Variation in seating depth

[UndFrm]

What could be the possible reasons for the variations in CBOL (ogive) length.
Considering that the total case length is the same, the projectile base to ogive length has been sorted to be the same, but yet after seating the bullet, there's variations in base to ogive length from cartridge to cartridge.

Using a Lee turrent press as single stage, but I do ensure that the cases are going as up in the die as possible, to remove any wiggle room there.

Thank you

 

[memilanuk]

Where the cone of the seating stem touches the bullet is not the same as where you're measuring BTO, so they don't necessarily have any corelation to one another. Not much you can do about this, normally. Technically there are some options but they are kind of off in the weeds. Usually 'better bullets' or 'does it actually matter on your target?' are the go-to solutions here.

Also, I have seen instances where large variations in seating force resulted in measurable differences in seating depth - that *did* correlate with the seating force. Best to sort out the seating force issues first if that is the case.

 

[UndFrm]

Where the cone of the seating stem touches the bullet is not the same as where you're measuring BTO, so they don't necessarily have any corelation to one another. Not much you can do about this, normally. Technically there are some options but they are kind of off in the weeds.

Also, I have seen instances where large variations in seating force resulted in measurable differences in seating depth - that *did* correlate with the seating force. Best to sort out the seating force issues first if that is the case.

I was reading about the Arbor presses and the Wilson seating die. Is that something that might be able to mitigate this issue?

 

[memilanuk]

Maybe. Helpful, I know

The seating stem is still going to be a smaller diameter than the bullet diameter, which is basically where the comparator is contacting. The reason you don't usually see manufacturers making the seater stem that big is the beveled cone area starts getting awful thin, and it starts belling out under heavy seating forces.

The other thing that sometimes happens is that the seating stem cone isn't deep enough, and bullets with long pointy tips - like VLDs, A-tips, or maybe some of the polymer tips - actually bottom out on the tip before they ever touch the ogive. Take the seating stem out, turn it over and drop a bullet into it. If it sits up relatively straight, that's probably *not* your issue. If it tips over to one side and you can see a gap around the rim of the seating cone... It likely *is* the problem.

Sometimes you can just order a new 'VLD' seating stem. Other times, you have to redneck diy it by taking a sacrificial bullet, coat the nose in something like JB bore paste, chuck it in a drill and lap the seater stem to fit. Or order a better seating die.

 

[straightshooter1]

What could be the possible reasons for the variations in CBOL (ogive) length.
Considering that the total case length is the same, the projectile base to ogive length has been sorted to be the same, but yet after seating the bullet, there's variations in base to ogive length from cartridge to cartridge.

Using a Lee turrent press as single stage, but I do ensure that the cases are going as up in the die as possible, to remove any wiggle room there.

Thank you

Various things will effect your CBTO (Cartridge Base to Ogive) measurement:

1. There are variations in bullet's BTO dimensions within a particular lot; more so with some brands of bullets than others, and always between lots of bullets. This is why some reloaders will sort their bullets to get better uniformity.

2. Variation in the neck tension results in variation in seating depth, which makes the CBTO measurement vary, of course. That variation in neck tension can come due to variations in neck wall thickness and/or variations in hardness of the neck walls due to work hardening the sizing process does to them.

3. Variation in the interference between the bullet and the interior of the neck wall (some may have more friction than others, even if the "neck tension" is the same). Depending on how case necks are cleaned and/or lubed, this can mitigate this kind of variance.

4. Play in the linkage of the press that's doing the seating can induce variance in seating depth.

5. Difference between where your comparator touches the ogive and where the bullet seating pin touches the ogive can vary, which will contribute to producing differences in CBTO.

Some of these things will have minimal effect and other can have great effect. All together, they can produce substantial differences. How little difference you want will dictate how you much attention you give any of these.

 

[McPotty]

I was out shooting a couple weeks ago and the man at the table next to me noticed the blue MTM case so of course asked if I was shooting hand loads. We started talking and me being rather new at it explained my process and asked if there was anything else I could do to improve accuracy. He asked if I sorted bullets based on base to ogive length; something I hadn't really considered. I did have a flier here and there but 3/5 5-shot groups were just below .75moa including them. Given that at longer distances the flier would be more pronounced is it THAT critical or is it more of a personal preference.

I'm not looking for butthole sized groups at 2 miles or anything close to that; just reliable/repeatable moa or better hits out to 800 or so is my goal.

 

[memilanuk]

See above, specifically

Usually 'better bullets' or 'does it actually matter on your target?' are the go-to solutions here.

Sorting by BTO or bearing surface is pretty far down the list of things that are going to make a meaningful difference in your group sizes.

Not saying that sorting can't or won't help... but the situations where the juice is worth the squeeze are pretty far and few between. If you want to, go for it. Just don't be surprised if you don't see huge returns on the time/effort expended.

 

[emrekt888]

It's seating stem geometry and net neck tension. Sorting bullets based on ogive is silly and a waste of time, buying decent bullets it won't really matter.

Make sure your seating die stem matches your bullet profile. You can check buy setting it on a table and seeing where it makes contact and how it well it centers naturally. If you can wiggle the round around and it's making contact on a sharp point, your stems the problem. If it centers naturally when you spin a round and it doesn't let you roll it in the stem when you apply pressure, it's making good contact.

One thing I like to do that really makes a huge difference is grab a bullet, a drill, your stem, and some lapping compound. Chuck the bullet in the drill, smear on some lapping compound, and press the stem into the bullet. This will polish and hone the stem closer to the bullet profile. Finish off with additional finer grits and some steel wool to normalize everything.

Clean it all up and go back to loading.

If you feel variations in seating force that will also jank up seating depth. Every round should take the same amount of force to seat otherwise you will get differences in depth as it crushes the tip against the force. Look for rings around the top of the bullet where the inside of the stem contacts for evidence of issues.

 

[straightshooter1]

See above, specifically



Sorting by BTO or bearing surface is pretty far down the list of things that are going to make a meaningful difference in your group sizes.

Not saying that sorting can't or won't help... but the situations where the juice is worth the squeeze are pretty far and few between. If you want to, go for it. Just don't be surprised if you don't see huge returns on the time/effort expended.

While sorting may not "make a meaningful difference in your group sizes", one just needs to be aware that their can be a significant difference from one lot to another that will. Don't take it for granted the the new box of the same bullets you just bought will the the same as your old one.

 

[Marine52]

Where the cone of the seating stem touches the bullet is not the same as where you're measuring BTO, so they don't necessarily have any corelation to one another. Not much you can do about this, normally. Technically there are some options but they are kind of off in the weeds. Usually 'better bullets' or 'does it actually matter on your target?' are the go-to solutions here.

Also, I have seen instances where large variations in seating force resulted in measurable differences in seating depth - that *did* correlate with the seating force. Best to sort out the seating force issues first if that is the case.

“Usually 'better bullets' or 'does it actually matter on your target?' are the go-to solutions here.”

^^^I believe this is important. Good bullets like Berger have a consistent ogive with minimal variation. They’re not perfect but they’re the best I’ve found.

Also, it’s important to have consistent results on your base-to-shoulder measure (bump) when you are sizing because you are seating the bullet based on cartridge BTO measurements. Remember, when the firing pin hits the primer, the case shoulder is pushed up against the chamber shoulder. For this reason, I do my seating depth setting and finished cartridge comparisons using the shoulder-to-ogive measurement. I also seat bullets with a seater that indexes off the case shoulder. This has given me very precise bullet seating results.

I refuse to go down the “bullet sorting” rabbit hole.

 

[Hawk in WY]

Check that the primers are seated slightly below flush.

There is a saying in medicine, "When you hear hoof beats, don't think of zebras."

 

[SNB]

is it THAT critical or is it more of a personal preference.

You have to determine this for yourself. If your hit probability at 800 yards suits you, then you don't need to tune anything.

 

[ACK]

Eons ago I used steel epoxy putty and filled the seater void. I seated a plastic tipped vld on an empty shell and let it cured in place (over night). I proceeded to load several rounds. My objective was to minimize distortion on the plastic tip. It worked. Not sure about seating depth.