Hello everyone! This is the first time I am am attempting to make 300 BLK brass. When I have gotten to the step of sizing it I am getting this weird outboard horn looking shape on the top brim. I can not put it into the comparator to see if the sizing worked. My theory is something in the Hornady custom die set is hitting the top of the brass. Nothing is unusual when I pull the lever, it is a smooth in and out. Remember the brass is perfect up u till I resizing it. I’ve never seen this on any of my match ammo I’ve realized in the past 12 years. Any thoughts here? Thanks in advance!
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300 BLK brass sizing issue
- Thread starter geronimo2011
- Start date
Have you checked the OAL of the brass to confirm it's in spec? Looks like the brass is bottoming out inside the die possibly and causing it to swell out.....or maybe the die is set to low. That's where I'd start looking....
You’re forming the BO brass with a sizing die. The flare you see at the case mouth is a byproduct of case forming. Get a dedicated forming die and use the sizing die to size.
....I would agree with this analysis, check to make sure your trim length is between 1.348 -1.368". If you look at the attached image of the Hornady Custom die cut-away, the red line points to the section where your case mouth may be contacting and belling outward. You can do a quick test by backing your die off a turn or two and try sizing a casing to see if the case mouth get belled or not.
- Nov 3, 2010
- 9,723
- 20,478
Thirds on trim length. I use a set of Lee dies to form all my brass and have never had an issue like that.
Too long.....I've converted 10,000's of LC to 300blk...
I've done it 2 different ways and both work great.
1st....chop long with jig in 4" chop saw....anneal, size in Forster FL sizing die with no decapping rod/expander ball... then, 21st Century mandrel then trim to length
2nd
All run on Dillon 650...no chopping....straight LC 5.56 in case feeder, 300blk trim die with RT1500 trimmer, 21st Century mandrel in last station.
Both methods work great and make perfect brass. 2nd method is much faster
I've done it 2 different ways and both work great.
1st....chop long with jig in 4" chop saw....anneal, size in Forster FL sizing die with no decapping rod/expander ball... then, 21st Century mandrel then trim to length
2nd
All run on Dillon 650...no chopping....straight LC 5.56 in case feeder, 300blk trim die with RT1500 trimmer, 21st Century mandrel in last station.
Both methods work great and make perfect brass. 2nd method is much faster
...BTW, are you converting 223 brass to make your 300BLK brass? If so, when you cut it down be aware that when you form it by running up into the sizing die, the overall length of the casing will shrink a bit, you will have to experiment with where you cut the casing and how much you trim that casing back to remove any burrs before you run it thru your sizing die.
...just a suggestion, but when I was forming brass I would use my Lee 300BLK sizer and just run the 223 casing up into it to do the basic forming before cutting the casing down on my mini chop saw. After cut down, trimming and anneal, I'd run them thru my RCBS SB/FL 300BLK die to set the final shoulder bump for MY chamber and uniform the case mouth diameter. That was back when 300BLK brass was hard to get, nowadays I just order mine from https://carolinabrass.net/ due my preference to use LC brass. John makes excellent brass and it's much less costly for my money & time wise. YMMV
...just a suggestion, but when I was forming brass I would use my Lee 300BLK sizer and just run the 223 casing up into it to do the basic forming before cutting the casing down on my mini chop saw. After cut down, trimming and anneal, I'd run them thru my RCBS SB/FL 300BLK die to set the final shoulder bump for MY chamber and uniform the case mouth diameter. That was back when 300BLK brass was hard to get, nowadays I just order mine from https://carolinabrass.net/ due my preference to use LC brass. John makes excellent brass and it's much less costly for my money & time wise. YMMV
...if I ever have to go back to making my own 300BLK brass, this is the way I'd do it. If I couldn't get the Dillon trimmer, I'd probably use the alternative of a router motor.
