I've got a Del-ton 5.56 M4gery that I picked up the dies (RCBS FL 2 die set) and bullets/primers for reloading on Friday.  Since then, I've been having issues with the RCBS dies and I'm beginning to think they aren't pushing back the shoulder enough.  Here's my issue.

I set the sizing die up as instructed (to shell holder, plus a 1/4 turn).  Sized the cases, removed the primer crimps (Federal and PPU brass) and loading a couple test rounds with Win748 and 77gr SMKs to a 2.260" length, I also loaded one to 2.250".  Cases measured right at trim-to length (1.750") prior to loading.  However, they won't chamber.

For a while, I though it was something to do with the SMKs, but the 2.250" length should have zero issues in a nato chamber.  The cartridge will load in the chamber and if I lower the bolt on it, it gets to right where the bolt needs to cam over to lock in and it won't budge.  Light push on the FA is no go.  Dropping the bolt on one in a magazine gives it enough force to chamber and lock the bolt, but it's stiff if you try to pull it back and remove it from the chamber.

After seeing this, I tried chambering both fired cases (won't close) and cases that had been resized with no further work done (still won't close, about the same amount ironically).  Unfired Federal and PPU rounds chamber effortlessly.

Any ideas?  I'm really stuck on this and I'm leaning toward out of spec dies, but this is my first time loading for my AR.  I've loaded for several guns before, including my Savage and Saiga guns in .308, but I've always used Lee dies with no issues.  This is starting to leave a bad taste in my mouth, because I'd really like to be shooting my 69gr and 77gr SMKs.

You could use a case gauge to check the headspace on your sized cases so you know where you are compared to a fired case from that chamber.  When I am loading for a new chamber I check a fired case with the gauge, and keep turning my die down until the sized cases are a couple of thousanths under the fired one.  You may want to try turning your die down some more so it will cam over and push the shoulder back some more, but without a case gauge you could over due it and shorten the life of your brass.

You really need a gauge to be sure.  Sounds like you need to turn it down a little more.

Common problem.

Size case, clean off lube, see if it will chamber.

If not turn sizing die down 1/8 turn.

Size case, clean off lube, see if it will chamber.

Repeat until case chambers.

Quoted: Common problem. Size case, clean off lube, see if it will chamber. If not turn sizing die down 1/8 turn. Size case, clean off lube, see if it will chamber. Repeat until case chambers.

What he said.
My chamber is my case gage.

Also, if that doesn't work, I had to resort to a Small Base Sizing die for one of my ARs.

If it's that close,, just lube the inside of the necks,, if you don't, then when you withdraw the expander from the case when sizing,, it stretches the shoulder ie headspace, out to the point it MIGHT chamber, but will be very hard to eject.
Just do it.
'Borg
ETA if you don't believe me, remove the expander and size a case that won't fit now

 Just check to make sure your deprime punch is not bottoming out inside the case when sizing and at the bottom of the stroke. Some (a lot of) presses have a little slop in the linkage and the die will have to bottom out hard on the shellholder. Dirt or a piece of brass shaving on the bottom of the die where it hits the shellholder will give a few thousandths less closure. I've seen shellholders from all the companies that do not meet spec. They should be .250" thick on the head that extends above the ram and depth from the top to the shelf that the case head sits on should be .125". Mine vary. I have an RCBS, Lyman, and Lee and they all differ just a little. The main measurement is from the top of the shellholder to the shelf the case sits on, .125".
If the dies are new, cleaning them good with some solvent might help. Using enough case lube and lubing the inside of the neck evenly might help. I bought a RCBS Precision Mic and also have Hornadys (formerly Stony Point) gauges to set my dies. You never know until you get a tool to check the shoulder set back what your dies are actually doing.

Thanks for your help guys.  I had to keep screwing in the die, another 1/4 turn before headspace would allow the case to chamber.  All seems fine now, but I didn't expect to have to cam over that much just to get the cases to chamber.

At least now I have some Mk262 knockoff ammo to play with.

Quoted: Also, if that doesn't work, I had to resort to a Small Base Sizing die for one of my ARs.

+1

The chamber maybe a .223 Wylde, that seems to need a SB die.

Quoted: Quoted: Also, if that doesn't work, I had to resort to a Small Base Sizing die for one of my ARs. +1 The chamber maybe a .223 Wylde, that seems to need a SB die.

I have several AR-15's with Wylde chambers and I have never needed a small base die.  However, every chamber is different, and dies vary from different manufacturers.

Quoted: Quoted: Quoted: Also, if that doesn't work, I had to resort to a Small Base Sizing die for one of my ARs. +1 The chamber maybe a .223 Wylde, that seems to need a SB die. I have several AR-15's with Wylde chambers and I have never needed a small base die.  However, every chamber is different, and dies vary from different manufacturers.

Wylde's are pretty generous in the body.  That shouldn't be the reason.

What dryflash3 said.  I use an RCBS SB die and its set up to run 3/8 of a turn past bottom.  Take a marks-a-lot to the case and color it real good.  Drop it into the chamber and let the BCG go home.  Yank the case out and take a good look.  Ten to one that they'll be a nice pretty ring just north (about 5/32") of the extractor goove from not being sized back far enough and that's where its sticking.

I doubt that it's the chamber.

It's probably has more to do with the way you do things.

This is how I re-size cases and how I check during the process, to ensure functionong ammo for the "family of ARs" that I own.  Note it's step #6 in my process.

6) I use a single station press (RCBS Rock Chucker). You could use a progressive Dillon IF you wanted to. It's a personal choice. But, with whatever press you choose, consider shell plate/shell holder and/or press "flex.”  I use a regular FL size/de-capper die, NOT the small base dies. To begin, FL size and de-cap, 1 or 2 cases for a test. Gauge the re-sized case(s), to confirm that the "correct size" has been achieved.  I use a Forster Products case gauge (the Wilson gauge is also a popular choice).  Insert a case into the die.  The headstamped end of the case, needs to be at or between the high and low cuts on the gauge, to pass. This checks the headspace.  While the other end, is used to check if the case will need to be trimmed (a job for later on).   IF, it’s not the “correct size,” your die setting will need adjustment. Lower the ram and simply screw the die in or out a little. Don’t forget about the lock nut. Then, re-size another couple of test cases and check your work again. Repeat the test and adjustments, as needed.  When you're satisfied that your test cases are properly re-sized, do the entire lot. For those who don't know about it.........IMHO…………"the secret" to re-loading a bottle neck cartridge is.......a case gauge.  There are many different brands and ways to gauge your re-loads.   Examples…….. www.sinclairintl.com/cgi-bin/category.cgi?category=REMTHT&type=store

Aloha, Mark