I am not sure why he told you it wouldn't work but as long as your .270 Handi is on an SB2 frame it is a strong action. A .270 shouldn't be on any other frame that I am aware of. Can you be more specific? Was the person telling you this the guy you bought it from?
I just sold a Handi .270 that did very poor with some powders and I had to load special low CUP pressure loads for the action to perform like my other handis. I sold it and gave the buyer the shells I had loaded for it, the recipe and primers and bullets it liked. He can shoot any shells he wants in it but I told him that to keep him from wasting money on other powder and bullets. If that is the case with you it may make sense, but that would be the only reason I could think of, the cratering primers keeping the action from opening smoothly from a hot load with the wrong powder..... Hope this gives you some kind of answer.
I sold mine in a face to face here in MN, but I explained exactly why the hot high pressure loads couldn't be used. If your gun is new it shouldn't be an issue. I though mine had excess head space but sent it to the gunsmith that H&R had me send it to and it was within tolerances. thejanitor