When testing seating depth what increments do you use, .01', .02' or more for ladder tests? I've got a load for 180 gr Sierra SPBT that is pretty accurate seated at 3.3' and I wanted to see if I could wring a little more out of it. How big of an increment should I use when doing a ladder test and how far in each direction should I go, +/-.1' or +/-.2' or more?
SEATING DEPTH QUESTION
- Thread starter On_Point
- Start date
This is what I do.
Load up groups of three or five rounds with differences of .005' or .010', then shoot and see which depth groups the best.
EDIT: Please note. For those of you that do not have an acurate reading of your chamber length, you need one. You do not want to inadvertenly load a round with a jam fit into your lands without knowing it, particularly if you are already on the hot side of things.
Something interesting to note in both tests below is how POI changes even though POA remains constant. As seating depth changes, so also does POI.
Then load groups +.001, +.002, -.001, -.002 on either side of the depth that grouped the best. In this example,'0' is 2.285,'+1' is 2.286 etc., you get the idea.
This time my original seating depth chosen from the .010' shot best. I have examples from different rifles where it got better when I either made small adjustments either up or down in the 'micro' tests. Notice these groups are larger than the first set, it was a considerably windier day than the initial test.
Then I shoot a five shot group with the best three shot group from the 'micro' test to confirm. Notice that this group, which is my rifle/cartridge ideal seating depth, is smaller than any of the other three shot groups in the initial test.
It's not bad for a completely stock factory rig.
Hope this helps. Good luck.
Load up groups of three or five rounds with differences of .005' or .010', then shoot and see which depth groups the best.
EDIT: Please note. For those of you that do not have an acurate reading of your chamber length, you need one. You do not want to inadvertenly load a round with a jam fit into your lands without knowing it, particularly if you are already on the hot side of things.
Something interesting to note in both tests below is how POI changes even though POA remains constant. As seating depth changes, so also does POI.
Then load groups +.001, +.002, -.001, -.002 on either side of the depth that grouped the best. In this example,'0' is 2.285,'+1' is 2.286 etc., you get the idea.
This time my original seating depth chosen from the .010' shot best. I have examples from different rifles where it got better when I either made small adjustments either up or down in the 'micro' tests. Notice these groups are larger than the first set, it was a considerably windier day than the initial test.
Then I shoot a five shot group with the best three shot group from the 'micro' test to confirm. Notice that this group, which is my rifle/cartridge ideal seating depth, is smaller than any of the other three shot groups in the initial test.
It's not bad for a completely stock factory rig.
Hope this helps. Good luck.
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