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Rifle Loads
gcs10
Member Posts: 32 ✭✭
I have gotten back into the centerfire rifle reloading process after many years of pistol and shotshell reloading. When searching for the load your rifle likes, how much change in powder charge is rational? Is a .5 grain change too small or too large?
I am loading a .308 Winchester with 44.0 grains of IMR 4064 and a Sierra 125 grain soft point and with 42.0 grains of Hodgdon Varget and a Sierra 168 grain Match King.
I am loading a .308 Winchester with 44.0 grains of IMR 4064 and a Sierra 125 grain soft point and with 42.0 grains of Hodgdon Varget and a Sierra 168 grain Match King.
Comments
At the lower end of the spectrum .5 grain change is not out of line for working up a ladder. When you get to the upper end .2 gr. change is more the norm.
Some people work in percentages. I've found this to be relative when backing off in big chunks to find starting loads. However, percentages don't measure huge pressure increases with small powder increases. Meaning they each have a curve and depending on where you make them meet, they won't meet again. Percentage increases proportionately. Added powder increases pressure exponentially.
I have always recommended one percent of the book maximum as the charge increment. If the book maximum is 100 grains, that would be a one grain increment. If the maximum charge is ten grains, that would be one tenth grain increments.
One percent works with ANY round.
[:)]
This is the manufacturer's suggestion for the load range of your bullets:
125 GR. SIE SP IMR IMR 4064 .308" 2.700" 46.0 2891 42,500 PSI 50.1C 3119 52,100 PSI
168 GR. SIE HPBT Hodgdon Varget .308" 2.800" 42.0 2520 41,200 CUP 46.0C 2731 50,600 CUP
In a recap:
There are no hard and fast rules regarding this process.
As pointed out small cases require smaller increments while larger cases can accommodate larger increases.
As you approach the maximum load, smaller increments are recommended since they can produce greater changes in pressure as you near the upper limits.
There is usually more than one accuracy 'node' for a cartridge/bullet/powder combinations. In essence, you don't have to stop at the first node with the lowest velocity but you can proceed upward with your testing ladder to the next node.
As Francf states, be aware of the environmental conditions as well. These can work both for and against you under some sets of conditions. Loads developed in the cool of winter may be a problem in the heat of summer.
Best.
Once you find a sweet spot, accuracy node or whatever you choose to call it, you might want to "tweak" the load a small amount either side to see if further improvement is possible. If, for example, you find a tight-grouping load at 48.5 grains, you might want to try loads at 48.3 and 48.7 or so to see if the true sweet spot falls between two normal increments. But it is pointless to try smaller increments than that because of all the other variables mentioned.
"I used the Sierra numbers while I suspect nononsense is using Hodgdon's numbers. Who is right?"
I don't think that it's a matter of right or wrong but just showing the variations of two separate loading suggestions. This is a good example of why most of us use several sources for reloading data and often compare them to each other. Powder manufacturers and bullet manufacturers often use different techniques to derive the data that they publish. Then there are the variations in powder lots which can be significant when testing data.
It also makes a point for testing loads in your own rifle instead of simply using the suggestions from the reloading manuals or other shooter's data. The process of working up loads is made for deriving information specific to your techniques and firearms.
Best.