Can Firing pin protrusion affect SD/ES



  • I have a RPR in .223 that has had problems with cratering primers at low pressures. The load I settled on was 23.9 gr of 8208 pushing the 80 gr eld’s at 2787 with excellent accuracy and single digit sd’s. I was getting real bad cratering and a random pierced primer here and there with no other pressure signs at all. Primers still looked brand new around the edges. This is a common problem for the RPR’s in .223 and last I checked ruger wasn’t fixing the ones that were returned, I’ve seen were a few people have filed the firing pin down and it solved the problem. My firing pin protrusion was .065 so I worked it down to .040 and it worked like a champ, no more cratering or pierced primers. Problem is now that load has gone to shit barely holding 1 moa, velocity dropped to 2750, the ES went up to 60 and the SD somewhere in the mid 20’s. I did a little load development this morning and the numbers were all over the place until I got up to 24.5 gr of 8208 and a velocity of 2825. Once I got to that point accuracy returned and the es and sd went down to decent numbers. These were only 5 round test so I’m still skeptical. My question is could changing the firing pin protrusion caused this or do I have some other issue going on. This rifle has just under 600 rounds through it and the original load has worked perfectly out to 825 yards without any issues, hell I even placed first in my class (FPR) at a 600 yard Fclass match with it.



  • Ignition is a big deal. Bigger than most people realize.

    However, .040 of protrusion is usually enough. Is the pin hanging up somewhere, robbing it of inertia?

    How are you seating primers?



  • @orkan pin isn’t hanging up anywhere that I can tell, moves freely by hand. The only difference I can see is the pin is a little flatter than it was originally, I may try to round it off a bit more. I seat them with a hand primer the same way I always have. Would love to have one of the primers you sell one day.



  • @bull81 The CPS lite is an amazing tool for $200. Not only do I seat my primers at a more constant depth, the speed at which I prime cases has gone up.



  • @norcal_in_az
    I don’t think it works on a forester press does it?



  • @bull81 No it doesn't. However a cheap Lee press for $40-$70 will provide you with a dedicated priming station.

    Just found this press https://www.midwayusa.com/product/403729/rcbs-partner-single-stage-press

    If you also do swaging for military crimps this press would work better than the Lee's.



  • I initially ordered the CPS Lite then went ahead and got the CPS Bench-mounted version. I'll never prime any other way....



  • Well my skepticism was spot on, loaded up 5 rounds of the 24.5 gr load this morning that look decent yesterday and it was all over the place. Looks like the bolt is fixing to be on its way to get bushed.


 

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