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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.

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