Here is a post I made in the "AR Basics" forum a week or so ago.

Ok, I'm 100 or so rounds into my new AR-15. I'm reloading 50 and 55 grain bullets in standard "book" recipes. I bought a Dillon head space gauge and check every piece of brass after it is primed but before loading the powder and seating the bullet to make sure it falls right into the gauge and there is no excess length. The bullets are seated at the published length for the rounds. Still, every once in awhile, I'll get a live round failing to completely chamber and it takes some good force to retract the charging handle to remove the round. What's strange is that I can take this same round that was "stuck" and it will drop right into the chamber and fire! This tells me that the round itself was in spec.

Do these random "jams" happen as a result of bad magazines? If not, what other things might be causing this behavior?

Thanks for any help you might offer.

Now, I've cleaned my chamber - made sure my resizing die is fully "camming over" - and even bought a factory crimp die and am now lightly crimping the finished reloads.  I have loaded 50 grain SIerras and 55 gr Hornady Ballistic tips.  Today I had my grandson out shooting my Browning 1885 single shot in .223.  I had a bunch of the 50 grainers loaded up.  First few shots - perfect.  Then I went to put one of the rounds into the chamber and it stuck with a full 3/8 of the back of the shell casing hanging out the chamber.  I pulled it out and took the gun inside and scrubbed the chamber - dry patched it - the put a thin, thin coat of oil in the chamber.  Didn't help one bit.  So I took every reloaded shell I had and used the 1885 to "check" for similarly swollen casings. Out of about 50 shells, 80% of them dropped into the chamber with ease. 20% wouldn't go into the chamber even with a pretty hefty push of my thumb.   ALL of these reloaded shells had dropped into the Dillon gauge without a hitch.   I'm trimming all brass to length and chamfering after resizing.

So I then took these "bad" cartridges and looked at what brand they were.  I thought maybe I had some .556 rounds and was trying to put them into a 223.  To my surprise, every "bad" cartridge was a Winchester with one R-P!!!  None of the Lake City brass had given me a problem.

I'm getting really frustrated.  What in the heck is allowing 80% of the brass I'm loading to work fine and 20% to apparently be swollen at the base such that it won't go into my Browning single shot or a TC 223 barrel, much less my AR-15.   As I plan on hunting with this AR-15, I've got to make sure my reloads are dependable.  I don't want to be out in the middle of nowhere and have one of these rounds jam into my chamber such that I can't retract it.  

Any ideas?

Some of your brass may be over expanded from a large chamber  small base dies might help like the ones from RCBS. The ones I run across will usually size real hard or you can see the swell at the base after resizing. Just a thought.

Are your trimming your brass?
If so, what trimmer are you using?

Coat a cartridge with Dykem bluing or just use a black Sharpie and chamber to be certain of the interference location.

I think the small base die may be worth investigating. On the other hand, it may be more cost-effective to simply sort out the Winchester and R-P brass and save them for future use (when you have a small base die). It's not that the brass was bad, but that it was fired in a looser chamber.

Should be pretty easy to see what the problem is...

Take 4-5 cases that would chamber and 4-5 that would not and measure every dimension of the case, neck, crimp, base, etc.

All of your chambered rounds should have measurements below x" while the unchambered bass will be above x".

You can put together a spreadsheet to compare all the measurements if that makes it easier.

It isn't the dies, its the process. Plenty of people used non small base dies before they existed and plenty still use them.

Shooting them from different guns leads me to believe its the process. Try taking a fired case you haven't resized yet and completely setup the dies like the instructions say.  I have loaded on an RCBS single stage press for a long time and my die doesn't contact the shell plate and I don't have feeding issues. Maybe run one or two cases through the process and seat a bullet and see if they chamber. I'd use a case that caused you problems before.  I also wouldn't personally crimp but that's my choice.  If you setup the dies using a case that didn't chamber before it might help you ing nose the problem.  Also check overall length of the cases as mentioned. If your cases are closer to 1.800" it's an easy fix. Trim everything to an even length like your reloading manual states.

Does your seating die also crimp? If so make sure it's backed off to not crimp on even the longest cases. With the issue being random I was thinking maybe on some longer cases the crimp part of a seating die might be slightly crushing cases at the base of the neck

If the empty cases fit the gauge before seating the bullet, check your seating die adjustment as stated above.

I guess I missed this but what is the overal length of the completed round ?
Is it over 2.260 ????
Do you bullets slide around after you are finished loading.
If you cam over on your press you may be causing the base of the case may be
getting "squished" or the top of the body of the case is being "squished" also this will enlarge the case by a few thousands .
Just trying to help...
John

I sure appreciate all of the suggestions here.  I went ahead and ordered a RCBS small base resizing die.  Will report after sizing with this new die.

• I am full length resizing with a slight "cam over" at the end of the stroke on my RCBS press.
  I am trimming all brass with a simple Lee trimmer, then chamfering the case to remove burrs.  
  I am not using any neck lube.
  The length of the loaded rounds right now are 2.205"
  Every casing and every loaded round have been put in a Dillon head space gauge.  All of them, including ones that subsequently "stuck" in the chamber, have dropped right into the gauge with absolutely no resistance. I carefully check casings to make sure they are not too long.  I guess I misunderstood the usefulness of this gauge.  I thought if a live round dropped right into the gauge, it would work in the chamber. Not!

Hopefully the new die will be the ticket.

You don't need a new die unless the one you own is defective. Small base dies are rarely ever needed, especially when using a 5.56 mm chambered rifle.

Buy Hornady's Lock-N-Load headspace gage, it will give you a true measurement in .001" increments for setting up your dies. Drop in gages are a waste of money, especially when the Hornady tool will work with multiple calibers straight from the factory.

Talk about feeling like a dummy.  Thanks to a fellow AR15.com member, I finally figured out the problem.  I PM'd the member and he called me.  Suggested I probably had the bullet seating die set too low and was crushing some of my casings, but not all of them.  I totally forgot to re-set my die after a year or more of not reloading 223's (just bought the new AR-25).  Sure enough, it was WAY too low.  Just crushing a small portion of the casings I was seating bullets into.

I would look carefully at the case measurement. Gas guns can be hard on brass. You might want to go with SBD's or look at bumping the shoulders back a .001 or so. I have to bump the shoulders on my 06 shot out of my garand.

It's good to hear you found a solution.