Touchy Pressures
Plus, there’s not much published, pressure-tested reloading data for the 6.5/300, and none of it includes bullets lighter than 127 grains. This isn’t due to a lack of demand (the cartridge appeared in 2015 and is pretty popular among hunters), but rather the simple ballistic fact that extremely high-velocity cartridges can be a little persnickety about pressure. During considerable load development I haven’t encountered any problems, but any cartridge with lots of powder capacity for the bore diameter will tend to be more “touchy” (as Hodgdon’s Ron Reiber describes the 6.5/300) than modest, well-mannered cartridges like the .308 Winchester.
The development of more really slow-burning powders has helped faster magnums considerably in recent years, partly because so many newer propellants are more temperature-resistant. It’s hard enough to handload the rounds the late P.O. Ackley called “overbore” without worrying about whether a warm day will blow primers.
The loads I’ve settled on in my rifle are the 127-gr. Barnes LRX and 91.5 grains of Hodgdon US869 for around 3,450 fps, the 140 Nosler Partition with 90.0 grains of US869 (3,300 fps), and the 143 Hornady ELD-X with 78.0 grains of IMR8133 (also 3,300). All were developed in Weatherby cases with CCI 250 magnum primers.
The 140 Partition may seem a little strange amid this mix, but has a decent BC for a flat-based softpoint. It also holds together on big game at close range, yet expands easily at longer ranges due to the relatively soft lead alloy used in the front cores of all Partitions.
In my experience, the 140 Partition also shoots accurately in just about any 6.5mm rifle, and is more forgiving of seating depth than most high-BC boattails. The 127 LRX and 143 ELD-X both required some experimentation with deeper seating to match the Partition’s 100-yard groups.
Despite the generational contradictions of the 6.5/300 Weatherby Magnum, it does come pretty close to having it all.
John Barsness’s Big Book of Gun Gack: The Hunter’s Guide to Handloading Smokeless Rifle Cartridges can be ordered through www.riflesandrecipes.com, P.O. Box 579, Townsend, MT 59644-0579, (406) 521-0273.
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