Bullet seating question for the precision guys…

[Klay23]

Do you all have better luck with setting the die to a specific spot to get you say 1.851” to the ogive and make every round there or do you say stop short of that number by .01 and then measure and adjust each round and seat to the 1.851” for example. This is 69gr smk in Lapua brass. Just curious which way is the most accurate. I don’t have much deviation but some are .001 or .0015 off or maybe .0005 or even .002 etc etc. Not sure how accurate my calipers are or even if that’s measurable also though. Just curious how you precision guys have had the most luck.

 

[nn8734]

Do you all have better luck with setting the die to a specific spot to get you say 1.851” to the ogive and make every round there or do you say stop short of that number by .01 and then measure and adjust each round and seat to the 1.851” for example. This is 69gr smk in Lapua brass. Just curious which way is the most accurate. I don’t have much deviation but some are .001 or .0015 off or maybe .0005 or even .002 etc etc. Not sure how accurate my calipers are or even if that’s measurable also though. Just curious how you precision guys have had the most luck.

What type of rifle is it and how is it to be used? Bolt gun? Carbine or precision/SPR-DMR? How far you shooting it and what must the target look like to meet your performance requirements?

 

[Klay23]

What type of rifle is it and how is it to be used? Bolt gun? Carbine or precision/SPR-DMR? How far you shooting it and what must the target look like to meet your performance requirements?

I’m running a terminus Zeus bolt action. I’ve had it to 500yds. It shoots great. Wondering because if after we find our fps node we check seating depth then it would make sense that it matters. Am I wrong? It’s a good shooter.

 

[Klay23]

Set it and forget it.

I would rather review the last 5 years of tax receipts than adjust a seating die for every individual round. You're definitely hyper-focusing on on a piece of micro-terrain. Zoom back out and consider how you want your load to perform. If you need to seat a bullet within .003" for it to be accurate, I don't want to devote time or money developing a load for it. Too finicky and high maintenance. You definitely want a more stable load than that.

There's a lot of different things that could create a .002" SD, .005" ES in seating depth. I'm sure we all pulled our hair out at one time or the other trying to figure it out. I don't fret it anymore.

This is exactly why I’m asking. Does it even matter? I have no interest in wasting the time if it doesn’t matter, lol. But knowing after we find our fps node we look at seating depth it would seem as it could and does matter…. Hmmm…

 

[nn8734]

I’m running a terminus Zeus bolt action. I’ve had it to 500yds. It shoots great. Wondering because if after we find our fps node we check seating depth then it would make sense that it matters. Am I wrong? It’s a good shooter. I’ve shot one whole groups and consistently shoots 1/2” or better at 100yds.

The tolerance of .001, etc you’re trying to hold isn’t necessary; as you mentioned you will be consuming time reloading at the expense of trigger time. If you’re getting those results on a consistent basis, id say you’re gtg - just put the load into production (for me, a prod lot = 400-600 rounds) and do your QC checks/monitoring along the way to ensure everything is consistent during production. Your brass choice is a big reason for the performance you’re seeing. If you were using lesser quality brass, you’d have to work harder to get the same or similar results

 

[Evintos]

Set and forget after finding seating depth window. The window is several thou wide.

 

[Klay23]

Set and forget after finding seating depth window. The window is several thou wide.

How big of a seating depth difference do you all set? .003” .005” etc. Meaning to find optimal window. Say I’m at 1.851”, where else should I look and in what increments makes sense?

 

[nn8734]

How big of a seating depth difference do you all set? .003” .005” etc. Meaning to find optimal window. Say I’m at 1.851”, where else should I look and in what increments makes sense?

For tangent ogive bullets (or hybrids), the nodes are typically very wide. Example: the 77smk, 169 & 175 shoot equally well at .030-.150 off the lands across numerous 5.56 and 308s respectively that ive owned over the years.

For my 77smk load (mk262 mod 1 clone), i just seat so that 1/4 the cannelure is visible. That’s it. I don’t even measure CBTO. And that load performs equally well across 5 different ARs including a 10.3 and a Mk12 mod 1. Same load, loaded on the same equipment using the same dies. My only concern was that the rounds fit in the mag and feed consistently w/o problems

 

[Evintos]

If you measure the BTO of the bullet themselves, you'll find that a lot of them are +/- .0005 to +/- .001, if the tolerance is larger than that, you need better, more consistently manufactured bullets.

I do .003 increments for testing. Windows can be even larger.

For your example, let's say your window starts at 1.851" with -0.003" window

Set die for 1.850" and forget. Your rounds will come out somewhere within 1.851" to 1.849". This is for bullets with +/- .001 tolerance.

You basically want to find a window and select a CBTO in which bullet BTO variation and throat erosion can be accounted for.

 

[Klay23]

If you measure the BTO of the bullet themselves, you'll find that a lot of them are +/- .0005 to +/- .001, if the tolerance is larger than that, you need better, more consistently manufactured bullets.

I do .003 increments for testing. Windows can be even larger.

For your example, let's say your window starts at 1.851" with -0.003" window

Set die for 1.850" and forget. Your rounds will come out somewhere within 1.851" to 1.849". This is for bullets with +/- .001 tolerance.

You basically want to find a window and select a CBTO in which bullet BTO variation and throat erosion can be accounted for.

I’m 20thou off the lans at 1.851”. What increment do you use to test seating depth?

 

[hafejd30]

I agree with set and forget. Find a window say for example .015-.025 where it’s happy, load to .020”. Then it won’t matter. If your playing the “kiss the lands game” like some fclass/bench guys do than it will matter more. But bullet sorting base to ogive will help that.

I typically run .020 off. Some are further because of mag length. My .260 is .015, 338 LM was .015, 308’s are .020, 300 WM was .030 off

 

[Klay23]

Appreciate the info fellas.. Happy Thanksgiving

 

[longrange772]

Another for set and forget. This is a pretty interesting article on bullet jump and vertical displacement. If you pick your set it spot well, the differences in seating on performance could be attenuated. Also, ties together with don't chase the lands school of thought.

Bullet Jump: Is Less Always Better?

About 2 years ago, Mark Gordon shared some preliminary research he’d conducted with the Applied Bal...

precisionrifleblog.com

 

[Evintos]

I’m 20thou off the lans at 1.851”. What increment do you use to test seating depth?

I do .003 increments but it really depends on how much you want to mess with this. Test at 200yds. 3rds (maybe) per increment.
If mag length allows it, I'd typically start at .002 off lands, going -.003 increments but until I find a window then find out how large that window is. I also bring a Lee hand press, micrometer seating die, and calipers for this test though (I have no arbor press).

So using your numbers the process would look like - Distance 200yds, 50rds would be more than enough. Any leftover rounds after finding the window will be loaded at your window.

- Load every single round at home with seating die set at 1.850" (they will be +/- .005 to .001 assuming you have good bullets, no need to measure every single rounds unless you're bored).

- Shoot 2 rounds of 1.850" , if the holes touch, shoot 3rd. If the holes don't touch, don't bother shooting the 3rd one at 1.850".

- Take 3rds of 1.850" CBTO rounds put it in the hand press and seat the bullets deeper using micrometer seating die to 1.847"

- Shoot 2 rounds of 1.847" if the bullets touch, shoot the 3rd. If it doesn't, take 1.847" and seat that deeper to 1.844" and seat 2 more at 1.844"

- Test the 1.844", repeating the same sequence in .003" increments until you find a window in which all the bullet holes touch and the point of impact is in the same area.

Lets say -
1.844" all 3 bullet holes touch and POI is 1" high at 12 o'clock from point of aim. 1.841" all 3 holes touch and POI is also 1" high at 12 o'clock, then 1.838" same as 1.844" and 1.841". Now if the 1.835" first two bullet holes touch but the POI is 5 o'clock from POA, then your window is closed.

Your window will be then 1.844" down to 1.838" which is a .006" wide window. At this point you can seat every round to 1.844" or 1.843" and more than likely the point of impact will be the same.
Lets say your throat eroded .001", your window basically shifts upwards by the same amount to 1.845" down to 1.839" but considering your window is .006", you still don't have to bother with changing your CBTO of 1.844" or 1.843".

The only time you would even bother is if your throat eroded .005-.006". In which case, simply add .005" to your CBTO (new CBTO 1.849" or 1.848").

The wider the window, the less you have to mess with this. For example if you find that your window is larger than .009", don't even bother tryin to find out how big it is. It could be as wide as .020" but all you'd do is just waste time confirming it.

But again, how much time do you really want to spend messing with this?

 

[Klay23]

I do .003 increments but it really depends on how much you want to mess with this. Test at 200yds. 3rds (maybe) per increment.
If mag length allows it, I'd typically start at .002 off lands, going -.003 increments but until I find a window then find out how large that window is. I also bring a Lee hand press, micrometer seating die, and calipers for this test though (I have no arbor press).

So using your numbers the process would look like - Distance 200yds, 50rds would be more than enough. Any leftover rounds after finding the window will be loaded at your window.

- Load every single round at home with seating die set at 1.850" (they will be +/- .005 to .001 assuming you have good bullets, no need to measure every single rounds unless you're bored).

- Shoot 2 rounds of 1.850" , if the holes touch, shoot 3rd. If the holes don't touch, don't bother shooting the 3rd one at 1.850".

- Take 3rds of 1.850" CBTO rounds put it in the hand press and seat the bullets deeper using micrometer seating die to 1.847"

- Shoot 2 rounds of 1.847" if the bullets touch, shoot the 3rd. If it doesn't, take 1.847" and seat that deeper to 1.844" and seat 2 more at 1.844"

- Test the 1.844", repeating the same sequence in .003" increments until you find a window in which all the bullet holes touch and the point of impact is in the same area.

Lets say -
1.844" all 3 bullet holes touch and POI is 1" high at 12 o'clock from point of aim. 1.841" all 3 holes touch and POI is also 1" high at 12 o'clock, then 1.838" same as 1.844" and 1.841". Now if the 1.835" first two bullet holes touch but the POI is 5 o'clock from POA, then your window is closed.

Your window will be then 1.844" down to 1.838" which is a .006" wide window. At this point you can seat every round to 1.844" or 1.843" and more than likely the point of impact will be the same.
Lets say your throat eroded .001", your window basically shifts upwards by the same amount to 1.845" down to 1.839" but considering your window is .006", you still don't have to bother with changing your CBTO of 1.844" or 1.843".

The only time you would even bother is if your throat eroded .005-.006". In which case, simply add .005" to your CBTO (new CBTO 1.849" or 1.848").

The wider the window, the less you have to mess with this. For example if you find that your window is larger than .009", don't even bother tryin to find out how big it is. It could be as wide as .020" but all you'd do is just waste time confirming it.

But again, how much time do you really want to spend messing with this?

Thank you sir. This is a whole lot of good info to digest

 

[Klay23]

.010" increments. Again, if XX.023" doesn't work but XX.026" does, and then XX.029" doesn't, it's too picky for me.

Also, keep in mind some of the advice above is based on the belief that seating depth is a function of accuracy being dependent on a specific jump to the lands. And when the lands erode, you have to chase them to maintain that same jump in order to keep that accuracy. There is another idea that people have that the jump to the rifling is all about harmonic timing and chasing the lands is councidenta

I get that for sure. I asked this question wondering if it even mattered as in my mind I don’t believe I have the ability even to measure it caliper wise perfectly consistently to the .0005” regardless or even to the .001”. I’m 1000% behind finding a seating depth node and moving on and not having to even think about that again for sure.