The Mossberg 930 JM Pro is a popular semi-automatic shotgun designed in collaboration with professional shooter Jerry Miculek. It is known for its competitive shooting features and high-capacity magazine. Here’s some information about the Mossberg 930 JM Pro with a 12-gauge chamber and a 10-shot capacity:

1. Gauge: The Mossberg 930 JM Pro is chambered in 12-gauge, which is one of the most common shotgun gauges and is versatile for various shooting applications.
2. Capacity: The “10-shot” designation indicates that the magazine of this shotgun can typically hold up to 10 rounds. This means you can load ten rounds into the magazine tube, plus one additional round in the chamber, for a total capacity of eleven rounds.
3. Semi-Automatic Action: The Mossberg 930 JM Pro operates as a semi-automatic shotgun. This means that after each shot is fired, the shotgun automatically ejects the spent shell casing and chambers a new round from the magazine tube as long as the trigger is held down and the gun is functioning correctly. Semi-automatic shotguns can offer faster follow-up shots compared to pump-action shotguns.
4. Purpose: The Mossberg 930 JM Pro is designed with competitive shooting in mind, particularly in the realm of 3-gun competitions. It has features that are beneficial for fast and accurate shooting, including an extended magazine tube, adjustable stock, and fiber-optic front sight. However, it can also be used for hunting and other sporting purposes.
5. Jerry Miculek Collaboration: Jerry Miculek, a renowned competitive shooter, worked with Mossberg to develop this shotgun. His expertise in competitive shooting sports influenced the design of the firearm.
6. Variants: The Mossberg 930 JM Pro may be available in different variants, with variations in stock and barrel lengths. The 10-shot capacity version you mentioned likely has an extended magazine tube to accommodate more rounds.

Before purchasing any firearm, make sure to familiarize yourself with local, state, and federal laws and regulations regarding firearm ownership and use, including capacity restrictions and any required permits or licenses. Additionally, seek proper training in firearm safety and usage, especially if you plan to use the shotgun for competitive shooting or any other specific purpose.