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Discussion Starter · #1 ·
I finally got my Hornady Neck Trimmer to use for my .300 AAC Blackout reloading. Not because I’m accuracy focused...but because I have some salvaged 5.56 cases. After processing and loading they won’t fit in my PSA barrel, as the brass is too thick at the neck.

Here’s where it gets challenging...the cases won’t fit on the 30 cal mandrel for the neck trimmer.

I’ve cut, formed and sized, trimmed, chamfered, and deburred these cases, only to find the neck openings are too small to fit onto the mandrel....so I can’t even get them close to the cutter, let alone do any cutting. They fit just fine on the 30 cal pilot for the Hornady Cam Lock Case Trimmer, though they had to be chamfered to slip on, but that’s as far as I can go.

The case necks readily take a bullet, even a 220gr Lapua Scenar L BTHP, but then the rounds won’t fit a case gauge, either. Is there another preparation step I’ve missed?
 
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Interesting problem. I wish I had an answer but I plan to wait around when it comes. Somebody will chime in.
 

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Have you tried the next smaller mandrel? If they came in a set, that might be .284" or marked 7mm. You don't, however, want any play between the case-neck and the mandrel.

Hate to say it, but the solution may be discontinuing the use of 5.56mm brass.;)
 

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I can't help you but maybe try sending a pm to Mingaa. He doesn't get on here all that much these days so it may take some time to hear back from him. He has made about as much .300 ammo from .223/5.56 cases as anyone I know.
 

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I'm sorry, I don't have a good answer for your original question, but I do have bad answer for you.

Here is a list of brass that should be avoided when converting from 223/5.56 to 300 blk. http://www.300blktalk.com/forum/viewtopic.php?t=88599 If you convert brass, bookmark this thread.
Some brass has walls that are just too thick to allow for easy conversion, it's just not worth your time or energy to do it.

Lake City range brass and other good brands are so dirt cheap right now. I know it would be super hard to scrap what you have already started, but it might be your best option.

Sent from my SM-G960U using Tapatalk
 

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Discussion Starter · #8 ·
Have you tried the next smaller mandrel? If they came in a set, that might be .284" or marked 7mm. You don't, however, want any play between the case-neck and the mandrel.

Hate to say it, but the solution may be discontinuing the use of 5.56mm brass.;)
Sad that the kit came with .22, 6mm, 6.5mm, and .30 cal. As it happens, the .30 cal mandrel is .305”, and my sized cases are .303”. This brass, MEN 15, German NATO cases, must’ve actually been made by Mercedes Benz...this is the thickest brass I’ve ever encountered, at 0.016”. A loaded bullet took the neck diameter to 0.3385”, well outside SAAMI spec. In the end, this brass isn’t on any of the “bad brass” lists I’ve found.

i have a K&M expanding die and mandrel on order, as well as pin gauges in 0.306” and 0.307”.

Meanwhile...on advice obtained elsewhere, I sacrificed a bullet to load and pull in a couple of test cases. The inside neck diameter is now 0.306”...perfect. I neck turned 2 cases, and the result is excellent. That Hornady Neck Turner is one fine piece of equipment, and neck turning isn’t the PITA you’d think it would be. After turning I resized the cases and seated the same sacrificial bullet...perfect. Fits nicely in both case checkers, and loaded from the magazine and extracted from my AR Pistol without a hiccup. Knowing that it worked well I’ll wait to complete the remaining cases.

Doing the math, I’ll only need to salvage and turn about 600 additional free 5.56 thick necks to recover my equipment costs...that’s all. Naturally, the labor is an act of love, and thus, is priceless.
 
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Excellent! There probably would have still been some play with a 7mm mandrel. With the brass being .016", neck turning might put them close to the typical .011" from the chart stupimlico linked to.

Hopefully, the priceless act of love will aid in accuracy. The case-necks will be more uniform inside and out!;)
 

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Discussion Starter · #10 ·
Here is a list of brass that should be avoided when converting from 223/5.56 to 300 blk. STICKY - Good/Bad brass list converting 5.56->300blk - 300BlkTalk If you convert brass, bookmark this thread.
Some brass has walls that are just too thick to allow for easy conversion, it's just not worth your time or energy to do it.

Lake City range brass and other good brands are so dirt cheap right now. I know it would be super hard to scrap what you have already started, but it might be your best option.
Stu, thanks for the advice. While I completely agree with your logic, I am perversely motivated to do what I shouldn’t. Actually, I really like the challenge. I grew up extremely poor, so the concept of throwing anything away is hard for me. It’s why I go scrounging for spent brass that can convert to 300 BLK despite having 225 brand new Norma cases...which I have yet to use. They have to wait their turn.
Despite by conservatism, I’ve always appreciated this quote from JFK. This is one of those “hard” things.
“We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard.
[Address at Rice University, September 12 1962]
 
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