I just polished my firing pin to make sure there is no drag and also shortened it a tad as it looks like it is protruding a tad too far.  I also broke out my 310 tool and set the primer adjustment to seat 0.004 below flush.  I am changing lots of variables at once which I hate doing but am trying to figure out what is causing the primers to back out.  The problem occurs one the first firing so it is not like the primer pockets are enlarged. I thought for sure that the Baco brass with 0.005 thicker rims would solve the problem but it seems like the make of primer is contributing more to the problem.  Sunday will be my next test day!  Tom

The primer indents appeared to be a bit on the deeper side. But even at that your Primers shouldn't be backing out. That is what is not making and sense if your head space is correct. Have you checked the primer pocket depths to see if they fall within specs. Here is the link to the specs. below.

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The more that I see how the Hepburn works the question seems to be why is the action not opening easily after firing as the primer can only back out until it hits the breechblock.   It seems like if the firing pin is indeed retracting, which now that I see how it works after taking it apart I can easily tell the next time out, then the culprit has to be that the primer is pushing so hard against the block to lock things up.  Cocking and firing again drives the spent primer back in far enough to allow the action to work as normal.  I would think that the small area of a protruding primer would not be enough to completely lock up the action.  There is no in between, the action is either locked or opens easy.  I guess the next step is to try to measure the diameter of my primers and see if one brand is larger.  This is getting better than watching murder mysteries on tv and trying to solve the crime!  Tom

Somebody could have used pistol primers in it. If so there might be an indent in the face of the block that the primer moves back into that is  locking it up.

Run a straight edge across the area where the primer contacts the face of the block it should be flat and minus any indents.

hepburnman wrote on Apr 29^th, 2020 at 4:18pm:


Indeed. Pressure is the essence of primer seating as it relates to deformation of the metallic cup. Primer seating depth is pretty much a tough thing to measure but pressure relates directly to full seating and resistance.  A crushed or deformed cup will result in altering the primer’s design sandwich consisting of explosive, retaining disc and flame anvil. A crushed primer will ignite but flame pattern will be disturbed resulting in uneven burn.