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Today’s Ask Josh is about the wide world of rifle magazines. Reader and range addict Matt K. asks . . .
What is the deal with all the different magazine sizes out there? I’ve been trying to find a Rem 700 that works with AR-10 magazines, but they only have AICS ones out there. Then, with the AR-10, there are different sizes as well, like SR-25. There should be one type of .308 size magazine to make it easier for everyone out there.
There’s a pretty straightforward answer here: the market tends to decide what’s best. Just like M-LOK vs KeyMod, the stronger commercial option usually (but not always) takes the prize. KeyMod is relatively unpopular now, and MLOK has become a virtual standard.
The same principal applies to magazines.
The AICS mags are the most common in bolt action rifles because their design works with more of them. They are narrow and single-stack.
AICS mags were originally designed for the first commercially successful chassis, the Accuracy International Chassis System (AICS). This type of magazine eventually grew in popularity to the point that a large majority of modern bolt action rifles feed from it. All of my modern 700-class rifles feed from detachable AICS style magazines.
The AR-10 magazine is also a bit of a misnomer, as there are several classes of them, with the most widely supported being the SR-25 type. These magazine types were typically the product of one company to start, and then were adapted as other designs flourished.
The most popular eventually became the standard, and the SR-25 magazines are now dominant. This is a double-stack mag that is rarely found in bolt actions, although guns like the Q Fix were designed to use them.
The Mag Well Is What Matters
The design separation between these magazines is based on their exterior dimensions, not necessarily the caliber. The AICS pattern short action magazine is essentially now the standard magazine for most bolt action rifles. This base .308 Win design can feed most .308-based rounds, such as 6.5 Creedmoor, .338 Federal, 22-250, 7mm-08, .243 Win, 450 Bushmaster, and so on.
There are, of course, some small tweaks that may need to be made for specialized rounds, such as in the case with 450 Bushmaster, which has an easy time from metal box magazines, but a harder time with the all-polymer versions due to case geometry. Basically, if you can make it fit in a .308 AICS magazine, it should feed in a .308 size action.
The AICS short action magazine well also accepts special .22LR and rimfire adapted mags, which share the same footprint and can thus use full-size accessories and chassis. The increasingly popular NRL22 sport is seeing constant innovation here.
It should also be noted that specialized magazines exist to allow the .308-size action to feed .223/5.56 rounds, including 300 Blackout. These are fewer available, but I hope to see that change soon.
A big plus of these bolt action mags is that they have the ability to allow for handloaded ammo with longer-than-normal overall length and can easily feed wildcat cartridges and neck-sized brass.
The SR-25 Blues
The AR-10 magazine family isn’t as forgiving as the bolt action AICS and its variants. This is largely due to the fact that a semi-automatic rifle is far more particular than a bolt gun and requires many moving parts to work together to get the gun to cycle reliably.
The end result is a bit more restrictive in terms of the overall length of the cartridge and the type of sizing it has. These semi-auto magazines will, depending on brand, have a hard time feeding with neck-sized brass and won’t feed longer-than-standard length cartridges.
That means if you have almost any semi-auto magazine for the AR-10, the ammo needs to be at (or very close to) factory spec and it shouldn’t vary much.
Why Not One Magazine Type?
I get asked this from time to time as to why someone doesn’t make an AR-10 that takes single stack magazines. I’m sure there is someone out there who does, but there isn’t really much of a need for that at this time. There may come a day when some company sees a need in a “high capacity” ban state, but I don’t see it as applicable right now.
The same goes for bolt actions with AICS mags. Since the AICS is meant as a bolt action mag, it functions great as what it is. The SR-25 mag is wonderful in the Q Fix, but that rifle was designed to use it and isn’t an adaptation of any other design out there. It’s that adaptation where things tend to fall apart, and for other bolt actions to use the SR-25 mag they would need what amounts to a different bolt setup entirely.
Even in the ever-flexible AR-15 platform there are wild magazine variations. The 450 BM functions in an AR as well as the AICS mag and it uses a special mag in the AR, where it uses the standard version in the AICS. The 300 BLK round functions from a 5.56 magazine, but there are improved versions out there that feed it better. Likewise the family of rounds like the 224 Valkyrie need a 6.8 SPC mag to feed correctly.
In the end, the only way you will get to have one shared magazine to rule them all is to set yourself up to do it that way. But if you did that, you’d really be limiting yourself to gun types.
I like what the AICS offers in a bolt action and I like what the SR-25 type offers for a semi-auto and dedicated bolt actions like the Fix. It’s best to play to your strengths and in this case, it’s better to leave well enough alone and accept that there just won’t be just one mag type out there.
Have a question for Josh? Email it to thetruthaboutguns@gmail.com.