I have short arms for my size. They aren't quite Tyrannosaurus arms, but they are an inch or two shy of average. This coupled with the fact I was shooting an AR-15 with a 30 round magazine meant I couldn't get my elbow in a position directly beneath the rifle. The magazine protruded far enough down that it was in the way.
The standard capacity magazine for the AR-15 is 30 rounds. There are magazines that hold more and magazines that hold less, but the bulk of magazines in the market today are 30 rounders. There was a time that 20 round magazines were more common, but even they tend to be a niche product today.
In an attempt to help, I drug out all the different magazines I've collected over the years and measured them. By looking at them, you may be better able to select a magazine that best fits you for shooting prone, or even from a bench. I've round 30 rounders can be in the way when shooting from a bench as well. Anyway, here are the measurements.
|Unknown||Steel, straight||20 round||5.25”|
|Master Moulder||Plastic, straight||20 round||4.75”|
|Bushmaster||Aluminum, straight||10 round||4.5”|
|C-Products||Aluminum, straight||10 round||3.5”|
|C-Products||Aluminum, straight||5 round||3.5”|
|Unknown||Aluminum, straight||5 round||3”|
|Kel-Tec||Plastic, straight||5 round||2.75”|
Notice the plastic mags in general are about a quarter inch longer than metal magazines of a given capacity. Also notice that the C-Products 5 and 10 round magazines are the same length, as they use the same magazine body for both. Lastly, don't take the fact that I measured a Master Moulder mag to think I'm endorsing them. They are crap, no one should buy them. I bought 2 for a couple bucks each just to play around with them. They are as bad as people say.