You don't say what cartridge you are using in your Rega/Project rig but I agree with Rlwainwright that it is most likely the heavier arm of the Pioneer.
However, it is possible to track the 1812 with a lower mass arm but you need to have a very high compliance cartridge to do it.
However, it is possible to track the 1812 with a lower mass arm but you need to have a very high compliance cartridge to do it.