Over the Columbus Day holiday, I took my new M&P-15 (along with a Savage Axis on which I installed a red dot sight) to my family's farm in Arkansas to get everything sighted in. I also took about 200 rounds of reloads with various bullets and powders along with my chronograph. I intended to collect a lot of data about the performance of the various rounds coming out of both rifles.

The chronograph was bolted to the top of a sawhorse about seven yards from my firing position. The target was a standard sighting-in target from the National Shooting Sports Foundation and was positioned about fifteen yards from the firing position.

The first round from the Savage (50 grain soft point on top of 19.5 grains of IMR-4198) generated enough muzzle blast that the 30 year-old yellowed plastic of the chronographs sky screens vaporized so no velocity data was recorded. Strangely enough, even without the sky screens, the chronograph would recognize and record rounds from a 9mm Parabellum pistol, but no such luck with .223 Remington.

Since this is a forum on the S&W M&P-15, I'll skip any further mention of the Savage. On the S&W, I started with 10 rounds of American Eagle 55 grain FMJ factory ammunition from the Magpul P-Mag that S&W supplied with the rifle. I used factory ammunition and the factory-supplied magazine to start with to eliminate my reloads should there have been a problem with the rifle. There were none. It took most of the first 10 rounds to get the point of impact even falling on the backdrop for the target.

Once the 10 factory rounds were expended, I switched to reloads (22.0 grains IMR-3031 under a 55 grain FMJ bullet in LC78 brass) fired out of third party aluminum or steel magazines. I used these rounds to obtain a group and then move that group beneath the point of aim. The front sight required much more adjustment than I would have expected to move the point of impact up to the point of aim, but in the end I got there.

I then moved the target out to 100 yards and fired five-round strings from the following loadings:

• 23.2 grains IMR-3031, 45 grain SP, LC80 brass
• 23.2 grains IMR-3031, 50 grain SP, LC80 brass
• 25.0 grains WW-748, 60 grain SP, TW73 brass
• 20.3 grains IMR-4198, 60 grain HP, LC74 brass [See note]

All of these rounds functioned as if they were interchangeable out to 100 yards, which is as far as I shot. Near the end of the day, the targets were blown off their backing board and so are no longer available.

I was very impressed by the performance of the M&P-15. It was accurate, repeatable and it functioned flawlessly with any combination of bullet and powder I fed it from any of three different magazines.

[Note] This load was assembled in November 1982 per data from the Hornady Manual 4th Edition. It was below the maximum load in that manual. Other manuals, including later editions of the Hornady Manual, list this as in excess of a maximum loading. You should always follow current published data.

If you look at older reloading manuals you will see almost across the board that the max listings have been lowered. This happened after the lawyers got involved because the shooter might be shooting the ammo in a older gun not up to the current standards.

The .223 was was originally developed in 1957 by Eugene Stoner, who was working at Armalite, and Remington. It was first officially chambered by Remington in 1959, not exactly prehistoric times.

The most likely reason for older data to have a higher max than in current manuals is that most of the companies derived data very much like current reloaders do; case head expansion, bolt lift, primer appearance, etc. Not exactly reliable ways to measure pressure. This progressed through "copper units of pressure" where the compression of a copper cylinder in a specialized receiver during the the firing cycle was measured and compared to a standard.

The current gold standard for measuring pressure is PSI measured with a transducer. The position of the transducer is defined by SAAMI. It is noteworthy that the .gov measures pressure at a different position on the case. This accounts for at least some of the difference between NATO and SAAMI specifications, although NATO is higher due to the chamber leade in NATO chambered rifles.