FtEj
22JUL03
20JUL03

FtEj is often a sign of a shortstroke, check that the ejector fully telescopes under the bolt face. The ejector spring should be VERY stiff. The ejector spring is, should be, the same spring as the one used under the selector detent, consider it a spare.

FtEx
27JUL03
14NOV03
7FEB05

Usually a weak extractor spring, can also be caused by overfunction, tight HS, rough chamber, or too small of a chamber. Check the extractor groove for signs that the extractor is firmly grabbing the case. If there is a mark from the extractor on the extraction groove then you probably have an overfunction or tight HS.

FtF
13AUG03
17JUL03
3AUG03
28JUL03
1MAY04

Often a sign of short stroke, perform short stroke check as outlined in the Troubleshooting Checklist Part 1 Part 2. Can also be caused by a bad magazine, retest with a known good mag. Can also be caused by mix and match of parts with M4 ramps. Uppers with M4 ramps require barrels with M4 ramps or the nose of the round will catch under the barrel extension. FtF may also happen if the barrel sits too far forward (>0.012" between the front of the mag well and the barrel extension) in the upper.

M4 ramps
ar15.com/forums/topic.html?b=3&f=118&t=174796
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Headspace
Headspace, Torque values, and Barrel Break-in
Need to check my headspace
Chris J. Pikus' HS article
Headspace Gauges
In general, longer HS leads to greater reliability, shorter HS leads to increased accuracy. The military favors reliability, some companies prefer accuracy.

HS gage dimensions as follows:
Military
FIELD 1.4730-0.0002"
NOGO 1.4706"
GO 1.4646+0.0002"
Civilian
FIELD 1.470"
NOGO 1.467"
GO 1.464"
Colt's FIELD II 1.4736"

0.0008"-0.0006" between the GOs
0.0036"         between the NOGOs
0.0028"-0.0030" between the FIELDs

New assemblies MUST be checked with a GO gage before test firing, use of a loaded round is not enough as loaded rounds can be shorter than the GO dimension. HS that is too tight can lead to FtEx and FtEj.

Chromed bores cannot easily have their HS deepened. Non chromed bores can be reamed deeper with a standard chamber reamer. Swapping bolts (assuming that the bolts are good) rarely changes the HS more than a few thousandths of an inch.

Dimpled primers

It's normal for chambered but unfired rounds to have a slight dimple from the firing pin.
03NOV04

to prevent