Could someone explain to me what's going on?

[grn9533]

I just started working on a 300 blk subsonic load. I've only been reloading a year with mostly .308 but I have never ran into any problem like this.

Here's what I have going on. 2 different types of 300 blk factory brass that I shot cleaned and prepped (summit, and gemtech), and I have converted .223 brass as well. Almost everything I do results in the shoulder being crushed on the brass. The goal was to make a subsonic load that will cycle in my AR and I planned on using sierra 220gr HPBT however all I could find was sierra round nose. I also picked up a box of Hornady 208gr AMAX to see if I could use a lighter round and still get reliable function.

Here is exactly what I did. I shot the factory brass, deprimed, ultrasonic cleaned, FL sized with an RCBS 300 blk FL sizer, deburr/champfer, reprimed, added charge, and TRIED to seat a 208gr AMAX round. 5 rounds all unsuccessful. OK now into problem solve mode. I thought since I can seat the bullets to a certain point, maybe the neck diameter wasn't fully expanded. As an experiment, I loaded dummy rounds will all different grains of .308 bullets I had on hand. here's the results. 5 rounds for each grain weight.
168 HPBT seated
175 HPBT seated
178 HPBT seated
208 AMAX crushed shoulder
220 round nose crushed shoulder.
I then proceeded to swap out my 300 blk expander ball for a regular .308 expander ball and here's what happened (once again 5 rounds for each grain weight)
168 HPBT seated
175 HPBT seated
178 HPBT seated
208 AMAX (NOW seating)
220 round nose crushed shoulder

First question- why are my lighter rounds seating and the heavier ones are not when they all have the same diameter and just vary in length?
Next question- why is it when I switch out my 300 blk expander ball with a 308 expander ball I can now get my 208gr AMAX to seat?
finally Why can't I get my 220 round nose bullets to seat?? I did some research and saw that some people do use 220 round nose bullets for their 300 blk load, so what am I doing wrong that I can't get these to seat? I even pulled some bullets from the factory brass and without resizing tried to seat the 220 round nose on them with still the same result! crushed shoulders. It can't be an issue with how far I set my dies on the press either. No matter how high or low I screw them in and adjust the seating stem, once the bullet reaches a certain point of depth on the brass it will not budge and the shoulder just collapses.

All I have to go with for sure is buy a new expander ball and then work from there. Is it possible that the bottom portion of the neck near the shoulder is not getting expanded enough and those 220 round nose FLAT BOTTOM rounds just get stuck? should I try 220 HPBT rounds or would that not make a difference? Am I really that stupid for not figuring this out?

 

[jwalts27]

I had a similar problem a few years ago loading copper plated 30. cal flat point bullets instead of FMJBT. I ended up flaring them a bit to correct the issue but then I had cycling issues. Wasted a bunch of time before I finally gave up.

 

[Salmoneye]

Looks like soft brass to me...

 

[Blue68f100]

Liquid cleaners remove all of the lube/carbon. I would try some mica/graphite lube on the necks and see if that helps. This is assuming your expanding the mouth and have the seater die backed off not to crimp way too early.

Measure your bullets and neck inside to see what difference you have. If the bullets are over size and neck is too small, causes problems. You only need around 0.002" difference for good neck tension.

 

[gamestalker]

A few things to try here.

1. Take a piece of brass, no bullet, no die, and place the brass in the shell holder, run the ram to full extension. Then while it's at full extension, thread your seating die in until you can feel it touching the case mouth. Once it touches, back it out 1-1/2 turns and lock it down. Lower the ram, insert your problem bullet weight and seat, using only the seating stem to adjust seating depth, not the die.

2. Another possible cause could be not enough chamfer to the inside of the case mouth.

3. And last, are you crimping? If so, it's almost certain that you are over crimping, thus collapsing the shoulders. If so, you will know by employing step #1 above.

GS

 

[243winxb]

http://www.ar15.com/forums/t_6_42/385765_300_Blackout_Master_Thread.html

I have converted .223

Necks may need inside neck reaming to remove a donut. Some brass has thicker than normal neck wall thickness. A loaded rounds neck diameter should not be larger than .334" http://www.saami.org/PubResources/CC_Drawings/Rifle/300%20AAC%20Blackout.pdf

 

[grn9533]

OK I got it all figured out thanks to Gamestalker. It turned out I was just massively over crimping these rounds! See I've been using redding dies for a while their competition sets have a separate crimp die. I did not realize the RCBS seating die also crimped the rounds. I guess I should have thought about that when I did not see a separate crimp die with the RCBS set
I followed exactly what you stated, placed an empty shell and raised the ram to the top. I noticed when I squeezed down on the die past where I felt it coming in contact with the shell you could see the crimp being applied to the neck.

Thanks for all the quick responses. That was a dumb thing to overlook but at least it was an easy fix. after I read this I went and loaded up those 220's with 10.9gr of AA1680. sounds really good with a can. thanks again guys

 

[gamestalker]

Don't feel bad grn9533, I learned from my mistakes too.

Glad I could help you!

GS

 

[Walkalong]

Definitely not the first one who has done this. It happens.

Let us know how they shoot.

Welcome to THR.

 

[grn9533]

Thanks guys! and glad to be here

 

[243winxb]

Die adjustment is most common.