I have resisted buying a semi-auto centerfire rifle for a long time. I have bolt and lever guns. I have very unpopularly (among most gun folks) expressed my belief that a 30 round magazine isn’t necessary for hunting or self defense. Well, after months of scarcity because of Covid panic-buying, I ran into a entry-level AR at my LGS and the hoarder in me made an impulse purchase.I walked out of there with a new Ruger MPR in 5.56/.223 for $769. It has an 18” 1:8 barrel, a 15” Magpul MLOC handguard with a full length top rail, one 30 round P-Mag and no sights. I installed a Sightmark 1-4x24 optic on it.I have had zero malfunctions with this rifle through 174 rounds fired. The spent brass barely had a mark on it. The trigger is Ruger’s upgraded two-stage. I didn’t notice it much during my tests. I think it has about a 4 lb. pull weight. Nothing about it distracted me from my target. It’s not competition grade for sure but not bad at all for an off the shelf rifle.
After a modest barrel break-in of cleaning between single shots, I began load development with 69 grain Sierra Match Kings that I had already. I bought new PPU brass. It was all I could find besides Lapua which I didn’t want to run through a semi-auto. I used FGMM primers and 3 different powders - Varget, N140, and N135. I seated all rounds to 2.255 to fit in a magazine. I used my .223 LFCD for the first time ever to apply a light crimp to each round out of an abundance of caution with a semi-auto.
I loaded 5 rounds each of ten different charges with each powder, starting at a consensus minimum charge and increasing in .2 grain increments. My chronograph is on the fritz so I looked for pressure signs on each primer. I saw none up to 23.5 grains of N135, 25.5 grains of N140, and 26.0 grains of Varget.
With Sierra’s 69 grain Match King:
Max charge of N135 is 23.8 in VV’s published data. Sierra’s data stops at 22.5.
Max charge of N140 is 25.9 in VV’s published data. Sierra’s data stops at 25.1.
Max charge of Varget is 26.1 in Sierra’s data and 26.0 in Hodgdon’s.
My best groups with each powder were with 22.7 grains N135, 24.7 grains N140, and 24.8 grains of Varget. Tests were shot off a Caldwell Tackdriver bag @ 50 yards with 4x magnification. Take the results for what they’re worth. I put the crosshairs on the black dot and pulled the trigger. I wasn’t terribly slow or careful. I’m confident that the winners of each powder test will meet or exceed my accuracy expectations for this thing. They will probably stay around 1 MOA out to a couple hundred yards. I’ll load some of each and go find out when it’s not 100+ degrees outside.
*Obviously each gun is different. Please consult published data and work up slowly from minimum charge. “Some guy online” is a decidedly unreliable load data source. Still, it’s always interesting to see what loads others find that work for them. I hope my results are interesting and informative to someone.
69 grain SMK
PPU brass trimmed to 1.750
FGMM SRP
2.255 COL
Light LFC
22.7 grains N135 2620 fps*
24.7 grains N140 2700 fps*
24.8 grains Varget 2690 fps*
*Velocity estimates according to Sierra’s data.
Temperature: 100 degrees but gun and ammo stayed in the shade so....90 ish? I may need to bump up the charge a couple tenths on the VV powders to get the same velocity when it cools off outside.
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