300 Blackout headspace Issues

kstone803 · Feb 7, 2021

So here's my issue. I take ten fully processed 300 BO brass and drop em in a lyman headspace gauge, they all drop in and out no issue. Run them through the press and load them with a 220gr Berry's SP with no crimp. Now 6-8 of them won't drop in the headspace gauge. Like you can't smack em home with a solid whack with the palm of my hand. Any thoughts on what's happening? I've never had these kind of issues before and am quite at a loss on how to approach fixing this. Thanks

John from MD · Feb 7, 2021

When you run a case alone into the seating die, what happens? What is the diameter of part of the bullet that goes into the case? What is the diameter of the bullet just before the case? What is the diameter of the neck after loading.

inkd · Feb 7, 2021

Maybe put a little taper crimp on them?

GunBum · Feb 7, 2021

Seating die is probably screwed in too deep. Not the seating stem, but the die body. I think that’s where John is going, and that’s what I’d guess.

kstone803 · Feb 7, 2021

John from MD said:
When you run a case alone into the seating die, what happens? What is the diameter of part of the bullet that goes into the case? What is the diameter of the bullet just before the case? What is the diameter of the neck after loading.

Case by itself in the seating die doesn't do anything. Bullet base is checking in at exactly .308-.309. Bullet just out of the case mouth is at .307. Neck diameter is .331 after loading.

kstone803 · Feb 7, 2021

inkd said:
Maybe put a little taper crimp on them?

Tried that but it didn't make a difference. I ran some of the non fitting ones through with a slight crimp but no change.

85MikeTPI · Feb 7, 2021

What headstamp won’t drop? Some have marginal to too thick necks to make good 300bo.

kstone803 · Feb 7, 2021

GunBum said:
Seating die is probably screwed in too deep. Not the seating stem, but the die body. I think that’s where John is going, and that’s what I’d guess.

So I'm using Hornady dies (which I hate) and the seating die is set to not crimp at all so it's not down very far.

ToolAA · Feb 7, 2021

kstone803 said:
So I'm using Hornady dies (which I hate) and the seating die is set to not crimp at all so it's not down very far.

I have Hornady dies, lynman gauge and I like to load Ranier Plated which are similar to Berry’s. I do lightly crimp. I have found that some brass like Focci and some others I cannot remember offhand are tight after seating. It’s not by much but just enough to keep the head from going all the way into the gauge. Now I try to only use LC brass because I’ve accumulated enough over the years to be discriminating.

GunBum · Feb 7, 2021

So then definitely not screwing up the case with the seating die.

Check neck diameter on the ones that fit the headspace gauge versus the ones that don’t.

Melnic · Feb 7, 2021

85MikeTPI said:
What headstamp won’t drop? Some have marginal to too thick necks to make good 300bo.

Somewhere on here, someone linked a list. I had problems with my 300BO but I was using .309 sized powder coated

Sure seems 300BO has issues with gauges and my 10.5" barrel had a tight chamber compared to my 16"

erwos · Feb 7, 2021

Are you using small base dies?

ToolAA · Feb 7, 2021

Melnic said:
Somewhere on here, someone linked a list. I had problems with my 300BO but I was using .309 sized powder coated

Sure seems 300BO has issues with gauges and my 10.5" barrel had a tight chamber compared to my 16"

I think it was Outrider who posted the link but my quick searches are coming up empty.

Melnic · Feb 7, 2021

Here it is, I just googled for it.
This is for CONVERTED brass, not brass with 300aac on the headstamp

http://www.300blktalk.com/forum/viewtopic.php?t=88599

kstone803 · Feb 7, 2021

GunBum said:
So then definitely not screwing up the case with the seating die.

Check neck diameter on the ones that fit the headspace gauge versus the ones that don’t.

Ones that gauge are running between .327 and .331 when I sampled ten of them. The ones that won't gauge are .330 to .334. so theoretically there is some overlap there where some gauge at the same size that don't. I even took two of each that were .330 on the outside neck and one gauged and one wouldn't go in the last quarter inch no matter how hard you push it.

kstone803 · Feb 7, 2021

erwos said:
Are you using small base dies?

Running commercially processed brass.

ToolAA · Feb 7, 2021

kstone803 said:
Running commercially processed brass.

I had purchased a bag of processed 300 b/o and there were quite a few mixed handstamps and some of those did not work. It was some noname supplier online but they were pretty cheap and I expected a few rejects.

GunBum · Feb 7, 2021

kstone803 said:
Ones that gauge are running between .327 and .331 when I sampled ten of them. The ones that won't gauge are .330 to .334. so theoretically there is some overlap there where some gauge at the same size that don't. I even took two of each that were .330 on the outside neck and one gauged and one wouldn't go in the last quarter inch no matter how hard you push it.

Rotate them and take diameter readings several times from different sides. I think then you’ll see a pattern emerge.

Melnic · Feb 7, 2021

you can take a sharpie to the case and then see where the contact with the gauge is.
start out with just marking the neck and shoulder to see.

kstone803 · Feb 7, 2021

So I took the bag that wouldn't gauge and figured it had to be something with the neck thickness after seating. So I set the lee factory crimp die to as low as it would go until the press cammed over and mashed about ten through it. 8 gauged after that. Probably killed the accuracy and subsonic velocity standard deviation I took forever to chase but better than throwing them out. They'll be range fodder. I swear if 300BO wasn't so damn fun to shoot suppressed I would have given up on it years ago. Keyholes, velocity swings, accuracy issues, this round is a PITA.

300 Blackout headspace Issues

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