Issues loading 300 Blackout. Round won’t headspace after bullet seated.

[Shooter14854]

Hey everybody I’m hoping somebody here could give me some guidance. I recently got the tools to convert .223/556 brass into 300aac. I’m using the RCBS short base dye for sizing. Trimming the case to 1.360. I’m loading Hornady 150gr HPBT. I measured the neck thickness (only using brass with .013 or lower neck thickness) of every piece of brass after trimming. All of my converted brass is seating perfectly in my Hornady headspace gauge. However when I seat the bullet into the case (2.090 COL) the completed rounds will not sit flush in my headspace gauge. About 95% of them stick out about 1/8th inch. I’ve tried resizing them with the RCBS dye again, a Lee dye and checked if it sat after doing a taper crimp. The round seem to seat fine in my rifle but I havn’t tired firing them yet. I didn’t have any rounds fail to fully seat in the rifle or get stuck.

Additionally, I tried running once fired factory 300 blackout brass through the same dye with the same process as my converted brass. All of the factory brass seats fine in the headspace gauge after the bullet has been seated. I’ve compared the measurements on my converted rounds to my rounds using factory brass and they are virtually identical. I have no idea what to do and am completely out of ideas. Any help would be very appreciated! Thank you all!

 

[MEHavey]

OOC:
- Are you seating/(taper) crimping in the same operation?
. . . (and if so) . .
- Why are/who recommended you crimp'g at all?

 

[mcb]

When I first started loading 300 BO, inconsistent case length led me to overcrimp some rounds and this would collapse the shoulder slightly causing them to swell just behind the should and not want to fully seat. I trimmed all my cases to the same length and back off on my crimp a bit and all my problems went away with chambering the rounds.

 

[jmorris]

If the case gauges fine after sizing/depriming and expanding but fails after you seat, I would take a look at the neck.

Some .223 brass has walls too thick in the neck area for converting and once you stick a bullet in the ID, the OD grows too large.

Take a look at the first post here and see if your problem brass is non the naughty list.

https://www.300blktalk.com/forum/viewtopic.php?f=141&t=88599

You can also add me to the list of people that does not crimp 300blk.

A doughnut would also effect only the lower portion of the neck OD, after seating a bullet, a pin gauge set would be handy to check for that.

 

[swg1]

But it fits in the rifle fine you say?

 

[243winxb]

A dount at the neck shoulder junction may be an issue. Some brass brands need inside neck reamed to stay under the necks maximum loaded outside diameter of .334"

 

[jmorris]

For illustration a donut is excess material that, upon firing and sizing can migrate up from the shoulder and into the neck.



You can also create one instantly, be firing an improperly turned neck, like this. When you blow the neck out, that ridge will be on the inside.



Sometimes you can mitigate it by not sizing all the way down the neck. You can also run a reamer inside the neck and cut away the extra material.

 

[Walkalong]

Neck reamers for the Wilson trimmer.

 

[Shooter14854]

Thanks for the advice everybody. I’ve made some progress on figuring this out… if I seat the bullet with my Lee die set the loaded round won’t headspace. If I seat it with my RCBS set (with no crimp) it headspace just fine I’ve tried various headstamped brass and referred to the list of good/bad head stamps. I really have no idea what would be causing this at this point. I’m starting to think maybe my gauge is out of spec. I ordered a Wilson headspace gauge and will try with that no see if i have different results.

 

[Maintenancan8193]

Hey everybody I’m hoping somebody here could give me some guidance. I recently got the tools to convert .223/556 brass into 300aac. I’m using the RCBS short base dye for sizing. Trimming the case to 1.360. I’m loading Hornady 150gr HPBT. I measured the neck thickness (only using brass with .013 or lower neck thickness) of every piece of brass after trimming. All of my converted brass is seating perfectly in my Hornady headspace gauge. However when I seat the bullet into the case (2.090 COL) the completed rounds will not sit flush in my headspace gauge. About 95% of them stick out about 1/8th inch. I’ve tried resizing them with the RCBS dye again, a Lee dye and checked if it sat after doing a taper crimp. The round seem to seat fine in my rifle but I havn’t tired firing them yet. I didn’t have any rounds fail to fully seat in the rifle or get stuck.

Additionally, I tried running once fired factory 300 blackout brass through the same dye with the same process as my converted brass. All of the factory brass seats fine in the headspace gauge after the bullet has been seated. I’ve compared the measurements on my converted rounds to my rounds using factory brass and they are virtually identical. I have no idea what to do and am completely out of ideas. Any help would be very appreciated! Thank you all!

Make sure you are using a 300blk seating die , because lee 300blk seating dies Do-Not crimp , the 3 die set comes with FCD for crimping

 

[243winxb]

a Lee dye and checked if it sat after doing a taper crimp

lee 300blk seating dies Do-Not crimp

LEE - IF Its a dead length seat die, no crimp. AS said above.

 

[Shooter14854]

Thanks everybody for the help. I finally figured out what the issue was. All of the rounds that I used my Lee bullet seater with had a dent/chip form around the case mouth. It was only visible after pulling the bullet from the case. I chamfered and deburred my cases a little more aggressively and used only my RCBS seat/crimp die and they all sat fine.