I'm going to start out my saying that I'm not sure if this a brass, rifle chamber issue or a bolt issue, but it started with brass.





I've recently gotten back into 300 blackout. I bought a bunch of formed brass from a vendor here, and started loading. One my first batch, I got a lot of cartridges that wouldn't feed into the chamber fully, causing the bolt to jam before it went into battery. This was with a mix of bullets, Hornady, Sierra, and MBC cast boolitts, and a variety of mags: Magpul, USGI, and Lancer.





Figuring I had wonky cases, I bought a Wilson case gauge and checked all my brass. Sure enough, I found that about 10% of the formed brass wouldn't pass the case gauge check. I set those aside to reform or recycle at a later date.





I loaded up a bunch last night, all brass that passed the case gauge check before and after reloading. Every loaded cartridge was checked to make sure it sat in the case gauge, and I rejected the ones that didn't and put them in the crap pile to pull the bullets later.





At the range today, I have 7 failures, all the same, the bolt wouldn't go into battery. I brought them all home, and the all pass the case gauge test. The other thing I noticed was that the brass was all from the same original manufacturer, RWS.





I'm not sure what to try next, other to see how it performs with factory ammo.





Any ideas? I'm about to go through my unused brass to remove all RWS and any brass that fails the case gauge check.

 

This can be caused by the brass being too thick at the neck. It happens on converted brass.

Here is a list of known good and bad brass: http://www.300blktalk.com/forum/viewtopic.php?f=141&t=88599

Thanks, that's really helpful. about of third of my brass is on the no go list.



 

The instructions with the Wilson gauge say it should be between even with the end and level with the low cut, and that's what I've been using as a standard, checked with a metal straight edge. Nearly all cases are level with the low cut, and any above the gauge end are moved into the crap ammo pile to be dismantled later for parts.
 

Did you run this newly purchased brass through your Full Length Sizer before loading?

If not, that was your first mistake.

Did you check to see if this brass chambered and extracted with ease in Your rifle, before loading and completed ammo?

What case guage are you using?  Sounds like OAL is to long.  The Sheridan gauge checks for OAL while the Wilson really only checks the case.

Yes on both. The brass that consistently jams chambers and extracts just fine when just brass, but jams every time when loaded.





       




 Wilson, as noted in OP. Case length is consistent at 1.35 from the brass supplier.





 

I am not a blackout owner/shooter but the first thing at your stage now I would check is the loaded round neck diameter.  Any cut down cartridge can be too thick there as was stated ready.

I would so black marker up a couple of your failed to chamber cartridges any look for scuffs where it binds up. Find that and it should be easier to back up your process to where it goes wrong. Oh marker up the projectile too on the off chance the ogive is hitting the throat.

FWIW I would have run every thing through my own sizer before loading; trust no one Mulder.

When using Hornady dies I wound up needing to go .003" below the low shelf on my Wilson gauge to ensure the rounds would function.  I checked Hornady and Remington factory ammo and they were also below the minimum according to my Wilson gauge so either the gauge is wrong or the ammo is wrong but when I use the factory ammo as a guide all of my rounds chamber and function just fine so I went with it.

Ok, did some testing with a suspect cartridge (RWS headstamp), and a known good cartridge (LC headstamp). I used two Amax bullets that measured as close to identical as possible in diameter  and weight.



SWC:

Length before resizing 1.3570

resized using Hornady FL die

neck outside diameter .3335

chambered and ejected OK

Loaded with Amax 308 208gr bullet

neck outside diameter now .3370

Sharpie applied to case neck, shoulder, and bullet ogive

Jammed on chambering, rub marks on bottom of neck and on shoulder



LC:

Length before resizing 1.3575

resized using Hornady FL die

neck outside diameter .3290

chambered and ejected OK

Loaded with Amax 308 208gr bullet

neck outside diameter now .3310

Sharpie applied to case neck, shoulder, and bullet ogive

Chambered and ejected with no issues,  hair thin rub line where neck meets shoulder



Pictures:



SWC:





LC:





The differences in diameters (~.0050) corroborate with the documented case differences in the link chrismartin posted. I'm guessing that the thick necks are causing my jams. I'm going to reload some LC brass only and test them in the next couple of days.

How can you say neck thickness when it's obvious that the should is rubbing?
Showing that it rubs on the mouth, maybe on the belling of the mouth and lack of flattening it out properly.
Again, size with lube inside the neck

There is enough scuffing on the RWS neck to want to get a better chamber measuement. No scuff on the LC neck there. Both had shoulder rings but only one chambered well.  Without it in my hands I might infer the ejector is forcing contact there  one could remove the ejector button and spring.  

Like I said,  it's not in my hands to get feedback.

Eta The scuff I am referencing is just foreword of the shoulder junction but only on the hard to chamber RWS.

Relevant

http://www.ar15.com/forums/t_6_42/448030_Update__Formed_cases_300_AAC_will_not_chamber.html