BB/Pellet gun legal to ship via USPS??

Is it legal to ship a pellet gun (spring activated, not CO2) through the U.S. Postal Service??

Correct, as per ATF regulations. OR to simplify it. There is no Serial Number on it, buying a new one over the counter does not require a 4473. Not a firearm.

It's not exactly the same but I've shipped a couple airsoft guns via UPS. They asked me what was inside and I just replied "bb gun" for the sake of simplicity and there was no problem. Maybe that will help?

If you buy one online they ship it to you UPS or fed ex, so probably so. Check the USPS website.

It's not a firearm. YET