Surprised with Berger 220 grain LRHT seating depth test

MtnHunterCO

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Oct 25, 2015
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Wondervu
Before I started load development with some Berger 220 grain LRHT bullets, I called Bob at Berger to get a bit of load data using N570 since Vihtavouri doesn't have load data for 300 PRC. Bob said to do a seating depth test before a ladder test. I've always worked on charge first, so I was surprised by that suggestion.
Since Berger obviously knows more than me, I made up three rounds of various seating depths. The results were more dramatic than I would have guessed:

3.5 MOA with .045 off the lands
2.8 MOA with .040 off the lands
2.2 MOA with .035 off the lands
1.2 MOA with .030 off the lands
0.5 MOA with .025 off the lands
1.1 MOA with .020 off the lands
2.0 MOA with .015 off the lands

Anyone else ever work on seating depth before varying their powder charge?
 

khuber84

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Jun 6, 2019
Messages
565
Seating depth is the coarse adjustment, powder is the fine. I usually run a 2 shot per charge rough ladder at initial start of development, find a spot where 2 dif powder charges are withing 10-15fps of each other, load my seating depth test in the middle of that node. Then shoot seating depths at distance in pairs of 2. I look for nodes of least vertical dispersion. Usually you'll find a 10-15k wide band that holds 1-1.5" at 600y. I usually work in there with my powder tuning now for groups at distance.
 

khuber84

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Jun 6, 2019
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565
I'd go further off the lands. You'll find a lot of Berger hybrids like to shoot in the 75-100k off window. Vlds too!
 

10ga.

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Aug 19, 2017
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5
I’ve never saw a gun go from .5moa to 3.5moa with just a .020 change in seating depth. I normally start load development at .010 jump testing powder charges. After I find a load with good ES and acceptable accuracy I do a seating depth test to tune in the group size.
 

khuber84

Senior Member
Joined
Jun 6, 2019
Messages
565
I’ve never saw a gun go from .5moa to 3.5moa with just a .020 change in seating depth. I normally start load development at .010 jump testing powder charges. After I find a load with good ES and acceptable accuracy I do a seating depth test to tune in the group size.
There's a lot of things to take account of here. I agree with you. We do not know shooter ability, any specifics or the gun, reloading equipment, lots of l unknown variables. I rarely have groups over 1.5 moa during all stages of load development if I'm holding tight to all my shooting and reloading disciplines.
 

hamilton1223

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May 16, 2017
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412
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Southern ID
IF that test holds, it sure isn't very forgiving. I am not sure how fast a 300 PRC throat will burn but I would bet you will be re-tuning quite often
 

Tumbleweed

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Dec 11, 2017
Messages
139
Location
Tillamook, Oregon
Yup I’ve found the same.

I literally just did a seating depth test last night with 245's out of my newly rebarrelled RUM +P. Previously, it appeared to like .035" jump but that spot was narrow with .005" either side opening a little bit. Case fill was a little low at that OAL with RL33 as well.

Latest test I went .050" - .100" jump in .010" increments at a random, low charge. All 3 shot groups between .070" and .100" were less than .3 moa at 250 yards! .080" went .191 moa. Best part...080" through .090" were perfectly flat with .100" dropping below that waterline only 3/8" or so. Conversely, .070" was only 3/8" above that waterline.

So, more proof that your statement is absolutely true. Now, I'm taking .080" jump up to the top end to see what the optimum charge will be.

049997394cb9c945505077f8e7af640d.jpg

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Sent from my iPhone using Tapatalk
 

hamilton1223

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May 16, 2017
Messages
412
Location
Southern ID
^^This is good info. Scott Satterlee has touched on this quite a bit and has changed his load philosophy to look for where a load likes to really jump... further than your typical .005-.050", more like .080-.12". Found that is was more forgiving
 

tdhanses

Senior Member
Joined
Sep 26, 2018
Messages
3,388
I literally just did a seating depth test last night with 245's out of my newly rebarrelled RUM +P. Previously, it appeared to like .035" jump but that spot was narrow with .005" either side opening a little bit. Case fill was a little low at that OAL with RL33 as well.

Latest test I went .050" - .100" jump in .010" increments at a random, low charge. All 3 shot groups between .070" and .100" were less than .3 moa at 250 yards! .080" went .191 moa. Best part...080" through .090" were perfectly flat with .100" dropping below that waterline only 3/8" or so. Conversely, .070" was only 3/8" above that waterline.

So, more proof that your statement is absolutely true. Now, I'm taking .080" jump up to the top end to see what the optimum charge will be.

049997394cb9c945505077f8e7af640d.jpg

1b25f1c1bbdc1872776657d3a811f9fa.jpg

f9f6a8e6a2f4ea3a39bb8d90087e25bc.jpg

b94b1de98f9701518242eb6742d4b232.jpg



Sent from my iPhone using Tapatalk
Yup I’ve don’t this with my 6.5cm, 270wsm and 300wsm, they all do exactly what yours did, I’m at .085 as my standard for all of these after testing a ton.
 
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