Any tricks?

I have a .38 S&W I slugged this morning. I used a 9mm Makarov cast lead bullet that mic'd .367". I drove it through the bore. Not such an easy task, mostly because I was worried the entire time that I would never get it all the way through.

Anyway, the slug has the rifling imprinted on it nicely and it now mic's .354". The reason for my question is that this is about .010" smaller than I would have expected.

Any thoughts? Just believe it? Re-do it? Any tips for re-doing it? I just drove it in with a wooden dowel and then pushed it through with a rod.

By the way, the pistol is a 1911 Colt Police Positive that seems to have been cut down to 2" barrel.

Thanks,
Jeff