NRA Rule #3.1:
(c) U.S. Rifle, Caliber 5.56 mm M16 series – In all courses of fire and in all positions the standard 10-, 20- or 30-round box magazine or a reduced capacity magazine of the same external dimensions will be attached. A case deflector (D.C.-T-30 or commercial equivalent) is allowed.
REDUCED CAPACITY MAGAZINES:
In some states, the public is limited to using reduced capacity magazines. When starting out, any legal magazine should be fine for initial practice or competitions. Eventual goals will be to standardize on something quality, that the competition rules also consider “standard”… AND is legal.
A straight 20-round sized magazine is most common. A quick internet search will yield many options to choose from in the form of what are commonly called “10/20” or “10/30” magazines. These are standard magazines with internal blocks to prevent more than said number of rounds able to be inserted. Be aware however (and do your own research) that California law requires that “blocked” magazines be done so permanently. This will typically mean that once the limiting “blocks” are installed inside the magazines, the floor plates are welded or riveted shut. Although this is now a legal magazine… It cannot be easily cleaned or maintained.
THE PROMAG 10/20:
A more than acceptable solution that is both legal and functional is offered by ProMag in Arizona. They offer a standard dimension “10/20” that has been modified to only accept 10-rounds – without the use of any external blocks. Ribs on each side of the magazine protrude deeper than the standard internal dimensions of the magazine, acting as the block. This allows for the use and function of standard springs and followers, but has been designed as such that no more than 10-rounds can fit atop the follower inside the magazine. The springs and followers can now freely travel AND the floor-plate can be removed for periodic maintenance and cleaning.
NOTE: As with any magazine purchase, it is always prudent to disassemble, inspect and clean before any serious range-work. Sometimes, regardless of manufacturer – magazines get shipped that have springs that have been dinged up or are installed backwards (causing the follower to tilt forward).
MSRP on this magazine is $27.25:
Riflegear in Fountain Valley, CA sells them for $17.99:
(FOR CALIFORNIA SERVICE RIFLE SHOOTERS):
THE “BULLET BUTTON”:
The public in California is limited by what is known as a “Bullet Button”. Basically, this replaces the normal AR15 magazine release and requires an object to be inserted into a small hole to drop the mag. Most issued competition chamber flags are the right dimension to operate this procedure, but… this now requires three things to be done during a magazine change in a rapid-fire string: 1: grabbing the flag 2: operating the bullet button and then 3: inserting the fresh magazine.
The Bullet Button can come loose (often at unfortunate times, like a match…). Blue Loctite CAN be used to secure these in place, but a careful snugging down during maintenance & cleaning should suffice. Two copies of this tool is suggested: one on your bench for cleaning and the other in your cart or range-bag.
AN OPTIONAL HACK:
An optional hack is a very inexpensive magazine modification to help work within the confines of the “bullet button”. While chamber flags will definitely function in helping to remove a magazine, a “nipple” or “nud” (for lack of a better word) can also be attached on the forward side of the magazine, down by the floorplate. This can act as a magazine removal tool. Now instead of having to reach for two things (flag and then mag), one can grab the next magazine and use IT to help remove the spent and continue on with the rapid string. These are easily made, but can also be purchased pre-packaged for a nominal fee:
Bullet Button Nipples – $5.99 for sale: here
SINGLE LOAD ENHANCEMENT DEVICE (or “SLED”):
Half or 3/5 of standard National Match competitions are shot in what is known as “slow-fire”. This is one… shot… at… a… time…, with the rifle being loaded with a single round out of the box at a time by hand. While a round can definitely be placed on top of a standard follower and sent home by closing the bolt, sometimes a round loaded like this might not want to go in straight and will tend to get bound up and not go into battery. Not only might this damage the round, but it requires a competitor to break their mental concentration – now having to attend to technical matters other than shooting clean shots.
A “Single Load Enhancement Device” (or SLED) is a standalone device with more generous real estate than a standard follower that also ramps towards the chamber to help ensure the round goes in straight during slow-fire loading (avoiding any binding up). Like a standard magazine follower, it will also lock the bolt to the rear after each slow-fire shot – allowing for ease of further single-loading. While “single load followers” are available if a spare magazine happens to be laying around, a “Bob-Sled” will be a worthwhile investment should a competitor need to start from scratch.
A sled is also a fabulous way to keep the rifle plugged with something when traveling while in California. Current law (requiring the bullet button) states that AR15’s must not have detachable magazines. A non-detachable single-round SLED is a good option here, en leu of traveling with a rifle than CAN accept any capacity magazine.
obvious disclaimer: Do all of your own research to verify the compliance of laws in whatever area you reside and / or wish to practice / compete.
NONE OF THE ABOVE IS MEANT TO CONSTITUTE LEGAL ADVICE.