It seems the 3D printed bullets got lost in the mail. He is going to print another batch and send them.  In the meantime, I went to the range today and tried out my five rounds of reloadable .30 rimfire ammunition using the cut down 7mm bullets. Here is a video of the fun.

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MANY years ago, I got from LEE some blank mould blocks, and cut some special moulds to suit a similar odd-ball requirement.   Don't know if they would supply them today.
CHRIS

Round ball the most often used simple loads in a pistol like yours. Cast with a proper mold is how the original was loaded and the best solution.

Low volume shooting, pure lead bullet, a bit too large for the bore, swaged to size in a simple shop made die & trimmed to length in the lathe would be my choice.

Plastic and 3D printing really most useful for complex shapes. Metal round projectile  so easy to shape with existing shop machinery no real reason to go 3D.Only plastics I have seen successfully used in bullets are primer or air propelled 

Opinion, others may differ 

Boats

I received the 3D and Lee 7mm soup can bullets. The soup cans will of course be cut way down and given a heel. I'll probably load one batch of each to try out in the Marlin. Then retire the little pistol to my collection.  Those remaining will be saved for the next little .30 rimfire pistol that follows me home 

I stopped at the range today and tried out the .30 rimfire 3D printed bullets. Check out the video.

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Indeed it is. Im also curious what velocity these 6.1gr bullets are moving out at.  Maybe another range trip to answer that question!