5.56 Chamber for Longer Bullets?

[RustyPin]

Can you modify the 5.56 Chamber for longer Bullets? Or will it shoot them as is?

 

[1911nut]

You can lengthen the throat with a throating reamer or shoot them seated deeper in the case. Seating the bullet base past the neck/shoulder (or the sized portion of the neck) seems to have less negative with boat tails than flat base bullets.

AR is magazine limited. Single shot gun is limited by the throat.

Maybe shoot what you have to see how good you can get it.

 

[RustyPin]

I was Looking at a barrel that already has the 5.56 Chamber and I'm wanting long distance accuracy with no regard to OAL or AR mag length.

 

[ronemus]

If it is a 5.56 chamber rather than .223 it will already have a long throat.

 

[Ned Ludd]

If it is a 5.56 chamber rather than .223 it will already have a long throat.

Not necessarily. Below is a chart pinched fro AR15.com that shows the dimensions for several .223 Rem match and 5.56 reamers. There are certainly .223 Rem match reamers available that cut a longer freebore than some of the 5.56 reamers listed. In fact, none of these reamers are set up for what I would consider "long" .224 bullets; "long" meaning bullets such as the 80 to 90 gr offerings currently available. Most of those bullets require optimal freebore lengths in the 0.100" to 0.200" (or more) range. The major difference is that they're not being loaded to mag length. By confining loaded rounds to mag length, you pretty much guaranteeing that the bullets won't be seated "optimally". So you're back to identifying the specific bullet(s) you wish to use, determining empirically where they will be seated when loaded at the maximum possible length so that they will still fit in a mag, and deciding whether a longer freebore is desirable, or even possible.

Depending on the specific rifle setup, concern over this may not even really be necessary. I have a .223 Rem bolt rifle that was chambered with ZERO freebore. I worked up a load with the Berger 80.5 Fullbore bullet that shoots extremely well. Because of the short throat, the bullets are seated well down in the case (i.e. the bullet boattail/bearing surface junction is well below the case neck/shoulder junction). Due to the diminished effective case volume with the bullet seated down so far (relative to "optimal", at least), I decided to use a slightly faster powder (H322). It worked very well; the load is very precise and I'm still getting decent velocity without any pressure issues. So sometimes, the easiest solution is simply to work up the best load you can within the limitations of your specific setup. Another option that may be useful if the rifle has sufficient freebore for a given bullet is to modify the lip of the mag with a Dremel tool (or similar) to allow longer rounds to be loaded. I've not had to do that as yet, but plenty of people have reported that it can work very well.