You pretty much thought the same way I was thinking in the beginning, that there would be a lot of pressure leaking into the action and bolt and quite frankly, a pipe bomb a few inches from my face is not a thing I fancy. MCA sport rep was thinking the same too.
Should have mentioned it but I live in Canada. Here the law is slightly different and yes, I actually asked a lawyer and the RCMP if there was anything wrong with the way I was doing things. They both answered that since I only received reloading materials, as long as both parties are happy, there is nothing wrong. I just had to make sure people I reloaded for have a valid Possession-Acquisition Licence before giving them the ammo.