Seating depth - does it even matter?

[Flyjunky]

Interesting. Yes, leade angle, freebore, and clearance in the throat are the factors commonly referenced.


I have, everything I can find with data taken to a significant sample size disproves that theory and further substantiates random distribution. The key there is "2 of each charge". The ballisticians are proving that when you shoot multiple groups of 30+ at each charge, or seating depth, the sinusoidal noise averages out. I've researched Satterlee, OBT, OCW, and listened to the podcasts or watched the videos with each, and they are all based on small sample size. I'm wondering if there is a hobby reloader with a hunting rifle that has proof of at least 10 round groups, where seating depth made a distinguishable difference outside of the statistical variability. I think when Alex Wheeler takes a 300 PRC case and shoots a 20 shot string with 8" of vertical, and then shrinks it to 3" of vertical on the next string by bumping up to .005" neck tension, there might be a case to be made. But there are still environmentals involved in those groups, and I think the average shooter with a hunting rifle probably can't shoot the difference in small changes like that, IF there was even a discernable difference. And 99% don't take it to a significant sample size anyways.

That’s interesting because Cortina doesn’t mess much with seating depth anymore but relies more on a barrel tuner. According to him a barrel tuner is, in essence, taking the role of seating depth in fine tuning that load according to positive compensation.

I know a lot on here preach the Hornady guys info but there a quite a few world class shooters who would/do have other things to say with the accolades to back it up. Heck, we have a guy on this forum who posted actual data w/pics who is shooting smaller groups (size wise) with large sample sizes compared to what the Hornady guys were doing with a rail gun. In other words, nothing is strictly black and white in shooting. To say that seating depth doesn’t matter is way too broad of a statement. Some combinations it does and some may not see as much.

I’m getting ready to start load development on a new rifle and I’ll post up my findings with pics.

 

[Vern400]

With all the data from Hornady flying around and all the testing I've done, I find they align and I'm convinced seating depth doesn't matter at all, or if there is a distinguishable difference in my hunting rifle I don't want to waste the components to prove or find it. Curious if anyone has proof or documentation of decent sample sizes where a certain seating depth shot noticeably better than another? Not 5 shot groups either, I'm talking minimum 10 both samples.

When I first started reloading I could not make any load shoot better than Remington 308 150 pointed core lokt rounds. Out of frustration I pulled the bullets with a kinetic puller and reseated the bullets 0.150 longer. My groups went from 1.50 inch to 4 consecutive groups shown. ( approx 0.62 to 0.82)
I then used Sierra 150 SBT bullets and replicated the loads with bullets same distance off the lands. It's well known that 308 tends to shoot better without a lot of jump, by probably thousands of people more knowledgeable than me.

I took my groups from 1.5 0 or perhaps larger down to 0.62 to 0.82 with a Remington 700 ADL I bought new in 1989.

Some calibers are probably less sensitive to seating depth than others. But anytime I help someone reload for 308 I start 0.015 off the lands and many times don't ever have to play with it. Factory rifles often have 10 or 12 times that much jump.

You asked for data. There's mine. It's valid. I do not have the original groupings that were 1.5 to 1.75 because frankly they were embarrassing.

Since that time, I have setback barrels, and rechambered to put the rifling exactly where I want it from the bolt face. That way I can get the bullet jump I want with the bullet I want, and still have it fit in the magazine. So I can tell you at least I believe myself enough to spend a lot of money doing it. And my rifles shoot. This is the least accurate centerfire rifle I have.

me.

 

[MuleyFever]

This is why I am quitting reloading. I cant stop myself from shooting over and over messing with seating depth for no reason, most likely, and pissing myself off. If I want a hobby that irritates me Ill start golfing again.

 

[Molon Labe]

OP I think you are approaching the question from the wrong side.

Maybe…”Seating depth…should it even matter?” Might be the correct question.

I noticed that no one has even tackled throat erosion. Most rifles will lose 4-7thou off the lands every 100 rounds AFTER barrel has been broken in. Lots of variables such as chamber…type of powder…speed of strings shot…temperature of chamber etc.

Here is a scenario that dozens of guys have talked to me about:
So you get that “perfect” seating depth that’s .012” off the lands with your powder charge. You have 40 rounds on your new rifle. You are excited. Awesome groups! All set for your big hunt. Well you took my advice to shoot your rifle and get comfy…after you shoot 100 rounds getting ready for your hunt and verifying dope you notice groups are opening up! What is going on?! Well you are now probably .020-.025” off and your rifle has sped up 80fps. Time to scramble the week before your hunt…don’t have time to get reloading and range time in. Nightmare zone!

Everyone keeps mentioning data size etc…tons of anecdotal but nothing very scientific. Three shot groups that change the seating depth 5-10 thousandths mean absolutely nothing. It’s a waste of time that will just end up frustrating the average reloader.

I have significant data with large sample groups that I use to make my decisions on seating depth. I’ve tracked erosion/group size/dispersion over 21,000 rounds shot in the past 4 years. This was 62 rifles (various cartridges) doing load development for people and through 8 barrels that I shot out and pulled on my personal rifles.

When I’m deciding the load to run at a match I will spend the first 150-200 rounds of a barrel “breaking it in” making sure I’m through any speed up. Also shows me potential of the new barrel. I shoot 10 shot strings less than 2 minutes at medium distance 400-600yds. Usually running a known powder charge for that barrel/reamer combo. I will move seating depth from jammed to 150-200 thou off lands. I’m looking for a wide zone where groups are decent.

Once I’ve established my zone for that barrel I will seat my bullet as far out ie closest to the lands at the head of the zone. So let’s say top of the zone is 30 thou off…well I know that after a couple thousand rounds I should be jumping 130-150. If I shot decent groups out to a 150-180 thou jump when I was breaking it in then I know I should be monitoring seating depth closely as I approach 2k down the tube. This is strictly out of laziness…I do not or will not chase lands or adjust seating depth. I would rather shoot than reload and chasing seating depth back in the day was frustrating and annoying for me. So I stopped.

The majority of the people on this forum are looking for some magic answer for seating depth but it does not exist.

Too many variables. Bullets make the biggest difference…I have noticed bullets that are very picky and have shortened terribly inconsistent seating depth zones BUT also bullets that are very forgiving over long periods. I prefer to shoot bullets that are more forgiving. I will take bullets that consistently shoot 10 shot strings around .5 over bullets that may shoot 2s or 3s but are seating depth dependent.

But that’s just me…I don’t need a small group I need a consistent group over several hundred rounds.

So my answer to OPs question…load your ammo so seating depth does NOT matter and you will be much happier over the life of your barrel.

And shoot more…everything gets better when you shoot more.

 

[Harvey_NW]

If no one's testing or sample size satisfies your curiosity, and you want to know if there's an actual difference, why don't you test it yourself. Shoot 30 round test strings at various seating depths and see if what your ballisticians claim is actually true.

I am, to a reasonable extent. That's the point of starting the post, to chat about the findings. Since I bumped my sample size up to just 10 it's been eye opening. Everything aligns with what the ballisticians are putting out.

Sure it's a lot of components, but what's 60 rounds? It might make a difference, it might not, but it seems these statistics you're using are purely theoretical.

No, it's the actual statistical variability. They run the numbers on the podcast and show that the math will encompass the outcome.

Heck, we have a guy on this forum who posted actual data w/pics who is shooting smaller groups (size wise) with large sample sizes compared to what the Hornady guys were doing with a rail gun. In other words, nothing is strictly black and white in shooting. To say that seating depth doesn’t matter is way too broad of a statement. Some combinations it does and some may not see as much.

I’m getting ready to start load development on a new rifle and I’ll post up my findings with pics.

Link to a thread? I forgot Cortina is all about tuners now and that's an interesting subject as well. I agree some combo's may be more finicky than others, just seeing what's out there for data from other shooters.

OP I think you are approaching the question from the wrong side.

Maybe…”Seating depth…should it even matter?” Might be the correct question.

I noticed that no one has even tackled throat erosion. Most rifles will lose 4-7thou off the lands every 100 rounds AFTER barrel has been broken in. Lots of variables such as chamber…type of powder…speed of strings shot…temperature of chamber etc.

Here is a scenario that dozens of guys have talked to me about:
So you get that “perfect” seating depth that’s .012” off the lands with your powder charge. You have 40 rounds on your new rifle. You are excited. Awesome groups! All set for your big hunt. Well you took my advice to shoot your rifle and get comfy…after you shoot 100 rounds getting ready for your hunt and verifying dope you notice groups are opening up! What is going on?! Well you are now probably .020-.025” off and your rifle has sped up 80fps. Time to scramble the week before your hunt…don’t have time to get reloading and range time in. Nightmare zone!

This scenario is exactly what I observed when I started reloading and was doing small sample size load development, and kind of the point to why I fully believe in shooting larger samples now. If you shoot a 3 shot group at .012" off that's .25", and then go to .020" off and it opens up to .8" for 3 shots, yikes right? No. That's still within the statistical variability of a load that shoots .5" on average. So the point is if they had shot 10 at .012" off, and 10 at .020" and let the groups paint the picture, they probably wouldn't be much different.

The majority of the people on this forum are looking for some magic answer for seating depth but it does not exist.

Agreed.

 

[wind gypsy]

I know a lot on here preach the Hornady guys info but there a quite a few world class shooters who would/do have other things to say with the accolades to back it up. Heck, we have a guy on this forum who posted actual data w/pics who is shooting smaller groups (size wise) with large sample sizes compared to what the Hornady guys were doing with a rail gun.

If you're talking about @TK-421, all or most of those groups are with factory ammo I.E. not tuned to seating depth which to me would support the argument that seating depth is at least frequently way overrated.

 

[Flyjunky]

If you're talking about @TK-421, all or most of those groups are with factory ammo I.E. not tuned to seating depth which to me would support the argument that seating depth is at least frequently way overrated.

I get that but I was referring to sample size.

As far as seating depth goes, I think you’d be hard pressed to find any top bench rest shooter, rifle builder, or top notch shooter who says seating depth doesn’t matter.

Like I said, all guns/bullets are different. I’m just not a fan of blanket statements and now every time someone brings up anything reloading it turns to , “ well, the Hornady guys found this”.

 

[Harvey_NW]

I get that but I was referring to sample size.

As far as seating depth goes, I think you’d be hard pressed to find any top bench rest shooter, rifle builder, or top notch shooter who says seating depth doesn’t matter.

Like I said, all guns/bullets are different. I’m just not a fan of blanket statements and now every time someone brings up anything reloading it turns to , “ well, the Hornady guys found this”.

But you also won't find any of the top shooters that have target samples of significant sample size to prove that 1 seating depth is better than another. You typically see a 3 shot sample of each, and both are within the statistical variability of that load for the sample size they shot. It's not just the Hornady guys either, Litz talks about his findings with the contract work he's been doing lately as well, and the Government has been doing it for way longer and on a much larger scale than both of them. I'm just trying to learn, and I have still yet to see a comparison of significant sample size where one variable changed the load so much that it went outside the statistical variability, and stayed consistent.

 

[JBahr]

I see seating depth testing most often done at 100 yards and results are muddy. People use their emotions to select a depth and roll with it and for most shooters this is fine. But OP is right, statistically irrelevant in most cases.

I took a different approach and do my seating depth at 600 yards and the results have been far more clear for most of my rifles. Certainly a lot of factors contribute to whether or not your rifle/load is seating depth picky or forgiving. Most of mine have nodes they like, similar to powder charges/velocities. Sometimes the difference between the worst and best is over 1 MOA. Just my experience.

 

[Flyjunky]

But you also won't find any of the top shooters that have target samples of significant sample size to prove that 1 seating depth is better than another.

I don't agree with that at all. If you mean they shoot 30 rounds at one time then maybe, but many of those guys will shoot 10 shot groups and I highly doubt they just call it good after that 10 shot sample. My guess is they will verify that with another 10 or 20. When you have shooters who make their living by shooting I'd bet they don't rely on 10 shots, or just willy nilly seating depth guesses. Like I mentioned earlier Cortina is using tuners now instead of changing his seating depth to keep a load in tune. So, by that statement you can see that he thinks seating depth makes a difference. So do many, many top shooters. Matter of fact I have never heard of any good shooter who just seats a bullet wherever and thinks they are good to go. If it didn't matter I don't think they would be wasting their time and components.

By the logic that seating depth doesn't matter I should be able to jam a bullet into the lands and also seat it .150" off and the groups will be the same?

You typically see a 3 shot sample of each, and both are within the statistical variability of that load for the sample size they shot. It's not just the Hornady guys either, Litz talks about his findings with the contract work he's been doing lately as well, and the Government has been doing it for way longer and on a much larger scale than both of them.

Didn't Litz write papers and books about when seating depth did matter? So, his findings before were wrong but now they are right? Who's to say that later down the road he is wrong again and seating depth matters?

As far as not seeing a variable make a significant change, even the Hornady guys said that if your load isn't shooting well then you should either change powders or bullets. Isn't that a variable that makes a significant change, or am I misunderstanding what you're saying?

 

[Flyjunky]

I see seating depth testing most often done at 100 yards and results are muddy. People use their emotions to select a depth and roll with it and for most shooters this is fine. But OP is right, statistically irrelevant in most cases.

I took a different approach and do my seating depth at 600 yards and the results have been far more clear for most of my rifles. Certainly a lot of factors contribute to whether or not your rifle/load is seating depth picky or forgiving. Most of mine have nodes they like, similar to powder charges/velocities. Sometimes the difference between the worst and best is over 1 MOA. Just my experience.

I would agree with you about 100 yards not being far enough to bring out the differences, even 600 can be difficult sometimes.

Don't you know there are no such things as nodes? Nodes don't exist, it's all statistics and noise.

 

[Dos Perros]

As far as seating depth goes, I think you’d be hard pressed to find any top bench rest shooter, rifle builder, or top notch shooter who says seating depth doesn’t matter.

Are there any controllable variables that those fellas say doesn't matter tho?

 

[Flyjunky]

Are there any controllable variables that those fellas say doesn't matter tho?

Just my opinion, but everything going into a loaded cartridge is part of a system and one variable affects the others…to what degree is what we are discussing.

When you have guys shooting agg’s of .1-.5 at 300 to 1000 over the course of an entire match (large sample size), I tend to listen to what they have to say. If the variables didn’t matter then I wouldn’t think they’d be wasting their time, energy, or components.

Maybe it doesn’t matter for hunting rifles but I’m of the mindset that I’ll do whatever to get the best accuracy I can out of my particular system. Whether that matters in the grand scheme might be debatable but in my mind I’ve done all I can and when I pull the trigger I have the utmost confidence.

Regardless, it’s always a fun discussion.

 

[Dos Perros]

Just my opinion, but everything going into a loaded cartridge is part of a system and one variable affects the others…to what degree is what we are discussing.

I 100% agree. And I wasn't trying to be argumentative. Just implying that the type of people who get into this sort of thing are generally control freaks who try to control as much as they can and tend to believe it matters. I say this as a guilty party myself.

I tried to think of an example of something that is controllable but nobody controls for, and I didn't get very far.

 

[eod.tek]

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.

 

[goathunter]

No, the last. I start with the shortest cartridges first, because if I find accuracy short I can reseat the longer ones.

I haven’t figured out how to make the short ones longer.




P

Collet puller

 

[Harvey_NW]

I don't agree with that at all. If you mean they shoot 30 rounds at one time then maybe, but many of those guys will shoot 10 shot groups and I highly doubt they just call it good after that 10 shot sample. My guess is they will verify that with another 10 or 20. When you have shooters who make their living by shooting I'd bet they don't rely on 10 shots, or just willy nilly seating depth guesses. Like I mentioned earlier Cortina is using tuners now instead of changing his seating depth to keep a load in tune. So, by that statement you can see that he thinks seating depth makes a difference. So do many, many top shooters. Matter of fact I have never heard of any good shooter who just seats a bullet wherever and thinks they are good to go. If it didn't matter I don't think they would be wasting their time and components.

I don't doubt their reasoning for their beliefs, I just find it interesting that the ballisticians are burning up barrels looking for the same trends, and they aren't finding them. What they are finding for the most part is that most of the differences in test groups falls within the statistical variability of a load, so without taking the groups to valid sample sizes for comparison, you can't confirm that one is better than the other. And Cortina explicitly states that he isn't willing to do that because of the cost of barrel life and components, which is completely realistic. I'm not either.

By the logic that seating depth doesn't matter I should be able to jam a bullet into the lands and also seat it .150" off and the groups will be the same?

That would be a drastic change in other factors in the load, so if you could keep all the metrics static and test that, maybe.

Didn't Litz write papers and books about when seating depth did matter? So, his findings before were wrong but now they are right? Who's to say that later down the road he is wrong again and seating depth matters?

Yes, but an example of the article linked in the beginning of the thread was from 2013, and from what I've gathered a lot of it was mostly based on smaller sample size testing. He claims that his recent discoveries were made with the contract work he's been doing where the sample sizes are significantly larger.

As far as not seeing a variable make a significant change, even the Hornady guys said that if your load isn't shooting well then you should either change powders or bullets. Isn't that a variable that makes a significant change, or am I misunderstanding what you're saying?

By variables I was referencing measurements like seating depth/CBTO, powder charge, neck tension, etc. They do claim dropping the powder charge can have an improvement on dispersion, but yes from what I got out of this recent dive into simplifying load development is that if you're not seeing the level of precision you're after within a few tests and changes to the load, you probably need to swap a component.

Maybe it doesn’t matter for hunting rifles but I’m of the mindset that I’ll do whatever to get the best accuracy I can out of my particular system. Whether that matters in the grand scheme might be debatable but in my mind I’ve done all I can and when I pull the trigger I have the utmost confidence.

Regardless, it’s always a fun discussion.

Completely agree, and not being argumentative either just like the discussion. The component shortage was hell on me, but it made me do more research to refine my process and be extremely conservative.

 

[NiteQwill]

Seating depth is the last thing I worry about in the load development process.

I believe there are larger variables that will affect accuracy before messing with seating depth.

I've been spoiled shooting 6mm variants... I personally don't mess with seating depth in these cartridges.

 

[Molon Labe]

Are there any controllable variables that those fellas say doesn't matter tho?

Brass weight sorting, neck thickness sorting, brass number of firings sorting, bullet weight sorting, bullet concentricity, bullet length, primer weight sorting, primer shell sorting….those just off the top of my head.

You can do all that stuff and it will have minimal effect on precision when compared to seating depth.

BUT the br guys will still spend the time because that’s what they do haha.

 

[Dos Perros]

Brass weight sorting, neck thickness sorting, brass number of firings sorting, bullet weight sorting, bullet concentricity, bullet length, primer weight sorting, primer shell sorting….those just off the top of my head.

You can do all that stuff and it will have minimal effect on precision when compared to seating depth.

BUT the br guys will still spend the time because that’s what they do haha.

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.