HECKLER AND KOCH
By not using the SR25 pattern, the HK417 magazine is more stoutly built than other polymer AR-10 magazines. More importantly, it has a far better feed geometry. At $85 each for both the 20and 10-round versions, the HK417 magazines are a bit expensive for polymer magazines.
It seems odd that when Heckler & Koch (HK) came out with its HK417—an essentially piston-driven AR-10—it chose not to use the SR25 pattern magazine with it. Instead, HK elected to use its own magazine design that was developed from the polymer magazine of its smaller HK416. This, itself, was based on the proven G36 magazine that has been in service with the German military since the early 1990s.
While it’s not compatible with other large-receiver AR variants, the HK417 polymer magazine fixed two main issues with the SR25 pattern magazine: the feed geometry and magwell size limitation. For the first of those, a former KAC engineer told me that Eugene Stoner knew about the original AR-10 magazine having a bad feeding geometry. When the cartridge is pushed out by the forward moving bolt, it first dives down before it comes back up again.
When Stoner was developing what became known as the SR-25 for KAC, he wanted to create a new magazine for it. However, Reed Knight overruled him, because it was cheaper to just use the existing original AR-10 magazine—but with modifications to the mag-catch cut and the feed lips. That set the pattern for all the modern large-receiver AR magazines; and, because of that, they all carry the same feeding geometry defect with various degrees of remediation and improvements. That’s why HK eliminated that problem completely by using a new magazine design that has a straight feeding geometry.
The other advantage of not using the SR25 magazine pattern is that it allows HK to have a better magwell design on the receiver. Because of this, the HK417 polymer magazine features thicker side walls, reinforcement ribs and an embedded stainless steel support at the front to prevent bullet tip pitting.
So, how would HK challenge the SR25 magazine pattern in the near future? Well, recently, the U.S. Army announced it would be adopting a variant of the HK417 as the M110A1 CSASS (Compact Semi-Automatic Sniper System) to replace its existing KAC SR-25-based M110 SASS.
The U.S. Marine Corps would certainty follow this, because it is also a user of the M110 SASS. Additionally, it already had another HK weapon in service—the smaller HK416-based M27 Infantry Automatic Rifle in 5.56mm.
Once gun makers see the advantage of the HK magazine (and the military adoption would help influence this, too), there’s a good chance we might start seeing other makers use the HK417 magazine.