Ruger AR-556 in 5.56 NATO Part II

09/27/2020
At McDonald’s, suggestive selling is, “Would you like fries with that quarter pounder?”. Another form of suggestive selling is pulling up at a customer’s house with a flatbed trailer to drop off a new snow blower, that is sharing space with a bright red, brand new,  Massey Ferguson sub compact tractor… bucket loader and back hoe attached. Fortunately, my wife was with me, to remind me I did not farm, I had no plans for woodland clearing and I had not yet talked or worn the new off of the bright yellow snow blower. OK, there is that, but…

Lunch time conservation was not as rewarding as might be expected, even though it was my day to pick the discussion topics. “Snow blowers; yellow or orange?”, “Snow blowers; electric start or manual?” “Snow blowers; two stage or three?”, “Snow blowers; why is the new snow blower so damn good looking?”. The crowd thinned after the electric/manual start method question until only my wife remained, but I noticed she was playing Yahtzee on her iPhone. So I went out to the garage, fired up the snow blower… manual start, and took a few laps on the driveway.

And then there are other toys…

The purpose a firearm serves is determined by circumstances and the hands that hold it. There is no doubt in my mind that the Ruger AR-556MRP is exceptionally good at providing security and defense. There is no doubt in my mind that the Ruger AR-556 can put food on a table up through deer size game.There is, however, also no doubt in my mind that the Ruger AR-556 can provide days on end of recreational target shooting and an outlet for mad scientist handloaders that are always working toward the unattainable, optimal round. No doubt, another centerpiece for many lunch time conversations.

Above, 223 Rem brass next to 308 Win cartridge for the sake of comparison. One of the reasons stated in Part I for selection of the Ruger AR-556 in 5.56 NATO is the rounds light weight and compact size. That is over one hundred casings in that small bin, not much more than a pocket full, but more than three 30 round magazines full.

The brass used within this project were all Winchester, once fired, sonic and walnut medium cleaned, full length sized, trimmed, and chamfered. RCBS small base dies were used with crimping done with a Lee collet crimping die. Why? I shoot a good deal with a silencer in place, which makes for chamber carbon residue. Small base dies are a way to ease the burden on autoloader cycling. Is this necessary? No. I am just overly cautious. A batch reloading process was employed and all charges were individually weighed.

Small magnum rifle primers were used across the board. In days past, while running pressure tests with a universal receiver and conformal transducer gear, magnum primers created a slightly higher initial pressure, with negligible impact on average pressure and with a shot to shot pressure consistency much like that of bench rest primers. So…

Smokeless powder selection

There are some similarities in powder characteristics and it may very well be that two different branded containers may contain the exact same powder. See discussions related to Hodgdon H414 vs Win 760. My perspective is that while reloaders may deem powders to be the same and load accordingly, manufacturers are not held to those performance standards. Subsequently shifts in vendors, locations of processing facilities, additives, and specific powder composition can vary. In fact, where powders may be suspected as being the same, and charges are the same, velocity differs significantly. But then you know that because you pay attention to those product cautions and you are a safe handloader. So a reference to a powder types here is literal as indicated.

The Ruger AR-556 MPR was shot with and without silencer. Soot, smudges and scope optic flushing became the earmarks of the former as is always the case. In both configurations, functional reliability was absolute, with one exception.

The AR-556 was quite quiet even in the presence of a clacking action and diminutive sonic boom. However, there is no way to hang a silencer on a firearm and not offer at least one subsonic listing.

In this case, the 55 grain load produced a very consistent 1,100 fps result, which should have been marginal as a subsonic round, but in fact was exceptionally quiet. However, no effort was made to accommodate this round by reconfiguring the AR-556 or silencer mounting, so it performed reliably, but did not cycle the action.

I intended to pick nits with Ruger until I receive a rational explanation as to why a 223 Rem AR has an AR barrel length of 16.1″ and a 300 Blackout barrel length is listed as 16.38″. My working theory is that this length is determined by the barrel’s taper and at what length the muzzle is the right diameter, by caliber, to accept threads, sight bands or whatever else is to be done at the barrel end.Yes, I do know what nominal length means, but that does not explain the differences. What does this have to do with anything? Not a thing.

And then there were nine…

Joe, why the hodgepodge of bullets? Ruger indicates that the Ruger AR-556 1:8″ 5R rifling will accurately handle bullet weights from 35 grain to 77 grains. Yes, Ruger is rifle with engineers, but why would you say that? If they had said 75 grains or 80 grains I would have left it alone and moved on to other areas, but that “77” stuck with me and I had to explore. If I got to 78 or even 80 grains, what would happen?

So the stubbiest 35 grain bullets were selected from 22 Hornet bullet inventory, and a couple of heavyweight and very long match bullets (A-Max since displaced by ELD product) from a quick twist 22-250 Rem bullet inventory, knowing that if a marketing claim scandal were to be uncovered, this would flush it out.

Warning: Bullet selections are specific, and loads are not valid with substitutions of different bullets of the same weight. Variations in bullet length will alter net case capacity,  pressure and velocity. Primer selection is specific and primer types are not interchangeable. These are maximum loads in my firearms and may be excessive in others. All loads should be reduced by 5% as a starting point for development where cartridges have greater than 40 grains in capacity and 10% for cartridges with less than 40 grain capacity following safe handloading practices as represented in established mainstream reloading manuals. Presentation of these loads does not constitute a solicitation for their use, nor a recommendation.