Try it with a spent casing. If a loaded cartridge has the bullet ogive hitting the leade in the throat, you are trying to cam a bullet into the rifling. The headspace would then be off and it's very difficult to push the bolt lever downward. It's possible that the headspace may be off, or the leade in the rifling is too close for that bullet profile.
Do the cartridges you are trying to load with considerable effort show rifling marks in the bullet close to the case neck when you eject a loaded cartridge (even if you don't get the bolt lever pushed down fully)? That is a very dangerous condition as there is no room for ignition pressures to build safely during firing as the bullet jumps before hitting the rifling.
If you don't have a spent cartridge yet, and you have another brand/type of ammunition then try that. Or take it (unloaded) to a gun shop for their opinion.
The problem may be the ammunition you have. Or, it may be another issue.