.223 vs 5.56

[svtruth]

As I understand it, 5.56 chambers are larger (longer lede) that .223 and that putting 5.56 round in a .223 chamber is a bad idea, while the reverse is fine.
Now doesn't the shorter lede make the .223 inherently more accurate than the 5.56?

 

[gennro]

Read Below.

 

[rcmodel]

Here we go again!

SAAMI MAX allowable pressure for the .223 Rem is 55,000 PSI.
That doesn't mean most of it is though.

5.56 NATO:
M197 HPT (High Pressure Test) is loaded to 70,000 PSI for use as proof loads.
M193 55 grain ball is loaded to 52,000 PSI.
M855 62 grain ball is loaded to 55,000 PSI.

The other thing is, SAAMI set the specs for the .223 Rem.
NATO set the specs for the 5.56 NATO.
But they both measure pressure differently.

This difference in measurement method accounts for upward of 20,000 psi (140 MPa) difference in pressure measurements. This means the NATO EPVAT maximum service pressure of 430 MPa (62,000 psi) for 5.56 mm NATO, is reduced by SAAMI to 55,000 psi (380 MPa) for .223 Remington.[18] In contrast to SAAMI, the other main civil standards organization, C.I.P. defines the maximum service and proof test pressures of the .223 Remington cartridge equal to the 5.56 mm NATO.

In actual fact, nobody I ever heard of in the last 40 years has had a problem.
There was an actual known problem back then with people tried shooting GI M193 ammo in Remington 40X benchrest & varmint rifles.

The Remington 40X always had minimum spec .223 chambers & barrels, and people were getting loose primer pockets.
But nothing blew up.

rc

 

[oldpapps]

Well said RC.

 

[svtruth]

Thanks, RC you are always a font of knowledge.
I've noticed, you never hear about .223s blowing up even though it seems theoretically possible. Maybe mfrs make the .223 actions strong enough, knowing eventually some one will put 5.56 in a .223 chamber.
But back to the original Q, is the 5.56 chamber inherently less accurate than the .223?

 

[rcmodel]

For ultimate gilt-edge benchrest accuracy it is.

But there are some awfully accurate match & varmint AR-15's chambered in 5.56.

In the grand scheme of things, a lot of other details influence accuracy much more then the chamber.

Take the quality of the barrel itself for instance.
A sub-standard barrel chambered in .223 will never be as accurate as a great barrel chambered in 5.56 NATO.

rc