The Remington BENCHREST primer is OK for 5.56 but not standard small rifle as M&P correctly points out. The CCI company puts out a milspec primer for 5.56 which I think is #34 but double check on that to be sure.
By the time I get to Camp Perry for long range they are all gone so haven't got any.
In the interim Wolf makes a heavy cup primer for 5.56 and I am using them with no problems.
As a point of interest if you are using heavy cup primers and you get misfires replace the striker spring with the next energy range up from "factory" which are available from Wolff Springs.
The old industry (SAAMI) recommendation for center fire rifle striker indent performance used to be .020" indent on copper. I understand they have reduced this to .016" at the request of some vendors.
The M16 requirement IS .022" INDENT ! ! ! ! This is the second hardest primer in US Gov't inventory. The hardest primer to ignite is the Cal 50.
Case in point I bought a new Remington 7615. I was getting reverse primer flow on not only Remington BR primers I loaded but M193 MILSPEC. I ordered replacement springs from Wolff and the reverse primer flow ceased adruptly.
Now the term "copper" is a pressure copper used in obtaining chamber pressures and HAS NOTHING TO DO WITH INDENT ON PRIMER. They are used in "copper holders" which resemble a headspace gage except it has a flat bottom hole in rear where primer would be. The copper is placed therein, weapon held vertically with muzzle towards floor and trigger pulled. Copper is removed and a bench inspection gage is used to determine the depth of the indent. Thusly if you find a headspace gage that doesn't say GO/NO-GO/Field Service that has a flat bottom hole in back you have a copper holder. I rather doubt you will find such in gun shows though I know one guy that sold his Carbine gage at a gun show in Denver about 30 years ago.
The next thing to cause misfires is offcenter striker indent. You striker dead center should not be offset from the dead center of the primer more than .020" for ignition reliability. The industry puts them out at one half offset which is about .030" as the strikers are generally around .060" diameter for medium and large bolt face rounds. Bottom line guys is the more dead centered your striker hits the primer then it doesn't get any better.
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