Originally Posted by OKFC05

Let's hang on a minute before we dismiss the manufacturer's advice.
1. Current Mossberg production has screw-in chokes rated for steel shot. How new is this fixed choke barrel?
2. Mossberg fixed choke barrels from earlier production are NOT rated for steel shot and steel shot WILL damage them.
3. The pure lead Forster-style slugs will not harm any barrel, but are usually inaccurate from tight chokes.
4. The sabot-style slugs require a rifled barrel to provide the spin and are pointless in smoothbores.

If you have indeed bought some "new-old stock" it is important to be certain exactly what you bought.