AR question, Is it ok to put 223 rem bolt in Yankee Hill Mil spec upper reciever?

[capt.hollis]

I have a 223 rem bolt carrier assembly, and I put it in a mil spec 5.56 Yankee Hill Upper reciever, or should I go with mil spec 5.56 bolt carrier assembly? This is my first AR build, and I'm scared of doing something wrong here. I finished the gun myself from scratch, but I havent shot it yet. I stayed with 223 ammo just to be sure. Is it safe to shoot 5.56 in the 223 bolt assem, and if I did put the 5.56 bolt I guess itd be fine to shoot 223 in it?
Thank You Guys, Yall are always a great help to us newbies.

 

[rcmodel]

There is no difference between the .223 & 5.56 except the way the chamber is cut in the barrel.

Bolt faces, extractors, and all that are identical.

Only suggestion I might have is:
If you have a brand new barrel extension in the upper, and an old used bolt out of another gun, it might be wise to replace the bolt with a new one and start wearing them in (or out) together so the locking lugs match the new wear patterns.

rc

 

[capt.hollis]

Thank You RC.

 

[aminyard]

And the fact that the 5.56 is rated for ~30% higher pressures.

 

[rcmodel]

And the fact that the 5.56 is rated for ~30% higher pressures.

No, they are not.
SAAMI MAX allowable pressure for the .223 Rem is 55,000 PSI.
That doesn't mean most of it is though.

An increase of 30% would be 71,500 PSI.
And no 5.56 NATO round was ever loaded to that pressure.
Except perhaps M197 HPT (High Pressure Test) 70,000 PSI proof loads.

M193 is loaded to 52,000 PSI.
M855 is loaded to 55,000 PSI

But it doesn't change the fact there is NO differance in the AR-15 internal parts for either caliber.

The only differance in an AR-15 between a .223 & 5.56 is which chamber is cut in the barrel, and probably the twist rate, but not always.

rc

 

[aminyard]

My bad (at my age relying on memory is not a good idea). The SAMMI spec for .223 is 55.000 cup, whiale the .56 spec is 62,000 cup, a still siggnificant differences, In addition there are very significant differances in the specs for the chamber (longer lead, sharper shoulder, etc.) SAMMI lists the 5.56 in a .223 rifle as a dangerous loading.

 

[rcmodel]

Yes they do say it is dangerous.
But they don't list pressure in CUP.
They actually list in MAP or Maximum Average Pressure, measured in PSI.
SAAMI does not have a standard for 5.56 NATO ammo.

And the military & NATO measures pressure in a different location then SAAMI.

This from Wackipeedia, which in this case is accurate:

The piezoelectric sensors or transducers NATO and SAAMI use to conduct the actual pressure measurements also differ. 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.

But it is not the pressure that is dangerous.

It is shooting a long military bullet like M856 Tracer in a tighter chambered short leade .223 chamber.

rc

 

[capt.hollis]

so to go safe , put the 5.56 bolt in the 5.56 mil spec upper reciever, that way you can shoot both 5.56, and 223 rounds safely?
Just asking guys incase I come across some 5.56 on the cheap side for plinking.
Thanks

 

[rcmodel]

Once again, there is NO difference between a .223 bolt and a 5.56 NATO bolt.
They are both the same thing as far as rifle bolts go.

If your barrel is marked 5.56 it is safe to shoot 5.56 ammo in it, regardless of what the bolt came out of.

What I recommended in the 2nd post was to replace the old worn bolt with a new bolt to go with the new upper, so the locking lugs can mate together equally from the get-go.

rc

 

[aminyard]

RC

Please do NOT post the picture of your face after half of it is blown off

 

[rcmodel]

I'll be sure not too.

Why don't you post picks of a .223 bolt and a 5.56 NATO bolt so we can see the differance!

rc

 

[barnetmill]

I assume headspacing must still be checked with any bolt change.

 

[rcmodel]

Yes, it should be.
But many people don't bother.

rc

 

[capt.hollis]

Thanks for the input Rc..