Extreme group difference with just seat depth

dan158

New member
I am shooting at 300 yards now with the 20 prac.. I changed my burris scope out for a working Nikon 4x12..
Anyway my 100 yard load wasn't working for 300 yards.. Even though I was under a dime at 100.. At 300 yards my groups went well over 3 with the closest bullets being 3 in a group out of 5 at 1.5 inches.. So I worked new loads and went from 3 inch group down to a 1 inch group..

Like this.. I loaded 3 at 26.3 and shot them at 1930 OG measurement.. That group was almost 3 inches.. My next 3 was loaded also at 26.3 but seated at 1925.. That 3shot group dropped to under a quarter at 300..

I also worked up 25.9 and shot 3 at 1930 and 3 at 1925 and 3 at 1920 all OG measurement.. Now the first 2 groups at 1930 and 1925 was large and uniformed.. The 25.9 1920 put 3 under a quarter at 300..


I also did 9 rounds at 26.1... 3 at 1920 3 at 1925 and 3 at 1930 They would not produce anything..


But has anyone else had this happen just with a seating depth change?? I got to powder charges now that shoots under a quarter at 300 with 2 different seating depths..


I will load up more of these charges and see if was a fluke or what?? Also the impact on the target from these 2 was very close to where they hit.. Almost identical really..

This was an extreme group shrink just from changing the seating depth.. Dan
 
Seating depth can make a huge difference. If I understand your numbers, you're showing a 5 thousandth difference in seating depth, measured off the ogive?

I started doing all my load work at 200 yards a couple years ago. Too many times a good 100 yard load fell apart further out. Usually if I can show consistency at 200, it holds true on out to 500.
 
Yes correct a 5 thousands on the 26.3 load and on the 25.9 its 10 thousands.. I just made up 5 rounds each and will go test them in a bit if weather still permits.. Dan
 
I've had a group of .30-06 110 Sierra HP go from 1" @100yds down to 5/16" by adjusting OAL. In all of my important loadings I get as accurate as I can by varying powder charge and then play with the OAL to dial it in better if possible.
 
2n07r4g.jpg

This test shows what you are describing. You will notice at .015" off the lands the group doesnt move point of impact regardless of powder charge. This is the perfect seating depth for this bullet.
This is a great way to find the sweet spot for your bullet

 
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Originally Posted By: Kevinfarmer3456
2n07r4g.jpg

This test shows what you are describing. You will notice at .015" off the lands the group doesnt move point of impact regardless of powder charge. This is the perfect seating depth for this bullet.
This is a great way to find the sweet spot for your bullet
Excellent idea, Thanks
thumbup.gif


 
Originally Posted By: Kevinfarmer3456
2n07r4g.jpg

This test shows what you are describing. You will notice at .015" off the lands the group doesnt move point of impact regardless of powder charge. This is the perfect seating depth for this bullet.
This is a great way to find the sweet spot for your bullet



Have you tried this with different bullet weights?? Thanks for a look at your way to do load test.. Dan
 
Originally Posted By: dan158Originally Posted By: Kevinfarmer3456
2n07r4g.jpg

This test shows what you are describing. You will notice at .015" off the lands the group doesnt move point of impact regardless of powder charge. This is the perfect seating depth for this bullet.
This is a great way to find the sweet spot for your bullet



Have you tried this with different bullet weights?? Thanks for a look at your way to do load test.. Dan ive never tried this at all. I saw this in a post on accurateshooter forum
 
Why would one care about consistent POI between mild and hot loads, apparently several grains apart? Why would this be useful?

Don't most of us shoot one single load, generally on the hotter side? Especially with modern temp stable powders like H4350 etc? Seating depth is pretty easy to be consistent (set it and forget it) compared to measuring powder where your measure might be off a tiny bit from shot to shot.

Wouldn't a consistent POI over a slight spread of powder weight be more important than the seating depth target posted above?
 
This is a method used to determine the best seating depth for that particular bullet in the gun. Basically you're finding the node for the seating depth. And it shows that if the powder charge varies a little bit one way or another your point of impact will not change this would be very useful for hunting and competition situations that way if your powder charge happens to be a few tenths of a grains off it's not going to affect your point of impact at all
 
Last edited:
Originally Posted By: Kevinfarmer3456This is a method used to determine the best seating depth for that particular bullet in the gun. Basically you're finding the node for the seating depth. And it shows that if the powder charge varies a little bit one way or another your point of impact will not change this would be very useful for hunting and competition situations that way if your powder charge happens to be a few tenths of a grains off it's not going to affect your point of impact at all
In this test you're saying the mild, med, and hot loads are all within a few tenths of a grain of each other? Because most cartridges require more than a few tenths to go from mild to hot. The exceptions are most likely some of the smaller 17cal cartridges etc.

When you say a few tenths of powder variation won't affect your point of impact at all, are you limiting your statement to 100 yards or does that also apply at 300 yards? How about 500 or 1000 yards? Does that special seating depth node neutralize the velocity variations caused by "a few tenths" more or less powder? Or does the velocity still fluctuate between powder loads but somehow the POI remains the exact same?
 
Originally Posted By: DiRTY DOGOriginally Posted By: Kevinfarmer3456This is a method used to determine the best seating depth for that particular bullet in the gun. Basically you're finding the node for the seating depth. And it shows that if the powder charge varies a little bit one way or another your point of impact will not change this would be very useful for hunting and competition situations that way if your powder charge happens to be a few tenths of a grains off it's not going to affect your point of impact at all
In this test you're saying the mild, med, and hot loads are all within a few tenths of a grain of each other? Because most cartridges require more than a few tenths to go from mild to hot. The exceptions are most likely some of the smaller 17cal cartridges etc.

When you say a few tenths of powder variation won't affect your point of impact at all, are you limiting your statement to 100 yards or does that also apply at 300 yards? How about 500 or 1000 yards? Does that special seating depth node neutralize the velocity variations caused by "a few tenths" more or less powder? Or does the velocity still fluctuate between powder loads but somehow the POI remains the exact same? not really sure on all of those questions, seeing as ive never performed this test yet. I just saw it as a post and the guy that showed it stated it was an easy way to find your seating depth.
 
Kevin's method is basically the same method we use to fine the tune on a benchrest rifle. It's all about harmonics. It works and is repeatable. A steady POI across powder charge is desirable.
 
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