Although this is true in Military 7.62/.308 and 30-06 Military brass it is less true with 5.56/223 brass. As a matter of fact most military 5.56 brass has more case capacity then civilian 223 brass.
I know this gets reapeated a lot on here, but I disagree. Mostly because I agree with Speer more than internet people. No offense intended.
I have the loadbooks for several calibres (GREAT investment for any reloader, period). Speer indicates that the loads do not have to be reduced BECAUSE they use IMI brass which is similar to LC. BTW, Speer shows the same load to be 27gr. (and not compressed) using IMI brass. Speer does not show pressures though.
While the difference may be more pronounced (I only use Federal Match right now in 7.62, got a GREAT deal on brass at a gunshow years ago, so I'm not all that sure experience-wise!). The LC brass I do have is much thicker, and I recall LC 7.62 brass being insanely thick.
However, it would seem to me that the difference would be more pronounced in the 5.56 due to the smaller diameter. I studied a lot of math, analysis in particular, so I tend to look at things a little different than the average bear. For fear of dragging this into a urination match, I'll leave all that out.
I don't doubt the load wingman fired was fine. But at 26gr. in military brass, you ARE approaching the max load earlier. Whether or not the difference is pronounced is irrelevant with max loads. That there is a difference at all in the data is very important. Max loads are rationalized to be safe because there is a bit of a safety net, the max loads pressure specs are not REALLY the max. A proof load is, and you only get to fire three of those on average before you blow a barrel.
Now the first proof doesn't blow it, and I think that gives some folks a false sense of security when they load a round and it seems to be fine, when in fact it is over pressure. You could also be firing slightly over pressure loads that aren't dangerous because they are only slightly over pressure but well under the "true max" or proof pressure.
Remember, we all load at our own risk. It is one of the few things like it you can do without the governement over your shoulder. Considering what is involved, and the state of affairs, I'm surprised it is legal at all (and that reason probably has more to do with their ignorance and the lack of media attention to KB's and such). Just don't get lured into a false sense of security.
What I'd really like to see is some kind of test device cheap enough to make that has subcalibre inserts and is used to check pressure only. Ranges could make a killing charging to use it! I'd certainly test every max load I made, in summer and winter.
Every weapon is different, so the data we use is a one size fits all and is usually safe, but max loads are a different story. Just be careful, that is all I'm trying to illustrate.
In the past, 308 PPU Brass produced high pressure with a safe starting load. Faulty Brass. 
