Quote:
Originally Posted by lclund1946
The primer flow shown is indicative of an oversized firing pin hole and not indicative of high pressures as you have explained and can be fixed by bushing the hole or replacing the bolt with a custom one. Remingtons are noted for this but the flow is still caused by pressure as that problem will also disappear as pressures drop to Saami pressures just as PRE does.
The primer flow I am measuring is into the firing pin hole at the center of the primer and usually happens afterflow into the outer radius or "flattening". It can be caused by a weak firing pin spring but is most likely caused by the pressure getting to the point that the firing pin is pushed back as pressure builds. I know that my 20 caliber rifles do not have this problem as it does not show up until pressures get well above Saaami Pressures for the 222/223 cases and PRE reaches near max. My 20-223 EXTREME has allowed me to compare results with those on Factory 223 ammunition and they are the same. In all 20 cal rifles that I have done this with, including CZ, Remington and Sako, this flow, would get to about 0.008" before Rem 7 1/2 primers pierce and occasionally they blow as the primer pocket stretches by 0.007" which takes a whole lot of pressure. This will usually happen without the bolt handle seizing with these cartridges although it may get" clicky". I have found this true in other cartridges as well and have only had a problem due to intentionally pushing to the limit to try and find the Max chamber dimension at the datum, in these wildcats, as my measurements keep me in the "safe zone" which is much before the bolt gets stiff .
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HW223: Of course you are right in that my results are for the scenarios that I have posted and vary from cartridge to cartridge and component to component. However the same principals apply unless you go to custom actions that have much closer tolerances and perhaps stronger firing pins. In that case the pressures will be higher before they show up on the primers and velocity spikes will likely be the most accurate way of staying in the "safe" zone followed by PRE. Brass does vary in how much it will resist PRE expansion and there is quite a difference in PRDiameter between new brass which has to be taken into consideration. Contrary to what most believe the larger base and thicker neck dimensions on 223/222 LapuaM brass does not make them resist pressures more than Lake City, Winchester, Hornady or even Remington or Norma for that matter. I know this as I have run the 55 Berger to over 3330+ fps, in both brass , with the same components (IMR 8208 & CCI 450 primers), and the Winchester brass will hold a primer while the Lapua will not. However this would not have happened if I had stuck to my pressure limits as indicated by primer flow as PRE was not reliable due to an oversize chamber at the base datum. I have since found the right combination using Varget that gets me safely to just over 3200 fps and targets show a potential "good load".