Seating Depth Testing

david g ranes

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I use an unprimed dummy case sized and given a minimum amount of neck tension. I seat the bullet long and ease it into the chamber. Generally it extracts without sticking in the lands. I now have a dummy round seated to touch. I've been using micrometer controlled seating dies or Redding competition seat dies. Use the dummy round to set the seater die to touch and then test fire a few. Very easy to screw the seater plug down by any amount that you want to. With the dummy you can always return the seat die to the touch position if you lost or forgot to write down the micrometer reading. Range pick up brass is good for this. I make a seater dummy for each type of bullet I use. Of course any loaded round must fit in the magazine.
i have used the seating method you use for years but I put a little glue in the neck and chamber the round and let set when glue sets up you have a consistent measurement because it can’t move. David
 

Laguna Freak

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Hey all. I just finished up doing some seating depth testing on my Remington 700 .243 Varmint rifle and figured it would be a good idea to post my methods and my findings on here. I like to do a lot of testing and I also like to help and share whatever I find and experience with others. I often recommend to others to test their seating depth. It can very much change your group size and your results as you will see below.

Before I get into my results, I’d like to explain my methodology and how I go about this test. First, I’d like to say every bullet is going to have preferences to bullet jump. There’s the thought that certain bullets are less sensitive than others, and that may be true, but in my testing and experience it seems they all can be tweaked to shoot their best. I highly recommend everyone to go over to the Precision Rifle Blog and read their latest articles on bullet jump and the results that Mark Gordon of Short Action Customs and other top shooters have found and tested. That is a very good read and it really opened my eyes up to test seating bullets even further from the lands than I ever did in the past. I’d also like to say, this is for guys who want to shoot at 100 yards or may only have access to 100 yard ranges most of the time. I have to travel an hour or longer to get to places that I’m able to shoot 300+ yards. I use this method to find good results at 100 yards where I’m able to shoot year round and is only 5 minutes from home.

When I go about doing seating depth, I first find my lands by using the Wheeler method. There’s a video on YouTube of Alex Wheeler demonstrating and explaining it. I will then load rounds up in .010 increments from say .020 off to .100 off. I like to load 3 at each length to shoot a group of 3 to better represent what they’ll actually shoot like. I have tried this with two shots and have seen others do it with one, but 3 gives you an average and a true group. For the test I did today, I just started 3gr below max in my new Peterson brass and shot the seating depth test. In my experience and the experience of others, if you have the right bullet jump, you can shoot any powder charge and your sweet spot in bullet jump will stay the same. I have experienced this in multiple rifles of my own and friends, and have seen the data from others to back this up.

There are also ways to fine tune your seating depth when you’re closer to the lands by adjusting in .002-.003 increments. The problem with having a load close to the lands is that it can be very sensitive to change. If you have a hot magnum you may erode the throat .005-.010 in 100 rounds. Then you have to keep chasing the lands. Finding a more forgiving bullet jump “node” like I show below will result in good groups even with some throat erosion. There may be a sensitive seating depth that shoots even better, but I find it annoying to have to chase the lands. So this is why I look for a window in seating depths that give good results and are not as sensitive.

Today I shot groups from .030 off the lands to .100 off. These were all shot with virgin Peterson .243 brass, 87gr VMAXs, 41.0gr IMR 4451, and Winchester Match primers. I took a few minute break between each group to let the barrel cool and to not get uncomfortable or fatigued behind the rifle. I started with a clean barrel and fired 3 rounds from my previous load on the bottom right target. That group was very good, but this load has some pressure signs in warmer weather and the ES is a little higher than I’d like. I then adjusted my scope down and put one in the center just to return to zero. Today’s test was mainly looking to see if I could improve on anything and to just do some more testing for fun and for data.

Here are my results. Starting from top left is .030 off and ending with .100 off on the third target on the bottom row. My conclusion is .090-.100 off looks really good and will be where I do some further testing. I will say I feel like I pulled one shot today and that was the lower impact on the .090 off group. I’m very happy with that .100 off group and the couple other good ones I shot today. This rifle sure hammers for a factory Remington with some bedding and handloads!View attachment 193964View attachment 193963View attachment 193962
Great vertical dispersion at 0.100! My interpretation of 0.090 is far less favorable than you have expressed. I find it consistent with the dispersions both sides of 0.70. Thanks for posting this. I am keenly interested as I am working up Scirocco II loads for my 300WSM and am tweaking depth for my .30-06. I start with vertical dispersion at 0.020 or 0.050 within velocity nodes (depending on projectile) and then advance to seating depth. I find that I can have 2 or 3 velocity nodes that provide basis for seating depth tests. Then I choose the velocity that best suits the projectile’s terminal ballistic performance.
 

Mikecr

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I start with vertical dispersion at 0.020 or 0.050 within velocity nodes (depending on projectile) and then advance to seating depth. I find that I can have 2 or 3 velocity nodes that provide basis for seating depth tests.
You got everything about seating wrong..

Seating testing is just as Jud96 has laid it out. It has nothing to do with vertical or velocities. Seating testing is not tuning. Powder testing is for tuning, Seating is prerequisite to seeing a good powder tune -when you get to powder testing (after seating).

Consider this; Jud96 testing showed .030off as a terrible place. You should not go into ladder or powder testing from that place. If you do, your distant ladder will be a holy mess, and you'll chase tail longer with incremental load development. That's why full coarse seating testing should be the first thing you do.
Good time for primer swap testing too (another non-tune item).
 
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TRexF16

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You got everything about seating wrong..

Seating testing is just as Jud96 has laid it out. It has nothing to do with vertical or velocities. Seating testing is not tuning. Powder testing is for tuning, Seating is prerequisite to seeing a good powder tune -when you get to powder testing (after seating).

Consider this; Jud96 testing showed .030off as a terrible place. You should not go into ladder or powder testing from that place. If you do, your distant ladder will be a holy mess, and you'll chase tail longer with incremental load development. That's why full coarse seating testing should be the first thing you do.
Good time for primer swap testing to (another non-tune item).
This sounds like reasonable advice on the order of things. So, if one should start out with seating depth testing, what guidance should be used to choose the powder and charge to do the seating testing with?
Thaks,
Rex
 

Jud96

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This sounds like reasonable advice on the order of things. So, if one should start out with seating depth testing, what guidance should be used to choose the powder and charge to do the seating testing with?
Thaks,
Rex
I just choose the powder I plan to use and load cartridges around 3gr under book max when doing seating depth testing.
 

Laguna Freak

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This thread has been enlightening. I’ve seen this accuracy conversation elsewhere. A well respected 1k shooter on another forum expressed that seating depth will bring the horizontal spread in when you have a velocity range that achieves a low decimal moa vertical spread that is stringing out horizontally. It was also suggested that tuning the seating depth In 0.003 increments helps to prevent bypassing a node you are close to and that seating depth nodes tend to tighten the velocity es too.

All very interesting in reflecting on my experience. I have some thinking to do about the 300WSM load I am starting to develop with 180 Scirocco II which is known to be seating depth sensitive. Thanks for all the constructive info!
 

Laguna Freak

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Here is the thread I referenced earlier. I’m posting it for reference because unless my reading and comprehension have taken a turn for the worse, it looks to me like Jud96/PRB and Erik Cortina methods are different. I’m looking for the straightest line from A to B. Again, great thread Jud96 and thanks for starting the combersation.

 

Laguna Freak

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You got everything about seating wrong..

Seating testing is just as Jud96 has laid it out. It has nothing to do with vertical or velocities. Seating testing is not tuning. Powder testing is for tuning, Seating is prerequisite to seeing a good powder tune -when you get to powder testing (after seating).

Consider this; Jud96 testing showed .030off as a terrible place. You should not go into ladder or powder testing from that place. If you do, your distant ladder will be a holy mess, and you'll chase tail longer with incremental load development. That's why full coarse seating testing should be the first thing you do.
Good time for primer swap testing too (another non-tune item).

I just now got around to actually reading the PRB and all I can say is “Thank You” Jud96 Mikecr. Their data certainly seems to support the conclusions and is also consistent with some recent seating depths I tested that turned out to be 0.057” off lands after I rechecked my chamber dimension.
 

Laguna Freak

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This thread and the PRB articles piqued my interest enough to switch gears in my 30-06 150 Nosler BT load development from starting with charge weight basis to first establishing seating depth. So, the attached 100 yard targets reflect that transition in my process.

The rifle is my 20 year old Steyr Pro Hunter which has always shot 1.6" to 1.75" groups at 200 yards with 180 grain Winchester Silver Tip factory ammo. It never shot lighter bullet factory loads as good. So, I decided to develop a 150 gr hand load.

The first target was the culmination of charge weight development. MV = 3,000+/-
fps. 0.020 jump

The 2nd target was 5 shot group with charge weight in the potential "lower node" at 0.015 jump.

The next two targets is where I changed gears to establishing seating depth first;
3rd target is self-explanatory.
4th target is 4 shot groups in a potential "lower node" charge weight. I selected this charge weight based in part on results not showed here in attempt to tighten up the groups with seating depth.

I'm curious where the LRH seating depth brain-trust would recommend I go from here in light of these results.
IMG_8722.jpg
IMG_8721.jpg
IMG_8720.jpg
IMG_8723.jpg
 

new2mud

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@Laguna Freak — Keep in mind the PRB articles suggest testing out to 0.100” or even 0.120”. That was a mistake I made—stopping too soon.

I would try 0.075” 0.090” 0.105” and 0.120” to complete the picture, if your goal is to find a forgiving seating depth that will withstand some throat erosion changes. I’m done chasing lands.

#4 is starting to shrink vertical dispersion and I suspect you will find something nice around 0.070-0.075”. Especially if it also holds at 0.080”
 
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Laguna Freak

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I’ve only read it once and need to read again, but I seem to recall PRB stating something about nodes being as small as 0.003” wide. Given the results above and today’s below, I know what I would be thinking if I had only fired 3 shot tests. I got 4th shot fliers at 0.062, 0.070, and 0.075. Yes, I let the barrel cool for 3 min between shots and it was 79 to 82 F during this morning’s session. Wind was at my 010 degrees @ 5 up to 12mph by the time I was finished.

I’m interested in interpretations from the LRH brain-trust. Keeping New2Mud counsel in mind too.

97DE04E2-B64C-4466-A928-ED1BB79F4A9B.jpeg
 
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