Need help with inconsistent bullet seating depth

[JOE62]

Had the same problem as the o/p, I'm a tightass on most things and enjoy making do with things on the cheap. That said I use basic R.C.B.S. dies, I sent the seating stem and 3 bullets to them and they machined a custom stem for the bullets and problem was solved. Now my c.b.t.o. is within a .001. Now it seems to me that a guy could do a couple coats of car wax on the bullet your using and do a custom stem with j/b weld.

As long as you drill out some of it to keep the tips of the bullets from bottoming out in the seater stem. Or you could lap the stem with lapping compound and the bullet you are using.

 

[bax]

Could it be that the CBTO value (a) using the seater stem and the CBTO value (b) using the measuring device vary? So A minus B is not a constant?

 

[Longtrajectory]

Good thread albeit a little old. I’m new(rookie) to long range shooting and slowly learning through my mistakes and others and soaking up a ton of great info here and there. I’m shooting 6.5CM with a Ruger RPR currently working through load development. I found my node and am now in the process of finding the best jump. All my load development has been with bullet 0.020” off the lands. Did some “macro” jump testing and narrowed the best jump(best SD’s) somewhere between the lands and 0.018 off the lands. As I began to seat the bullets for finer granularity jumps I saw as much as 0.004” variance between each seated bullet where I was attempting/expecting to see maybe a 0.0005” variance. After reading this thread and others I quickly learned that trying to maintain a 0.0005” variance without tuning for each bullet is unrealistic due to variability in bullet curvature .

I’m using a Forster Bench Rest Ultra Micrometer seater die in a RCBS RC Supreme press, loading Hornady ELD-M bullets into Lapua SP brass. My goal is to establish a consistent seating variance of no more than +/-0.002”.

I took some measurements on a bullet to see how far the seater stem touch point was from the bullet comparator touch point and the lands touch point(pic below). Was surprised at the distance between the seater stem touch point to the lands.

My question to the experts here, other than having to adjust the die to seat each bullet is there a different method(s) or tool(s) or combo of the two that would enable me to achieve the +/-0.002” depth tolerance with a single actuation of the press? Thank you

 

[Marine52]

It is perfectly normal for the seating stem, comparator, and rifling to contact the bullet ogive at different locations. As long as the bullets are produced with a consistent ogive (the curved part of the bullet), you should be ok.

— measure a few bullets with your comparator and make sure base to ogive (BTO) is consistent.
— is the tip of the bullet bottoming out in the seating stem? This sometimes happens with VLD bullets

you said you are finding a variance of as much as .004. Is that cartridge base to ogive or overall length?

 

[Longtrajectory]

It is perfectly normal for the seating stem, comparator, and rifling to contact the bullet ogive at different locations. As long as the bullets are produced with a consistent ogive (the curved part of the bullet), you should be ok.

— measure a few bullets with your comparator and make sure base to ogive (BTO) is consistent.
— is the tip of the bullet bottoming out in the seating stem? This sometimes happens with VLD bullets

you said you are finding a variance of as much as .004. Is that cartridge base to ogive or overall length?

I measured 4 bullets BTO and found up to 0.003” variance so definitely variance in the bullets themselves. I will check if the bullet is bottoming out in the stem to see if that is also contributing. Variance I’m finding is Cartridge base to ogive. My primer pockets have been uniformed and the primers do not protrude.

I’m wondering now if there may more BTO variance between bullet lots. I opened 3 boxes(100 count each) of bullets and weighed/sorted them so the lots were mixed together.

Sounds like I’ll have to live with adjusting the seater die for each bullet?

 

[Marine52]

Well that’s a lot of work adjusting seating die for each bullet and that will only insure a consistent comparator measurement where it contacts the ogive. What youre really trying to achieve is consistent jump to the lands and if the bullet ogive has a .003” variation you are stuck with that. The Bergers I shoot have about +-.0005 variation with an occasional .001 And yes, don’t mix bullet lots. maybe you should try some Bergers and see if that helps. But it does sound like the bullet ogive variation accounts for most of the .004 variation you have found.

Also, make sure the shellholder on your RC has a bit of cam over when it contacts the bottom of the seating die. This will insure consistent insertion of the cartridge into the die.

 

[Longtrajectory]

Thanks @Marine52! I’ll be ordering some Bergers if I can find them.

 

[straightshooter1]

Good thread albeit a little old. I’m new(rookie) to long range shooting and slowly learning through my mistakes and others and soaking up a ton of great info here and there. I’m shooting 6.5CM with a Ruger RPR currently working through load development. I found my node and am now in the process of finding the best jump. All my load development has been with bullet 0.020” off the lands. Did some “macro” jump testing and narrowed the best jump(best SD’s) somewhere between the lands and 0.018 off the lands. As I began to seat the bullets for finer granularity jumps I saw as much as 0.004” variance between each seated bullet where I was attempting/expecting to see maybe a 0.0005” variance. After reading this thread and others I quickly learned that trying to maintain a 0.0005” variance without tuning for each bullet is unrealistic due to variability in bullet curvature .

I’m using a Forster Bench Rest Ultra Micrometer seater die in a RCBS RC Supreme press, loading Hornady ELD-M bullets into Lapua SP brass. My goal is to establish a consistent seating variance of no more than +/-0.002”.

I took some measurements on a bullet to see how far the seater stem touch point was from the bullet comparator touch point and the lands touch point(pic below). Was surprised at the distance between the seater stem touch point to the lands.

My question to the experts here, other than having to adjust the die to seat each bullet is there a different method(s) or tool(s) or combo of the two that would enable me to achieve the +/-0.002” depth tolerance with a single actuation of the press? Thank you
View attachment 7827792

OK, I've posted this on a couple other threads before, but I'll do it again here as I've got your solution.

First, let me point out the "jump" simply is not very important as seating depth is (seating depth being how far the base of the bullet is into the case, which changes the volume that the powder can reside in and that has a big influence on the pressure curve that effects the bullet timing in relation your barrel's harmonics for consistent POI's). So, don't focus on jump, but focus on seating depth. Measuring to the lands is only important to find out the space you have to work in. After that, seating depth is what you want to adjust after you've found a decent powder load that's at you're starting seating depth.

The issue you're talking about is one that confounded me for a while as no one else seems to have a good solution for the variation between the seating stem contact point and the contact point of one's caliper insert for the ogive. . . which is what tends to produce those seating depth variances, even when the bullets are sorted by BTO's. To solve this, I decided to sort my bullets by the distance from the base to the seating stem contact point (for me, that's the point as you've pointed out in your picture for an LE Wilson seating stem). Now that I sort bullets this way, I have very little variance in seating depth, even though the CBTO (Cartridge Base To Ogive) can vary, which is not important (the jump variance).

For my 6.5 bullets, I found Sinclair 17mm comparator insert contact point to be very close to the con Wilson seating stem contact point. So that's what I use to sort my .264 bullets with. I do use Berger's and find they often don't need sorting as the variances are often very small. For other brands, they almost always need sorting to get the kind of consistency I want.

So, the key is in sorting your bullets and sort with a comparator insert that has the same diameter at the contact point as your seating stem does.

Keep in mind that comparator inserts for the same caliber vary and the one you have probably won't give you the same measurement as mine even though it's the same brand. It's a "comparator", not a precision measurement. Always use the same CBTO comparator insert to keep tract of the distance to your lands. That distance changes over time and you don't have to try and keep that distance (the jump) the same. Just keep your seating depth the same for the one that gives you the good results.

 

[Snuby642]

My thoughts.
Col is a nominal measurement to ensure it will fit in magazine without loading problems.

Bto is a determining measurement. It changes jump and volume at the same time so whichever you think is more important, fine doesn't matter since they can not be separated without building new bullets.

I just measured 25 308 / 168g smk's I loaded, today and pretty much had a 0.0025 + / - bto.

Inexpensive Lee press and dies.

Getting rid of that extra 0.0025 tolerance will cost time and money.

Bullets will vary bto, and the base to tip and the bto would change pressure and can be sorted out costing time.

Bergers and Sierra are the most consistant bullets I have measured.

Getting rid of that "normal" variance is not in my budget at the moment and hopefully the node is forgiving.

I got a EC tuner brake to take care of the problem.

 

[spife7980]

Good thread albeit a little old. I’m new(rookie) to long range shooting and slowly learning through my mistakes and others and soaking up a ton of great info here and there. I’m shooting 6.5CM with a Ruger RPR currently working through load development. I found my node and am now in the process of finding the best jump. All my load development has been with bullet 0.020” off the lands. Did some “macro” jump testing and narrowed the best jump(best SD’s) somewhere between the lands and 0.018 off the lands. As I began to seat the bullets for finer granularity jumps I saw as much as 0.004” variance between each seated bullet where I was attempting/expecting to see maybe a 0.0005” variance. After reading this thread and others I quickly learned that trying to maintain a 0.0005” variance without tuning for each bullet is unrealistic due to variability in bullet curvature .

I’m using a Forster Bench Rest Ultra Micrometer seater die in a RCBS RC Supreme press, loading Hornady ELD-M bullets into Lapua SP brass. My goal is to establish a consistent seating variance of no more than +/-0.002”.

I took some measurements on a bullet to see how far the seater stem touch point was from the bullet comparator touch point and the lands touch point(pic below). Was surprised at the distance between the seater stem touch point to the lands.

My question to the experts here, other than having to adjust the die to seat each bullet is there a different method(s) or tool(s) or combo of the two that would enable me to achieve the +/-0.002” depth tolerance with a single actuation of the press? Thank you
View attachment 7827792

Allow me to introduce the bob green comparator, sort your bullets by that dimension and they will all seat and contact the same for that lot.

https://greensrifles.com/new-product-page

 

[Longtrajectory]

OK, I've posted this on a couple other threads before, but I'll do it again here as I've got your solution.

First, let me point out the "jump" simply is not very important as seating depth is (seating depth being how far the base of the bullet is into the case, which changes the volume that the powder can reside in and that has a big influence on the pressure curve that effects the bullet timing in relation your barrel's harmonics for consistent POI's). So, don't focus on jump, but focus on seating depth. Measuring to the lands is only important to find out the space you have to work in. After that, seating depth is what you want to adjust after you've found a decent powder load that's at you're starting seating depth.

The issue you're talking about is one that confounded me for a while as no one else seems to have a good solution for the variation between the seating stem contact point and the contact point of one's caliper insert for the ogive. . . which is what tends to produce those seating depth variances, even when the bullets are sorted by BTO's. To solve this, I decided to sort my bullets by the distance from the base to the seating stem contact point (for me, that's the point as you've pointed out in your picture for an LE Wilson seating stem). Now that I sort bullets this way, I have very little variance in seating depth, even though the CBTO (Cartridge Base To Ogive) can vary, which is not important (the jump variance).

For my 6.5 bullets, I found Sinclair 17mm comparator insert contact point to be very close to the con Wilson seating stem contact point. So that's what I use to sort my .264 bullets with. I do use Berger's and find they often don't need sorting as the variances are often very small. For other brands, they almost always need sorting to get the kind of consistency I want.

So, the key is in sorting your bullets and sort with a comparator insert that has the same diameter at the contact point as your seating stem does.

Keep in mind that comparator inserts for the same caliber vary and the one you have probably won't give you the same measurement as mine even though it's the same brand. It's a "comparator", not a precision measurement. Always use the same CBTO comparator insert to keep tract of the distance to your lands. That distance changes over time and you don't have to try and keep that distance (the jump) the same. Just keep your seating depth the same for the one that gives you the good results.

Wow, great info, thanks!. A ton of new info for me here. I thought it WAS all about the jump distance and the jump distance influenced the first order affect on barrel harmonics but it makes a lot of sense that consistent pressure/pressure curve is the key to consistent harmonics and to low SD’s & tight POI’s. Darn, I have 50 rounds ready to go with precise jump offsets. Oh well I’ll take advantage of this and shoot the 50 rounds then load 50 rounds with precise seating depths then shoot those And compare. I should expect better results with the precise seating depth rounds.

I learned how important barrel harmonics are. I had my scope zero’d then attached the V3 Magnetospeed to my barrel which shifted the POI considerably I.e. 2” @100yards which I rectified by mounting the Magneto speed off the barrel.

@straightshooter1 what exactly is the process/tools you use to measure seater stem contact point to base?

 

[Longtrajectory]

My thoughts.
Col is a nominal measurement to ensure it will fit in magazine without loading problems.

Bto is a determining measurement. It changes jump and volume at the same time so whichever you think is more important, fine doesn't matter since they can not be separated without building new bullets.

I just measured 25 308 / 168g smk's I loaded, today and pretty much had a 0.0025 + / - bto.

Inexpensive Lee press and dies.

Getting rid of that extra 0.0025 tolerance will cost time and money.

Bullets will vary bto, and the base to tip and the bto would change pressure and can be sorted out costing time.

Bergers and Sierra are the most consistant bullets I have measured.

Getting rid of that "normal" variance is not in my budget at the moment and hopefully the node is forgiving.

I got a EC tuner brake to take care of the problem.

@Snuby642 sorry, maybe I’m slow, not sure I understand what problem the EC tuner brake solves?

 

[straightshooter1]

Wow, great info, thanks!. A ton of new info for me here. I thought it WAS all about the jump distance and the jump distance influenced the first order affect on barrel harmonics but it makes a lot of sense that consistent pressure/pressure curve is the key to consistent harmonics and to low SD’s & tight POI’s.

Yeah, I though the same thing as it seemed so many posting from people emphasized jump. Then there's Erik Cortina who's a highly competitive shooter and has YouTube videos and emphsizes to "stop chasing the lands". You might also find the following series of articles regarding bullet jump of interest (if you haven't already read it):

You searched for bullet jump - PrecisionRifleBlog.com

precisionrifleblog.com

Darn, I have 50 rounds ready to go with precise jump offsets. Oh well I’ll take advantage of this and shoot the 50 rounds then load 50 rounds with precise seating depths then shoot those And compare. I should expect better results with the precise seating depth rounds.

I learned how important barrel harmonics are. I had my scope zero’d then attached the V3 Magnetospeed to my barrel which shifted the POI considerably I.e. 2” @100yards which I rectified by mounting the Magneto speed off the barrel.

@straightshooter1 what exactly is the process/tools you use to measure seater stem contact point to base?

As you did in your picture above, I spun a bullet in my Wilson seating stem, then measured that diameter with my caliper. The measurement is not "precise", but it's plenty close enough. Then I get a comparator insert that will make a mark on the bullet at that same location or have one made with the same diameter as that will have the same contact point.

As I mentioned before, for my 6.5 (.264) bullets I found the .172" (17 Caliber) Sinclair Comparator Insert has a contact point close enough to my Wilson seater stem contact point that give me good results. This one:

SINCLAIR INTERNATIONAL Products for Sale Online - 237 Products

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www.sinclairintl.com

Then I use this insert in my caliper and measure from the base of the bullet with for sorting just as you would measuring BTO's.

 

[Longtrajectory]

Got it, thank you!

 

[spife7980]

Got it, thank you!

But then you have people who say it’s not “how deep it is in the case” but rather when it exits the muzzle and so by altering seating depth you change the amount of time it takes for the bullet to travel the barrel and this when it leaves. Sooner later further deeper. Which is sorta one aspect of the obt I think

There’s all sorts of theories and they all sorta work until they don’t and then you move to the next until it doesn’t.