap strap cutting as mentioned earlier (more an engineering/design issue than anything), the throat erosion aspects are nearly so severe (assuming the accuracy issues would even manifest at handgun distances). Rather, the real issue becomes ridiculous muzzle flash, concussion, and recoil.
Muzzle flash is caused by unburnt powder spraying out the front while still on fire; a given when your cartridge volume rivals the barrel volume, and is full of slow burning magnum rifle powders for something like an XVR. In addition to being blinding, it is also a sign of waste; that burning powder is not driving the bullet faster. Concussion is caused by the bullet exiting before the powder gasses fall from their peak pressures near when the bullet first gets moving; again, slow powders lengthen this period, compounding the problem for short revolver barrels. Again, a sign of inefficiency since less of the potential pressure curve is able to drive the bullet before it exits the muzzle. Lastly, is the recoil; powder is lightweight and driven at the same pressure as the bullet, so it accelerates to extreme speeds (~4000fps) almost instantly when there is no bullet in front of it. This generates recoil for the shooter the same as the bullet itself, often a significant fraction of the total impulse. All that unburned powder blown out the end is not only not contributing to bullet speed, it still contributes to felt recoil. All these drawbacks *can* be worth the tradeoff, because more powder means you can potentially stay near peak pressures longer early on, so a super-short barrel can eke out a few more precious fps.
In a semi-auto where necked cartridges are more common, loud fire-breathers with mild recoil like Tokarev or 5.7 add a different dimension to the concept, since projectile weight can be reduced via the reduced diameter enough to offset the contribution to recoil by unburned powder and then some. The wasted energy is still as much an issue, however.
TCB
The term is most important in rifles as far as the effect on throat erosion, since this effects accuracy, and rifles tend to attract accuracy-nerds. The real physical phenomena is that short barrels firing voluminous cases throw high-velocity still-burning powder granules across the delicate throat and leade area of the chamber, burning it away much faster than for more leisurely cartridges. Naturally it gets worse the more extreme the constriction from a necked cartridge, and of course for large magnum cartridges with lots of slow burning powder to spray down the bore.
In a revolver, you typically have a much smaller volume of powder and a straight wall case, but the same kind of steel. So apart from cylinder-gap strap cutting as mentioned earlier (more an engineering/design issue than anything), the throat erosion aspects are nearly so severe (assuming the accuracy issues would even manifest at handgun distances). Rather, the real issue becomes ridiculous muzzle flash, concussion, and recoil.
Muzzle flash is caused by unburnt powder spraying out the front while still on fire; a given when your cartridge volume rivals the barrel volume, and is full of slow burning magnum rifle powders for something like an XVR. In addition to being blinding, it is also a sign of waste; that burning powder is not driving the bullet faster. Concussion is caused by the bullet exiting before the powder gasses fall from their peak pressures near when the bullet first gets moving; again, slow powders lengthen this period, compounding the problem for short revolver barrels. Again, a sign of inefficiency since less of the potential pressure curve is able to drive the bullet before it exits the muzzle. Lastly, is the recoil; powder is lightweight and driven at the same pressure as the bullet, so it accelerates to extreme speeds (~4000fps) almost instantly when there is no bullet in front of it. This generates recoil for the shooter the same as the bullet itself, often a significant fraction of the total impulse. All that unburned powder blown out the end is not only not contributing to bullet speed, it still contributes to felt recoil. All these drawbacks *can* be worth the tradeoff, because more powder means you can potentially stay near peak pressures longer early on, so a super-short barrel can eke out a few more precious fps.
In a semi-auto where necked cartridges are more common, loud fire-breathers with mild recoil like Tokarev or 5.7 add a different dimension to the concept, since projectile weight can be reduced via the reduced diameter enough to offset the contribution to recoil by unburned powder and then some. The wasted energy is still as much an issue, however.
TCB
CraigC
Sixgun Nut
I really don't care about a proper definition of "ovebore" but yes, absolutely, the same phenomena occurs in handgun cartridges. This is the reason why cartridges like the .30Carbine, .327Fed, .357Mag and heavy loads in the .32-20 have such a sharp crack. It's the pressure, coupled with the powder capacity relative to the bore size.
No it isn't. In handguns, the powder is burned shortly after the bullet leaves the case, at most. What you're seeing are still-expanding gases, not unburned powder. If what you say were true and we used faster powders until the muzzle flash went away, we would be achieving maximum velocity but that simply isn't true.
Jim Watson
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Overbore: Cartridge is so big (relative to caliber, see also expansion ratio) that you cannot keep adding available powder for increased velocity without excess chamber pressure. As slower burning, more progressive powder became available, larger rounds became feasible. The Nosler series of big bottlenecks would not have been worth fooling with a couple of powder generations ago, they would have been considered overbore.
Overbore: Cartridge burns so much powder (see also powder grains per square millimeter of bore, etc.) that barrel life is too short for the application. Varies depending on whether you are a target shooter going out every weekend or a trophy hunter making that bucket list trip for a Himalayan tahr seen only from one mountain to the next.
Overbore: Cartridge burns so much powder (see also powder grains per square millimeter of bore, etc.) that barrel life is too short for the application. Varies depending on whether you are a target shooter going out every weekend or a trophy hunter making that bucket list trip for a Himalayan tahr seen only from one mountain to the next.
Varminterror
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That is NOT the definition of "overbore," barrel LENGTH has absolutely no bearing on over-bore status. Overbore is about the cross-sectional AREA of the bore, not the barrels combustion capacity. You're discussing powder combustion efficiency, not bore capacity - the two are NOT the same.
With your definition, I could make a 7mm rem mag barrel long enough to eliminate it from "overbore status"... That's not how it works. It will remain to burn out its throat at an accelerated rate, regardless of its powder utilization efficiency, as dictated by its barrel length.
Following the rest of the discussion:
Pressure really isn't a driver for overbore either. Sure, increased pressure causes increased barrel wear, but recall, the 308win operates at higher pressure than the 7mm Rem Mag - the former NOT an overbore cartridge, the latter decidedly so.
Top strap cutting in the Max isn't an overbore issue either - as in an overbore cartridge, no bullet weight will save you. Top strap cutting or forcing cone obturation and cracking are factors of pressure and ejecta velocity, which is a factor in overbore cartridges, but the difference, in my experience at least, is that I can't load ANY BULLET at full power level in 7mm rem mag which eliminates the overbore issue, whereas in the Max or 357/44 B&D, I can avoid the issue by not running 110-125grn bullets... So that's "over speed," not strictly overbore.
Think about it with your revolvers - revolver cartridges are considerably smaller in capacity than rifle cartridges, and often are much larger diameter bores, per their capacity. If a 35 Remington isn't overbored, why would you think a 357mag would be? If a 45-70 isn't overbored, how could the 45colt be so? If 458 Lott isn't overbored, how could 454Cassull be so?
So simple answer - no, revolver cartridges are not overbore cartridges.
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gotboostvr
Member
Vsrminterror, good write up. I knew the 357max didn't fit into "overbored" in the classical sense, but I figured it was as close to fitting that category as possible in a revolver.
Break action and bolt action pistols have much the same pitfalls as their rifle brethren. Hence my classifier "maybe" with the 357max reference. No straight walled cartridge I'm aware of comes close to over bored.
Break action and bolt action pistols have much the same pitfalls as their rifle brethren. Hence my classifier "maybe" with the 357max reference. No straight walled cartridge I'm aware of comes close to over bored.
CraigC, I must admit that what I see with my .30 Carbine Blackhawk, I also see and hear from my S&W .357. The flash and crack. No better nor worse between the two of them. And I use Hodgdon H110 with both.
For 110 gr. to 125 gr. bullets with my .30 Carbine, I go with 14-15 gr. of H110.
For 110 gr. to 125 gr. bullets with my .357, I go with 20-21 gr. of H110.
Both pretty much per Hodgdon's reloading website.
For 110 gr. to 125 gr. bullets with my .30 Carbine, I go with 14-15 gr. of H110.
For 110 gr. to 125 gr. bullets with my .357, I go with 20-21 gr. of H110.
Both pretty much per Hodgdon's reloading website.
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