Why is .338-06 with 200 grain bullets faster than .30-06?

I was wondering why a .338-06 would drive a 200 grain bullet so much faster than a .30-06 could. Anyone know? They have the same powder capacity. My thought was that perhaps because the 200 grain .30 caliber bullet was longer, and had more contact with the barrel, this could explain it, but that's a lot reduced velocity. Is this the whole reason?
 
 The 200 grain .338 even has the .30/200 beat by 100 fps out to 300 yards. Superior sectional density allows the .30 to catch up a bit, but not all the way till beyond 400 yards.

Hawkeye
 Not trying to be a smart a%$# here but you answered your own question perfectly ! Folks could go into great detail giving scientific data and all sorts of things but basically you hit the nail on the head. I have a 338-06 Ackley Improved and love it. Its on a Win 70 action, # 5 barrel at 23 inches including brake, High Tech stock. Took my first elk with this rifle.
 Charlie

That's a good efficiency gain, moving up to .338-06, because you increase velocity AND bullet size, while not increasing powder charge or recoil (assuming 200 grain bullets). Plus you have the added advantage of being able to step up to the 225 and 250 grainers for elk and moose (or grizzly). Nice deal. I am not sure which rifle of mine is going to become a .338-06, but one of them sure is. It's between my Dakota 76 and one of my pre-64 Winchester 70s.

Expansion ratio:
 
 Within a given bullet weight and given case size, when loaded to equivelant pressure, a larger dia. bullet will achieve a higher velocity.
 
 My 338-08 will shoot a 180 gr. bullet faster than a 308, but slower than a 358.
 
 JimF

I guess that's because the .358, based also on the .308, has an even larger diameter than the .338-08. Is this strictly because of less surface area in contact with the barrel, or are there some other forces of physics involved? Could it also be because, at the base of the bullet, the larger diameter bullets provide more of a surface for the expanding gasses to act on? At first thought, that seems to make sense. I don't know, myself. Never took an advanced physics class, so this is all murky water for me. Curious though.

It's the expansion ratio. The ratio of the case capacity to the bore volume.

Think I got it. So, basically what I said above is correct, in different words?

Hawkeye
 Like my dad used to say, " You got er by the balls on a down hill drag".
 Charlie

I believe I can answer this one.....and it's not too technical. The diameter of 30 cal. is 0.308" and 33 cal. is 0.338". Now find the area of the base of the bullet.......where the pressure of the burning gases would be pushing. The rear of the bullet is just a circle and the area of a circle is PI times the radius squared. Using this formula you will find the area of a 30 cal. bullet to be 0.0745 sq.in. Similarly, for the 33 cal. the area is 0.0897sq.in.
 
 If you took the 33 cal area and divided it by the 30 cal area you will see that the 33 cal has about 20.4% more area for the pressure of the burning gases to act on. Therefore, if the same pressure is applied to the rear of the bullet (from the burning gases) the force exerted on the 33 cal bullet will be 20.4% greater. More force on the rear of the bullet pushes it to higher velocity
 
 Here is an example: Assume 60,000 psi (which is 60,000 lb/sq.in. ....... or said another way, 60,000 pounds of force that will act on each inch of area) If there were 1sq.in. of area at the rear of the bullet, 60,000 psi would produce 60,000 pounds of force on the bullet. It is calculated like this
 
 (60,000 lb/sq.in.) x (1sq.in.) = 60,000 lb
 
 If the area was 1/2 sq in, the force would be 30,000 lb. Here is the calculation for the 308 and 338 bullets using the areas calculated above:
 
 (60,000 lb/sq.in.) x (0.0745sq.in.) = 4,470 lb (308)
 
 (60,000 lb/sq.in.) x (0.0897sq.in.) = 5,382 lb (338)
 
 The additional force acting on the bullet is responsible for the increased velocity. This does not mean there will be a 20.4% increase in velocity. There are other factors that must be considered. Many have already been mentioned such as friction between bullet and bore, expansion ratio, efficiency/burn rate/pressure curve of the chosen powder, etc.
 
 The principle is the same as is used in hydraulics. A larger diameter cylinder can lift more weight than a smaller diameter cylinder even though the pressure of the hydraulic fluid acting on the base of the piston is the same.

Hogwild, thanks for that detailed explanation. That makes perfect sense. I had an intuitive feeling this was a big part of the explanation, but you've really put it in words so it is really clear. That steam piston example made it perfectly clear. I can visualize how a narrow piston would lift less weight from the same source of steam pressure than would a broader one, because there are fewer square inches being acted on by the pounds per square inch, even though the pressure remains constant for both pistons. Good job.

Hogwild is right on the money.
 
 It's the same reason why a .45Long Colt operating at 25,000 PSI can equal the velocity of a .44 Mag at 35,000 psi when both are pushing 300gr bullets.
 
 MM

and the recoil feels less with the 338-06, too, doesn't it. i think it has something to do with the expansion ratio, also. i noticed it with equivalent rifles shooting equivalent loads in 8x57 and .30-06. the 8x57 somehow is easier on the shoulder to shoot. seems to me the 338-06 more so since the diameter is slightly larger than the .323. but there is no science to my opinion. just plain old shoulder experience.

Fish:
 
 The 8X57 delivers about 12% less recoil than an '06 because it uses about 20% less powder to get similar velocities with 180 gr. bullets.
 
 You can credit expansion ratio for the velocities, but not the reduction in recoil.
 
 JimF

ah, jim f, glad to know. that certainly makes sense to me.
 recoil also is subjective, as well, but no way to measure that except with opinion.
 thanks.

"I was wondering why a .338-06 would drive a 200 grain bullet so much faster than a .30-06 could. Anyone know? They have the same powder capacity."
 
 No, they don't. The .30-06 holds more powder than the .338-06 when both are loaded to the base of the neck. When you neck any cartridge OUT (larger), the neck becomes longer (and the shoulder correspondingly shorter), reducing the net capacity of the body and shoulder.
 
 The .25-06, OTOH, holds MORE powder than the .30-06 when both are loaded to the base of the neck. When you neck any cartridge DOWN (smaller), the neck becomes shorter (and the shoulder correspondingly longer), increasing the net capacity.

Ken, be that as it may, is it true that if loaded so as to produce the same pressure levels, the .338 would be faster?

Ken, I always learn something from your posts. I had never given this any thought before. Thanks.

TRH:
 
 I would defer to the estimable Mr. Howell on this if he disagrees but you are correct. Theoretically, the slightly larger capacity of the '06 might give an advantage if both were loaded at maximum loading density, but they practically never are.
 
 JimF

I have never sat down with close observation to investigate the advantages of the 338/06 over the 30/06. This is an interesting thread.

Actually, if you take the same case, say the 30-06 case, and neck it to different calibers, say .30 cal., 8mm cal, .338 cal and .35 cal, and load them with the same bullet weight to the same pressure, say all at 60,000 psi, then the larger diameter bullet will always go faster at the muzzle. This is because the base of the bullet is bigger, has more surface area for the pressure to push against, and thus will accelerate faster, since more foot lbs of energy are pushing against it. Any good physics text book will explain this somewhere in it.

Oops, I only read the second page, didn't see all the earlier posts that explained this much better than I did.

What about the fact that you can use a faster burning powder in a larger bore and keep things at the same pressure with the same weight bullet. What is the physics explanation for this?

Bb

Same reason a .308 will push a 130gr bullet a lot faster than a .260 will?

space time continuum, it's tied in there with the theory of relativity

In addition to larger bullet area for the gas to push against, I had it in my head that because the bore is larger, there is more volume in the bore to act as a gas expansion chamber.

To that end I think that a larger bore size to some extent acts similarly to adding a couple of inches of length to a barrel. Both have the effect of increasing bore capacity and velocity potential.

I am prepared to be shot down in flames if that's wrong.

All I know is it allows me to push a 160gn bullet to over 3000 FPS with a .308 case necked up to .338. Can't do that with a straight .308 or a .308 case necked to 7mm, .260, 243, etc.

bobnob,

That's also correct.

There's actually more than once factor that goes into the velocity advantage a larger bore has over a smaller one, given the same case. The general rule is that potential velocity will increase at 1/4 the rate of any increase in bore area. The .338 has a bore area of about .0897 inch, versus .0745 in a .30-caliber bore. Do the math and we find the .338 has just about a 5% advantage over the .30 caliber, given the same bullet weights.

Case capacity for this formula (or any other purpose) is best measured using water, with a bullet seated in a fired case, instead of just filling a case with water to the base of the neck.

Muzzle velocity is one factor. But with the lower sectional density of a 200 grain .338 bullet compared to a 200 grain .308, I would expect the terminal effect on Game past one hundred yards would be different.

Am I wrong? Someone tell me if I am.

Originally Posted by idahoguy101

Muzzle velocity is one factor. But with the lower sectional density of a 200 grain .338 bullet compared to a 200 grain .308, I would expect the terminal effect on Game past one hundred yards would be different.

Am I wrong? Someone tell me if I am.

Sounds like you are right but no expert am I.

The wounding effect might well be different for a couple of reasons: the SD difference could cause more or less penetration; while the extra calibre size will cause a bigger hole on entry at least.

Add to that, that all other things being equal, the .308 cal version of the 200 grainer will have a superior ballistic profile and carry speed better the further away the target.

So I'd have thought anyway.

- Bob

Spliting some mighty fine hairs. The 200 gr bullet from the 30-06 will still out penetrate 200 gr bullets from the 338-06 at all ranges.

The 100-150 fps or so advantage at the muzzle gives the 338-06 an energy advantage at close range, but it is offset by less penetration. Either will take any animal in North America at close range. But at ranges beyond the 200 yard mark the 30-06/200 will be faster, penerate deeper, and have more energy. The difference is small, but it is there. Since the 338 starts faster, it is still slightly flatter shooting, at least to 500 yards which is as far as I ever ran the numbers. But the difference is less than 1" at all ranges.

I owned a 338-06 for several years. Liked it well enough. But it offers no real performance advantage over a 30-06 loaded properly.

The .03" diameter advantage is a non-factor. Shoot both into game, measure the diameter of recovered bullets after expansion and I'd bet you could never tell the difference.

You'd probably have a hard time telling the difference on most game animals either. You buy a 338-06 to have a good round that is just a little different from what everyone else is using. You buy the 30-06 to keep your life simple. Neither is a bad choice. I sold my 338-06, not because I didn't like it, just to simplify my life.

Egad! This thread is 11 years old!

A good one though.