Can you use Pistol Primers in a rifle? In an AR15?  People say it can't be used because the primers pop.  But what if we lower the pressure to same/similar pressure that small pistol primers are designed for? Will it work good?
Pistol Primers in Rifle
Pistol primers have thinner cups than rifle primers.  So if you use pistol primers in a rifle, like an AR15, at rifle pressure, they will blow, like the picture on left. 

Pistol primers are designed for pressures, generally under about 40k PSI
Rifle Primers are designed for generally under 60k PSI
Rifle Primers for 5.56, such as CCI41, or Winchester 21 556 primers are made for higher pressure, and I think they are good for ~65k PSI and under.  These are just general estimates, and not facts.  But you get the idea.  The higher the pressure, the thicker the cup, the more recinforced the design.  And Pistol primers are thinner than rifle.

So the picture on the left is pistol primers, that are designed for generally under 40k PSI, being operating at basically 56k PSI.   They blow. 

So how can we make pistol primers work in an AR15?  You may already know the answer, because its obvious.

Pistol Primers in AR15:  Lower the pressure!
Ok, top row, with that 1 nickel Winchester brass, s 24.0 grains of Accurate 2230.  This is 55 grain FMJ 2.250 max charge for basically 56k PSI would be around 25.5 grains, bceause of the super long OAL.  With 2.200 it would be 24.9.  The following are general estimates, using various methods, such as one popular pressure calculator.
24.0 AA2230 ~51k PSI  Super flat primer.  Cratered.
23.5 AA2230 ~48k PSI  Super flat primer.  Cratered.
23.0 AA2230 ~44k PSI Super flat primer.  Cratered.
22.5 AA2230 ~41k PSI Less flat primer.  No crater
22.0 AA2230 ~38k PSI Slightly flat primer.  No crater
21.5 AA2230 ~35k PSI Rounded primer, normal looking firing pin strikes

All loads, easily cycled a "non adjustable, normally gassed" direct gas impingement 20" AR15.

And the 21.5 shot soft, low recoil.

If Pistol primers were all I had? I would use them in my rifles, without even hesitating, and load them to estimated 35k pressure, like above 21.5 Grain AA2230 load.

That doesn't mean we are telling YOU to do it.  Do not do what we do.  Consult your powder choice manufacturer first, to understand their recommended minimum.  I would recommend Shooters World Tactical rifle powder, which is designed for this, as it can go as low as ~18 grains and still cycle most AR's. 

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