Whats .001 of seating depth worth?

[Straightshooter1]

Bullet seating measurement...CBTO or shoulder datum point to ogive?

Was recently looking at a video featuring the Accuracy One seating depth comparator which got me wondering if one method is better than the other. Opinions?

forum.accurateshooter.com

If I were loading my cartridges where they're into the lands, I would want to measure shoulder-datum point to the point on the ogive that touches the lands. That Accuracy One comparator would be the way to go. This way, as the throat erodes, I'd be the same amount into the lands.

But I don't load into the lands where throat erosion is not really an issue. I load to maintain the one seating depth that gives me the best groups and the groups stay good even though jump increases with the throat erosion. I don't chase the lands.

 

[6BRA]

If I were loading my cartridges where they're into the lands, I would want to measure shoulder-datum point to the point on the ogive that touches the lands. That Accuracy One comparator would be the way to go. This way, as the throat erodes, I'd be the same amount into the lands.

But I don't load into the lands where throat erosion is not really an issue. I load to maintain the one seating depth that gives me the best groups and the groups stay good even though jump increases with the throat erosion. I don't chase the lands.

That point at which the bullet is jammed is just a reference point. Do you think the throat will only erode if you are jammed? Unless you have a combo and jump that is extremely consistent grouping over a wide seating depth, the erosion will eventually require you to seat farther out. It is just a reference point.

 

[Mulligan]

.001” is small, small enough that without the proper skills and tools it can get swallowed in the combined tolerances.

What tools and procedures have proven most repeatable for measuring seating depth on record rounds?

Thanks
CW

 

[LVLAaron]

These guys aren't shooting Berger's.

I'd be willing to bet the same applies to any bullet maker.

 

[Alex Wheeler]

You measure shoulder bump and oal on every record round if your getting serious. I actually like to mis match my seater stem datum and my comparator datum. That way if I measure it being off you can catch an odd bullet. Seating force can effect the oal length too. Anything that is off goes into the sighter pile. But with the custom bullets your measuring little to any differences.

 

[Alex Wheeler]

.001” is small, small enough that without the proper skills and tools it can get swallowed in the combined tolerances.

What tools and procedures have proven most repeatable for measuring seating depth on record rounds?

Thanks
CW

Clay, Im sure theres plenty of ways to do it. If you can measure a round 10 times and you get the same number then dont let anyone tell you you cant measure that good. Calipers can be very good. Not tenths good, but certainly better than a thou. I have some tapered comparators from Sinclair that are good but need to stay clean. That taper is sensitive and will pick up bullet material. When they start getting fussy I clean them with a copper solvent. I made some that are just a hole a few thou under bullet diameter with the edge just broken, the contact point is small and touches in the same place as the lands. I do like those a little better. Buy good calipers too.

 

[jackieschmidt]

From what I gather, the vast majority of shooters are using semi custom bullets.

I make my own bullets, and I can not picture any automated process that offers the level of precision obtained by an skilled bullet maker pulling the handle on every core seat and point up on each bullet. Not to mention the dedication to precision in getting everything set correctly to where all of the effort pays off with each bullet being an exact copy as the one before.

 

[PracticalTactical]

What I'm seeing when I look at the group is not that 0.001" is a critical tolerance we need to hold, but that 0.001" past the max of +0.008" is significantly detrimental.

Everything up to +0.008" looks pretty good.

I suspect that at +.009 enough force is imparted on the bullet to re-seat the bullet in the chamber. Or at the very least cock the projectile on an angular relation to the bore.

I do not see that we should all go freaky and obsess about holding 0.001" total variance. But if you did, it certainly wont hurt you.

It's a small sample of shots, so it's hard to draw definitive conclusions, except to stay short of +0.009" at least until there is more throat erosion.

 

[geo.ulrich]

You measure shoulder bump and oal on every record round if your getting serious. I actually like to mis match my seater stem datum and my comparator datum. That way if I measure it being off you can catch an odd bullet. Seating force can effect the oal length too. Anything that is off goes into the sighter pile. But with the custom bullets your measuring little to any differences.

Damn Alex how many sighters do you shoot....

 

[6BRA]

I'd be willing to bet the same applies to any bullet maker.

get some custom bullets...Berger's are not much if any better than Sierra or Hornady. Truth..

 

[6BRA]

Damn Alex how many sighters do you shoot....

when you take a reloading process from 3 steps to 20 steps...I would bet he doesnt have 10 percent in that pile. 5 out of 50...

 

[LVLAaron]

get some custom bullets...Berger's are not much if any better than Sierra or Hornady. Truth..

I have some. I didn't share the data because I don't want to break the forum.

 

[Straightshooter1]

That point at which the bullet is jammed is just a reference point.

My starting reference point is when the bullet is touching rather than jammed.

Do you think the throat will only erode if you are jammed?

Obviously not.

Unless you have a combo and jump that is extremely consistent grouping over a wide seating depth, the erosion will eventually require you to seat farther out. It is just a reference point.

Yes, I've found in my own experience that erosion will eventually require some adjustment to the seating depth to maintain the accuracy. But that seating depth adjustments I've had to make had nothing to do with distance to the lands. The initial measurement to the lands is indeed a reference point . . . to start from.

 

[6BRA]

depending on the bullet the distance between touch and jam could be .100 or more.

 

[Alex Wheeler]

Damn Alex how many sighters do you shoot....

None anymore, I sold my rifle
But I only needed to make 20 good rounds to shoot LG for a weekend so its not bad. Normally I wouldnt get that picky even but that rifle has a zero in it so its worth it.

 

[Alex Wheeler]

The context here is 1k BR so no one needs to do anything. But even in the big stuff I play with the seating window is about the same. If I move the bullet .002 either way on my 300s or 338s you see it open up a good amount on a 1k target. At least with a vld or hybrid type bullet.

 

[Orr89rocz]

I assume that change at 100 yards would be hard to notice? Whats the closest distance you would expect to see noticeable changes from something like this? 300? 500? 700? I also assume it wasn’t conditions varying to cause the group change

 

[geo.ulrich]

it can even be noticed at 100

 

[jackieschmidt]

it can even be noticed at 100

^^^^^^^
This is another thing that makes the Short Range game different from 600/1000+ yard shooting.

 

[Clancy]

get some custom bullets...Berger's are not much if any better than Sierra or Hornady. Truth..

Oh come on now, I’ve seen some sierras that were pretty salty and might on a real good day hand with Bergers, but Hornady? Really?

Many a good target has been shot with 105/108 Bergers in BR.

I have several brands of custom bullets and of course they’re better, but the gap between custom and Berger is much narrower than that between Berger and hornady, in my opinion.

In all fairness, those A Tips aren’t too shabby if you just love spending money.