5.56/5.45 Interchangeable?

[servantofinari]

Can you put a 5.56 bullet in a 5.45x 39mm case and get it to work in a 5.45 caliber weapon? it's only a .11 mm difference. that's what? the width of a piece of paper?

 

[bobotech]

NO.

The 5.45x39 barrel is smaller diameter than a 5.56x45 diameter barrel.

If you do the opposite (put a 5.45x39 bullet into a 5.56x45 bore), you will get keyholeing like crazy.

If you do what you said, you could create seriously high pressure problems which could be quite dangerous.

 

[Sport45]

If you do what you said, you could create seriously high pressure problems which could be quite dangerous.

I doubt it would even chamber with the neck expanded to fit around a .224" bullet. But if it did bobotech is right. You could get obscenely high pressure as you try to swage the bullet into the smaller bore.