A301's were available with choke tubes that had a knurled nut that held the tube in the barrel but they're fairly rare. These were pre Mobil choke era and all 301's I've seen and/or owned had fixed chokes.
Generally speaking, most people will put steel through a fixed choke if it's constricted no more that Modified, that is to say, 20 points of constriction.
I'm not in any way saying you should do that, just that it's commonly done.
301 barrels are interchangable with A300's through A304's, so picking up a barrel that has mobil chokes that are steel rated should pose no problems or large expense. These are very well built guns that last a long time and are worth putting a bit of money into if you plan on keeping it for a while. I plan to never sell my A303 and I've had guys with brand new 391's try to trade me straight across for it!
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