Quote:
Originally Posted by HW223
On your pressure ladder it appears that you have a spread of 1.5 grains
On my grid it’s 1.2 grains ,yours is a ladder but mine is “fine tuning “
How does that work ?
I guess it’s all perspective, we will have to agree to disagree on methods , how ever there are so many variables on your ladder that are not accounted for how can you be sure it’s a pressure spike causing the bullets to spray around also why do I not see it with my varmint stuff using Boyer’s method over almost the same spread ?
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I do not disagree with your method if it works for you that is fine. It does depend on what cartridge I do a pressure ladder for as to the increments that I use. On small capacity cartridges especially with smaller calibers, I prefer to use0 .1 grain increments as sometimes pressures can rise very quickly but I will start low, with larger increments, when starting with no pressure data available. Actually I have used spreads as low as 0.3, in 0.1 grain increments , for many loads especially if just changing bullets or bullet weights. I don't know what variables that you are referring to , in regards to my ladder, as the only thing I change from shot to shot is one small measured powder increment??
If I have a cartridge, powder, bullet combination that allows for a low pressure node and a higher pressure node with a full case, like 8208 and 39/40 grain bullets I will do a ladder in 10 or more increments looking for the nodes. Then I will do 5 shot groups, as I have shown, within those nodes to select the best load. Pressure spikes are confirmed by the chronograph velocity readings as it does take more pressure to push a bullet 30 + fps with a 0.1 grain increment. This also tells me that the brass is beginning to yield and the pressure can be measured by the Pressure Ring, or Base Datum, expansion as well. I believe that the pressure/increment drops off until the next brass yield point as it is also indicated by a pressure spike as indicted by primer flow, velocity or PR expansion. This is why I call it a Pressure ladder and what you are doing as Fine Tuning as I could do the same thing as you are doing within the Good Nodes to fine tune them. You are already working within a pressure range that is well known and have more than one node, likely at each increment that your powder thrower throws, as that is what Tony Boyer does?
The first cartridge case that I pictured earlier, or the one you referred to as a week load, was actually a new Winchester brass loaded with 21.4 grains of 8208 pushing the 39 BK to about 3500 fps which is my good light gopher load.
The Rem 7 1/2 primer showed no pressures signs at all although it would have likely blown if that bullet was pushed to that velocity in a 20 VT. It would have looked great in a 20 Tac or 204R but accuracy would likely not be great at that velocity. The New Winchester brass expanded about 0.0005" which left about 0.001" chamber clearance at the base datum. Upping the charge to a full charge of 22.4 grains, in the second case which you called a light load, actually pushed the 39 grain bullet to about 3650 fps, which is close to what a 20 Practical/tactical will do at about 60,000 PSI. The Rem 7 1/2 primer flows into the firing pin hole by about 0.0010" as shown in my resent post to sns2 and the base expansion was about 0.0010" leaving about 0.0005" chamber clearance. I really do not like to pressure my loads any more than that as I do begin to get some case stretch and may have to trim after 7 or 8 firings??