They got a list of calibers I'd be interested in reviewing and a few weeks later I had a box of three different .223 loads sitting on my front porch. There was one box each of Remington UMC 55gr MC, PMC Bronze 55gr FMJBT, and Sellier&Bellot 55gr JSPBT.
Life got busy for a while (in truth, it's still busy), but I finally had a confluence of time, weather, and health sufficient to get to the range to take care of this.
I added a box of my own plinking ammo - American Eagle (Federal) 55gr FMJBT - just for comparison's sake.
All testing was done with my AR-pattern rifle, which is a 20" A2, stainless 1/8" HBAR, with a (tight) .223 chamber, with a rough battle zero (0-300 with no adjustment). I used a front rest only and shot from the bench. It was approximately 11am, temps were in the upper 70s, and wind was varying 5-to-15mph, gusting slightly higher, from about 10-11 o'clock.
I started by running one short magazine (5 rounds) of 45gr JHP at 25m to check zero and foul the barrel. This was the result:
Two inches low (8MOA) from center and 1/2" left (2MOA), 3MOA group. As a battle zero, this is quite acceptable and the group met my standards. (Which are low, but I do have them!)
Following that, I ran five rounds from each box through, at a rifleman's cadence, and allowed a few minutes between each group for the barrel to cool. This was how things came out (again, 25m):
Aim points were the *outside* corners of the large black square, and groups are located accordingly.
Top right: American Eagle, 4MOA left, 12MOA low, 7MOA group.
Top left: PMC Bronze, center windage, 6MOA low, 6MOA group.
Bottom left: Sellier & Bellot, center windage, 4MOA low, 5MOA group.
Bottom right: Remington UMC, 4MOA left, 4MOA low, 4MOA group.
I *should* have made a windage adjustment to my sights and gone about 3-4MOA right, but chose to not fiddle with it.
From there, I moved the target back to 100m and swapped to shoot'n'see targets (which are something of a misnomer, cuz I can't see hits at 100m). I shot ten rounds at each target, at cadence.
Top right: American Eagle, 3MOA left, 1MOA high, 6MOA group. (Possible breathing issue, the group is 3MOA wide and 6MOA tall.)
Top left: PMC Bronze, 2MOA left, zero elevation, 4MOA group.
Bottom left: Sellier & Bellot, 2.5MOA left, 2MOA high, 6MOA group. (Again, possible breathing issue?)
Bottom right: Remington UMC, 4MOA left, 3MOA high, 4MOA group.
From *there*, I had five rounds of each type left and decided to stretch out a little bit. My club has an 18" steel at the far end of the range - 250m and slightly uphill. It's visible in the top left corner of this picture:
I found that my front sight (a KNS hooded reticle) completely obscures the plate at 250m, but good hits were entirely possible by simply making sure the target was hidden.
American Eagle: 2/5
PMC Bronze: 3/5
Sellier & Bellot: 1/5
Remington UMC: 2/5
There were no failures of any kind from any of the ammo - good feeding, ejection, and ignition on everything. If there were going to be issues, this would be the rifle to show them. It's ripped the rim off steel-cased stuff more than once (requiring a dammit stick to remove the spent case) and has blown primers when I unintentionally put in a magazine of 5.56x45.
There were a few things of note, aside from the shooting characteristics. Remington tends to wildly over-package their ammo, in a rack that holds each round separate and immobile. Probably overkill for plinking ammo, but the racks are great if you handload precision rounds and want to keep them from rattling around. S&B and Federal both use a small plastic divider to keep rounds lined up, which works well but may allow minor contact between cartridges.
PMC doesn't use any divider, which results in things like this, which is what I saw when I opened the box:
19 rounds. Where's 20? Buried sideways between the rows of bullets.
Of particular note on the Sellier & Bellot: the box is labelled .223, but the brass is headstamped 5.56x45.
I decided to shoot the ammo anyway, and checked the brass for pressure signs after the first few rounds. The primers appeared to be on the verge of cratering, but otherwise there were no signs of issues - no blown primer, no pierced primer, nothing.
I pulled out a few pieces of the S&B brass and a couple pieces of known .223 when I got home and checked water capacity; they were all within a tenth or two of 30gr water capacity. I can only assume the brass isn't stamped properly and wouldn't hesitate to use it again.
As far as accuracy goes, any of these would be perfectly acceptable as a plinking or practice round, with a slight nod to the Remington UMC or PMC Bronze. There is some question about the effectiveness of lighter rounds (namely, the 45gr I started with) in higher-twist-rate barrels. At least at the 25m I started at, that doesn't appear to be an issue - although some would argue that a 1/8" rate is not a faster rate.
Your best bet for finding a good practice ammo, of course, is to buy a few boxes and test it out.