Necking 223 ammo for semi autos

[1hotrod]

I am going to reload 223 for my ar15, and I've read a lot of articles about necking your ammo in bolt actions.

Now what is the story about necking 223 for a semi auto? Is it bad or good? The Sierra reloading manual says not to do it, but doesn't give an explanation.

Thanks for the high insight.

[.22guy]

For any auto-loading gun you need to full length size and not neck size. It has to do with chamber dimensions and feeding, I believe.

Full length sizing works the brass more, which wears it out faster, but it has to be done for semis. And watch your case lengths. Hope this helps.

[dustoff31]

In reloading there are two resizing operations. Neck resizing and full length resizing. Neck sizing only resizes the part of the case that holds the bullet, whereas full length resizing resizes the neck and the entire length of the case.

In a bolt action, if you reload the same brass and fire it in the same rifle you can generally get by with neck sizing only, as the case expands to fit that particular chamber. This is also true of semi-autos to some extent.

Full length resizing, which neck sizes in the same operation, is always advisable when reloading for semi-autos. This is due to minor chamber size differences from rifle to rifle and in this case, minor differences in case dimensions between .223 and 5.56mm. If three of us have a 5.56mm rifle, a neck sized case might fit yours, have trouble in mine, and not even go in on his.

[1hotrod]

OIC,

I didn't realized the full length die and the small base dies did any necking. I thought necking was a separate process. Now, it makes total sense now.

Thanks for clearing that up.

[rksimple]

FWIW, when using the cases in the same rifle, only a couple thousandths of shoulder bump is necessary, even in semi's. You don't need to overdo it.