Quote:
Originally Posted by HW223
With many of the loads I develop I find that primer flow around the firing pin is the first indicator that I am nearing Max Pressure. To measure this I use my calipers and zero them on the length of a fired case. I then punch the primer and measure the difference which is primer flow. In my 20 EXTREME there is Zero primer flow with 39/40 grain bullets running at 3500 fps with my low pressure gopher loads. Push them up to 3650 and I get measurable PRE and primer flow which I like to keep at less than 0.003" which is less than some factory rounds in 223 and 204R. Primer flow can reach as much as 0.008", without piercing, but there will be CHE and perhaps even blown primers at these pressures if the bolt does not get sticky.
Primer flow is not necessarily a function of pressure,it is usually more related to mechanics of your particular bolt and chamber set up , pm me and I can explain , we run over 70,000 and have no measurable primer flow or signs of over pressure . All has to do with proper and exact fit of brass , dies and chamber
|
Primer flow will be worse in a rifle with a loose fitting firing pin or loose fitting brass, as you describe, however it is a function of pressure and will grow with each incremental increase in pressure once started. No doubt some cartridges, or even different loads in some cartridges, will produce more pressure on the primers than others and some primers take more pressure than others. I would like to know which cartridge you are running to 70,000PSI and how you are measuring that pressure. The reason that I ask is that the Ramshot Manual show a Compressed Load of 27.7 grains of LT32 pushing a 68grain FB bullet to 3130 generating only 57,896 PSI in a 6mmPPC.
My 20 Extreme runs very close tolerances as I can size with ZERO HS (usually 0.005"), 0.001" clearance at the shoulder and the same at the base datum. Primer flow in my CZ 527 does not look as ugly as it does in a Remington but it is still there after about 58,000 PSI.
The following chart, perhaps what qwert was wondering about, show the results of measurements taken while doing a Pressure Ladder test in a 20 EXTREME LB chamber which was 0.001" larger at the base datum than my 20 EXTREME. It clearly shows incremental pressure increases by Primer flow (protrusion) and corresponding base expansion. Springback is actually brass/ chamber clearance at the Chamber Base Datum and is usually 0.001" less in a standard EXTREME Chamber. You will note that the pressure spike at shot #5 was indicated by the chronograph as well as the PRE and primer flow and remained stable to the pressure increase at shot #9 where I stopped primarily due to the primer flow that was about to go up over 0.0025" where I like to call max even though the case could have taken more.
[IMG]
[/IMG]
Subsequent 5 shot targets (3) showed 20.8 grains of H 322 right on target with a 0.54" group. This summer I tested this load in my new 24" Benchmark barrel installed on my original CZ 527 in 20 EXTREME. It was a Calm day at 24Celsius and this load shot right on target and placed 5 shots into 0.32". The Lab Radar clocked it at 3509 fps and while the Winchester brass grew 0.0005" at the base datum (PRE) the primers did not have measurable flow. I had the same results with AA 2015 at 21.3 grains which was a near full case only the 3541 MV showed slightly higher pressure as the primer flow measured .0015".
I would post targets but PhotoBucket is not uploading??