I was reading Guns and Ammo while on the porcelain throne (s**t at both ends according to some) and came across a comparative photo of 30 and 338 RUM cartridges.

It seemed to me they were a bit arse about face (to continue the theme) why is the 338 shorter and have less powder capacity when the 30 is presumably getting on for overbore and the 338 might actualy use the length/ increased capacity? Also from the photo it looked to me like you could get a 338RUM to chamber in a 30RUM and headspace on the bullet, can you?

Ps In case you think I have abandoned my passion for low/medium velocity turn of the (last but one) century this is only for interest.

I read that it was a liability decision. You can't stick a .300 RUM in a .338 and close the bolt. It could keep someone from blowing their face off, I guess. With that said, what about a 7mm RUM. Maybe the danger isn't so great if a 7mm gets shoved into a .300 RUM?? I read the above about the .300 and the .338 somewhere and wanted to ask about the 7mm, but you can't ask a magazine squat.

Well, you can ask a magazine squat, but it doesn't answer squat. My wife pointed out this fact to me. Isn't she helpful. I don't think you can close the bolt on a .338 RUM in a .300 RUM chamber unless you had a very short bullet, seated way down in the case. I'm not going to try it, just to see, though!

My understanding of the difference in case length was that with certain 338 bullets seated at the canalure the 700 mag box was too short.

I have also heard that the decision was based on the traditional cannalure location on most .338 bullets, and that a full length case crimped at the cannalure would have resulted in many cases with a cartridge length greater than magazine length.

I manage to stuff 106 grains of powder behind a 200 grain Nosler BT as a target load, so I wouldn't really consider the case capacity of the .338 RUM to be lacking. After playing around with both I've arrived at the conclusion that the .338 is more veratile than the .300.

Rust-
What kind of FPS are you getting with the 250 gr. bullets in the 338rum??? Is this hotter than the 340 Weatherby???Thanks MD

The other reason that the .338 RUM is shorter at the shoulder than the .300 is because expanding the .300 case to .338 doesn't leave enough neck to grip the bullet adequately. The only 250 grainers I've shot were the factory rounds. They chrongraphed at 2890 fps with a SD of 7 fps. I've worked up handloads with Barnes-X 225 gr bullets and 97 gr of RL-25 that clocked 3150 fps out of a 26" barrel. More powder didn't show any increase in velocity. Next, I'm going to try loads with IMR-4227 and IMR-4831.

250s are showing a velocity of about 2800 in my rifle with my loads. I've been using AA8700 as a primary powder for several reasons.

1st, load density is 95 percent to compressed. The powder is actually a bit slow for this case allowing high load density.

2nd, safety factor. These velocities are achieved at lower than maximum pressures. There is very little load data with pressures available out there and I prefer to stick with soemthing a little more idiot proof under the circumstances.

3rd, accuracy. The 8700 has given very good results so far with pretty good consistancy. My velocity deviations have been acceptable, normally running 30 fps or under. I consider this to be pretty good in a cartridge this size.

I would like to give RL-25 a whirl but there is a dearth of information for it. Some folks have reported very high velocities with 25. This could indicate an ideal match of powder to case capacity and bullet weight, or an overly hot load. I do not like relying on case head expansion as an indicator as different lots of brass have given different results in other cartridges. I do not have an Oehler 43 which I would consider about the only truly safe way of determining pressures for the hobbyist.

Perhaps this is overly cautious but it is my rifle and my face behind it.