What a P320 Magazine Extension Does

A P320 magazine extension is a metal or polymer piece that attaches to the bottom of a standard P320 magazine to add extra rounds to your magazine capacity. Instead of the factory 17-round capacity in a full-size P320 magazine, an extension can push that to 21 or more rounds, depending on the model and manufacturer. The extension slides onto the magazine's baseplate and is held in place by the magazine's spring and follower.

Extensions are aftermarket parts — they do not come with the gun from SIG Sauer. They are sold separately by third-party manufacturers and are legal to own and install in most states, though some jurisdictions restrict magazine capacity by law. Before purchasing, check your local and state laws to confirm what capacity is permitted where you live and carry.

Key Takeaways

  • Magazine extensions add 4 to 6 rounds to a standard P320 magazine by replacing or extending the baseplate.
  • Extensions are made by third-party manufacturers like Taran Tactical, Hensoldt, and others, not by SIG Sauer.
  • Installation takes less than a minute and requires only disassembly of the magazine's baseplate and spring.
  • Some states and cities restrict magazine capacity by law, so you must verify local regulations before purchasing.
  • Extended magazines may not fit in all holsters or magazine pouches designed for standard-capacity magazines.

How to Install a P320 Magazine Extension

Installing an extension is straightforward and requires no tools beyond your hands. Start by removing the magazine from your firearm and ensuring it is unloaded. Press down on the magazine's baseplate — the flat metal or polymer piece at the very bottom — and slide it toward the rear of the magazine. The baseplate will separate from the magazine body, and the spring and follower (the plastic piece that sits on top of the rounds) will come loose.

Slide the extension onto the magazine body where the baseplate was. The extension has a slot or groove that fits over the magazine's feed lips or body. Once the extension is seated, place the spring back into the magazine, then the follower, and finally slide the extension's baseplate (or the new combined baseplate) forward until it clicks or seats firmly. Rack the magazine a few times by hand to confirm the rounds feed smoothly and the extension does not shift.

Some extensions come as a single unit that replaces both the baseplate and adds length; others are spacers that sit between the original baseplate and the magazine body. Read the manufacturer's instructions for your specific extension, as installation steps vary slightly by brand.

Common P320 Magazine Extension Brands

Several manufacturers make extensions for the P320. Taran Tactical produces aluminum extensions in various capacities and finishes. Hensoldt makes polymer extensions that are lighter and less expensive. Dawson Precision offers steel extensions with witness holes so you can see round count from the side of the magazine. TTI (Tactical Tailor Inc.) makes extensions designed for competition shooting with aggressive witness markings.

Each brand has slightly different fitment, material, and price. Some extensions are designed specifically for competition use and may have features like aggressive witness holes or witness rounds (colored rounds at specific intervals). Others are built for duty or carry and prioritize durability and reliability. Check reviews and manufacturer specifications to confirm the extension fits your magazine generation — P320 magazines changed slightly over production years, and not all extensions work with all magazine versions.

Magazine Capacity and Legal Restrictions

Standard P320 full-size magazines hold 17 rounds. Most extensions add 4 to 6 rounds, bringing capacity to 21 to 23 rounds. Compact P320 magazines start at 15 rounds, and extensions can bring them to 19 or 20. The exact capacity depends on the extension design and the ammunition type — hollow-point rounds take up more space than full metal jacket rounds.

Magazine capacity is restricted by law in several states and cities. California, Colorado, Connecticut, Hawaii, Maryland, Massachusetts, New Jersey, New York, and Vermont all have capacity limits ranging from 10 to 15 rounds. Some cities within otherwise unrestricted states also have local bans. Federal law does not restrict magazine capacity, but state and local laws override federal law. Before purchasing an extension, search your state's attorney general website or contact your local police department's non-emergency line to confirm what is legal in your jurisdiction.

Holster and Carry Compatibility

An extended magazine will be longer than a standard magazine, which affects how it sits in a holster and how the gun carries. If your holster is molded specifically for a standard-capacity magazine, an extended magazine may protrude beyond the holster's bottom edge. This can be uncomfortable when sitting or drawing, and it may expose the magazine to snags or damage.

Magazine carriers and pouches designed for standard magazines may also be too tight for extended magazines. Before installing an extension on a magazine you carry regularly, test the fit in your holster and any magazine pouches you use. If the fit is poor, you have two options: purchase a holster designed for extended magazines, or keep the extended magazine as a spare in your range bag and carry standard-capacity magazines for duty or personal carry.

Reliability and Feeding Concerns

Quality extensions from established manufacturers are reliable and feed rounds consistently. However, the extra weight and length of an extended magazine can affect how the magazine seats in the gun, especially if the extension is poorly made or installed incorrectly. A magazine that does not seat fully may cause feeding failures or the gun to not lock into battery.

Before relying on an extended magazine for carry or defense, load it fully and fire at least 50 rounds through your P320 to confirm reliable feeding and extraction. Pay attention to whether rounds feed smoothly from the bottom of the magazine and whether the gun cycles normally. If you experience any failures to feed, failures to extract, or double-feeds, stop using that magazine and contact the manufacturer. Do not assume the problem is the extension — it could also be the magazine itself or a combination of both.

Frequently Asked Questions

Will an extension void my P320's warranty?

SIG Sauer's warranty covers defects in the firearm itself, not aftermarket parts. Installing an extension on a magazine does not void the gun's warranty. However, if a malfunction is caused by the extension or a modified magazine, SIG Sauer will not cover that repair. Keep your original magazines and extensions separate so you can test with factory parts if a problem arises.

Can I use an extended magazine in a P320 compact or subcompact?

Yes, if the extension is designed for the compact or subcompact magazine. Full-size extensions do not fit compact magazines. Compact extensions add fewer rounds than full-size extensions because the magazine body is shorter to begin with. Confirm the extension is listed as compatible with your specific P320 model before purchasing.

Do extended magazines affect the gun's balance or recoil?

An extended magazine adds weight and length to the magazine, which can slightly shift the gun's balance toward the rear. Most shooters do not notice a significant difference, especially in full-size P320s. Compact and subcompact guns may feel the change more noticeably. The best way to know is to load an extended magazine and fire a few rounds to see how it feels in your hands.

Are there any P320 magazines that come with extensions from the factory?

No. SIG Sauer sells P320 magazines in standard capacities only. All extensions are aftermarket products made by third-party manufacturers. SIG Sauer does not manufacture or endorse specific extensions, though some are widely used and well-regarded in the shooting community.