Opening up 300 Blackout neck

[gvanzeggelaar]

Has anyone opened the neck up on a 300 blackout barrel with a 7.62x39 neck reamer to 0.340” to accept cast loads with converted brass more readily?

[DAFzipper]

Not that. I use a NOE expander mandrel for the Lee universal expander for cast. They come in multiple sizes

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[gvanzeggelaar]

I am referring to the actual chamber of the firearm

[DAFzipper]

Sorry. I should have read it more carefully

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[Gtek]

I think I remember many discussions about converted brass neck thickness even with .308" jacketed having issues. Discussions also included the wall variance between manuf's. Inside neck reaming is an option, are yours much thicker than .011"-.12" if so might be a lot easier to fix brass not chamber.

[dannyd]

Neck turn the brass once and it works great; bad thing about working on the chamber you may have a hard time trying to sell it later if you want too.

[jimkim]

I remember seeing someone ask a similar question once. He was told to open his up with a 32 H&R reamer. I believe that would be better than using the 7.62x39 reamer.

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[44Blam]

I have a 300 BO AR barrel and I just size to .309 and I coat the boolits with hi-tek. I don't have any factory 300 BO brass because I convert .223/5.56 brass and I turn the necks as a step in converting the brass... Personally, I turn the necks to 0.011". I've shot 0.013" without problem but I saw issues with 0.015" (WOLF)...

[Lloyd Smale]

I have a 300 BO AR barrel and I just size to .309 and I coat the boolits with hi-tek. I don't have any factory 300 BO brass because I convert .223/5.56 brass and I turn the necks as a step in converting the brass... Personally, I turn the necks to 0.011". I've shot 0.013" without problem but I saw issues with 0.015" (WOLF)...

I had one of my 5 bo that had a tight chamber neck. It gave me fits with 310 bullets so i tried 309 and still had some issues. Went to 308 and never had another problem. By the way those 308s shoot just as well in all my Bos as 310s did. My 16 inch gun will shoot 100 yard 5 shot groups under 1.5 inches. That said i shoot a gaschecked bullet and cast them at least 16 bhn and pc them (before sizing) Id try 308 bullets before id run a reamer in it.

[Drew P]

I noticed that my 32-20 cowboy dies expander is, well, perfect for that. So, that’s what I use. Oops I also misread you’re talking chambers. Never mind.

[a.squibload]

from 300blktalk.com
http://www.300blktalk.com/forum/viewtopic.php?f=141&t=88599&hilit=brass+list
Part of the list shows acceptable brass, the other part is not so great brass.

I sort the 556 brass, good ones get trimmed for 300blk, others get reloaded for 556.
Basically the American made brass and some others are thin enough to not cause a problem,
the cheaper(?) foreign stuff is thicker for some reason. The additional thickness x 2 plus the boolit
can be a bit large for the chamber. Easy enough, after a few sortings you can start to remember
which are good for 300. LC brass is good and pretty common.

[quilbilly]

Being cheap, I use an old knife sharpening steel with round tapered point to ream out slightly my 308 and 30/30 brass. Works just fine for me and does remove much or any brass with just a firm twist. I see these old style sharpening steels often at garage sales for about a dollar.

[rockrat]

The diameter of the x39 case is larger than the 300bo, won't work. You will need a neck/throat reamer

[a.squibload]

I think the deal is when you make 300blk you're making a neck out of what was the 556 case body.
Some brass doesn't have the taper in the body so it's thicker at that point, maybe too thick for a case neck.
Hope I said that right...