Has anyone used these before?
From what I understand, Remington makes the Remington Ultra Magnums(or, RUM) and takes a Magnum, and Re-Magnumizes it.
What are the pros and cons?

Pushes the same bullet as it is brother magnumfaster, harder and flatter
Handloading dream
(pro)

Stouter recoil
Reduced barrel life
Factory ammo limited and downloaded
(con)

Don't own but know afew who have 300RUM's. A little stoutfor mypoor shooting shoulder but a great cartridge. One guy has shot everything from deer to grizzly with his and Nosler Partitions.

A few well versed owners on here will probably point out otherpros to the RUM for you.

Re-Magnumizes? Is that a new word?

The RUM family of cartridgesare based on a different case altogether than the traditional magnums. It's non-belted and has more internal capacity, thus it holds more powder which results in slightly more velocity with the same bullet weight.

I've never owned one myself, but I like the idea of a non belted case, for no other reason than I just think they look better.

Yep, I just thought it up. I hear MontanaBob shot his elk this year with his .300 RUM. (Looked cool in those glasses)Made a clean hole in the elk's shoulder!

The case is based on a 404 Jeffries case. The case headspaces on the shoulder, and it does not have a belt. Many consider this the reason for the caliber's superb accuracy. Case is capable of holdig 100 grains of RL 25. I consider it an awesome cartridge. I have owned 1, shot 3, and loaded for 3. All were great shooters. I like the heavier bullets, but with heavier bullets you loose some case capacity. I am going to try some Retumbo, I have heard of some good results. The factory loads shoot great, but in my opinion are pricey. If you do not reload it could be an expensive rifle to shoot. Tom.

Younggun,
I have owned 4 300 RUM and still own one in a Winchester Mod 70(it was the first one I bought).The .300 RUM is a great round,it has lazer like trajectory,hit's like a hammer and will flat pancake elk.I shot the 180 gr Noslers for years in the one's I've owned and the oneI shoot now sends a 165 Nosler boattail 3300 fps.Sighted in at 300 yds givesme a top of the back hold on elk out to 500 yds if I ever wanna send it that far.I have shot deer,antelope and elk with this round and I have yet to see one do more damage(internal) than this,turns vitals to liquid chunks.
I have also had the plesure of shoot the .338 RUM,now when you touch this Mamoth round off on deer the results are quite humorus,I've seen a Barnes X tear the spine out of a deer where you could fold it in 1/2 and stuff it in a cooler.
BUT.....
all this comes at a price,for bechshooter time at the range with these rounds can be painfull,I can comfotably shoot 20-25 rounds in sitting after that my teeth start to ache.Barrle life is shorter,but probaly if you use it for hunting and occasinal shooting it will last a life time.
Factory ammo is exspensive and alot of places sell out due to the fact that they only stock so much of just a few diffrent weights.
I realy like the .300 Rum and the .338 Rum,you could just about cover all your bases with just these rounds.
What I would realy like to see is a necked down case inbetween the full size RUM(404 J) and bigger then the WSM
and chambered in the .260 size.Maybe somthing called the .260 MUM(Medium Ultra Mag) now that would be beanfeild killer or a .280 with a sharper shoulder could be a .280 SEM(Super express mag).
But all in all we as hunters have about all the avabile chamberings needed,and IMHO the RUM's are at the top.
BBJ

260 MUM- I think that is a great idea. Count me in for one. Tom.

I had a 338 RUM and really liked it. I sold it in a fit of practicality. I used to shoot 225gr accubond @ 3140fps. It was a super flat shooter and hit like lightening. I'll be getting a new one soon. Retumbo was my powder choice.