Home Forums Hunting & Shooting AR and Tactical Rifles Case differences - .223 Rem vs 5.56x45 and .308 Win vs 7.62x51

In the last couple years I've picked up about 2000 pieces of once-fired 5.56 brass, mostly PSD and LC, at my local range. It has all been sized and the primer pockets have had the crimp removed and been swaged. A couple months ago I bought some primed LC 7.62x51 pull-down brass form Midway. As yet I have not reloaded any of either type.

In preparation for heading to the range with my newly finished and as yet unfired Aero/Faxon .308 AR10 build, I decided to check my standard handloads in it for fit and function. Most are right at max COL and a couple are a tad over (as in 0.007"). Most barely fit in the Magpul magazines but a couple of the heavies were a few thou too long. In any case, I decided I need to build shorter versions of any I want to use in the AR10.

While pondering the need to develop the shorter loads, I decided to check the variance in case weight for the .223, 5.56, .308 and 7.62x51 brass. Since it is all sized, any variance had to come from case wall thickness. The .223/5.56 results surprised me, as I had always heard 5.56 had thicker walls.

Granted, my sampling was unscientific as I weighed just enough cases to get a feel for the variance for each case type. In some instances that meant weighing 5 or 6 cases and 10 to 12 for others. The 7.62x51 brass was primed so I weighed 10 CCI 200 primers @ 52.0 and divided by 10 to come up with a per primer weight of 5.2. The CCI primer weight may be a tiny bit different than those used by LC but I figured it is close enough for my purposes. The estimated 5.2 primer weight was deducted from the weight of the primed cases in the results shown below.

Here are the results.

.223 =====================
94.4 to 96.7 = WW
96.9 to 99.9 = Hornady
93.6 to 94.2 = Speer Nickel
92.6 to 93.1 = FC Nickel
93.7 to 99.9 = WW Nickel

5.56 =====================
91.1 to 93.9 = FC
92.3 to 93.6 = LC
92.2 to 93.2 = PSD


.308 =====================
154.2 to 156.1 = WW


7.62x51 ==================
179.3 to 181.5 = LC (after 5.2 deduction for primer weight)



That the 7.62x51 cases weighed more was no surprise but 25 grains is a substantial difference, especially when combined with the need for a shorter COL to fit the magazines.

The surprise to me was the .223 cases weighed MORE than the 5.56 cases. Has anyone else noticed this?

I don't see anything in that chart I wouldn't have expected weight wise.

Found in 223WW was touted, it actually had the widest spread.

And that while RP was said to be junk, the nickel RP had one of the least spreads.

And that LC will do everything you want in 223/5.56 unless you intend to shoot benchrest and even then....it might be good enough.

Its been years since I weighed cases though.