im no expert on this but i dont see why it would cause feed problems unless the magazine was bad
and accuracy i dont think it would be a problem
there are a lot of very accurate bolt actions out there that have detachable box mags
Unless the action or the magazine(as Flea mentioned) is borked, a magazine shouldn't affect accuracy or feeding in the least.
In fact, in the field it might just be the other way around. If you reload an internal magazine round by round with dirty fingers, you might just build up some dirt in there, while a preloaded magazine is quite easy to exchange, without touching the ammo.