Problem with 5.56 reloads

[Stats Shooter]

I have personally had the exact same problem twice. The first time it happened, it was because I attempted to crimp the load, which bulged the shoulder out a little, and the bolt would not fully close...that was with a SAIGA .308.

The second time was because, like you, I short stroked the re-sizing die.

Another common FTF cause is high primers, where the firing pin essentially pushes the primer deeper into the pocket rather than cause ignition....this is can also happen with loose primer pockets.

Finally, untrimmed cases or bullets seated too long can have the same effect.

The issues above are more common in a semi-auto because the bolt cams in a bolt action are far more powerful than the spring in an auto loader. Therefore the bolt can be forced closed and the round will fire though the bolt may be "heavy".

 

[CTSixshot]

I've also had some cases (7.5 Swiss) that I annealed (too much) that distorted while seating the bullet.

 

[HiBC]

Good job post 19!

Something about gages: There can be a "plunk" gage,which should resemble a min spec chamber.
But that is NOT the function of the Wilson and similar case gages.The bushing type case gages check LENGTHS ONLY.Not diameters.To do their job,the must have clearance on the diameters.They check the cartridge trimlength,and the cartridge headspace length.Thats it.

If your cartridge is getting stuck in the bushing gage,its a high probability the shoulder was bulged by over crimping.You are getting a locking taper effect.

Now,you may very well have inadequately resized the brass.You may have brass where the shoulder was not set back enough.That needs attention,its important,but I think its a red herring from your initial issue.

Someone explain to me how the neck of a loaded cartridge,filled with a bullet,can enter a sizing die far enough to bump a shoulder back.

The partial sizing described reduced the diameter of the bulged shoulder.Thats a patch on a symptom.Now,crushing the shoulder with the seater die/crimp will cave in the "headspace" as it bulges the shoulder,but the root cause of problem "A" is in the adjustment of the seater die.

YES! If you intend to crimp,the case lengths need to be uniform after sizing.
Yes,a collet crimp die is more forgiving.

OP,if I may ask,did you start out setting up for a very light crimp? OR did you just run the seater down to contact the shellholder? That is the best,the classic way to bulge the shoulder.Did you plan,and set up to crimp? There is controversy over crimping for an AR.I don't.A lot of other folks don't.Some say if you should set a bullet back in feeding,it can cause a kaboom.Thats another thread for discussion.If you do not intend to crimp,Put a sized,trimmed case in the shelholder.Ram up.Screw your die down.You will feel it stop on the case mouth.Back it up a bit.!/4 turn is good.Lock down your ring.
Crimping is very sensitive if you are not crimping intoa cannelure.It has no place to go,besides swaging the bullet down.Its easier for the shoulder to crush.
If you choose to crimp,get a Lee factory crimpdie.They are cheap,and they work good.

Maybe you did short size them.You need to get that down,and verify it with your bushing gage.

But there is a critical difference between a case that is too long(the locking lugs may not go to full battery,)and a case that has too large of a shoulder diameter.Its the large diameter that gets stuck in the chamber or gage,in the taper.

More on the gage: A bushing gage for setting the shoulder length in the sizing process is USELESS if it gives results based on diameter.It MUST have diameter clearance to measure length.
A gage for tool setting must ISOLATE ONE VARIABLE or how else do you know what you are setting?