I have one with the mum completely ground off. I don't think it matters whether the mum is partially or completly gone. The soldier who owned it, scratched it off because he was goinging to be captured thereby preventing dishonor from having the symbol fall into surrender. The mum meant it was property of the Emperor. The prices of those rifles ranges from about $250 - $400. I personally haven't seen any for sale for more than that price, even with the mum intact. I would imagine that if the rifle were in excellent condition, it might be worth more.
Here is a site that will tell you the meaning of the other markings on your rifle.