223 Brass

[Danth]

Picked up some 223 brass on the range today. One case was marked "Win USA, 223 Rem". Another was marked "Win USA, 5,56 MM". What's the difference? Why the different marking?

[1blue]

If your rifle is marked as 5.56, you can shoot either 223 or 5.56. If your rifle is marked as 223 then you should only shoot 223. 5.56 is a hotter round and should not be used in a 223 rifle.

[Happyguy]

Unless you have a 223 Wylde chamber then you can shoot either.

[DeanoBeanCounter]

The 5.56 (made for military) has a smaller and/or crimped primer. You need a reamer to open the primer pocket to reload. You can get the tool at your local gun store. I have used a variable speed drill, put the shell in mouth first, tighten the chuck just enough to hold the shell still, and you can clean the well right out. It's a good idea to check all the shells.
Dean

[rodnocker1]

FWIW, Both use the same size primers although the 5.56 MAY use a harder Primer. I've found and reloaded both of those headstamps and I use CCI #41 Arsenal primers for all of my small rifle primer reloads (whether it's .223/300 blk/whatever), mainly because years ago I bought an "ample" supply of them for $17.00 a thousand. I used to use a Dillon Super Swage to swage out the primer crimps rather than removing any material by using a countersink tool like a lot of people do but to each his own. I only reload Winchester .223 brass now and I just tumble and resize the brass, then use a Lee hand primer without removing crimps. I'm NOT recommending that anyone else do it this way but it works for me and I've prepped and primed LITERALLY tens of thousands of pieces of rifle and pistol brass.
I have noticed that since Winchester took over the Contract at the Lake City Ammunition Plant, they are now putting out ammo with the headstamp- "LC" ".223 Rem" but I don't reload it even though I know it's manufactured by Winchester.....(I'm just a "tad" OCD, LOL!).

[Danth]

Ok, I understand "223" marked rifles should not shoot "5,56" ammo, but why not? Higher pressure? If so, why: hotter loads, smaller internal case capacity?

[Happyguy]

The 5.56 specifications for size and pressure are slightly longer and higher. You can resize 5.56 brass in a 223 die and use it in marked 223 barrels. Factory 5.56 should not be shot in 223 barrels, can you yes you can and you may not have any issues but that is a big if. 223 Wylde chambers have a longer throat allowing a decrease of pressure when shooting the 5.56 in the 223 Wylde barrel. I hope that helps.

[rodnocker1]

Here's the best explanation I know of : https://www.thetruthaboutguns.com/5-56-vs-223/
Looking at the posted Ballistics on Winchester's site, it does show that their 5.56mm 55 gr ammo (except for M193) appears to be loaded a "Tad" hotter than their .223 Rem by about 30 FPS @ the muzzle but they don't really say WHAT chamber each round was shot out of. I've always heard that the .223 chamber is "tighter" than a 5.56 whereas a .223 Wylde chamber is "looser" and allows you to shoot either. I don't have any .223 chambered rifles, mine are 5.56 so it's not really a concern to me.
ETA: Happy, you posted while I was typing, LOL!

[Danth]

Ahhh. Thanks Guys. Great explanations.