Some people think that any rifle can be improved by slapping an M4 buttstock on it. Got an AK? Slap an M4 stock on it! A 10/22? Slap an M4 stock on it! A converted semi-auto RPD? Slap an M4 stock on it! When it messed with the HK91, this M4 buttstock fetish went a little too far. The HK91 may be an obsolete, overweight, brass-chewing monster that kicks like a mule, but it has earned its place in history. It should be allowed to keep its dignity . . .
An M4 Stock? Really?
The fixed buffer tube of the AR platform has always been one of the weaknesses of Eugene Stoner’s versatile design because it can’t fold for storage or transport. It also makes that annoying ‘clunnnggg’ sound when you fire it with ear protection.
The collapsing M4 stock is an improvement over the original A2 fixed stock for most military purposes, but it’s still not a very good design by modern standards. What? How dare I blaspheme the name of Gene Stoner?
Let me explain: because of the mandatory buffer tube, an AR stock can never fold out of the way. And because of its rear charging handle, the AR can never have an adjustable-height comb for a perfect cheek weld with optics.
Don’t take me for an AR hater: I’ve tested several, I own one, and I’m currently waiting with mounting impatience for my second one to arrive at my FFL.
There are much better options out there if you absolutely must replace an HK stock. But I’m going to tell you, flat out, that you still shouldn’t.
Don’t Mess With The HK
The PTR-91 is a semi-auto version of the German HK91, which was based on the Spanish CETME. The CETME itself was designed after the experimental StG45 shown here. If you think you see a family resemblance from the StG44 all the way forward to the MP5, you’re right.
Internally, all these guns use a roller-locking breech to keep the chamber closed until after the fired bullet has left the muzzle. Externally, they all share a similar stamped-steel receiver construction and humpbacked appearance.
The StG44/45 sired a great family of firearms in the second half of the 20th century, but the line has lost its vigor. The CETME and the HK91 along with their smaller sibling the 5.56mm HK93, are no longer fielded by any major Western armies. The MP5 has served on into the 21st century by virtue of its extreme reliability, but the limitations of the full metal jacket 9x19mm cartridge have become glaringly obvious in the age of battlefield body armor.
The roller-locking design tends to produce exceptionally stiff recoil from full-powered rifle cartridges, and those rifles are also fairly heavy. Civilian shooters love the history around these guns, but hate that their fluted chambers make their once-fired brass unusable for reloading.
It may be functionally obsolete in comparison with the evolved Stoner platform and other newer gas-operated designs, but the HK pattern has earned its place in history. Let’s not do a George Lucas-style hack job on it, trying to make it hip and modern.
If you really need your hard-kicking, brass-chewing battle rifle to wear a collapsible stock, spend a few bills and find a surplus H&K OEM collapsing stock like this one. Is it comfortable? Hell no. Does it give a good cheek weld? Hell no. In fact it doesn’t give any cheek weld.
But it’s part of the history of the rifle, and you definitely wouldn’t shoot any HK91 for its wonderful ergonomics anyway.
Whether or not you like H&K rifles or AR-style stocks, I think we can all agree that this genetically-modified PTR-91 is an abomination in the eyes of Eugene Stoner and Ludwig Vorgrimler alike.