Powder burns...you mean sooty case necks? (black case necks)
That usually means the powder is too slow for the bullet weight...I've never shot bullets that light in the 300, but if I was in your shoes...I'd switch to one of the 4895's and see what happened. (IMR is generally a tad faster burning than H...and may be what you're looking for)
The reason it happens in the Remington and not in the Browning...just a guess, but I'd say its the "giraffe throat" that Remington likes so much...too much bullet jump before the pressure really spikes enough to swell the neck and seal it off.
Its not dangerous as far as I know...