Brass inconsistency

CoachChris

CoachChris

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Aug 28, 2008
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Hoback, WY
I fire formed 200 pieces of new Norma 300WM brass for a new Proof carbon barrel.
The base to datum measurements range from 2.2755 to 2.2835 using a Hornady comparator gauge.
I'm not sure what to do?
I sorted out about 30 pieces that ranged from 2.2810 to 2.2835.

I'm running short on time to get a load together for elk season
 
I'm going to assume you are talking about headspace of your brass and not the CBTO (Case Base To Ogive) dimension of your loaded round. Your headspace dimension may not be fully expanded to the chamber yet on your new brass. Do you have any older brass that has been fully formed to the chamber that you can take a headspace measurement on? This should tell you about how much more expansion of your new brass is needed to be fully fire-formed to your chamber.
One or two more moderate loads fired on the new brass may give you the consistency in headspace you are looking for.
 
Sounds like you need another round of fireforming. I recommend a moderate load with the bullet jammed into the lands so the cartridge base is firmly seated against the bolt face. This gives me the best results with my Ackley rounds. If you can anneal the necks/shoulders I also recommend doing this as well.
 
Don't worry about that as long as they all chamber freely in your rifle. It may take 2-3 firings before you are actually bumping the shoulders back. The brass shoulders are probably not making contact with the die in that area yet. Same with my 7 rem mag that I load for. Also, google search the Redding Competition Shell Holders. Buy a set for your 300 WM.

Good luck
 
Okay so you are using a 420 I hope. I think like everyone else you havnt formed the brass yet. Set ur die so that ur brass chambers with a a slight amount of pressure then shoot again. You can start doing some load development with 1 fired brass but can't do a final load until your brass is formed and bumped .002-.0015
 
I would neck size only for a few firings. Once the case begin to feel snug on chambering, then bumps shoulders thereafter. Seating bullets into the rifling may or may not work since the firing pin impact could possibly push the case forward onto the bullet depending on neck tension. @AkleyFan if you have to seat bullets to rifling to form your brass, your barrel isnt headspaced properly. There should be a snug fit at the neck shoulder junction which is why I use Manson HS gauges on all my ackleys, the .004 crush fit is built into them. I've never had to jam bullets.
 
CoachChris said:
Yes I am
I was baffled by these measurements too
I measured each case multiple times
Click to expand...
Are you positive the headspace on your barrel is set correctly? Do you have a NO-GO gauge you can try?
As already mentioned, the nominal reference datum should be at 2.2700"-.0070" for a 300WM per the SAAMI spec. If your headspace is longer than that you are asking your brass to stretch a lot farther during fireforming and would possibly need a hotter load to fully form every case.

I don't know that I have ever seen such a large discrepancy in fire-formed shoulders, not even in the wildcat that I just built.

My next thought is that there is a pretty large potential to impact those measurements by how you go about performing your measurement. For example, if you are measuring the shoulder with the primers still installed and allowing the primer to rest directly against the jaw of your calipers, the primers themselves can cause variation in the measurement. To solve this I use a bullet comparator under the primer pocket (installed on the jaw opposite the bump gauge) so that the primer itself does not have any contact with the calipers. If your headspace is indeed longer than SAAMI spec you could certainly have some primers that are partially sticking out past the bottom of the case after fire forming. Also, initial primer seating depth could cause this as well if you if you aren't seating the primers below flush with the bottom of the case.
The angle you hold the brass at while measuring can also impact your measurement as can any deformation at the bottom of the case such as heavy ejector marks or swipe. My point is, there are a number of ways to screw up making a consistent measurement. Trust me, I found out the hard way.
 
You have a chamber NO-GO gauge and it indeed does not chamber in your rifle? I'm not talking about a case gauge.
 
CoachChris said:
The base to datum measurements range from 2.2755 to 2.2835 using a Hornady comparator gauge.
Click to expand...
Does the reading change as you spin the case? Hornady is known for making oblong holes in comparators.

I changed to SAC comparators and Mitu calipers, and I now get more consistent readings. At each step of my progression from Hornady to SAC, and $20 cheap-o to Starrett analog to Mitu digital calipers I get me more consistent measurements.

AkleyFan said:
Sounds like you need another round of fireforming.
Click to expand...
X2. Several times it's taken my brass up to three firings for brass to stabilize to the point of decent consistency.

Seabeeken said:
I would neck size only for a few firings.
Click to expand...
10/10 agree. Don't sweat it until they don't chamber and need to be sized. If they chamber shoot them.
 

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