Cartridge selection is likely one of the hardest, most complicated aspects of a build to get right for some people (or maybe just me, idk!) if it's one they aren't already set up for. Because of that, this is gonna be a novel, but it's how my mind works, so I apologize ahead of time!
This build started around first, what I physically wanted out of a rifle (compact, around 9 lbs, handy, supressed, and bombproof) and second, what performance I wanted, which was a 30 cal 200-215 grain bullet around 2850-3000 fps.
The first set of requirements narrowed it down to a short barrel, 18-20". Then, I had to find a cartridge that would meet my performance requirements out of said barrel. I didn't want to go too much over, as that burns unnecessary components and barrel life.
So, talking to the long range pistol crowd (thanks
@Ernie specifically!) as well as some other open minded rifle smith's and experienced shooters as to the performance they have first hand seen with different cartridges from the 300 SAUM up to the 300 Lapua AI in short barrels, and that narrowed the playing field. I needed to have good brass available, either Peterson, Lapua, or ADG, that cut a couple out. At this point, I had decided on the XLR magnesium folding chassis, which uses a CIP length magazine in the long action, so 3.750" roughly depending on manufacturer was my limit for cycling. That help narrow it down more, to these -
300 WSM didn't quite make the cut, save a very few "fast barrels" (or hot loads), though that cartridge in a short barrel would have caught me less hate ha ha. The 300 wm, while a little bit, wasn't much ahead of that either. The 300 PRC is there or pretty close, but if not made with the right chamber/die combo, will end up giving clickers after a few fireings, and needed to be loaded warm to get there, and may not have a good node in the velocity range. The 30 Sherman mag (300 prc Sherman improved) seems to do it, and the case design and current dies fixed the clicker issue. Also, the 30 nosler met all the requirements as well. It goes without saying that the larger cases will meet the performance, and could possibly run with somewhat reduced loads, giving lower pressure and longer barrel life to offset the larger capacity, however the 300 RUM was simply way too long to mag feed. The 300 Norma and NAI were a consideration, but I didn't want to step up to the .585 Bolt face and larger/heavier action to go with it.
So at this point, the 30 Sherman mag and 30 Nosler fit the bill for performance. They both have great brass available, Lapua for the Sherman, ADG for the Nosler. They both have good efficient case designs. Some may argue the 35° shoulder of the nosler will feed better than the 40° shoulder of the SM, and they are probably right, especially if your feeding from a stagger feed, but I haven't ever had a hiccup from my 40° .260 AI fed from a s/a AICS mag, and as this will be a long action AICS, feeding is a draw for me. I currently don't have dies for either. Sherman dies are spendy, but so are any quality bushing style die that I would get for a 30 nosler, so that is also pretty much equal. The Sherman has the right throat, but I would just have my smith throat the nosler for the bullet I want to shoot, so also 6 one, half dozen the other.
Now we're getting down to splitting hairs....I haven't shot a factory load in any of my personal bolt action centerfire rifles in nearly 20 years. The Sherman is the same as an Ackley in that you can shoot factory 300 PRC ammo just fine. I probably see more long range options for the 300 PRC in factory ammo, but I see plenty of both available. Again, I don't care about any of this anyway ha ha. So why the 30 nosler......
Limited supplies, and not as dramatic of fireforming with the 30 nosler. I know, I know, virgin brass must be fireformed even in a SAAMI chamber to get a 100% accurate reading on your load, but there is less of it with the Nosler. I know I could just develope a "fireforming" load for the Sherman that would be plenty accurate, albeit reduced from full potential and just use that for a while, but I also know myself, and I know I wouldn't be happy with a fireforming load. I would blast through those first 50-100 rounds of brass as fast as I could while not overly torching the barrel, so I could develope a "real" load for the rifle, and loose all that precious powder and primers to fireforming, and to a lesser amount of importance, 100 rounds of barrel life. Also, with the same bullet seated properly in the neck of both cartridges, the 30 nosler will be about .040" shorter OAL. This may not matter, but the 205 SBDII I plan on running is a long bullet, and it may (or may not) make the difference, I haven't run the numbers yet.
Also, I have a few Sherman rounds, and I like them very much, and Rich is a fantastic, helpful, and very friendly guy that has given me tons of advice with loads for his cartridges. However, I also just want to try something different.
So, there is my nearly 1000 word dissertation as to why I picked one cartridge over another. Ha ha, it is stupid the amount of thought that has gone into this, but whatever, it's what I enjoy doing!!!
