Depending on the manufacturer of the rifle, and the age of the rifle, the recommended powder charges vary. In pellet form, many modern inline rifles can handle 150 grains. In loose form, that IS NOT THE CASE. Many of the manufacturer's recommendations for loose powder vary from 100-120 grains of powder. You then have to consider the grade of powder. Also on some rifles the weight of the projectile they shoot makes a difference.

What I recommend is that the person you are talking about be certain that the rifle they are shooting is ACCORDING TO MANUFACTURER SPECIFICATIONS, able to handle those powder charges. If they have any doubt or do not know the specifications of the rifle, then reduce those charges to no more then 100 grains until they can confirm with the gun maker the correct amounts.