Seating depth - does it even matter?

[ID_Matt]

Just my anecdotal data as I sit in my truck waiting for my barrel to cool while doing load development lol.

I'm working up a load in my 300 Norma Magnum. After an ocw test I did a seating depth test in .010 increments from .020-.070. I noticed that .040-050 were centered to the point of aim. .060 was left about .1 mil at 100 yards, and .070 was .1 right. I wrote that off as me having sloppy trigger control, or noise of only shooting 3 round groups.

Fast forward a few days and I was testing the .070 load, because it produced the best groups, and decided to seat some 3 shot groups rounds in .003 increments from .064-.076. and wouldn't you know it, the .064 and .067 were slightly right of point of aim and the .070 and up were just right.

Could this have been me? Absolutely. Is it three shot group two small to be statistically significant? Absolutely. If I load it up a hundred of each would it potentially all aggregate out to being close to the point of aim, quite possibly. But when you have a rifle that only has a barrelife of 600 to a thousand rounds, I personally just take two separate tests on two separate days as enough aggregate information to pursue a load, and if I'm wrong and it all doesn't matter then realistically I'm fine with whatever I choose. But in this load I am sticking away from the .060's and thruing my rifle off the .070s and hoping that that turns out to be correct. But in the end, I usually end up having to round up or down .05 of a mil anyway on a shot correction so a tenth of a mill left or right of center can stack over long distances but it also just becomes some level of the noise of loading and shooting.

To add to this... how fast is that throat growing in a monster like a 300 norma? I imagine it doesn't take many shots to burn .003"....

 

[eod.tek]

To add to this... how fast is that throat growing in a monster like a 300 norma? I imagine it doesn't take many shots to burn .003"....

I try not to think about it, it's too painful. But with using n570 it probably only takes 50-100 to burn .003. I'm going to explore n565 after the NF match.

 

[Molon Labe]

I know guys that brass and bullet weight sort. Regardless, sorting is more like creating different subsets of loads (unless you're scrapping out the ends--I know guys that do that too). I think they could contribute to tighter groups (more precision) but not increased accuracy since the front of the box will be a different load than the rear of the box.

Yeah. I used to do a bunch of that stuff. BR guys getting in my head haha. Now all my Sinclair gauges sit in boxes in a permanent time out.
From what I remember I don’t think I had the barrels or systems or skills to shoot the tiny differences anyway.
Ended up flipping the time switch to spend more time shooting and less on the reloading process. The time spent shooting was a WAY better investment and my groups tightened up a ton.
I became a much better shooter and recommend to most guys not mess with that small stuff.

 

[Dos Perros]

Yeah. I used to do a bunch of that stuff. BR guys getting in my head haha. Now all my Sinclair gauges sit in boxes in a permanent time out.
From what I remember I don’t think I had the barrels or systems or skills to shoot the tiny differences anyway.
Ended up flipping the time switch to spend more time shooting and less on the reloading process. The time spent shooting was a WAY better investment and my groups tightened up a ton.
I became a much better shooter and recommend to most guys not mess with that small stuff.

I stopped at the turning necks point. Got all setup with quality gear, turned a bunch of necks, made scant difference. Now I have a few hundred rounds that were so preciously assembled I can't hardly stand to shoot them--like having them is better. That's when I knew I was stupid.

My boy is almost 9 and I haven't reloaded a bullet since he was born. Just don't have the time for it. I've killed an elk and three nice bucks with rifles since then shooting factory ammo. I'm a boring boring man now.

 

[Molon Labe]

I stopped at the turning necks point. Got all setup with quality gear, turned a bunch of necks, made scant difference. Now I have a few hundred rounds that were so preciously assembled I can't hardly stand to shoot them--like having them is better. That's when I knew I was stupid.

My boy is almost 9 and I haven't reloaded a bullet since he was born. Just don't have the time for it. I've killed an elk and three nice bucks with rifles since then shooting factory ammo. I'm a boring boring man now.

Neck turning? I did 600 pieces of one lot a few years ago. I would rather have someone pull all my fingernails out with a pliers than neck turn another case. Hahahah.

Good decision going factory. Time with children is not replaceable. Plus I started reloading for my dad when I was 12…so you will soon have some cool time with your kid and get a task accomplished.

 

[Jhaury7]

Makes a huge difference to me

 

[Go West Old Man]

So, if you do your seating depth testing with 3 round groups how many groups do you expect to have to shoot?

Let’s say you pick a starting point, whatever it is …… or whatever your off the lands, touching lands, or jam philosophy is. Then you decrease or increase (whichever direction you choose to go from a starting depth) the seating by .003 or whatever “x thousandths”. Geeze, this could get to be a heck of a lot of rounds fired trying to find a node or reliable small group !

I know, all depends on lots of variables but what’s your experience?

 

[Buglebrush]

When shooting ABLR it makes a huge difference.

 

[COPrecisionRifle]

I have been talking with a few guys about this lately. With the development in bullets, barrel manufacturing, lapping, etc its starting to become less important for some rifles. I have a 6 Creed that doesn't care what you put in it, it will just shoot it. I have done load dev on a couple 300 PRCs that have shown pretty significant changes with just seating depth. So I think the sample sizes on these tests cant just be with one rifle too but different calibers, different bullets, etc.

The most important part is what kind of accuracy are you trying to achieve? A rifle that shoots consistently in the .5-.75 range is pretty easy to achieve and acceptable for the shooting most of us do. Getting a rifle to stay in the .25-.3 range consistently is another beast.

 

[Pharmseller]

So, if you do your seating depth testing with 3 round groups how many groups do you expect to have to shoot?

Let’s say you pick a starting point, whatever it is …… or whatever your off the lands, touching lands, or jam philosophy is. Then you decrease or increase (whichever direction you choose to go from a starting depth) the seating by .003 or whatever “x thousandths”. Geeze, this could get to be a heck of a lot of rounds fired trying to find a node or reliable small group !

I know, all depends on lots of variables but what’s your experience?

I start with 0.04” changes then fine-tune from there, if needed.





P

 

[Go West Old Man]

I start with 0.04” changes then fine-tune from there, if needed.





P

That’s the question……, do it in something like .040 increments or something extreme (?) like .003 increments? Guess it depends on what YouTube videos that one takes advice from.

 

[Harvey_NW]

View attachment 560646
Makes a huge difference to me

I would question the first one, whether something was loose or how the rifle was positioned. But also, there's statistically about 60-70% variability to 3 shot groups. So if that were a rifle that averaged 1 MOA, statistically it can produce 3 shot groups as low as .3", and as high as 1.7", if you were to repeat it 10x. So really doesn't look that far off. I would question the repeatability of that load.

So, if you do your seating depth testing with 3 round groups how many groups do you expect to have to shoot?

Let’s say you pick a starting point, whatever it is …… or whatever your off the lands, touching lands, or jam philosophy is. Then you decrease or increase (whichever direction you choose to go from a starting depth) the seating by .003 or whatever “x thousandths”. Geeze, this could get to be a heck of a lot of rounds fired trying to find a node or reliable small group !

I know, all depends on lots of variables but what’s your experience?

My experience aligns with what the ballisticians are substantiating, that it doesn't really matter and there will be significant variance from group to group, it takes a large sample size to see. What you will see is a lot evidence showing the variability in small sample size testing, what you won't see is the end result and the bad result during the test taken to a significant sample size and compared to prove it is in fact substantially better, and outside the statistical variability of the average group size that load produces.

When shooting ABLR it makes a huge difference.

Everybody says that but not one has large sample sizes proving it. If someone had at least 10 shot groups where one seating depth had an ES of 1.2" and another had as ES of .4", I'd be inclined to believe there might be a difference there. But the variability in ES is still 30-40% from the average 10 shot group sizes, so a rifle that averages .75" can produce 10 shot groups from .5" to 1". This is why I consider 3 shot confirmations invalid. I still think small sample size testing is effective if used correctly, but a 3 shot proof group tells you nothing really.

A rifle that shoots consistently in the .5-.75 range is pretty easy to achieve and acceptable for the shooting most of us do. Getting a rifle to stay in the .25-.3 range consistently is another beast.

I don't think it's easy at all if you try to prove it. Shooting a 3 shot group is pretty easy, but actually proving your system and shooting ability is able to hold .5 MOA would be extremely impressive. But I find it pretty hard to even shoot a 10 shot group in the .5" range.

 

[bmart2622]

^^^^^Completely agree with your last statement!!! Not nearly as easy to do with 5 or 10 shot groups as the internet makes it out to be

 

[willfrye027]

I just screwed on a new prefit. I’m tempted to do some “large” sample size testing while getting the first 100-200 rounds down the tube for some “data”. Although I can see now the naysayers/ultra-tuner guys saying that the barrel isn’t settled in, doesn’t count…

Confident I will end up with a 1.25” 10-20 shot group gun, with very little tinkering, which is plenty for cold bore hits beyond a reasonable hunting distance.

 

[Harvey_NW]

I just screwed on a new prefit. I’m tempted to do some “large” sample size testing while getting the first 100-200 rounds down the tube for some “data”. Although I can see now the naysayers/ultra-tuner guys saying that the barrel isn’t settled in, doesn’t count…

Confident I will end up with a 1.25” 10-20 shot group gun, with very little tinkering, which is plenty for cold bore hits beyond a reasonable hunting distance.

Right on, looking forward to seeing your results! In my limited experience, I haven't observed a notable change in a barrel I've tracked for roughly 160 rounds, other than a velocity increase of 30-40 fps. Otherwise the same load I originally landed on kept producing good results of group size. That barrel is getting set back and I'm having the chamber punched out to something a little more optimal for the platform, but I'll be doing some more testing soon as well

 

[Jhaury7]

It was repeatable at 800 yds off a bipod….

SD 4
ES 10

 

[bmart2622]

That group is .060 longer than the other group you posted?

 

[Jhaury7]

My throat grew 6 thou because I’m burning 83 grains of N570

 

[Jhaury7]

The numbers aren’t important. The point is, on this particular rifle, a few thou in seating depth matters a lot in accuracy

 

[bmart2622]

Both groups look great, based of off small sample sizes, but still great. Its reloading, its all numbers