Load development with SEATING DEPTH first

[BoydAllen]

View attachment 1101460 Why not do both at the same time?

Nice test. To answer your question, because I want to establish what the maximum load is. Also, using my method I can discover or confirm the spacing between nodes and how many there are. What I described was an initial test of a new powder, using that information I would do further testing. I just want to know where the limits are. So often I see friends start to do detailed testing, stopping where the manual says to. In many cases individual rifles and lots of powder will safely exceed that charge weight by a significant amount. I presume that you have compared the manual top loads for the 6PPC with what many competitors actually use. That is my point. You can miss a lot by not knowing what your actual upper limit is.

 

[Ccrider]

After getting mediocre results working up a 6BR load in a 28” CBI threaded to a SA 700 I’ve decided to try this route. The idea of finding the “best” group as a starting point based on seating depth removes a potential variable from muddying my already frustrated psyche.

Just dump the 6br and get a CREEDMORE!

 

[Tim Singleton]

Nice test. To answer your question, because I want to establish what the maximum load is. Also, using my method I can discover or confirm the spacing between nodes and how many there are. What I described was an initial test of a new powder, using that information I would do further testing. I just want to know where the limits are. So often I see friends start to do detailed testing, stopping where the manual says to. In many cases individual rifles and lots of powder will safely exceed that charge weight by a significant amount. I presume that you have compared the manual top loads for the 6PPC with what many competitors actually use. That is my point. You can miss a lot by not knowing what your actual upper limit is.

29 gr of LT 32 is about the upper limit
I can tell this by the way the groups form at that load compared to 28 and 28.5 it spits one out
That's the good thing about having it all on one piece of paper a lot of information there

 

[Lucky Shooter]

Tony Boyer book-----Tuning Your Rifle----Keeping The Rifle In Tune

As regards seating depth, I'm not sure how to interpret Mr. Boyer's wording.

Did he imply that seating depth is barrel-specific and should be adjusted to chase
the effects of throat erosion ?

There are some comments on pages 256 & 257 concerning ".012" off the jam".

Anybody want to read this book and comment ?

A. Weldy

 

[Boyd L.]

Just dump the 6br and get a CREEDMORE!

I've had one for quite a while. Owning it hasn't helped the BR shoot better yet.

 

[Hengehold]

With a new powder, the first thing that I do is to do a sort of ladder/pressure test at 100 yards. I say sort of, because I am not just looking at elevation. I am looking for how shots cluster. I drop down to a low charge that literature tells me is not too low to be safe, and load one shot per charge at an interval that is appropriate for the case volume, on cases like the .222 up through the .308 .3 gr. I shoot all of the shots on a single target, over flags, on a morning when the wind is not difficult, and continue until bolt lift tells me that I should stop. One needs to pay close attention to do this. So many time I have seen fellows who after a clear indication that a load was too hot, ignored the obvious and chambered another one. Do not do that. After I get signs of excessive pressure, I note the temperature and humidity, and the charge just below it as maximum. Obviously, a max charge arrived at in cold weather will require retesting when the temperature is significantly warmer. At the end of the test I will usually have a target with some clusters of bullet holes made by consecutive charge weights. At that point I will load a three shot test using the middle load of the most promising cluster. I do this with the bullet seated into the rifling by an amount that I have found good results with before, so that my maximum pressure will be worst case, since jumping with that load would result in lower pressure. After I have a charge weight, I experiment with seating depth. Generally, if I can, I do all of this loading at the range. My friends who do not, generally have to invest several trips to the range into getting to a point that I can get to in less than two hours.

BoydAllen,
The process you have described is exactly what I have traditionally used for load development. I like to try new cartridge/powders so I typically go through the full range of powder charges to be on the safe side.

Everyone else,
In my early days of learning to reload I measured the OAL that I needed to be on the lands in a new barrel. I made a mistake somehow with the stony point tool and ended up seating the Sierra SMK bullets with a .120 jump instead of a .020 jump. After a couple matches I corrected the mistake and loaded the remainder of my ammo to .020 jump. I did not notice any significant change in accuracy at the time. This was used in a Palma rifle for 1000yd NRA highpower competition. That early experience left me with the impression that seating depth would have a smaller affect on group size than powder charge.

I appreciate hearing about the experience of others to the contrary.

-Trevor

 

[Texas10]

Tony Boyer book-----Tuning Your Rifle----Keeping The Rifle In Tune

As regards seating depth, I'm not sure how to interpret Mr. Boyer's wording.

Did he imply that seating depth is barrel-specific and should be adjusted to chase
the effects of throat erosion ?

There are some comments on pages 256 & 257 concerning ".012" off the jam".

Anybody want to read this book and comment ?

A. Weldy

I don't own that book, but I suppose it would depend upon what he means by "jam". It could mean bullet seated to touch the lands as opposed to off or out. Or he could be referencing "hard jam" where you seat a bullet long into a fire formed case with light neck tension, chamber it and force the bolt closed causing the bullet to be forced back into the case. That will give you the maximum OAL that you can load that bullet in that chamber. In my experience it can be up to .030" into the lands, maybe more, from the touch dimension.

I keep dummy cartridges that I've used to find distance to lands, with data written on the case. I can use these later to document throat erosion, and "chase the lands" if I need to seat to a particular distance into or off the lands for best performance. Some bullets don't seem to care how far they jump. Others are quite particular.

Only your barrel knows for sure.

 

[BoydAllen]

Base to bullet OGIVE is far more important than seating stem contact. The bullet OGIVE is what hits the rifling and determines jump.

If you are really going to find a good load you need to ladder test and find the nodes. Moderate loads won't get it done. Sure you may get lucky, but you won't find what is best for the rifle. Barrel length matters as you may have 2 or 3 nodes.

Shoot ladders in 5 shot groups, 0.1 grain increments. Keep an eye on average velocity and SD. When velocity is climbing slowly and SD's are under 10 (under 6 if your scale reads 0.00) then you are on a node. When velocity is climbing or dropping rapidly, it is a place you don't want to be - you should only have slight verticles in your groups. Once you find the nodes, adjust your seating depth to clean up the L-R in the groups. If things are not working out, try a different bullet.

Don't do this with NEW brass. New to the rifle and FLS is okay, but new brass itself typically has a lot of movement so it won't yield the consistency that is needed.

I think that you may have missed my point. It is the bullet to bullet variations in the distance between where the seating stem contacts a bullet, and where the rifling will first touch that are the primary cause of variation in case head to bullet ogive measurement. In order to have less of the second, you will have to successfully deal with the first. I was attempting to describe one way to do that.

 

[golong]

I think that you may have missed my point. It is the bullet to bullet variations in the distance between where the seating stem contacts a bullet, and where the rifling will first touch that are the primary cause of variation in case head to bullet ogive measurement. In order to have less of the second, you will have to successfully deal with the first. I was attempting to describe one way to do that.

Yes and no on missing your point. I agree that seating stem impact can cause the variation, but in truth I don't see it happening hardly at all. However, since I started sorting base to ogive it is extremely rare that I see differences in seating for each group in the sort.

So yes I agree that where the seating stem makes contact matters. I just don't think it is more important than sorting. All good either way - whatever gets it done!

 

[BoydAllen]

I don't own that book, but I suppose it would depend upon what he means by "jam". It could mean bullet seated to touch the lands as opposed to off or out. Or he could be referencing "hard jam" where you seat a bullet long into a fire formed case with light neck tension, chamber it and force the bolt closed causing the bullet to be forced back into the case. That will give you the maximum OAL that you can load that bullet in that chamber. In my experience it can be up to .030" into the lands, maybe more, from the touch dimension.

I keep dummy cartridges that I've used to find distance to lands, with data written on the case. I can use these later to document throat erosion, and "chase the lands" if I need to seat to a particular distance into or off the lands for best performance. Some bullets don't seem to care how far they jump. Others are quite particular.

Only your barrel knows for sure.

The traditional competition short range benchrest definition of jam, much corrupted in the last few years on the internet, is the length to which a bullet is pushed back when seated long and chambered, or to put it another way, the longest length that it can be seated without being pushed back when chambered. Shooters would and do say that they are seating some number of thousandths off of jam. When determining jam the neck sizing should be just as it would be for loaded ammunition. Ultimately, jam is a specific seating depth that varies depending on how barrel is chambered, worn, the bullet shape, neck tension, and the coefficient of friction of the inside of the neck. The reason that it was used was that it was so easy to determine. While I am loading at a match, I can load a round a little long, measure it tip to head, note that, go to the line while it is hot, chamber the round, unchamber it and repeat the tip to head measurement, noting the difference from the first measurement, add the amount I want to be shorter than jam to the amount the round was shortened, and reset my seater to produce that dimension. After reseating the bullet by this slight amount I can check to be sure that I have what I want, and then measure using the ogive tool and record that along with the other load data. All of this can be done in less time than it takes to explain.
Added a little later: I have the book, and recommend it.

 

[Straightshooter1]

Yes and no on missing your point. I agree that seating stem impact can cause the variation, but in truth I don't see it happening hardly at all. However, since I started sorting base to ogive it is extremely rare that I see differences in seating for each group in the sort.

Likewise, when I sort by base to ogive (or even by bearing surface length), it's the thing, for me, that has the most impact on getting consistent seating depth with my Forster Micrometer Seating Die.

 

[Ned Ludd]

Sorting bullets base-to-ogive (BTO) will not correct seating depth variance caused by bullet nose length length variance in the region between the two critical points on the bullet ogive where we measure cartridge base-to-ogive (CBTO, i.e. the point where the caliper insert seats on the bullet) and the seating die stem contact point. In the cartoon below, those points are indicated by the blue and red arrows. As Boyd indicated, those two points lie outside the bullet BTO dimension and sorting bullets by BTO will not address length variance in that region. For that reason, seating depth variance caused by bullet length variance in that region can only be corrected by using a tool that sorts bullets based on the distance between the two critical contact points, such as Bob Green's comparator.

 

[Straightshooter1]

Sorting bullets base-to-ogive (BTO) will not correct seating depth variance caused by bullet nose length length variance in the region between the two critical points on the bullet ogive where we measure cartridge base-to-ogive (CBTO, i.e. the point where the caliper insert seats on the bullet) and the seating die stem contact point. In the cartoon below, those points are indicated by the blue and red arrows. As Boyd indicated, those two points lie outside the bullet BTO dimension and sorting bullets by BTO will not address length variance in that region. For that reason, seating depth variance caused by bullet length variance in that region can only be corrected by using a tool that sorts bullets based on the distance between the two critical contact points, such as Bob Green's comparator.

View attachment 1145398

How much variance can one expect to find in that "critical distance"?

And it would seem, the larger the caliber, one would tend to find larger variances . . .???

 

[Ned Ludd]

It totally depends on the Lot of bullets. Some are very uniform, some are not. It's possible to find variance in that critical region of several thousandths (or more), enough to give you fits when seating bullets and measuring CBTO, at any rate. If it's of any help, at the bottom of the following link to Bob's Comparator webpage are some length variance numbers for the critical region as provided by a customer for one specific bullet (http://greensrifles.com/New_Products.html). I can't really state with any certainty whether you can directly link bullet length variance to caliber, as I've observed it in different calibers. I suspect it might correlate more with the specific manufacturer, but even manufacturers that generally produce very uniform bullets can occasionally put out a Lot that has noticeably more variance that others.

Using Bob's Comparator is a relatively simple sorting method to facilitate more uniform seating depth as caused by bullet length variance between caliper insert and seating die stem contact points, but it will not correct seating depth inconsistency caused by some other issues, such as the seating die itself. Further, Bob doesn't make a Comparator in .22 cal, and I shoot a lot of .224" bullets, so I've had to come up with sort of a "poor man's comparator tool" to help with this issue. In my hands, bullet nose length variance generally contributes more to bullet OAL variance than does the bearing surface or boat-tail regions. That is not to say that there can't be length variance in those regions, I just generally find there to be more in the nose region, which isn't all that surprising given the manufacturing process of lead core/jacketed bullets. For that reason and for the purpose of pointing them, I sort my .224" bullets by OAL. Although not as good an approach as using Bob's tool, which sorts based on the critical region between caliper insert and seater die stem contact points, I have found that .224" bullet sorted by OAL will generally give noticeably more uniform seating depth and less jockeying around with the seating die micrometer than with unsorted bullets. YMMV.

 

[dmoran]

My input to bullet qualification/segregation:

1 - Base to Ogive - is critical for the consistency in the bullets relationship to the lands/rifling.
Myself use a comparator with a hole size near bore diameter for these qualifications.

2 - Base to Seater Stem - is critical for the consistency of the seating depth in the case.
Myself use the actual seater stems from dies, or make a comparator with the same size hole, for these qualifications.

Lot dependent if the two coordinate together. Some times they do, some times they don't - IME
Which determines if I have to do both qualifying steps or if I can get by just doing one.

3 - After qualifying/segregating my bullets to both BTO & BTS, I then qualify them by OAL, for consistency gains in BC.
4,5 - Then there is bullet diameter and weight qualifications, if your anal as I am !.!.!

---------------------------------------------------------------------------------------------------------------------------

 

[mikecr]

BTO affects seating depth (not land relationship).
Faith in BTO beyond this is no more than amusing to me.

The qualifying of ogive datums with a BGC, in itself, means nothing to land relationship nor seating depth. But it is prerequisite to knowing these things.
Depending on the cartridge shoulder angle and headspace control, and with qualified ogives, CBTO can hold meaning to land relationship.

 

[dmoran]

^^^^ Your first sentence and your last sentence contradict each other. But think as you want, shall will I.

 

[Straightshooter1]

It totally depends on the Lot of bullets. Some are very uniform, some are not. It's possible to find variance in that critical region of several thousandths (or more), enough to give you fits when seating bullets and measuring CBTO, at any rate. If it's of any help, at the bottom of the following link to Bob's Comparator webpage are some length variance numbers for the critical region as provided by a customer for one specific bullet (http://greensrifles.com/New_Products.html). I can't really state with any certainty whether you can directly link bullet length variance to caliber, as I've observed it in different calibers. I suspect it might correlate more with the specific manufacturer, but even manufacturers that generally produce very uniform bullets can occasionally put out a Lot that has noticeably more variance that others.

All understood.

If there is several thousandths (or more) of variance in that critical distance, then it surely would be worth taking that into consideration and making appropriate adjustment for loading. It just seems to me like that small segment of the total bullet length wouldn't have that much variance (depending of the bullet and how well it's manufactured). But . . . there is a way to find out. And I'm going to give it a go and report back.

On taking a look at that link and noting the reference to what Dean Mihalovits reporting a variance of .003-.007, would be in line with what I typically see with my 168 and 175 SMK's when I sort using BTO measurements. I would expect that measuring base to SSCP would produce close to the same "variance" numbers.

BTW: I misspoke with my reference to "caliber". I really meant to refer to a bullet's overall length. My late night mind was thinking in terms of the correlation between calibers and bullet lengths.

 

[holstil]

I've learned a ton about bullets when I started making them. Many conversations with Randy Robbinette and George Ulrich getting me going. Very Interesting, watching the effect the amount of lube has on bullet dimensions.
I sort bullets by bs and oal then loaded rounds by bto.
Still learning but this has significantly sped the process.

 

[Rdlningcltchdmpr]

I recently received some reloading advice from one of the prominent bullet making companies that we all use. The advice was to begin load development with a moderate powder charge and shoot for groups by adjusting the SEATING DEPTH and leaving the moderate powder charge constant.

For example, shoot 5 shot groups of the following:

.010 jam, 45.0 gr Varget
.005 jump, 45.0 gr Varget
.040 jump, 45.0 Varget
.070 jump, 45.0 Varget

After testing different seating depths, Pick the seating depth that resulted in the best group. The second step is to adjust the powder charge while keeping the seating depth constant.

For example let’s say .040 jump provided best groups in the initial testing of seating depth. Now we will shoot 5 shot groups with the following:

.040 jump, 45.0 Varget
.040 jump, 45.3 Varget
.040jump, 45.6 Varget
.040 jump, 45.9 Varget
Etc.

I have never considered using seating depth as the first step to find the tune of a barrel. I have always done load development the other way around with adjusting the powder charge first and then fine tuning with seating depth.

Question: Does anyone else here prescribe to the “seating depth first” approach to load development?

My background is in NRA high power competition. Maybe this is something that is common among the benchrest community?

Thanks,

-Trevor

No,no,no. Just because someone at a bullet manufacturer says it , doesn't make it valid. Imo. Bad- bad advice. I am able to develop super accurate loads in only the minimum number of shots fired. If you want the smart easy way information just pm me.