Why such a big difference, 30-06 vs 338-06

[ArchAngelCD]

I'm looking at the Hodgdon load data site and I was wondering why there is such a difference in velocities between the 30-06 and 338-06 with the same bullet weight and powder. I can't understand why the 338-06 can deliver higher velocities than in the 30-06 with the same weight bullet and same powder. After all, they are the same exact case with a blown out neck.

Example:
30-06 / 180gr SIE SPBT / IMR 4064 / 2700 fps / 58,200 PSI
338-06 / 180gr NOS BT / IMR 4064 / 2920 fps / 61,600 PSI

30-06 / 200gr SPR SP / IMR 4064 / 2469 fps / 57,400 PSI
338-06 / 200gr HDY SP / IMR 4064 / 2729 fps / 61,800 PSI

30-06 / 200gr SPR SP / IMR 4007 SSC / 2497 fps / 57,800 PSI
338-06 / 200gr HDY SP / IMR 4007 SSC / 2729 fps / 63,000 PSI

Other than the fact the pressures are higher in the 338-06 rounds I can't figure it out. The difference in pressures don't seem like it would be enough to generate that much more velocity. Also, why are the the pressures in the 338-06 higher than the 30-06? I'm thinking of putting a 338 in my rifle line and I'm not sure if I should go with the 338-06 or the 338 Win Mag. (cost and availability of ammo are not a factor since I reload my own ammo) The performance of the 338-06 is fairly close to that of the 338 Win Mag with much less powder and form what I've read less felt recoil. I do know velocity is surprisingly higher in the 338-06 than the 30-06 with the same weight bullet although they are wider. I'm a little confused here...

 

[Jim Watson]

Pressure is higher in the .338-06 because they put in more powder.

Velocity is higher because they put in more powder AND the .338 has more cross sectional area for it to act on. Or lower sectional density if you want to express it that way.

 

[readyeddy]

I asked the same question about the 35 Whelen. The larger diameter mean a larger bore which equals for space for the powder to ignite. Also I suspect the larger case neck means more powder capacity.

 

[Haxby]

more cross sectional area

That's it.
Compare 30/06 125 gr to 25/06 120 gr. Same thing.
Or 243 vs 260 95 gr.
Or 180 gr in 308 & 338 Federal.

 

[Offfhand]

It's simply a matter of comparative expansion ratios. Just do a little homework in interior ballistics 101, nothing complicated about it.

 

[rcmodel]

Bigger bore = bigger piston for the pressure to act on.

Same reason you ream out the cylinders and put bigger pistons in your hot-rod car engine.

rc

 

[ArchAngelCD]

Bigger bore = bigger piston for the pressure to act on.

Same reason you ream out the cylinders and put bigger pistons in your hot-rod car engine.

rc

RC, your apology of the engine made everything completely clear since I'm been a car/truck mechanic all my life!

Thank you to all the other answers, you have been helpful as well.

 

[fguffey]

Ream the cylinder? Ream the valve guides, bore the cylinders, then there is honing.

F. Guffey

 

[Offfhand]

Arch, your comparisons of velocities and pressures with the two calibers with same bullet weights and same propellant is basically invalid (apples and oranges) unless the data also includes the propellant charge weight. If the charge weights are the same, the velocity and pressures of the .30/338 will be much lower than with the .06. (Assuming equal barrel length , etc) In order to generate the velocities and pressures you list for the 06/338 it would require propellant charges that would be greatly over max for the .30/06. Likewise, the comparison of using boring out cylinders for larger pistons is equally invalid unless you factor in that the purpose of doing so is to consume greater volumes of fuel and oxygen. When fed the identical amounts of fuel and air the larger cylinder is less efficient than the smaller. As I advised in earlier post, study interior ballistics 101 and it's easier to understand expansion ratios.

 

[DM~]

RC, your apology of the engine made everything completely clear since I'm been a car/truck mechanic all my life!

Thank you to all the other answers, you have been helpful as well.

Don't forget, you have to add more gas too....

The .338-06 does not need more pressure than an 06 for more velocity, it's all about "expansion ratio"....

Keep in mind, the bore of a rifle is also is part of the "case capacity", when speaking of "pressure". SO, the larger bore of .338 allows you to use more powder than in a .308 bore, and you end up with a the same or more V at the same max pressure of an 06.

I want to add here, many .338-06 owners brag they get the same V as the .338 Win. Mag., using LESS powder... The only way they can do that is to use HIGHER pressures... There's no magic, they are over loading their .338-06's...

Lastly, i want to add, i've been useing a .338-06 since the 70's when i had P.O. Ackley build my first one.

DM

 

[LNK]

Wouldn't a .338 projectile of the same weight of a .308 projectile be shorter and have less bearing surface also. Thus possibly less resistance and more speed?

LNK

 

[ArchAngelCD]

Arch, your comparisons of velocities and pressures with the two calibers with same bullet weights and same propellant is basically invalid (apples and oranges) unless the data also includes the propellant charge weight. If the charge weights are the same, the velocity and pressures of the .30/338 will be much lower than with the .06. (Assuming equal barrel length , etc) In order to generate the velocities and pressures you list for the 06/338 it would require propellant charges that would be greatly over max for the .30/06. Likewise, the comparison of using boring out cylinders for larger pistons is equally invalid unless you factor in that the purpose of doing so is to consume greater volumes of fuel and oxygen. When fed the identical amounts of fuel and air the larger cylinder is less efficient than the smaller. As I advised in earlier post, study interior ballistics 101 and it's easier to understand expansion ratios.

I'm not a scientist, just a dumb reloader from PA. Maybe I understand more than I let on and only wanted to start a discussion about something rarely talked about...

 

[DM~]

I'm not a scientist, just a dumb reloader from PA. Maybe I understand more than I let on and only wanted to start a discussion about something rarely talked about...

OR, maybe you'd just like us to "think" that now...

Anyway, IMO the biggest advantage the .338-06 has over the 30-06 is the heavier bullets that it can use for the bigger big game.

I'm just NOT a fan of using the lighter weight bullets in .338" diameter.

DM

 

[DanTheFarmer]

Hi All,

Here's my $0.02.

Remember what pressure is. It is force per unit area (p=f/a). We know a 338 cal bullet has more cross sectional area than a 30 cal bullet. Since we state that the pressure is the same and the bottom of the fraction is bigger for the 338 the top part (the force) must be bigger as well. .33 = 1/3 or 2/6.

The 338 bullet has more force acting on it.

Dan

 

[jdh]

Because reloading manuals have always been conservative on 30-06 loads to keep folks from hot loading them and blowing up older 1903 Springfields and those who built 338-06 were more selective in the actions they used?

Look at the loads he quotes all of the 30-06 load are 3-4k psi lower than the 338-06 loads. For ****s and giggles load the two to the same pressure level with the same bullet weight and see what you get.

 

[ljnowell]

Think of it as a hydraulic system. If the pressure in the system is the same, but you increase the size of the piston its acting on, the force goes up.

 

[Offfhand]

Quoted from above post:
"Think of it as a hydraulic system. If the pressure in the system is the same, but you increase the size of the piston its acting on, the force goes up."

The key phrase in the above statement is "If the pressure in the system is the same.." IF pressure is equal, force (call it horsepower if it makes the concept simpler) the larger piston will indeed deliver greater power. BUT, here's the kicker that seems to be a cause of confusion): If the pressure is to be equal, it requires greater energy (More propellant, get it?) to make the pressure equal. But if only a fixed amount of energy is applied to a fixed amount of fluid the larger piston has less force because of the greater volume of the cylinder. It's the same with rifle bores, it takes more gas to fill the volume of a larger bore.

 

[DM~]

Quoted from above post:
"Think of it as a hydraulic system. If the pressure in the system is the same, but you increase the size of the piston its acting on, the force goes up."

The key phrase in the above statement is "If the pressure in the system is the same.." IF pressure is equal, force (call it horsepower if it makes the concept simpler) the larger piston will indeed deliver greater power. BUT, here's the kicker that seems to be a cause of confusion): If the pressure is to be equal, it requires greater energy (More propellant, get it?) to make the pressure equal. But if only a fixed amount of energy is applied to a fixed amount of fluid the larger piston has less force because of the greater volume of the cylinder. It's the same with rifle bores, it takes more gas to fill the volume of a larger bore.

This is exactly right...

DM

 

[Haxby]

IF pressure is equal, force (call it horsepower if it makes the concept simpler)

Horsepower is not a unit of force.

 

[Comrade Mike]

Pressure is force divided by area.

Larger bore means lower pressure for the same given powder charge. So with larger calibers we can put more powder in the case, push the bullet harder and maintain a safe pressure level.