The .300 Remington Short Action Ultra Magnum (RSAUM) was introduced in 2002 in the heyday of the short-action craze. It has taken a long time for the load to enjoy real acceptance. There is nothing wrong with the .300 RSAUM; its worst problem is that it, like all the short magnums, came with marketing ballyhoo in abundant oversupply.

The RSAUM's case volume is slightly smaller than the .300 Winchester Short Magnum, and as a result, the factory performance claims are a hair slower. The .300 RSAUM performance is also slightly slower than the .300 Winchester Magnum, but the difference between the three cartridges isn't enough to make any practical hunting difference.

Lately, there has been some interest in using the .300 RSAUM as a sniper-rifle cartridge. I don't believe that case design--excepting radical departures from convention--has much, if anything, to do with accuracy. The .300 RSAUM shot very well out of my 11⁄4-inch-diameter pressure barrel, but that's no surprise. With a good barrel and good bullets it is pretty uncommon to make loads that aren't accurate.

Being a .30-caliber cartridge, there are plenty of bullets in all weights and categories. I used standard large primers for all loads. I saw no reason to use magnum primers, but if you insist on using them, don't even think about starting at any load level above the starting loads listed. That advice really always goes for any change in anything. Drop back to the starting level when you change anything. You might waste a little powder and a few bullets, but your eyes are worth the trouble.

.300 RSAUM Load data*
BULLET	BULLET WEIGHT (gr.)	POWDER	PRIMER	CASE	START LOAD (grs.)	MAX LOAD (grs.)	MAX. MUZZLE VELOCITY (fps)
Nosler Ballistic Tip	125	Hodgdon H4895	Rem. 9.5	Rem.	54.0	60.0	3,500
Barnes Triple-Shock	150	RamShot Big Game	Federal 210	Rem.	56.0	64.0	3,190
Speer Mag-Tip	150	VihtaVuori N540	CCI-200	Rem.	52.0	58.5	3,180
Berger VLD Match	155	Alliant RL-15	Win. Large Rifle	Rem.	52.0	58.0	3,120
Hornady InterBond	165	Accurate 2520	Federal 210	Rem.	48.0	55.5	3,000
Swift Scirocco	165	RamShot Big Game	CCI-200	Rem.	56.0	62.0	3,050
Sierra HPBT	165	Winchester 760	Rem. 9.5	Rem.	58.0	64.0	3,060
Hornady InterBond	180	IMR 4350	Win. Large Rifle	Rem.	54.0	60.0	2,900
Nosler AccuBond	180	VihtaVuori N550	Federal 210	Rem.	51.0	58.5	2,900
Speer Trophy Bonded	180	Hodgdon Varget	CCI-200	Rem.	48.0	56.0	2,890
Sierra GameKing	180	Norma N203	Rem. 9.5	Rem.	47.0	55.0	2,860
Berger VLD Match	185	Accurate XMR 4064	Win. Large Rifle	Rem.	48.0	56.0	2,930
Swift A-Frame	200	Norma N203	Federal 210	Rem.	44.0	55.5	2,650
Barnes RN Solid	220	RamShot Big Game	CCI-200	Rem.	47.0	54.0	2,480
* Figures taken from a 26-inch pressure barrel.

WARNING: The loads shown here are safe only in the guns for which they were developed. Neither the author nor InterMedia Outdoors Inc. assumes any liability for accidents or injury resulting from the use or misuse of this data.

The .300 RSAUM (center) compared with its close relatives, the .308 Winchester (left) and the .30-06. The .300 RSAUM holds a little more powder than the .30-06 and has the same overall length as the .308.

Powders are not a bit of a problem. There are so many useful powders that I couldn't begin to recommend any one as the perfect one for this cartridge. If you use what you have available, you will get satisfactory performance--unless you use a terribly unsuitable powder. That's why I make a point of showing loads for a bunch of powders. That shows you what workable choices you might have.

I didn't have any trouble finding loaded ammo that I could use for calibration and a fired-case source. All the .300 RSAUM cases at this writing come from Remington. This is probably a good place for a comment on the performance of reloads. The Remington factory ballistics folks didn't leave a bit of performance on the table when they loaded the factory ammo.

If you are one of those fortunate folks who has access to a chronograph, here's a tip. If the velocities of your reloads exceed the velocities claimed by the factory, be very careful. If you are getting higher than factory velocity, you are probably exceeding the cartridge's working pressure limits. I did find that the factory ammo I chronographed agreed very closely with the published velocity claims. The general availability of chronographs has eliminated many of the wildest performance claims we used to see.

There are dies available from several sources. This month's dies came from Hornady. I suppose all of the die makers will hate me for this, but there are a half-dozen companies that make a good product. Each die maker has one or more special features that it pushes. That's just good business marketing. Use whatever strikes your fancy.

There is nothing at all special about loading for the .300 RSAUM. The reloading steps are exactly like any other bottle-necked cartridge. As long as the bolt closes without a lot of resistance, you can't have too little headspace. If your gun has a deep chamber it's probably best to back out your sizing die a bit to neck-size only.

That keeps you from working the cartridge case's brass too much by setting the shoulder back after each firing. Too much headspace will show up as stretched cases. If your cases seem to be stretching a lot, you might want to go searching for the cause. I shot the same cases a number of times in developing these loads and didn't find any stretching.

Accuracy isn't a problem for the .300 RSAUM, as this three-shot, 100-yard group indicates. The recipe? Fifty-five grains of Accurate XMR 4064 behind a 185-grain Berger VLD Match bullet.

The best accuracy load in this series of tests came with the 185-grain Berger VLD bullet pushed by 55 grains of Accurate XMR 4064 powder. That produced a 100-yard three-shot group that was a little over .3 inch center-to-center. That was, of course, out of a very heavy barrel from a machine rest. You probably can't expect to do quite as well with your hunting rifle off a sandbag, but all these loads shot to at least good hunting accuracy, the worst being something like an inch and a half at 100 yards.

The .300 RSAUM is a good cartridge whose performance falls in a narrow gap between the .30-06 and the full-length magnums like the .300 Weatherby. In short, you're going to get significantly better than .30-06 performance out of a .308-length cartridge.

But that begs the question: "If you had a good .30-06 and a good .300 Weatherby, would you go out and buy a .300 RSAUM to fill the gap between them?" I wonder.