Seating depth - does it even matter?

[Flyjunky]

I remember hearing in one of the Hornady Podcasts where they said that on bullets with a sharp angle on the ogive it will matter more than on the sleek bullets with a smooth transition at the ogive.

Yes, that was on the Q & A episode. Long ogive bullets tend to be more sensitive to seating depth, as well as sloppier chambers.

 

[Harvey_NW]

Yes, that was on the Q & A episode. Long ogive bullets tend to be more sensitive to seating depth, as well as sloppier chambers.

They stated that's a possibility, but I still haven't seen legitimate proof.

 

[FLS]

If seating depth doesn’t matter, why does Berger make Classics and Hybrids?

 

[Walmart Greeter]

Seating depth matters. How precisely it matters depends on your goals, your rifle, and which bullet you’re using. The end.

 

[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.

The importance of seating depth varies with caliber because of the chamber dimensions and chamber clearances. If you take a 308 with a standard SAAMI chamber, it can be just a little finicky. Sometimes it takes six or eight tries or combinations to get something it really likes.
I have one rifle, a "B" serial prefix, that took group sizes from 1.75 to roughly 0.7 average simply by pulling factory ammunition bullets and seating them at maximum mag length. This held true for the entire life of the barrel. It just did not like all that free bore they gave it.

A match chamber would probably shoot well with a higher proportion of different cartridges. But for crying out loud, the baby's pretty much chambered to be a machine gun if that's what you want. And this is precisely why 223 Wylde exists!

So some of the folks that are shooting the more modern cartridges maybe 20 years old or so won't find a dramatic change in accuracy by playing with seating depth. Benchrest shooters will continue to religiously spend time on it. Because 0.100 improvement separates the champions from the losers.

I hope the attachment comes through. It shows four consecutive three shot groups without cooling the rifle. I repeated the test the next day and then I almost believed it. I loaded up a hundred and it continued to consistently shoot in the 0.7/0.8 range and then right back up to 1.5 to 1.75 groups with the "control" box of stock ammo.

I bought a Remington 700 vs back when Remington was making good rifles. The first thing I did was pull the barrel off and rechamber it and rethread it to pull the rifling closer to the bolt face. I can't remember if I set the barrel back by two threads, or three threads at the receiver. Can't tell now because it's clocked properly.

I really think seating depth is a minor consideration in many of the more modern cartridges like the prcs and the 65 creedmoor.

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.

 

[Formidilosus]

I hope the attachment comes through. It shows four consecutive three shot groups without cooling the rifle. I repeated the test the next day and then I almost believed it. I loaded up a hundred and it continued to consistently shoot in the 0.7/0.8 range and then right back up to 1.5 to 1.75 groups with the "control" box of stock ammo.

and yet when those four groups are overlaid into one to form an actual group, it’s 1.43”- not .7” or .8”.

 

[Harvey_NW]

If seating depth doesn’t matter, why does Berger make Classics and Hybrids?

Because the chamber geometry might not like a specific projectile profile, but that has nothing to do with seating depth.

Seating depth matters. How precisely it matters depends on your goals, your rifle, and which bullet you’re using. The end.

Feel free to post data or results to substantiate that, because that was the point of this thread. 9 pages in, still not one valid example.

 

[ddowning]

and yet when those four groups are overlaid into one to form an actual group, it’s 1.43”- not .7” or .8”.

View attachment 658036

You are making a valid point. However, if multiple 4 shot groups went from 1.7 to .7 then the 30 shot group likely went from 3.5-4" to 1.5-2". If he shot 1 group that was 1.7 and proclaimed it garbage and then proceeded to shrink it to multiple .7 groups (obviously with a 1.4" in there randomly somewhere after enough shots) then he did nothing.

You are 100% correct that he does not have a .7 moa weapon system. However, if he is comparing the average of multiple 4 shot groups of one load to the average of multiple 4 shot groups of the other, then he did have an improvement in precision from one load to the other.

The biggest problem with how most people do this is in testing and confirming. I am as guilty as anyone, but I also understand. If a load shoots 2 moa for 3 or 5 shots during load development, I am done with it, but it COULD be possible that you cound shoot 1000 shots into that group and it would never get any bigger. If I get a little tiny 5 shot group then I will test that load with a couple or 3 10 shot groups. If I get what I want I am happy. I know that a 30 shot group will likely be 1.5x the size of the 10 shot group average, and if I shoot 100 shots that 3 or 4 of those shots might land outside of a 30 shot group. I also understand that just because I shoot a 10 shot group that is 1 moa three times with a load that made a 5 shot group of .75 moa, that doesn't mean the 5 shot group that shot 1.5 moa might not do the same thing. The reality is that it might have, but I will never know. I could have wasted a little time and ammo when I could have just picked a load and gotten the same result.

Anecdotal evidence does support load development to some extent. I have just picked a load and ran it A LOT. Most of the time it works. There have been times when I can't hit what I want, so I shoot a few 10 shot groups and come to the realization that something is wrong. A lot of times it is something loose on the gun or a broken optic. A few times it has been the load, and after doing load development (with small sample sizes) it has become significantly easier to hit what I want to with the gun. I'm talking a few hundred rounds of fighting it versus the rest of the barrel with the load from load development. I have a decent system for load development to get me to the level of accuracy that I want...but I still hate doing it. It is a pain to develop a load for every barrel when you have 4 people shooting multiple calibers all the time. It's a lot easier to pick something and run, especially if you have history with the cartridge and chamber reamer.

One other thing that keeps coming up (not from Form) is chasing the lands. There is nothing more counter productive. Whoever named it should have named it chasing your tail. It doesn't matter if you are close to the lands or jumping. We got a prize table gun in 6 Dasher once with a tight freebore. We had to load short and touch the lands as a small part of the lands was still present all the way to the cartridge neck (zero freebore basically). The reamer supposedly has a .150" freebore. The gun shot under .5 moa and it was free. We just kept shooting it that way. It shot well for 2600 rounds with that same load. Most loads will shoot well for damn near the life of the barrel. Most cartridges have throat erosion of .003"-.010" per 100 rounds fired. Who wants to chase the lands knowing that? People will argue that, but normally they are not using the same bullet to measure, are using a method that isn't very accurate, or are measuring on a dirty barrel. It doesn't matter though because the jump is not critical, just the overall length.

In reality, the problem is with people's perception. They believe that small sample size load development is finding them THE BEST load for their gun. Some verify that it will be good enough for the task at hand by firing multiple groups and overlaying or larger shot number groups. Many of these people are still of the impression that they have "the best" load when any one of the small sample size groups that were within the large sample size could possibly be just as good. They just didn't look as good because of the random nature of 3 and 5 shot groups. The people that really should get dog-piled on are the ones that think their gun will hit the bolt on the target hanger at 1000 yards EVERY time because they shot a 3/4" 2 shot group at 1000 yards 1 time.

If I wasn't typing out of boredom, the tldr version is, everybody wants to be right. Most are, partially. The "your groups are too small" guys want to jump on the small sample guys. The small sample guys, if they are thorough, likely have some validity to their results. Their guns, however, are not 1/4" all day long "if I do my part" and their pet load is likely not THE BEST possible load for their rifle either.

 

[rcook10]

Here's some data from my 270 win load development. These are only 5 shot groups and I sadly didn;t save the target since I usually dump them once I've uploaded my data. Makes a pretty big difference to some for sure! Interestingly barnes are reputed to be jump happy and by far my best grouping was with only 15thou to the lands.

 

[Walmart Greeter]

Because the chamber geometry might not like a specific projectile profile, but that has nothing to do with seating depth.


Feel free to post data or results to substantiate that, because that was the point of this thread. 9 pages in, still not one valid example.

I posted my personal experience and there is no shortage of research to substantiate the rest

 

[FLS]

Because the chamber geometry might not like a specific projectile profile, but that has nothing to do with seating depth.


Feel free to post data or results to substantiate that, because that was the point of this thread. 9 pages in, still not one valid example.

It absolutely has to do with seating depth. Hybrids were developed for magazine fed rifles, where the OAL length restriction may create a longer jump (due to seating depth). The VLDs were hard to tune due to magazine length restriction ( seating depth/ jump to rifling). The hybrid profile engages rifling sooner, making sheathing depth less critical. It 100% has to do with seating depth.

 

[eoperator]

and yet when those four groups are overlaid into one to form an actual group, it’s 1.43”- not .7” or .8”.

View attachment 658036

Can you overlay targets like that within the Hornady analysis app?

 

[Vern400]

and yet when those four groups are overlaid into one to form an actual group, it’s 1.43”- not .7” or .8”.

View attachment 658036

There is some credibility to what you show here. Please consider that is a target from 1990. I've shot countless groups of 3 and 5 since then, and I recall few if any over an inch. You may also be aware that how you hold a light rifle changes the point of impact slightly. Even reloading the gun and repositioning, or taking a heavy jacket off will often change poi with a light rifle more so than with a 9 lb gun.
Why do I not have four similar groups with the factory ammunition you ask? Because one group can basically prove you're bad. I don't use the flyer excuse. All shots count. But it takes many groups to prove you're good. I shot a very poor 1.75-in group with factory ammunition at the outset, and confirmed it at the end after load development with another 1.9 inch group with the factory ammo. At the time, I was simply trying to improve the performance of my rifle, and I'm sure I did. If I had thought I would be defending the improvement 34 years later, I might have kept more thorough records.

I'll maintain my position that I did get an improvement. And older cartridges with possibly looser chamber tolerances can be more picky than newer cartridges designed for punching paper like a 6.5 creedmoor - they are more forgiving. Also, bullets with secant ogive design can be less sensitive to bullet seating then spire points or other types.

In the end, if I had intended to measure a single group I would put it all 12 bullets on the same Target.

Your analysis, with your assumptions, is nevertheless correct.

 

[Harvey_NW]

Here's some data from my 270 win load development. These are only 5 shot groups and I sadly didn;t save the target since I usually dump them once I've uploaded my data. Makes a pretty big difference to some for sure! Interestingly barnes are reputed to be jump happy and by far my best grouping was with only 15thou to the lands. View attachment 658068

That's interesting, and could definitely lead one to believe it makes a substantial difference. But running the numbers on that data only one group barely falls outside the statistical variability. The average group size was 1.095, and there can be 60% variability in 5 shot groups. So the only one outside the statistical expectation by less than .1" is the highlighted group, which could be encompassed by slightly skewed results from a shoulder fired rifle. I would be very interested in seeing what large samples produced, but as far as the results it looks to me like you're still observing random distribution of smaller samples sizes that fall within the statistical expectations.

I posted my personal experience and there is no shortage of research to substantiate the rest

Sorry, but I don't take some guy on the internets personal experience with no data or pictures as credible evidence. If you're researching on YouTube and getting your information from the small sample testers regurgitating the same old Fuddlore, sure. But if you research the cone of fire, and the statistics ballisticians have come up with after testing a lot of these theories and shooting millions of rounds, quite the opposite. That's why I started this post.

It absolutely has to do with seating depth. Hybrids were developed for magazine fed rifles, where the OAL length restriction may create a longer jump (due to seating depth). The VLDs were hard to tune due to magazine length restriction ( seating depth/ jump to rifling). The hybrid profile engages rifling sooner, making sheathing depth less critical. It 100% has to do with seating depth.

Yeah so like I said, different bullet shoots better, nothing to do with seating depth. The part I'm hung up on is "The VLD's were hard to tune", that's the point of my post. I haven't seen one valid example of seating depth making an improvement outside the statistical variability of the sample size, and being repeatable. So I started this thread.

Can you overlay targets like that within the Hornady analysis app?

Not yet, but in a recent podcast they mentioned specifically they are working on it.

 

[Walmart Greeter]

Sorry, but I don't take some guy on the internets personal experience with no data or pictures as credible evidence. If you're researching on YouTube and getting your information from the small sample testers regurgitating the same old Fuddlore, sure. But if you research the cone of fire, and the statistics ballisticians have come up with after testing a lot of these theories and shooting millions of rounds, quite the opposite. That's why I started this post.

When hundreds of people across different forums get similar results its a good indicator of a trend. Your initial comment is that seating depth doesn’t matter. If that’s the case then load five rounds at different lengths, jam one into the lands while you’re at it, and shoot a 5 inch group at 500 yards. Should be easy since it’s only a 5 round group

 

[Harvey_NW]

When hundreds of people across different forums get similar results its a good indicator of a trend. Your initial comment is that seating depth doesn’t matter. If that’s the case then load five rounds at different lengths, jam one into the lands while you’re at it, and shoot a 5 inch group at 500 yards. Should be easy since it’s only a 5 round group

When ballisticians shoot statistically valid sample sizes looking for those trends, they disappear. I suggest reading this thread in it's entirety, but specifically see posts #432, & 464 for a similar result. Also might google the cone of fire in your spare time.

Painless load development (mine)

That is interesting, I didn’t know that small primers could cause ignition issues in CM size cartridges. Are the ignition issues limited to CCI primers, is the powder type and ambient temperature a factor? In my limited experience with CM sized case I have only had issues with the CCI 450...

rokslide.com

 

[Flyjunky]

When ballisticians shoot statistically valid sample sizes looking for those trends, they disappear. I suggest reading this thread in it's entirety, but specifically see posts #432, & 464 for a similar result. Also might google the cone of fire in your spare time.

Painless load development (mine)

That is interesting, I didn’t know that small primers could cause ignition issues in CM size cartridges. Are the ignition issues limited to CCI primers, is the powder type and ambient temperature a factor? In my limited experience with CM sized case I have only had issues with the CCI 450...

rokslide.com

Like I've said before, there are NO absolutes in loading/development. Blanket statements don't work in most areas of life, and load development of one of them. It might not make a difference in somebody's combo but you can't say that for everyone.

Since the Hornady guys are referred to as the absolute experts on this board, episode 108 starting at 22:22. Basically Miles says that anything with a more modern reamer/throat design is much more forgiving, hence, seating depth doesn't matter as much. Then he goes on to say that "older saami spec chambers or bullets with more secant ogive, then seating depth may be something to explore, might be more of a make or break in that situation"

Also, around the 27ish minute mark they were talking about a question someone asked in regards to a universal seating depth as it relates to bullet designs. That's worth a listen as well because I believe Jayden said every combo is unique, especially the barrel, what might work good in one barrel may be terrible in another using the exact same components. So, if that is the case than how does seating depth testing not make a difference? It all comes back to what chamber and bullet combo you have.

 

[sveltri]

Does Hornady offer bullet similar in design to a Berger VLD, I sincerely do not know? I haven't messed with VLD's really at all because I had always heard they were jump sensitive, either wanted to "jammed" or "jumped a mile". Having shot mostly factory guns and touch, jam, real close, wasn't an option without single feeding.

 

[Harvey_NW]

Does Hornady offer bullet similar in design to a Berger VLD, I sincerely do not know? I haven't messed with VLD's really at all because I had always heard they were jump sensitive, either wanted to "jammed" or "jumped a mile". Having shot mostly factory guns and touch, jam, real close, wasn't an option without single feeding.

Not that I'm aware of, all of their heavier or high BC options are more of a hybrid or tangent.

 

[pbroski]

I did a seating depth test today with my CZ527 American in .17 Hornet. The scope is an old Leupold Vari X III 6.5-20x40 EFR.

The load is Hornady brass, Hornady 15.5 gr NTX bullet, CCI 400 primer and VV N120 powder. Velocity is approximately 3975 fps. The range was 99.7 yards fired off of a front and rear sandbag rest.

The first group is 10 shots with a cbto of 1.480". The second is 9 shots at cbto of 1.483" and the third is 9 shots at cbto of 1.486". All shots were fired round robin style.

Pretty interesting results, I would say.

BTW, it was my first time using my new Garmin chronograph. It picked up every single shot where as the LabRadar I used previously had not picked up even a single shot. I'm very impressed with the Garmin.