I don't think there'd be an issue with the new Rochucker Supreme, RCBS Rock Chucker Supreme Single Stage Press - MidwayUSA,
however, I've have the Rockchucker II, I think it is, one genration removed from the new 'Supreme', and I do have to angle the cases, with bullets held in place by hand, into the seating die. No big deal, though. Find out which generation it is.
Same here I use a Rock Chucker press as well and I don't have a problem at all with mine I load for the RUM to . Mine is also an older model but my friend has a newer one that he got last year and it looks to me to be identical.
I use an old(er) designed Rockchucker press, same one for the past 29 years. It handles my 300 RUM and 300 WBY just fine.
If the newer ones are even bigger - all the better.
You have bigger things to think about. Start at the Sinclar web site - order one of their catalogs, take a careful look at the case prep goodies.
If you are thinking about a 416 Rigby or 378 WBY based wildcat in the future, taking a look at one of the larger presses may not be a bad idea. However, the long stroke of that press when only loading a 308 based short cartridge will wear you out. I recently went to Wyoming for a PD shoot, it required 1800 rds for 2 shooters. The thought of running that many rds thru a x-large press makes my arm hurt just thinking about it.
I did call RCBS right after I posted this.
They said no on the old Rock Chucker it has 3.3 window and the 300 RUM needs 3.6 but the Rock Chucker IV and Supreme though is a 4.5 window and handles it fine.
i have used the rock chucker on a 300 rum, but it gets annoying, and if you are fooling with seating depths at all it gets annoying putting a loaded shell back in. i like the redding ultra mag press, but the price is a bit higher than the press i have, a redding boss 2, it handles my 338 edge fine i don't have a 300 rum anymore
Take a look at the Redding Ultra Mag Press-pricey but, worth every penny. It handles my 300rums with ease. +1 on the Sinclair catalog...they have some great stuff, rare if anything isn't in stock, have always got my order correct and on time, decent prices and they do a nice job on their catalog. They carry the Ultra Mag Press