Yep, different cartridges have different gas length gas systems that are suited to them. .458" SOCOM is actually limited in powder choices if you go mid-gas b/c it was designed around a carbine length gas system.
The problem comes in though, when you realize that there are no absolutes. You also have to define your philosophy of use. In my case, I knew I wanted mine supersonic. Going with the carbine length tube gave me what I wanted, I did not have to go changing buffer weights, and it just works. Even with subsonics. A prime example is the M4gerys out there. They were designed around the carbine length gas system. They are known to batter the rifle, heavier buffers were devised, finally the mid length gas system was introduced. The mid length is not milspec by the way. The mid length is considered the better option now. It's even been talked about on this forum. Generally I agree. Use the tried and true, but sometimes there are better options.
Lots of good data I wonder what the smallest bulk order is? 100,000 would make a nice group buy, get a bunch of us together and purchase it Still might be looking at a better deal buying a Dillon 1050 and components. Hard to say w/o prices of the steel case 300. Even a Dillon 650 or Hornady LnL would churn out lots and lots of ammo for a minimal initial investment. That brass 300 is quite reasonable, I was thinking the steel would be really cheap. hmmm
I have quit using LilGun in 300 BLK. I am agreeing with what so many other people are saying. It burns too hot. There are reports of damage to firearms. I don't know, don't think mine have been damaged, but I do know that 410 shells don't last long, they melt. I have 2 pounds left. It is my powder for 250 Bushmaster, when it's gone, I don't think I will buy more.
In my opinion .300 AAC Blackout is getting more popular because of what you can do with it. I bought an AR-15 in .300 Blackout for supersonic shooting and I really like it thus far. Edit: I found a gun shop near me that sells 20 rounds of 124 grain .300 Blackout for $12.14.