Welcome!

If there is no oral history of grandpa having a problem with the rifle, and if he was using it right up to the end, and if is has been kept relatively rust-free there is probably no reason at all why you should not shoot it. You really do not need a Krag expert to look at the gun - any well-established 'smith should be able to give it a good safety check.

I will say that the arm has been subjected to a lot of "home-gunsmithing" in that it is a assembly of dis-associated parts, and the barrel has been modified - or may not even be a Krag barrel. Many Krags were re-barrelled with one from a 1903 Springfield. The stock is from a much earlier carbine. Since I cannot see the bolt notch clearly I cannot tell if it is from an 1896 or 1898 model, but it still would not have come with that receiver. These are not safety issues, only cosmetic - the gun will still be fun to shoot. Enjoy!