From a shotgun, you can either fire "shot" or "slugs." Shot shells are plastic cartridges filled with tiny metal pellets and should always be fired from non-rifled shotgun barrels. Slugs are essentially a single, fairly large metal bullet loaded in a plastic cartridge.  The kind of shot used in shot shells also varies and it is important to understand the way shot is sized. Birdshot contains smaller pellets for use on smaller animals or targets, while buckshot rounds are filled with larger pellets for use on larger animals or targets. Slugs are available in rifled varieties, for use in smooth-bore barrels, and "sabot" varieties, for use in rifled barrels. Shotguns come in many different gauges, and the ammunition will correspond to that gauge. You must use 12 gauge ammunition for a 12 gauge shotgun, 20 gauge for a 20 gauge, etc. A 20 gauge shell will fit in a 12 gauge gun, slide about halfway down the barrel and stick if you try to fire it. This can be very dangerous, so it's critical to make sure you buy the appropriate size of shell, regardless of style. Longer shells contain more powder and more shot per shell, or a larger slug. The standard shotgun chamber size is 2 3/4 inches for all gauge shotguns. Some shotguns have a 3 inch chamber. Shotguns are known to favor different loads and different shot, so experimenting with various combinations in search of a good match can be useful. 12 gauge shot shells are the most common shotgun shells sold, and are typically available in three different shell lengths:  Regular shells are 2 3/4" long - safely fired in a shotgun with a 2 3/4" or 3" chamber Magnum shells are 3" - safely fired in a shotgun with a 3" chamber Super-magnum shells are 3 1/2"  Make sure that the chamber of your shotgun is as long or longer than the shells you choose.  Do not use 3" or 3 1/2" shells in a 2 3/4" chamber or 3 1/2" shells in a 3" chamber. The shot number will be printed on boxes of ammunition and refers to the size of the individual pellets in the shell. Larger shot numbers mean...

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Write a summary of the previous text in Chinese:
区分最基本的猎枪弹样式。 买适合你猎枪规格的弹药。 决定你正考虑的弹药长度。 弄清弹丸数。 了解子弹尺寸。