Forming .300 blackout brass

[hanken]

I bought a set of rcbs .300 ACC blackout SB t/c dies and tried to form .223 cases into .300 blackout. Didn't work. No matter how I adjusted the sizzer die it colapased the case. I called RCBS and they told me they did not design their dies for this purpose. I need help.
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[hanken]

I solved my problem. Even though the cases were clean I ran them thru the viberator for an hour then relubed . They turned out great after that.

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[Ivan the Butcher]

Redding and other companies make a tapered expander "ball" to expand the necks. On my 221 Fireball, I can't get the shoulder correct out of 223 brass, but Lapua 222 Rem makes wonderful high quality brass for Fireball, that might be a fix for your Blackout also.

 

[Streaker]

I have made thousands of .300 Blackout cases from .223 cases. I use Hornaday dies and have not had a problem. Are you cutting them to the correct length, removing the burrs, and lubing them generously before trying to neck them down? I use one shot spray lube and it works fine.

 

[125JHP]

I also use the Hornady dies, however I pull the decapping stem and neck them down first, then cut to length & process from there.

 

[Plottman Pops]

This is procedure I have used for 1000s of 300BLK cases with good success... thought it might be useful here.

Processing 300BLK Brass

Starting with brass ready to reload as 223 or 5.56
(ie) inspected, deprimed, cleaned, primer pockets swaged (if mil brass))

Do a small number of cases to start, maybe 5 to 10 cases:
Do each case as a batch: taking one case at a time through all the steps,
to get everything set and adjusted correctly.

1. Cut case to 1.365" to 1.370" - cutting the neck and shoulder areas off the case.

2. Debur the new mouth inside and out.

After Step 2, check case wall thickness with calipers. If over .0125 it will not chamber correctly once a bullet is pressed in. This is very important if you're using misc brass, and you'll start to see a pattern of which cases aren't going to work and you can skip trying to convert them. if you elect to use 7.62x39 bullets (typically .310" diameter), take the neck wall thickness into consideration = meaning that case neck wall thickness should be .012" or less.

3. Anneal

4. Lube cases.

5. Form in FL resize die.

6. Check case forming in a case gauge. Adjust size die as necessary.

7. Trim case to Trim-to-Length: 1.358"

8. Deburr the mouth inside and out, again.

9. Check trim in the case gauge. Adjust trimmer if necessary.

10. Clean cases of lube.

Once cases go through all the above steps and come out right,
go into "production" running the rest of your allotted cases as a single batch,
doing each step to all cases with occasional gauging to make sure everything stays good.