Seating Depth Testing

Jud96

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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!
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Savage 12BVSS

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At .100 you got a good calm point in barrel position for sure, can see it closing down at .090. that will be easy on the throat as well. I think I tend to check to heavily between .010 and .040 and don't bother with longer distances off lands. Changes my way of thinking and testing in the future somewhat.
 

LongBomber

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That PRB series is bery interesting, def pushed towards prs or similar shooting where targets are fairly large (moa ish) and the round count in a weekend is high. Not looking for the ultimate in precision, but for consistent poi over a range of seating depths is a different way to look at it. Going by the prb idea you have a couple good ranges in there.

I shot a ladder style group at 250 (normal longer range still has snow..) interesting to see that over a significant range of seating depths it held impacts into a central cluster, with only a few seating depths moved. Depth# 7 is where I have been seating for the last 150 rounds, depth#9 is touching the lands. Of course to be really meaningful more rounds would be needed, but I thought I would see what correlation if any there was in seating depth and vertical poi.
 

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mwkelso

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That was a good article posted by PRB, and even better to see it put to the test.
0.070”, what do you think made that group go tight while groups on both sides of it were more spread?
 

Jud96

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That was a good article posted by PRB, and even better to see it put to the test.
0.070”, what do you think made that group go tight while groups on both sides of it were more spread?
I believe it was a sweet spot and maybe .065 and .075 would do well, but it’s just a narrow seating depth window. That’s my thoughts.
 

aushunter1

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A couple of really nice groups there.
I am curious why you didn't start at .050 or .010 off the lands??

Im am also curious what if any velocity spreads there were between .030 & .100?
 

Jud96

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The closer you are to the lands, the less forgiving your load will be with varying seating depth from throat erosion. I wanted something I didn’t have to tune every 100 rounds. I will test velocity next when I do my powder charge work to find the sweet spot in velocity. I’ll leave my seating depth where it is and just work up my powder charge to find my velocity node. I don’t trust groups with the Magnetospeed attached so that’s why I didn’t record velocities. I do my load development in a three step process. I test seating depth, powder charge, and then go back and verify my findings.
 
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aushunter1

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The closer you are to the lands, the less forgiving your load will be with varying seating depth from throat erosion. I wanted something I didn’t have to tune every 100 rounds. I will test velocity next when I do my powder charge work to find the sweet spot in velocity. I’ll leave my seating depth where it is and just work up my powder charge to find my velocity node. I don’t trust groups with the Magnetospeed attached so that’s why I didn’t record velocities. I do my load development in a three step process. I test seating depth, powder charge, and then go back and verify my findings.
Depending on the cartridge your probably talking 2000 rounds + before throat erosion plays a major role in accuracy imo!

There is an aftermarket off barrel bracket available now that would help with that, I saw some guys on here using it.
I would love to get it at some point but I have import it.


Anyway good luck with what your doing.

Its all food for thought!
 

Jud96

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Actually your barrel can erode much faster than you think. With a hot magnum or fast 6mm you could erode .005-.010 of the throat in 100-200 shots.
 

aushunter1

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Actually your barrel can erode much faster than you think. With a hot magnum or fast 6mm you could erode .005-.010 of the throat in 100-200 shots.
Sure I wouldn't discount it.

My .22-250 which is classes as overbore took close to 3000 rounds before throat erosion affected the accuracy which I did try to then chase for a bit after doing some testing just decided easier to rebarrel.

Nothing lasts forever right!

Handloading results are up to your own interpretation & you can wear a barrel before its time is due just by doing to much testing as well!

I am happy & confident in my methods of testing new loads which I can usually get a 1/2moa result in 40 rounds.

Throat erosion is going to happen anyway, who is to say that throat erosion isn't still going to affect a load whatever the jump??

If your in the overbore range then I don't see seating depth having any major affect on your throat erosion anyway!

Anyone got any data on that?
 

Jud96

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If the load shoots well at .090 and .100 and then I seat bullets at 0.090 off and the throat erodes .010 it will continue to shoot well when it’s now .100 off the lands. It’s a forgiving seating depth node that I’m looking for.
 

aushunter1

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If the load shoots well at .090 and .100 and then I seat bullets at 0.090 off and the throat erodes .010 it will continue to shoot well when it’s now .100 off the lands. It’s a forgiving seating depth node that I’m looking for.
Sounds good in theory, keep us posted as I am genuinely interested to see how that goes for you.

It took me 10+ years at the amount I shoot the 3000 rounds & to blow the barrel on my .22-250 which I am happy with.

I am not discounting your theory but unless your shooting a hundred rounds a month I don't get the importance what your trying to achieve.

But definitely, anyone who discounts the fact that changing CBTO wont affect accuracy should see this.

A very good lesson for any newbie handloader for sure
 

Jud96

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If the groups are good at a wider seating depth range, then why not seat there. Why seat bullets in a narrow window that could be sensitive to minor variations in throat erosion or even BTO changes in bullets or loaded ammo. It’s the same reason to select a powder charge that’s in the middle of a wide node that is forgiving than a load that has erratic velocity changes with just a minor change in powder charge.

If you read the articles on the Precision Rifle Blog, they will help you better understand what I’m after here. I’m not a PRS shooter or a high volume shooter, but if I can find a forgiving load that is consistent day in and day out and round after round, then why not use it? Making a clean one shot kill for us is very important, so having a load that is forgiving and stays in tune longer is important in my opinion.

There’s a dozen ways to skin a cat and everyone has their own methods. Even if I never have to worry about throat erosion, the proof is on the target that .100 off shot extremely well. The .090 load wasn’t as good, but it was certainly better than .080 off. So that shows .090-.100 is a .010 window in seating depth where the rifle groups well. The .070 off load shot well, but .060 and .080 weren’t too hot. So .090-.100 is the sweet spot for this rifle.
 

aushunter1

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There’s a dozen ways to skin a cat and everyone has their own methods.
You nailed it there!

I like where you have gone with this BUT every projectile is different.

If you have taken this on as your method od testing different projectiles then thanks for putting it forward.

At the end of the day every rifle, every powder, every projectile determines their own CBTO length!
 

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