Where and who to ask about technical bullet seating depth

6

65shooter

Member
Hello. Just starting out in hand loading, and I'm trying to figure out the technical limits of bullet seating depth so that I don't ruin anything. Not looking for "It's in the manual" because I've already looked. Anyone know who or where I could ask questions like this to? I know I have to 'experiment to find out what my rifle likes' but I need to know left and right limits before I begin these experiments. Thank you.
 
well basic spec is listed for all "normal" cartridges.
but lets start with what cartridge, what rifle, what use, what bullet
buy a hornady tool for checking bullet seating length) was stoney point)
i start all my loading at TOUCH and typically back off from there.( touch is typically high pressure point when using this process)
 
This is for basically all calibers and all rifles. It's a theory/fundamental question with no specific rifle in mind. I'm looking for absolute minimums and maximums. Precisely how far out can I seat a bullet in the neck? I hear one caliber's worth. Quantify that. Why. What happens if I don't-AND, how do you know? (assuming no interference with from the lands of course) Now, if I'm jamming say 20 thou, precisely what does that do to pressure? How do I know? How do you know? Will I have to reduce charge? By how much? Is there a formula concerning say case capacity, burn rate etc etc? I don't care to guess much, since my face is soo close to all the fun goin on in the chamber.
Now the opposite. Say I have a SUPER short leade; how far can I press that bullet into the neck to keep from jamming? How far is that pressure going up? Not really caring to see 'if the primer's flattening out'. I'm looking for true scientific data. If I seat too deep, what's the rule for how much I yank from the powder charge?
If someone can point me to a person that can answer these question with more than a guess, I'll pay.
 
i doubt you can afford the answers . it is not known scientific data. as an example, powder is "compared" to one lot in a closed bomb test for certification....and it is seldom done today. it aint as much science as you think it is. it trial and error and notes, until the next lot of powder or bullets or primers. you can buy most of the tools but everything changes when you change one part of the load
 
Understood. I was hoping for more concrete answers though. So it's a 'load to minimum charge and pray' kinda thing?
 
65shooter said:
Understood. I was hoping for more concrete answers though. So it's a 'load to minimum charge and pray' kinda thing?
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suggested loads
No, do not load to min and pray, look here for suggested loads for the caliber that you are using. Start a little under and work up.

The questions you are asking about bullet depth seating are dependent on your rifle, your bullet (may have to change depth with different lot of the same bullet) your load, and your powder. It is typically adjusted for accuracy reasons, not for pressure reasons. Stick with pressures that give good groups without pressure signs.
Since you seem to be concerned about pressure, find the touch point on the lands with a Hornady Lock & Load seating depth gage. Set bullets at touch, and adjust into the lands, or away from the lands in a .002 or .003 steps with a safe or recommended load. Let the target tell you the accuracy point.
You only have to worry about pressure increases if you jam into the lands a LOT with a hot load. For me, a LOT being the .020 you mentioned. At that point there is a good chance when you extract an unfired cartridge, the bullet and a bunch of powder will remain in the barrel. I typically put it .006 to .010 into the lands and it won't pull the bullet. Many people "jump" the bullet, ie, have it .020 or .060 away from the lands for best accuracy.

You second post talks about how far you can push the bullet into the case neck. The answer is, just enough that the bullet doesn't fall out of the case to as far in as past the end of the neck, and compressing the powder. Yes this will have some pressure effects, but unless you are doing something whacky, the common sized bullets and common loads result in a cartridge that looks normal and doesn't have high pressures.

Buy some loading manuals, they will give the loads and pressures that are safe. Don't go whacky with strange combinations until you have more experience. The one thing that manuals will give is Cartridge Overall Length. This is typically to insure the cartridge will fit in a magazine and will feed properly, and is somewhat typical of the load. I generally ignore it, I load to Base to Ogive Length (not given in any manual, depends on your bullet and barrel) which relates to the touch point in the barrel where the lands start.

Lastly, if you are still worried about pressure, you can glue strain gages on the barrel, and measure the stresses due to the pressures. This will work, it is difficult, and the pressure spikes you may see will drive you insane. You will have to trust the strain calculations, as there is no way to calibrate the results. I have done this, dove down the rabbit hole, and decided it was not worth the trouble.

The loading manuals are your friends. Good luck.
 
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powderbrake said:
suggested loads
No, do not load to min and pray, look here for suggested loads for the caliber that you are using. Start a little under and work up.

The questions you are asking about bullet depth seating are dependent on your rifle, your bullet (may have to change depth with different lot of the same bullet) your load, and your powder. It is typically adjusted for accuracy reasons, not for pressure reasons. Stick with pressures that give good groups without pressure signs.
Since you seem to be concerned about pressure, find the touch point on the lands with a Hornady Lock & Load seating depth gage. Set bullets at touch, and adjust into the lands, or away from the lands in a .002 or .003 steps with a safe or recommended load. Let the target tell you the accuracy point.
You only have to worry about pressure increases if you jam into the lands a LOT with a hot load. For me, a LOT being the .020 you mentioned. At that point there is a good chance when you extract an unfired cartridge, the bullet and a bunch of powder will remain in the barrel. I typically put it .006 to .010 into the lands and it won't pull the bullet. Many people "jump" the bullet, ie, have it .020 or .060 away from the lands for best accuracy.

You second post talks about how far you can push the bullet into the case neck. The answer is, just enough that the bullet doesn't fall out of the case to as far in as past the end of the neck, and compressing the powder. Yes this will have some pressure effects, but unless you are doing something whacky, the common sized bullets and common loads result in a cartridge that looks normal and doesn't have high pressures.

Buy some loading manuals, they will give the loads and pressures that are safe. Don't go whacky with strange combinations until you have more experience. The one thing that manuals will give is Cartridge Overall Length. This is typically to insure the cartridge will fit in a magazine and will feed properly, and is somewhat typical of the load. I generally ignore it, I load to Base to Ogive Length (not given in any manual, depends on your bullet and barrel) which relates to the touch point in the barrel where the lands start.

Lastly, if you are still worried about pressure, you can glue strain gages on the barrel, and measure the stresses due to the pressures. This will work, it is difficult, and the pressure spikes you may see will drive you insane. You will have to trust the strain calculations, as there is no way to calibrate the results. I have done this, dove down the rabbit hole, and decided it was not worth the trouble.

The loading manuals are your friends. Good luck.
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Thank you for that. I appreciate it! On the seating depths vs pressure thing; I understand it's chamber dependent, but pressure spikes coming from seating too far into the lands is a thing on every chamber. I was just curious if the super basic load info given in reloading manuals like my Hornady for example, cover general rules like what to do if loading to 20 thou jam for instance. I ask this because I have seen general rules of thumb for a family of cartridges like "drop this much percent for starting off but with this bullet weight instead of the advertised one." Since they gave a percentage of a drop, was just asking if there was one for a load utilizing jam, (or the opposite, a ton of jump). I know how to find the lands and back off 20 thou and start there, but like I said, I love learning the theory of things and how they work. To me, having a good grasp of that theory before you go experimenting with gunpowder is a prudent thing. I ask because in all the reading I've done in official loading manuals, I've never seen a load describing jamming the lands, so to me that's not an officially sanctioned Sierra or Berger practice. So since you dont see those loads, I gotta ask, what am I getting into when experimenting with that?
You know, kind of like the very first benchrester (who knows, somewhere in the 1950's maybe?) who decided to try a deep jam load without realizing there would be a pressure spike and not adjusting the charge for it, sure, maybe he didn't blow his chamber but maybe split a case. Since he was the first, what was the official recommendation before the first jam load ever? "Try it and see." lol. Not with my guns lol. So what you're saying is, that if I begin at the bottom of the officially recommended charge weight in the manual, and I jam 20 thou, I shouldn't be splitting cases or blowing chambers. (with an approved load out of a manual)

Overall, I already pretty much understand how to experiment with this, but if you never learn your mins and maxes or 'left and right limits', what's to stop a person from seating way to far or shallow during their 'adjust 3 thou and see what that does to the group size.' phase? Say I'm only 30 thou deep into the neck on a 185 Juggernaut, with a super long throat, and my groups shrank to .3. Ok, will only 27 thou deep into the neck give me a .2 or .25 group? I was just wondering what that limit was before something catastrophic happens lol. Again, just like the other general rule of thumb where people say try not to seat the base of the bullet (i guess not counting the boattail?) below the shoulder neck junction. There's a 'general' but not super strict rule that was created for accuracy concerns. That's all I was really looking for honestly, but more for safety concerns rather than accuracy. I know accuracy (really consistency) runs in nodes and will shrink and grow and then shrink groups again, but safety is something different.
So, thank you for all the help thus far, I really appreciate it guys.
 
Pretty much, its the powder one has to be concerned with, not the seating depth. You aren't plowing new ground. Stick with published loads and you won't blow anything up.

I use as my benchmark the OAL of a loaded round, measured from where the bullet will touch the lands to the butt of the case, measured with a comparator attached to a Vernier caliper. Polishing the bullet after each reading, I keep pushing the bullet into the case until I can just barely see land marks on the bullet, this is my Benchmark for that bullet. Not all bullets are the same so this should be done for each make and lot. Write that number down. you now have a basis to work from.

It helps a lot to have a micrometer seating die when doing this work. Also helps a lot to have a good bullet puller. If you want absolutes, this will take you there.
 
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Off of the lands we rarely see the node beyond .06 and into the lands .05. This obviously varies slightly by bullet style and is completely not applicable to VLD bullets. Neck tension goes hand in hand with your seating depths.
 
firearmsunlimit said:
Off of the lands we rarely see the node beyond .06 and into the lands .05. This obviously varies slightly by bullet style and is completely not applicable to VLD bullets. Neck tension goes hand in hand with your seating depths.
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I settled on .006" IN many years ago and find the powder charge that delivers the magic. At .006" in, one can open the bolt with a loaded round and eject it without pulling the bullet and why I use .006"
 
Here's my course on the Basics of Seating Depth...

First, some terminology and then some fundamentals principles...

Hard Jam - this is when the bullet is seated so long in the reloading process that the barrel rifling engages the bullet AND pushes the bullet further into the case when you close the bolt. Physically, the bullet cannot be seated longer. This position is dependent on other factors of your case prep and components. Neck tension, neck wall thickness, brass hardness, bullet shape, etc. all produce variances in 'hard jam length'.

Just Touch - this is when the bullet is seated out until it just barely touches the lands of the rifling. This is definitely a feel thing -- remove the firing pin and try closing the bolt on bullets that you seat progressively deeper by a thou or two until you can feel that the bullet is not scraping on the lands as you close the bolt. Some folks look for engraving on the bullet, but the feel method get you closer to the actual 'just touch length'.

Touching The Lands: Record both the Hard Jam and Just Touch measurements for a particular load (brass/bullet combination). The key here is that 'touching the lands' is not a single value. The difference between the measurements is the range of seating depths where you are touching the lands, but not moving the bullet. For example, my 65gr 6PPC bullets typically have a range of .025"-.035" of lands engagement. Bullet shape has a lot to do with this value and VLD bullets can be significantly different than standard tangent ogive bullets.

Reference System - Some folks like to track seating depth from the Just Touch point, describing the depth as X thousandths into (or off) the lands. Other folks (myself included) like to track seating depth as X thousandths in from the Hard Jam. The key here is that your reference matters. When someone says, "I'm jamming the bullets .010", you really have no idea where they are measuring from.

Trouble Spots - Because of tiny variations in individual bullet shape and loading techniques, I like to stay away from the critical measurement points by .003-.005". Basically, setting the seating depth very near at Just Touch (long or short) or at Hard Jam (long) can lead to inconsistencies in performance.

Pressure: Two Kinds - From an internal ballistics view, there are two different pressures that correlate to seating depth adjustments.
  • Peak Pressure is the basic reference for your max-load value. As a general rule, modern centerfire rifles typically have a safe value of around 60-64,000 pounds/sq-in (psi).
  • Shot Start Initiation Pressure. This is the amount of pressure that has to build in the case before the bullet starts to move. A generally accepted number for bullets that are not engaged in the rifling is around 3625psi. The Quickload internal ballistics simulation software suggests adding 7,200psi (for a total 10,825psi) if the bullet is engaged in the lands, but that isn't the whole story...
Tuning with Seating Depth - This is primarily concerned with tuning with the bullet touching the lands. Because there is a range of values from Just Touch to Hard Jam, there is also a range of values that you can add to the standard Shot Start Initiation Pressure. For my 6PPC, I have found that the Just Touch position is simulated by adding about 4000psi to the 3625psi standard, while the Hard Jam length requires adding nearly 10,000psi. This variation in Shot Start Initiation Pressure results in a change in Peak Pressure roughly equivalent to 2 full grains of powder. Turn this around, and if your powder charge is within plus or minus a grain of a "best amount", you can likely fine tune the rest of the way with small adjustments to the seating depth in the Just Touch to Hard Jam range.

Obligatory Safety Reminder - Remember that touching the lands can be roughly equivalent to adding 2 grains of powder... it is even more important to start load development on the low side and work up!

Personally, I find that tuning with seating depth is much more precise that varying powder charges. I shoot a few groups to get the powder close, then focus my testing on seating depth changes to look for stabile accuracy nodes.

Rod
 
well i disagree.
to me "touching" is just that, the point where the bullet just touches the lands.
the inverse is the point where the first land no longer touches the bullet.
so the first -.001 in seating and there are 3 vs 4 marks..it aint "touching", and ii move the bullet out .001 and i get 4 marks, that is MY TOUCH.
and yes i chase the throat.
yeps its my definition, but it is defineable and repeatable.
i start all load development at my touch...because it is high pressure, and a ladder will show when to stop. then groups, then adjust depth, recheck load, adjust neck tension, re check...... but remember i do not do well in short range still a new kid, i do well in long range, and i load the same way.
 
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Best to strip the bolt completely including the ejector. start with a case that offers no resistance then I keep pushing the bullet into the case until I can just see faint land marks on a polished bullet. This is touch or Kiss for me. I them measure this round using a Stoney Point comparator on my Vernier caliper. This becomes my "benchmark" with this particular bullet. Record this measurement then begin testing. I almost universally use .006" into the lands. Why? Well, One can always remove remove a loaded round from the chamber without sticking a bullet in the lands and I have found 006" to be my accuracy place almost universally. I measure every loaded round and measuring close where the bullet will engage the lands. I use a turret press and keep a collet bullet puller next to my Vernier seating die and make every loaded round exactly the same length using those parameters. I know I have done the very best I can do at that point to have as close to perfect ammo as I can make. Makes me feel better. :)
 
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For seating depth, I find the 'stripped bolt' method to be the simplest and most reliable. Once the 'T.P.' (touch point) is found for each bullet, that seating stem length gets written on a label that's pasted to the seater die box. Then the stem length can be easily and quickly changed by using shims or adjusting the stem length. No wondering or fussing about it .🤔 Bada bing, bada boom. Done.

In any barrel, I start with the the bullet as far past the T.P. as I'll ever go with as much neck tension as I'd ever use. That way, there's only one way to go with the bullet when tuning seating depths.

With all the subtle differences in bullet profiles and throat angles, I've never found a specific magic number for seating depth.

Just my thoughts over the first cup of Sulawesi this morning. 🌄

Good shootin' -Al
 
To simplify your seating depth quest I would set the range for testing at .010+ and .010-. After you play with the seating depth tool mentioned above make up a dummy round based on a .05+ seating. Use some 1/0 steel wool twisted around the bullet until the shine is gone. Chamber the dummy round. If your setting is truely at .05+ you will see marks from the barrel lands that are square. In other words the will be as wide as they are long. Proceed with test and tune from there.
 
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