Since talking recently about the collapse of Prime Ammo as it related to their contract with RUAG for some 6.5 SAUM ammo ( Prime Ammunition vs RUAG - High drama ), I figured I would delve into it deeper here about this caliber.
The 6.5 SAUM has been one of the few 6.5 calibers that has the long-range shooting crowd all excited over the past several years, since around 2011. It had certainly been a wildcat of varying degree for a while, and was typically based on necking-down either a .300 SAUM, or 7mm SAUM to 6.5. One could also use a .260 Rem as a parent case, as mentioned here: 260 Remington SA Ultra Mag Back when all of these new 6.5’s were some sort of proprietary or wildcat, and before the standardization / explosion of 6.5 Creedmoor or 6.5 PRC, the 6.5 SAUM was lurking along side the 6.5x284 Norma and the like, vying for industry relevance. Some smaller outfits like Copper Creek were loading and selling it at high prices, but it was mostly a hand-loader thing.
Jump ahead to late 2017 when the Creedmoor was already established with lots of new buzz, and the 6.5 PRC was soon to be released, and Prime Ammunition of Arizona was concocting an all-or-nothing deal with their parent-manufacturer RUAG to produce a huge quantity of this ammo for retail sale in the U.S… This was a gamble at the time, which basically ignored, or didn’t know about the nearly identical 6.5 PRC, and was hoping to one-up the Creedmoor with the cult following which it already had going. As it turns out, Prime had major issues with RUAG and never paid for (correctly paid for, according to RUAG) or received this ammo, and all of this 6.5 SAUM ended up being auctioned off, mostly it seems to TargetsportsUSA. Prime is fuming about this and has filed a lawsuit presently which will probably fail. This quantity of 6.5 SAUM is probably enough to satisfy shooters of this caliber for around a year or more, since so many of them prefer their own hand-loads in general, but basically everyone who owns one of these guns will be compelled to buy a box or two of this Prime stuff to try it out eventually. Similar to if some outfit were to make a new run of .22TCM whereas only Armscor produces anything now, almost everyone with a pistol in that caliber would feel compelled to buy some - one would think.
I am not aware of any other headstamps for this caliber yet. I have read that the “4S” is a remnant of the original wildcat designation which stood for “Super Secret Squirrel $h*t” as a tongue-in-cheek joke, but hangs on as part of the designation, in the same way that you still sometimes see “AAC” used in the .300 Blackout name. Apparently some of the early 6.5 SAUM’s which were necked down from 7mm SAUM were not ideal for something like a Rem 700 platform, and so the 4S version from GA Precision (who build rifles for this) has a more advantageous freebore for 700 type platforms, and this optimized variation has become the standard for the caliber as a whole it seems.
In the photo below, the SAUM is the middle cartridge, with Creedmoor to the left, and PRC to the right. The boxes have no proof-house mark since this caliber is not CIP or SAAMI documented (I guess), and the Prime box from RUAG says only: “Produced by Ruag Ammotec, made in Sweden”.