Exterior Case Dimension Comparison

.308 Winchester
O.A.L Base- Base- Base Shoulder
Base of Neck Shoulder Diameter Diameter
2.015 1.71 1.56 0.47 0.454
51.18mm 43.33mm 39.62mm 11.94mm 11.53mm

7.65x53 Belgian Mauser
O.A.L Base- Base- Base Shoulder
Base of Neck Shoulder Diameter Diameter
2.09 1.86 1.75 0.47 0.425
53.09mm 47.24mm 44.45mm 11.94mm 10.80mm

For some reasons these do not want to correctly line up. I cut and pasted from Excell. Sorry.

Before I begin loading I have been thinking about how I will go about it. Hornadys book is loaded too low. They used a Model 1881 Commission rifle. Hodgdon used some rifle with a 29.1 inch barrel, which is correct but they too are low. Norma has a 180 grain factory load at 2,600 fps. Accurates book states Normas loads did not exceed 52,000 psi in Accurates test gun. I now have a working standard.

Noticing the dimensions of the Belgian and .308 are very similar with the Belgian being slightly larger, with a larger bullet diameter, tells me I can load to the same velocities as the .308 at less pressure with less powder.

Using the conversion of 1.2x(Pressure CUP)=psi and vica versa, the Belgian produces ~43,400 CUP max versus (52,000 CUP)x1.2 = 62,400psi for the .308.

That said, I wondered why. The Model 1909 Argentine Mauser action has been chambered for practically every cartridge. Brno currently chambers for the .300 Win which is a high intensity cartridge. Theoretical bolt thrusts for the .300 Win. = 13,228 pounds versus Belgian = 9,021 pounds tells me it isn't this.

I decided it is due to the idea that "old" rifles deserve lower pressures. Since I do not know what rifle was used by Hodgdon and I do know a Model 1881 was used by Hornady the emperical evidence bears this out. Accurate used a 24 inch long Douglas barrel to produce 2570 fps at 51,000 psi or 42,500 CUP. All they could get out of the .308 was 2616 fps at 49,200 CUP or 59,040 psi (max is 52,000 CUP).
Both listings were for XMR-2520, 45.0 grains for the Belgian and 44.5 grains for the .308. So they are producing relatively the same velocity with the Belgian using less powder at less pressure. This supports my original hypothesis.

What does this mean? I have a bit of leeway to play with. Particularly in the realm of powder choices and heavy bullet weights. I can load 100 fps hotter than the book and still be within pressure. Or I can extrapolate heavy bullet loads using .308 Winchester data and be in safe pressure for the Belgian.

I have looked at heavy bullets and there are only two; 215 grains from Hawk and Woodleigh. I think the optimal bullet weight for this cartridge would be 200 grains. That would allow 2,400-2,500 fps.

I will fire some Norma factory cartridges in my 1909 to check velocity for my barrel length 29.1 inches. I will compare this to the book velocities for a 24 incher. When I have the empty cases I will use the exceedingly accurate scales in one of the labs to measure case volume. I will update accordingly.

[This message has been edited by Roger Rothschild (edited 09-25-2001).]

Thanks!
That was so good I put it into favorites. I have class in about 45 minutes so I couldn't look at it closely.

Roger,

I believe Hornady (as do many others) used a M1891 Argentine military rifle. That model Mauser is not recommended for over 45,000 psi. Argentine M1909s used ammo loaded to the same specification because so many of the 1891s were in service at the same time. That does NOT mean that the 1909 has to be loaded to those pressures. Pressures similar to the European loadings of th 8x57 Mauser which coincide with your expectations are correct in rifles in good condition and properly headspaced. In such rifles, performance midway between .308 Win and .30-06 can be expected. Conversely the cartridge must be loaded conservatively in the M1891 rifles and carbines but you can easily equal military loadings and shoot to the sights. Performance is on par with the .300 Savage. That's still not too shabby since the .300 Savage matched the original loadings of the .30-06.