What bullets would go in that cartridge?
According to the limited data I saw on the internet the new 360 will drive a 200 grain bullet to about 2100. At that speed most expanding bullets meant for 10mm handguns would come apart.
I've successfully used the 200gr XTP 10mm bullets from Hornady at velocities in excess of 2100 fps.
Hornady uses these same bullets in its .45 caliber sabots for muzzleloaders (see
here)
Moreover, various other muzzleloader sabot use .400 caliber projectiles in a variety of weights (see
here another from Hornady using their SST bullets)
Every state I have lived in requires expanding bullets for hunting and the only heavier bullets I have seen in 10mm are cast.
Every state in which I've lived that has had a similar restriction has defined "non-expanding bullets" as FMJ. Thus, hard cast has been treated no differently than bullets which only partially expose their lead, like JSP.
There are plenty of JSP, JHP, hard-cast and generally non-FMJ 10mm bullets available.
Bullets meant for 404 and 416 rifles are designed for water buffalo, not deer, and would probably not expand well at lower velocities.
Noted, but we are talking about necking up to 10mm/.40 caliber, which 404 and 416 are not.
Being a bullet maker Remington can make any type of bullet they want...Even if they wanted a 10mm version they probably decided designing a 10mm bullet that performed well at rifle velocities wouldn't be worth the trouble.
Your first point here is an important one: Remington is not your average hand-loader. Even if there were not already appropriate or readily adaptable 10mm bullets on the market, like Winchester had to with the 350 legend, manufacturing rifle-ready 10mm bullets would be trivial.
Your second point is speculative.
But this is a cartridge meant to fill a very particular and narrow niche market, hunting in states that require a straight case.
This is not a reason to effectively make it even more narrow and niche by putting it in a segment already occupied by two cartridges (350 legend and 357 maximum). Indeed, it is all the more reason to use a 10mm/40 caliber projectile and place it in a segment where there is no competition.
If changing hunting regulations eliminate the niche this cartridge is designed for demand for the ammo would dry up. At least with the 358 bullets reloaders could find something that works in any 360 Buckhammer rifles they have. With 10mm they could use handgun bullets for plinking but 10mm rifle bullets would be scarce.
See above re: viable 10mm bullets at the moderate velocities advertised for the 360. Also, if you'll allow me to speculate a bit, I don't believe Remington takes into consideration the handloading opportunities to early adopters in the event the 360 proves a failure.
