Home Forums Hunting & Shooting Ask The Gunwriters case capactiy, bore diameters, barrel length and spreadsheets... OH MY

So I was thinking about barrel length compared to bore diameter and cartridge case capacity, and threw together some numbers... not scientific at all. But I wanted to compare some pretty standard cartridge barrel combinations to their larger brothers that share the same case. I'm a big fan of bigger bore diameters and shorter barrels, (I realize the trend right now is generally the other direction, and smaller bores and longer heavier bullets). But I thought I would put some numbers to it, and it really kinda matches what I think people find anecdotally in the real world:



Assuming that you are using similar burn rate powders, These barrel lengths should be about the same "efficiency" given the proportion of case capacity to the interior dimensions of the barrel for gasses to expand.

I've got the formulas in the spreadsheet, its pretty easy to play with and experiment.

Just curious...how did you calculate barrel volume?

Set it to 11 and then used a decibel meter

Using the formula for the volume of a cylinder?

That’s s lot for an old Plumber to process

Think of a barrel as if it were a pipe.

volume of a cylinder, first you get the surface area of one of the sides, typical area of a circle calculation:

radius (half of bore diameter) x PIE squared (Pie-R-Squared)

Then you multiply that times the length of the cylinder to take that 2 dimensional measurement and make it 3 dimensional.

I said to hell with the groove dimension, although it could probably be estimated, (take the difference between the land and groove diameter like a donut, and divide by 3 or something like that) I figure this is a chalkboard exercise and it wouldn't make enough difference to matter either way.

The hard part was finding a resource that had case capacity as they aren't similar even though they are usually built on the same parent case.

I have a theory that larger bore diameters and heavier bullets are more "efficient" (maybe the wrong term). I think they provide more downrange energy with the same amount of powder in a shorter barrel, or significantly more energy in a similar length barrel. Additionally, they are quieter in the shorter packages which matters in real world hunting scenarios where portability and shooting without ear protection are real concerns.

Food for thought if you take these calculations taken to the extreme, a .22-250 would need a 30" barrel to have the same Case Capacity-Barrel Volume ratio as the 338 Federal with a 17" Barrel.

Furthermore, in a hunting scenario, the larger frontal area should create a larger wound channel and deposit more energy into tissue that it contacts. Don't want to debate bullet design, as I have my own dogma on that, but all else being equal (think 200 gr. .308 bullet in the '06 and a 200 gr. bullet in the 35 whelen both Barnes TTSX or whatever brand you choose) The larger diameter bullet should cause more tissue damage, assuming the bullet impacts at an appropriate speed to work as designed.

Much like heavier arrows out of the same bow utilize more of the bows energy and carry more momentum and penetrate better than their lighter faster counterparts out of the same bow, I think that bigger bullets out of the same "package" will out perform their smaller, faster counterparts on game...

In a bow the extra lost energy is manifested as sound and vibration through the bow. In firearms, it is manifested in muzzle blast and excess powder burned/ gasses expanding after the bullet has left the barrel.

Case-to-bore expansion ratios generally use the same figure, both representing volume in a common term such as cubic inches, rather than comparing grains to cubic inches. And the bore measurement v. the lands measurement in a particular barrel has a greater effect in smaller calibers v. larger ones on overall barrel volume.

As far as a 30 caliber bullet and a 35 caliber bullet both at 200 grains having different abilities to destroy tissue, no, they don't. They will destroy exactly the same amount of tissue. You just run out of tissue to destroy, as the smaller caliber will exit more often than the larger, given the same bullet path. And your arrow analogy is just as skewed. Heavier arrows denote a heavier bullet of the same caliber, not a larger caliber, but yes, heavier bullets have more momentum, but are propelled at a slower speed, and thus the same energy to destroy tissue as a lighter, faster arrow.

You would think that if velocity and bullet construction where identical that the larger diameter bullet would produce the widest wound channel. Given the expanded diameter of the bullet would be larger.

Some gun writer has written some about this, in various ways in several different publications--including powder capacity/bore ratio, and how much tissue various bullets potentially destroy. I will just state that some of the assumptions based on the formula might be a little too extensive.

Your barrel volumes are wrong. Volume of a cylinder is (pi)(radius squared)(length), not (pi squared)(radius)(length)or (pi times the radius) squared times the length.

I'm unsure as to why you are concerned about barrel volume unless it's for muzzle pressures and/or sound level. When it comes to comparing cartridges and their velocities I'm usually interested in bore diameter vs powder charge weight, for a simplistic view of overbore ratio in regards to barrel life.

Corrected

Just for the record, in the interest of whatever...volumes should be (rounded to 2 or 3 places):

20" .224 = .788

8" .308 = .596

20' .308 = 1.490

24" .308 = 1.788

17" .338 = 1.525

19" .357 = 1.901

I once looked at foot pounds energy produced per grain of powder used.

Seems the closer to a straight wall case, the more foot pounds generated per grain of powder you burned. If I remember correctly.

Good question.

I have a tendency to chop barrels. I always thought it was a little odd that all calibers had a standard 24" barrel and magnums had a 26" barrel. especially when you look at the difference in volume between them.

I think that ammo/ firearm manufacturers have hinted at this. If you look around you can find things about barrel length and velocities and cartridges like .22lr and 300 blk , its like 6-9" or somewhere in there where they usually have the peak velocity. Most cartridges discussed on this forum ned a barrel longer than that to start to see diminishing velocity 30+ or probably 40+ for overbore magnums like the 26 Nosler.

I think Wayne van Zwoll had an article on the .338 federal a decade or so ago, that talked about how that cartridge produced 30-06 or greater speed and energy out to 200 yards with both shooting 180gr. bullets. the 338 federal traveling faster with less power/ smaller case.

My next logical step on that path is that the fatter bore/bullet gives you "room to spare" ballistically compared to it's .30 caliber brothers at appropriate ranges. (I've killed more animals offhand inside 30 yards with my .338 Fed than I have at over 200 yards with any rifle, so 400 yard ballistics are fun to look at but practically useless to me in the areas I hunt.

I just thought I would put some numbers to a 35 Whelen project I had going before I got the hacksaw out... Sound/ muzzle blast definitely matters, but I am really trying to put some objective numbers to answer the question: "how short do I cut this thing?" I would love to get it to balance perfectly, but thats almost not possible to figure out until you cut to far and want to add an inch or two back onto the barrel =]

So short story long. I think a short whelen will probably have similar muzzle blast to a standard barrelled 30-06. Ballistically, it will be superior at my hunting ranges even with the velocity loss of the shorter barrel. So should I cut the Whelen to 19", 20", or 21"

?????

I gotcha... I needed an extra parenthesis in there... my ^2 was squaring the radius and pie... I redid it should be correct now. cleaned it up and added a few more for fun also...

Uh, yeah.