Rounds jammed in AR chamber

[triggerhappy243]

I compared your loaded round to mine. your neck dia. is 3 thou. larger than mine. I use winchester brass.

My brass is trimmed to 1.745, my OAL is 2.250. The outside dimension of the loaded rounds is .251 and the bullet measures .2235 just in front of the case mouth. The case rim is .3775 and the base of the case measures .3755. They drop in and out of an EGW .556 case gauge. The barreled upper will be back on Tuesday and I will super clean the chamber and bore. I will load up and mic a few dummy rounds and see what happens when I chamber a case. I've had in the past the shoulder collapse slightly when too aggressive a crimp was used and had a round not fully chamber (maybe 1 in 1,000). Since using the EGW chamber checker, I catch any out of shape rounds even that look good to the naked eye. I'll let you guys know what happens. Rod

[rodsvet]

I just went out and randomly mic'd 5 loaded rounds neck diameter and they were all .246-.248. The .251 was where the crimp was applied and those rounds were too short to accept the lee factory crimp die correctly. They were 1.740. My Brass is mostly once fired FBI brass. Much of it fired full auto 12 inch barrels. Rod

[triggerhappy243]

try loads with no crimp. I never crimp.... no need to crimp in my setup. Your crimp may be putting a slight bulge in the neck, and that is where it is jambing.

[rodsvet]

With the short brass (1.740) the Lee factory crimp die was just barely catching the case mouth and causing a slight drag in the chamber. It's the shoulder setback that appears to be the problem. Rod

[triggerhappy243]

AH....... Wonders never siece.

[joelpend]

Exactly. I work some as a RSO at a local indoor range and I see this all the time. Real easy for improper crimp to swell the case just behind the shoulder. You can see it upon close inspection normally.

try loads with no crimp. I never crimp.... no need to crimp in my setup. Your crimp may be putting a slight bulge in the neck, and that is where it is jambing.