Seating Depth Increments?

[Mickp7]

Great discussion here for guys like me that are newer and trying to figure out our process.

The guys at Short Action Customs recommend seating depth testing first. Here is their email to me:
What we recommend if you are doing 100 yard load development is the following.

.010" off the lands 3 shots
.020" off the lands 3 shots
.030" off the lands 3 shots
.040" off the lands 3 shots
.050" off the lands 3 shots
.060" off the lands 3 shots
.070" off the lands 3 shots
.080" off the lands 3 shots
.090" off the lands 3 shots

Complete two tests with these at 100 yards and see which ones group the best consistently. Then perform a charge weight test the same way.

I'm still tweaking process as I learn, but here is what I did on my last load (I've only done a couple so far):
1) Load .020 off lands in .5 powder increments until I find pressure
2) Back off 1-2 grains depending on pressure signs and velocity goal
3) Load 4 rounds at .010 and then out to .100 in .010 or .015 increments. I shoot for groups at 420 yards (that's the max distance I can shoot on my property)
4) Fine tune in .002 or .003 increments to determine width of node
5) Load to the longer length to stay in node as throat erodes

I then take the load (or two if I'm still unsure) to a buddy's property about 2 hours away where we can shoot out to 1400 yards.

Feedback is welcome.

 

[sep]

I've changed my reloading procedures as a result of three things. Trying Erik Cortina's method (.003 increments), Hornady's results specified in podcasts #50, 52, 60 and 121 and my results testing a new Sako 85 30-06 shooting 168 TTSXs last summer.

Here are my results summarized: I ran Eric's test shooting 3 shot groups every .003 at 100 yards for a total of .087 variation in seating depth. Found a sweet spot or node spanning .006 where three consecutive groups were smallest. (.85, .68. 1.17)

Loaded up and shot nine more three shot groups within this .006 sweet spot or node. Then I crunched the numbers comparing the average group size of the 12 groups in the sweet spot vs the entire span of groups I shot in testing (which included the 12 groups). I also tested a few other seating depths shooting a few more groups too.

In all, I shot 45 three shot groups. Average of all these groups is 1.31. Compare this to the average of the 12 three shot groups in the .006 sweet spot. That average was 1.26. So, half a tenth of an inch difference between the two groups. I no longer believe seating depth plays a big role in group size with the 168 TTSX. I have no idea how other bullets will respond to seating depth testing.

So, what did I do with the Sako 85 30-06? In hindsight, I should have backed off the powder charge to see if it would shrink the groups. Instead I tested both 165 and 180 Accubonds. I worked up a load with the 180 Accubond and H4350 which averages just under MOA for ten 3 shot groups. That will do everything I need a 30-06 to do. So, going forward with regards to seating depth, if I'm shooting Barnes bullets I simply seat them .050 (fifty thousandths) off the lands which was Barnes original recommendation. With other bullets I seat them so they fit in the magazine. Not sure I'm gonna bother with much seating depth testing in the future for my hunting rifles.

 

[USAFRet]

I've changed my reloading procedures as a result of three things. Trying Erik Cortina's method (.003 increments), Hornady's results specified in podcasts #50, 52, 60 and 121 and my results testing a new Sako 85 30-06 shooting 168 TTSXs last summer.

Here are my results summarized: I ran Eric's test shooting 3 shot groups every .003 at 100 yards for a total of .087 variation in seating depth. Found a sweet spot or node spanning .006 where three consecutive groups were smallest. (.85, .68. 1.17)

Loaded up and shot nine more three shot groups within this .006 sweet spot or node. Then I crunched the numbers comparing the average group size of the 12 groups in the sweet spot vs the entire span of groups I shot in testing (which included the 12 groups). I also tested a few other seating depths shooting a few more groups too.

In all, I shot 45 three shot groups. Average of all these groups is 1.31. Compare this to the average of the 12 three shot groups in the .006 sweet spot. That average was 1.26. So, half a tenth of an inch difference between the two groups. I no longer believe seating depth plays a big role in group size with the 168 TTSX. I have no idea how other bullets will respond to seating depth testing.

So, what did I do with the Sako 85 30-06? In hindsight, I should have backed off the powder charge to see if it would shrink the groups. Instead I tested both 165 and 180 Accubonds. I worked up a load with the 180 Accubond and H4350 which averages just under MOA for ten 3 shot groups. That will do everything I need a 30-06 to do. So, going forward with regards to seating depth, if I'm shooting Barnes bullets I simply seat them .050 (fifty thousandths) off the lands which was Barnes original recommendation. With other bullets I seat them so they fit in the magazine. Not sure I'm gonna bother with much seating depth testing in the future for my hunting rifles.

I still want to do a little more testing on a few rifles, but just going .050 and calling it a day sure does save components.

 

[Mickp7]

I still want to do a little more testing on a few rifles, but just going .050 and calling it a day sure does save components.

Prior to getting into reloading, I had a guy that custom loaded for me. He'd send a handful of color coded loads and we'd boil it down by seeing what shot best. Barnes 150 gr ttsx going 3350 out of my 28 nosler, killed a bull at 560. (Was the only bullet we could find at the time)
Measured it the other day while I was developing a load for the same gun, .215 off the lands.
I realize a lot of bullets would take up powder space at that depth, but shows there is more than one sweet spot.

 

[Laguna Freak]

I still want to do a little more testing on a few rifles, but just going .050 and calling it a day sure does save components.

As a guy who started at 0.050" off for 3 different ogives, I would recommend testing well beyond that. None of my rifles like that jump. They're all > than 0.060" off and one is at 0.073 +\- 0.001". I've read of plenty who are well over 0.100" off lands.

 

[USAFRet]

As a guy who started at 0.050" off for 3 different ogives, I would recommend testing well beyond that. None of my rifles like that jump. They're all > than 0.060" off and one is at 0.073 +\- 0.001". I've read of plenty who are well over 0.100" off lands.

I still have a .060 to test. Those groups were tightening up. May load some .070 and .080 until I hear the crunch. Thanks.

 

[birddog 68]

I've read of plenty who are well over 0.100" off lands

I had a Ruger 280 Rem that liked over .100 jump when using Berger. I prefer much closer but the rifle is the boss, not me.

 

[waspocrew]

I start .020" off the lands and then if needed, adjust in 0.020" increments.