When I first got into the gun thing, it became apparent that there would be certain topics of discussion that would always create controversy. The most obvious examples include GLOCK vs. 1911, .45 vs. 9 mm, large caliber/slow bullets vs. zippy/small caliber bullets, AR vs. AK. You get the idea One of those points of contention that’s firmly rooted in the gun world is direct impingement vs. piston driven. Both have pros and cons, and within the piston discussion, you can even discuss short stroke vs. long stroke systems. The whole thing can be quite confusing . . .
opinions seem to be firmly rooted. But, if you’re a gunny who counts yourself interested in converting your DI gun of choice to a piston system, Osprey Defense has a solution for you.
Osprey’s kit comes attractively packaged in a cardboard tube that includes the necessary retrofit parts along with replacement two piece hand guards for your typical milspec M4gery or M16 style rifle. Osprey makes some bold claims on their website and in their incredibly detailed white paper. The big ones that hop off the screen:
• 4 Minute Install
• 13X Increased Reliability
• Semi-Auto or Full Auto
• Suppressed or Unsuppressed
• Will Outlive Your AR15/M16/M4
• True Drop-In Solution
• No Permanent Gun Modifications
• No Valves/Screws/Springs
• 5 Year Warranty
• 100% Made in U.S.A.
Several of these claims could not be put to the test. Namely, the 13X reliability number, full auto (damn you, NFA), suppressed, outliving my gun, or the warranty. What I was able to test with relative ease was the install time (spoiler: it doesn’t take four minutes), and some minor function testing. But first, let’s talk about how this retrofit works.
Nick gladly handed over his MEAN Arms AR as the donor rifle for this project. The MEAN gun is about as M4gery as it gets, sporting a two-piece plastic hand guard, A2 style gas block/front sight combo, and a carbine-length gas system.
Nick assured me that I was receiving an utterly reliable gun, but I don’t trust him now that he’s skinny, so I took it to the range and burned through about 100 rounds of mixed 5.56 and .223. As promised, the gun was utterly reliable. And as with any DI gun, it was filthy by the time I finished. I gave it a thorough scrubbbing, and then took it to the laboratory for retrofit.
As a short stroke system, the Osprey kit has a small kidney shaped chamber of sorts that is pinned to the gas block. A similarly shaped piston slides inside that chamber and is connected to a rod that acts on the retrofit bolt carrier that ships with the Osprey system. The firing cycle, instead of blowing hot gas and carbon inside the action, acts to move the piston a few inches. This sharp tap is enough to send the bolt carrier back, completing the cycle.
Installation of the Osprey system might take 4 minutes for an experienced armorer all hopped up on Red Bull with an endless loop of speed metal playing in the background. For a more sedate, whiskey sipping Texan listening to Bob Dylan, this install took roughly a half hour, or the duration of Highway 61 Revisited. To complete the install yourself, you’ll need a nice set of punches like the ones supplied in the Geissele Armorer’s Kit along with some way to immobilize the front sight. Various places sell a Delrin block for that sort of thing, but I’ve always gotten by with a few 2x4s and a strong bench vise.
The first order of business of course is to check that the gun is empty and safe. Once that’s done, remove the upper from the lower. Set the lower aside. Take a sip of scotch. Then remove the bolt carrier group and the two piece hand guard. At that point, you’re free to remove the pin that holds the old gas tube in place. Remove the gas tube. I used this opportunity to run a brush and some solvent through the gas block, but you really don’t have to.
Once the old parts are cleared out, pin the chamber in place. This part stays permanently connected to the gas block, and the attachment point seems to be fairly solid. The next order of business is to finagle the piston, rod, and receiver bushing into place. This was easily the most time-consuming part of the whole install as everything seemed to be a very tight fit.
I finally ended up sliding the rod all the way into the receiver sans bushing, assembled the piston parts, and then delicately put everything back into place. Once it is all lined up, pin the whole thing with the retaining clip. This whole system can be disassembled at a later date for cleaning, but the manual indicated that it would be several thousand rounds before that might need to happen.
The last step is to reinstall the hand guard. The Osprey kit ships with two clamshell pieces, and in the interest of a thorough review, I used those. They appeared to be identical to the pieces that came off the donor rifle.
One of the things that piqued my curiosity about this system was weight. One of the major detractors of a piston system to those high speed/low drag operators who care about such things is that a piston driven gun automatically weighs 40 pounds more. Obviously, your everyday mall ninja can’t be expected to hump that much weight around and still be operationally efficient, so the DI system is better. Or so I hear.
In the world of science and reality, I found that the Osprey system added a whopping 3.15 oz. My trusty scale used above says that 8 rounds of Federal XM 193 weighs 3.25 oz. Use that as a reference point for decision making. Personally, I find 3 oz to be fairly trivial in the grand scheme of things, but I’m more of a half speed, standard drag kind of operator.
Tier 1 Operators might also be asking themselves if they can use a free float rail with this system. Nothing on the Osprey website confirms that you can use a free float hand guard but several threads on AR15.com here and here seem to indicate that Midwest Industries and Seekins Precision make free float rails that will be compatible with the piston system from Osprey.
Ultimately, this sort of retrofit is all about the reliability, baby and the Osprey kit didn’t disappoint. I ran 250 rounds of mixed .223 REM and 5.56 through it. And I truly mean mixed. Every time I go to the range, or a I clean out the shop, I inevitably end up with loose rounds. I throw them in a bag and keep them for gun tests exactly like this one. The sack contained all manner of high power, low power, hollow point, FMJ, as well as clean and dirty rounds.
The MEAN gun fired all 250 without a hiccup. I ran it until the fancy new hand guard smoked and never got it to choke. So I handed it back over to Nick who had a Bump Fire stock to test. That’s it in the embedded video, above. And as you can see, the operator failed before the gun did. With 250+ rounds down the tube, I feel confident saying that reliability will certainly not be impacted by the addition of the Osprey kit.
Specifications: Osprey Piston Kit
- Steel, black oxide finish.
- Handguard – Reinforced polymer composite, black.
- Kit includes preassembled piston assembly, bolt carrier, handguard, and instructions.
- Carbine kit fits 11½” to 16″ barrels with .875″ O.D. or smaller, and carbine-length gas system.
- Rifle kit fits 20″ barrels with .875″ or smaller O.D. and rifle-length gas system.
- Price: $299
Ratings (out of five stars):
Fit and Finish * * * * *
All of the parts fit together well and showed the high quality finish you’d expect in a $300 item.
Reliability * * * * *
I put 250 rounds into it. Leghorn is putting a lot more through and neither of us have experienced any failures related to the piston kit
Cleanliness * * * * *
As a piston kit is want to do, it kept the guts of the MEAN gun completely clean. After 250 rounds, I soaked a Q-tip in KG1 and ran it through the receiver. I came away with a slightly oily swab and that’s about it.
Overall * * * * *
I’ve never been so bothered by a rigorous cleaning schedule that I’ve felt compelled to make the switch to a piston-driven AR. But if I ever change my tune and I want to retrofit a gun I already have a significant investment in, I’d be hard-pressed to find a better kit than the offering from Osprey. It was relatively easy to install, it kept the action clean, and ended up displaying an unfailing level of reliability. You really can’t ask for much more than that.