A right handed bolt isn't impossible for a left handed shooter to use, but it is less convenient. Shooting prone, you can cycle the bolt very quickly with your right hand if shooting off a bi-pod or bags, but is a bit slower if you are supporting the rifle with your non-shooting hand. In this case, the best technique is to roll the rifle to the left with your right hand, which provides your left hand access to the bolt handle. But a right hand bolt for a left hand shooter is a compromise at best, and if it can be avoided, so much the better.