First go at reforming 556 for 300 BO

stagpanther · January 6, 2016, 01:31 PM

Since I have thousands of spare 5.56 cases I've been amassing for many years my latest AR builds have been variants of necking up or down the basic 5.56 x 45 case--but the 300 BO is my first go at a case OAL cut and neck-up. My first few goes at simply cutting and trimming with home gear kinda sorta worked--but wasn't especially consistent or squared--so I bit the bullet, so to speak, and bought a Litlle Crow trimmer.

For some reason I was dumb enough to think that people actually simply trimming down full-length 5.56 x 45 cases but quickly figured that wouldn't work. Similarly, the cutter (at least mine) won't do any trimming until the trim diameter is the actual neck diameter for the 300 BO.

My solution is pretty simple--start with the 5.56 case and using the cheap Ryobi bench belt sander and grinder combo I simply grind down the case to the base of the shoulder, resize in the 300 die (with decapper removed of course) and then use the Little Crow trimmer to do final case trim. Worked well for me.

These are left-over LC and FC cases which have all been pocket swaged though most of them didn't seem to need it. nosler 125 accubonds driven by W296 between 16 and 17.5 grs.

Sharkbite · January 6, 2016, 10:42 PM

Yep. Guys have been using the Harbor freight mini chop saw to cut cases at the shoulder, then running em thru their sizing die.

stagpanther · January 7, 2016, 02:16 AM

Thought about going that route--along with buying a jig for holding the cases--but the sander grinder costs about $40 at Home Depot and I already had it sitting around not doing much of anything--and it grinds down the brass very quickly. Some of the brass is pretty darn old and mangey looking--be interesting to see how it fires. : )

I'm going to try and test these puppies today--but we have snow and ice on the ground and it's in the teens not sure I can get through to the range I shoot at. Thanks to your advice I put a "velcro fuzzy" on my shell deflector.

January 6, 2016, 01:31 PM	#1
stagpanther Senior Member Join Date: March 2, 2014 Posts: 11,772	First go at reforming 556 for 300 BO Since I have thousands of spare 5.56 cases I've been amassing for many years my latest AR builds have been variants of necking up or down the basic 5.56 x 45 case--but the 300 BO is my first go at a case OAL cut and neck-up. My first few goes at simply cutting and trimming with home gear kinda sorta worked--but wasn't especially consistent or squared--so I bit the bullet, so to speak, and bought a Litlle Crow trimmer. For some reason I was dumb enough to think that people actually simply trimming down full-length 5.56 x 45 cases but quickly figured that wouldn't work. Similarly, the cutter (at least mine) won't do any trimming until the trim diameter is the actual neck diameter for the 300 BO. My solution is pretty simple--start with the 5.56 case and using the cheap Ryobi bench belt sander and grinder combo I simply grind down the case to the base of the shoulder, resize in the 300 die (with decapper removed of course) and then use the Little Crow trimmer to do final case trim. Worked well for me. These are left-over LC and FC cases which have all been pocket swaged though most of them didn't seem to need it. nosler 125 accubonds driven by W296 between 16 and 17.5 grs. __________________ "Everyone speaks gun."--Robert O'Neill *I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!*

January 7, 2016, 02:16 AM	#3
stagpanther Senior Member Join Date: March 2, 2014 Posts: 11,772	Thought about going that route--along with buying a jig for holding the cases--but the sander grinder costs about $40 at Home Depot and I already had it sitting around not doing much of anything--and it grinds down the brass very quickly. Some of the brass is pretty darn old and mangey looking--be interesting to see how it fires. : ) I'm going to try and test these puppies today--but we have snow and ice on the ground and it's in the teens not sure I can get through to the range I shoot at. Thanks to your advice I put a "velcro fuzzy" on my shell deflector. __________________ "Everyone speaks gun."--Robert O'Neill *I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!*

January 6, 2016, 10:42 PM	#2
Sharkbite Senior Member Join Date: November 4, 2013 Location: Western slope of Colorado Posts: 3,679	Yep. Guys have been using the Harbor freight mini chop saw to cut cases at the shoulder, then running em thru their sizing die.