Seating depth variation

nksmfamjp

nksmfamjp

Well-Known Member
Joined
Jan 5, 2004
Messages
3,345
maximini14 223 said:
I hold seating depth to .0000 tolerance!
Click to expand...
Wow! How do you do that? I've run about 8 different seaters, annealed, sorted brass by brand, use premium brands, etc. I have about +/- 0.001" variation.

How much can I expect to see on target, if I eliminate that variation?

I'm really excited to hear how much you are seeing on target….
 
nksmfamjp said:
Wow! How do you do that? I've run about 8 different seaters, annealed, sorted brass by brand, use premium brands, etc. I have about +/- 0.001" variation.

How much can I expect to see on target, if I eliminate that variation?

I'm really excited to hear how much you are seeing on target….
Click to expand...
I go through my seating depth process and those that aren't exact get set aside. Using my Sinclair Comparator gauge I go back thru and adjust seating stem as needed to get exact measurements as taken from ogive. I'm getting 3/4" groups with SFAR308...my goal is half inch.
I'm still fine tuning seating depth...I'm seeing a sweet spot at 045 off jam and have 20 rnds ready to go in + - 005 increments on either side of 045.
 
I think this has been discussed before, but I will try and summarize:

Trying to seat a bullet perfectly, say .005" from the lands is a real feat. And seating exactly to zero jump, without jamming into the lands nearly impossible. Reproducible distance to the lands is very hard to get perfect.

Why? Several reasons.
-- Because you seat the bullet with your seating die with the cartridge base at the max distance, but the act of firing pushes the cartridge forward in the chamber, relocating whatever headspace you created in the sizing process to the rear of the cartridge. Did you account for this in whatever process you used to determine your CBTO? Are your sized cartridges identical to the dummy round you used? And if you did go to all that trouble, remember that your brass will have variable spring back, even if you have annealed. All this amounts to at least a little, say 1-2 thou variance.
-- Then add to that some variation in the bullet itself. The very best are close to perfect, but most are so-so. A thou difference to the ogive is certainly within spec for most manufacturers. A lot more for some.
-- Then add that your seater is almost certainly NOT seating from the ogive, but somewhere further towards the tip. More variance.
-- Then add the reality that over time, your rifle's throat is eroding.

So, if you are aiming for say a nice modest .025" thou jump, a .002" thou variance is just 8%. Not a lot.

And if you aim for a .005" jump, that .002" variance has now ballooned to 40%

Variance is the poison to accuracy.

And if you are trying to get to the lands perfectly, you WILL not get it right. Some will be jammed, some .002" off. The difference is huge in terms of accuracy. The bench rest guys just have a loose neck, jam every bullet into the lands and they get perfect uniformity.

Worthless for a hunting rifle. You must back off in my opinion. I suspect anything closer than .010" is asking for trouble in terms of accuracy. But that's an opinion -- would like to hear seasoned shooters thoughts.
 
nksmfamjp said:
Wow! How do you do that? I've run about 8 different seaters, annealed, sorted brass by brand, use premium brands, etc. I have about +/- 0.001" variation.

How much can I expect to see on target, if I eliminate that variation?

I'm really excited to hear how much you are seeing on target….
Click to expand...
cdherman said:
I think this has been discussed before, but I will try and summarize:

Trying to seat a bullet perfectly, say .005" from the lands is a real feat. And seating exactly to zero jump, without jamming into the lands nearly impossible. Reproducible distance to the lands is very hard to get perfect.

Why? Several reasons.
-- Because you seat the bullet with your seating die with the cartridge base at the max distance, but the act of firing pushes the cartridge forward in the chamber, relocating whatever headspace you created in the sizing process to the rear of the cartridge. Did you account for this in whatever process you used to determine your CBTO? Are your sized cartridges identical to the dummy round you used? And if you did go to all that trouble, remember that your brass will have variable spring back, even if you have annealed. All this amounts to at least a little, say 1-2 thou variance.
-- Then add to that some variation in the bullet itself. The very best are close to perfect, but most are so-so. A thou difference to the ogive is certainly within spec for most manufacturers. A lot more for some.
-- Then add that your seater is almost certainly NOT seating from the ogive, but somewhere further towards the tip. More variance.
-- Then add the reality that over time, your rifle's throat is eroding.

So, if you are aiming for say a nice modest .025" thou jump, a .002" thou variance is just 8%. Not a lot.

And if you aim for a .005" jump, that .002" variance has now ballooned to 40%

Variance is the poison to accuracy.

And if you are trying to get to the lands perfectly, you WILL not get it right. Some will be jammed, some .002" off. The difference is huge in terms of accuracy. The bench rest guys just have a loose neck, jam every bullet into the lands and they get perfect uniformity.

Worthless for a hunting rifle. You must back off in my opinion. I suspect anything closer than .010" is asking for trouble in terms of accuracy. But that's an opinion -- would like to hear seasoned shooters thoughts.
Click to expand...
I agree! That is why tolerances exist, whether it is +/- .xxx (more realistic) or +/- .xxxx. In short, there is an acceptable tolerance and variation.
 
As most target shooters realise, there is a sweet spot variation within about .003" gap of optimum distance. Varying by .003" is acceptable, even when jammed or just touching. I have used this amount with success. Drop out of this optimum amount and the load will shoot like Dick.
Seating depth for me starts at sorting CBTO, then pointing and tipping (if necessary), then seating depth is tested first with a non-tuned powder load in the middle of the load, say 3 grains below max.
Once seating depth is found, it rarely ever changes with powder nodes.

Cheers.
 
Annealing every time and using a Zero Press and selective shellholder I'm getting less than .0005 variation . Once in awhile an odd one pops up and I mark it for a fowler. I'm at .005 off but I have a pair of wbee 338-378's that shoot 1/2 moa at 1000 that jump nearly a quarter inch.
 
cdherman said:
-- Then add that your seater is almost certainly NOT seating from the ogive, but somewhere further towards the tip. More variance.
-- Then add the reality that over time, your rifle's throat is eroding.

Worthless for a hunting rifle. You must back off in my opinion. I suspect anything closer than .010" is asking for trouble in terms of accuracy. But that's an opinion -- would like to hear seasoned shooters thoughts.
Click to expand...
Shooting to extreme distances is one of my greatest pleasures. Making near-perfect bullets ... matched to the barrel's harmonics ... is what puts round after round onto the target. But, I can also say, the wind WILL throw off any shot no matter how good your bullet's made.

There IS a seating depth sweet spot for every rifle out there. I've loaded rounds for people who were pulling their hair out. Perfect seating depth is a breeze after the focus and perseverance of addressing all the other variables. But, it's usually more time and money than most folks are willing to sacrifice. And, even after you've shown them, they'll just buy 3 or 4 different brands of cartridges and hunt with the best of the lot.

I didn't understand how radically seating depth affected precision until I mounted a press to my truck and started final-seating out at the range. If you make two good shots and the bullets don't print one over the other ... you'll have to tweak that depth ... not even any need for a confirmation shot. The only trick to it is getting everything else right first. You can tell you haven't got everything else right if you're throwing an occasional flyer. "Playing Around" with seating depth is a waste of components and barrel life ... if it's not the last step in your build process.
 
This will be a hard pill to swallow for many, as our personal opinions on reloading are as deeply held as many religious beliefs. I was in the same camp as everyone on this thread, fussing over seating depth. Having an engineering and medical background I approach reloading from a science based perspective. I have never been able to understand or reconcile the fact that there are so many various reloading techniques that all produce sub quarter MOA results. Everyone claims their particular technique is the best way to make small groups. But from a scientific perspective, if 4 or 5 different reloading processes produce identical results, then the process itself can't be as critical to the end result as we think. So which steps in the loading process truly affect group size?

I recently read the following article and then listened to Hornady Podcasts #50 and #52 and the answer to the question became crystal clear. I no longer worry about seating depth. What you see in 3 to 5 shot group sizes is statistically invalid, nothing but noise and not a reliable judge of what your rifle is truly doing.

www.outdoorlife.com

Rifle Nodes: How You’ve Been Wasting Your Time and Money on Load Development

Everything you know about rifle nodes and load development might be wrong. Click here to see the results for yourself.
www.outdoorlife.com www.outdoorlife.com



 
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VenatusDominus said:
I was in the same camp as everyone on this thread, fussing over seating depth. Having an engineering and medical background I try to approach reloading from a science based approach. I recently read the following article and then listened to Hornady Podcasts #50 and #52 and no longer worry about seating depth. What you see in 3 to 5 shot group sizes is, statistically, nothing but noise and not a reliable judge of what your rifle is truly doing.

www.outdoorlife.com

Rifle Nodes: How You’ve Been Wasting Your Time and Money on Load Development

Everything you know about rifle nodes and load development might be wrong. Click here to see the results for yourself.
www.outdoorlife.com www.outdoorlife.com



Click to expand...

Hornady sells factory ammo. When a factory ammo maker tells you that factory ammo is as good as you can get take it with a grain of salt. Precision reloaders know its hogwash that DOES apply to factory rifles and factory or untined ammo
 
Willys said:
Hornady sells factory ammo. When a factory ammo maker tells you that factory ammo is as good as you can get take it with a grain of salt. Precision reloaders know its hogwash that DOES apply to factory rifles and factory or untined ammo
Click to expand...
The article and the podcasts have nothing to do with their factory loaded ammo. In the two podcast above, Hornady never claims their factory ammo is as good as hand loaded; in fact, I don't recall factory ammo being discussed or even mentioned. They also sell seating depth dies.

The article is by an independent reviewer that was skeptical about what Hornady was reporting and verified their findings independently by firing groups of 30. The two engineers in the podcasts are competitive shooters that reload for precision competition and after doing their studies, no longer fuss over seating depth. If you have an understanding of statistical analysis, small sample sizes in any statistical analysis are meaningless. You need sample sizes in the 20-30 numbers to start getting valid information.

The large sample sizes used demonstrate that small changes in seating depth and powder charges do not produce statistically significant changes in group sizes for a given powder and bullet combinations, except that generally group sizes open up slightly as you increase the powder charge. By far the largest effect on group size is the powder and bullet used.
 
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VenatusDominus said:
This will be a hard pill to swallow for many, as our personal opinions on reloading are as deeply held as many religious beliefs. I was in the same camp as everyone on this thread, fussing over seating depth. Having an engineering and medical background I approach reloading from a science based perspective. I have never been able to understand or reconcile the fact that there are so many various reloading techniques that all produce sub quarter MOA results. Everyone claims their particular technique is the best way to make small groups. But from a scientific perspective, if 4 or 5 different reloading processes produce identical results, then the process itself can't be as critical to the end result as we think. So which steps in the loading process truly affect group size?

I recently read the following article and then listened to Hornady Podcasts #50 and #52 and the answer to the question became crystal clear. I no longer worry about seating depth. What you see in 3 to 5 shot group sizes is statistically invalid, nothing but noise and not a reliable judge of what your rifle is truly doing.

www.outdoorlife.com

Rifle Nodes: How You’ve Been Wasting Your Time and Money on Load Development

Everything you know about rifle nodes and load development might be wrong. Click here to see the results for yourself.
www.outdoorlife.com www.outdoorlife.com



Click to expand...

Not only that, which I believe, with seating depth you're chasing a moving target. Every shot moves the lands a bit farther away. Even in a mild benchrest chambering the lands are moving faster than one might think. Weatherby may have had it right. The throat will wear rapidly in his magnums so go for speed with a long freebore and forget about seating depth. In a rifle with 800 rounds of good barrel life, do you want to spend a good chuck of that chasing lands that move with every shot?
 
VenatusDominus said:
This will be a hard pill to swallow for many, as our personal opinions on reloading are as deeply held as many religious beliefs. I was in the same camp as everyone on this thread, fussing over seating depth. Having an engineering and medical background I approach reloading from a science based perspective. I have never been able to understand or reconcile the fact that there are so many various reloading techniques that all produce sub quarter MOA results. Everyone claims their particular technique is the best way to make small groups. But from a scientific perspective, if 4 or 5 different reloading processes produce identical results, then the process itself can't be as critical to the end result as we think. So which steps in the loading process truly affect group size?

I recently read the following article and then listened to Hornady Podcasts #50 and #52 and the answer to the question became crystal clear. I no longer worry about seating depth. What you see in 3 to 5 shot group sizes is statistically invalid, nothing but noise and not a reliable judge of what your rifle is truly doing.

www.outdoorlife.com

Rifle Nodes: How You’ve Been Wasting Your Time and Money on Load Development

Everything you know about rifle nodes and load development might be wrong. Click here to see the results for yourself.
www.outdoorlife.com www.outdoorlife.com



Click to expand...

I totally agree that it is dangerous to use small sample sizes and extrapolate results. However, a three shot cloverleaf does show promise but concluding you have "found the load" is jumping to conclusions.

In general, there is a fundamental lack of understanding of statistics in this country, especially when it comes to LR shooting.
 
Bad Loads shoot as well as Good Loads! Luck alone determines your groups! Nodes are a figment of your imagination. Seating depth changes don't show up on target. Is the world still flat?
Good gawd men, do you guys reload precision ammo? Do you shoot?
 
Willys said:
Bad Loads shoot as well as Good Loads! Luck alone determines your groups! Nodes are a figment of your imagination. Seating depth changes don't show up on target. Is the world still flat?
Good gawd men, do you guys reload precision ammo? Do you shoot?
Click to expand...
Did you read the article? It concludes that you cannot determine a "good" vs "bad" load with small group sizes, they are statistically meaningless. The data shows that you need a sample/group size of 30 to have statistically significant data. Shoot ten 3 shot groups (or six 5 shot groups) of your sub quarter MOA load and you will find that your average group size is larger than you think. And YES, for those that ignore science, the world is still flat.

From the article:

"I did not experiment with changes in seating depth in this test. One of the things that Neville and Quinlan observed in their testing was that changes in seating depth, like charge weight, didn't result in any meaningful changes in accuracy. I used to experiment with seating depth and load bullets as long as they'd fit in the magazine, but a couple years back, I started loading everything to the cartridge overall length that the reloading data suggested. I have noticed no difference in accuracy. An easy proof of this would be to shoot a 30 shot sample at your "ideal" seating depth and another at a different seating depth (at least a .030-inch change). They will look different with 3-, 5-, or 10-shot samples, but will that hold up with 30?"
 
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