Help!! Berger seating depth, distance to lands??

[KsKevin]

Guys, my distance to lands is driving me nuts. I'm an engineer so the details and precision are something I can't let go off and I'm off deep into the rabbit hole. Would appreciate some perspective.

Have a GAP 280AI and had been measuring distance to lands every couple hundred rounds or so. The distance was decreasing with increasing round count (impossible). My measurement approach was a very loosely seated bullet in the same once-fired case (in my chamber), cycle the bolt closed, measure CBTO (hornady comparator guage/calipers), repeat several times to ensure consistency, log the info. The decreasing distance and some significant variation really had me questioning everything. Thus, I switched to the Wheeler method of measuring and this has led to at least very consistent results on 'kissing' the lands BUT.... this distance to kissing the lands is significantly shorter than what I was getting with the loose bullet seating/cycle bolt method especially on Berger VLD bullets. Here's the comparison data

Round Ct	Berger 168g VLD	Nosler 160g AB	Hornady 162g Amax	Comments
45	2.790"	2.861"		Loosely seated bullet, measure CBTO
111	2.800"	2.869"	2.805"	"
311	2.790		2.778	"
400		2.869"	2.774"	"
550	2.653	2.821	2.697	WHEELER Method
DELTA Wheeler vs Previous	-0.137"	-0.048"	-0.077"

Note the change in CBTO for each bullet to just 'kiss' the lands via WHEELER method vs previous results is significantly shorter.

So Here is my dilemma....
Up until now (prior to WHEELER measurements) I've been thinking i've testing various 'jump' distances during load development by seating the bullet deeper at increments of 'at the lands', -0.040", -0.070", -0.110" but in reality according to CBTO via WHEELER method I was actually, in the case of the Berger bullet, starting off jammed as much as +0.137" and never even seated the bullet deep enough to ever test any jump (what I thought was -0.110" / 2.680" was really still jammed +0.027" according to WHEELER measurements).

Notice with the Nosler 160g AB the difference in CBTO for WHEELER method vs base method was much less of a delta. Given this, I'm wondering when measuring CBTO via chambering a loose fitting bullet if the much more slender nose of the Bergers and Hornady AMAX results in more easily jamming the bullet very deep without even realizing it and in much higher measurement error/variation. Just seems crazy I was really jamming the bullet this much via previous method. Seems WHEELER method is a more precise/true measurement of just 'kissing' the lands.

Therefore, I think I need to re-test seating depth for all my loads using the WHEELER method as my chamber leade distance for each bullet and then test deeper seating depths vs that as my reference point. Does this sound right? Other Thoughts?

Appreciate any enlightenment you have to offer.... #frustrated

Kevin

 

[L.Sherm]

Use the Wheeler method and trust those.
In my opinion the loose bullet method can pull the bullet out of the case when you jam the bullet into the lands and then pull it out.

 

[cajun]

Use this method. Find hard jam then back off from there. I understand how engineers think. I have worked with them for 35 years. Your overthinking this. Fyi there is increasing evidence that seating out from the lands a good bit more forgiving. What you need is a reference point to work from. Let the rifle tell you what it likes. If your .020 off or .060 off it doesnt matter. What matters is the results on target.

Bullet Jump Research: Executive Summary & Load Development Tips

This is the last post in a series of articles focused on bullet jump research that has been conduct...

precisionrifleblog.com

 

[wnc-coyote]

Duplicate

 

[wnc-coyote]

Is the rifle shooting good? If so who cares what the numbe is. I used to be just like this until I realized this is not a 1:1 thing were dealing with. Most of the time just because your lands may move doesn't always mean the bullet needs to follow. I have a 243 that's land measurement has changed almost .03 since load development and still shoot bug holes with the same ammo. If I had tried to follow the lands in this barrel I would have pulled it long ago thinking it was burnt out. Watch Eric Cortinas video on chasing the lands. He explains what I am doing. I had a Smith teach me this years ago.

Cajun beat me to the video link. This has worked for me for many rifles.

 

[jraulsten]

No matter how careful you may think you are measuring with a Hornady comparator you are almost always jamming the bullet. Wheeler is by far more accurate.

 

[QuietTexan]

When you say re-test, do you mean re-measure? Or actually change your load. I'm about the fifth person to say this, but if the load shoots well you do not need to re-test everything. You can remeasure everything to describe the ogive-to-lands measurement more accurately and precisely, but a better measurement does not a better load make. I wouldn't change my CBTO seating depth on a load that shoots just because I was changing how I measure the rifle.

I'm also of the school of thought to jam a bullet into the lands hard to measure. All this mess about kissing and light pressure misses the point that when you pull the trigger the bullet is rather violently jammed into the bore, so what matters is where the real point of resistance is. Stick the SOB in there hard. Call it +0.020" jammed if that makes you feel better, but to people who say "you don't know exactly where you are" I say I know exactly where I am: at the end where you can't load any longer. Everything else is back from there, it only moves one direction away. To me, that is 0.000 right there, and I get measurements that are repeatable and consistent down to the thousandths that way.

 

[SO I HUNT]

Tagging in

 

[jraulsten]

It doesn't matter if your initial measurement is right on or off as long as you stick with that measurement throughout the loading process.

 

[KsKevin]

When you say re-test, do you mean re-measure? Or actually change your load. I'm about the fifth person to say this, but if the load shoots well you do not need to re-test everything. You can remeasure everything to describe the ogive-to-lands measurement more accurately and precisely, but a better measurement does not a better load make. I wouldn't change my CBTO seating depth on a load that shoots just because I was changing how I measure the rifle.

I meant do I need to re-test / re-develop the load. My rationale is that with all the previous seating depths I was doing, all of them were jammed to some degree based on the Wheeler method for distance to kissing lands so i've never tested seating depths that were deep enough that were true jump vs the kiss depth. Thinking I need to take these same powder charge weights and see if going deeper on seating depths with some "true" jump leads to even further tightening of the groups.

 

[QuietTexan]

How did you find the load in the first place? You specifically mentioned VLDs which Berger specs to move back in 0.040" increments. Nothing but your first load would have been jammed. Bracket the second interval at +/-0.010" and 0.020" and you'll have a stack of five depths in 0.010" increments around an unjammed load.

For the A-Max and Nosler BTs tangent ogive test of starting 0.015" off the lands and backing out in 0.005" intervals, you would get unjammed in the first 4-5 intervals. Add a couple on the back end and keep backing out to see if they do any better, but you don't need to reset where the 0.000" point was, use the CBTO setting to back them out.

 

[L.Sherm]

I can assure you you use light neck tension jam them into the lands and open the bolt on a loaded round you'll have a chamber full of powder ask me how I know.

 

[KsKevin]

****, now you guys have me thinking I need to go the other way.... Scrap this lightly seating, just kissing, etc methods and do the hard jam, measure and start backing off from there. For those of you who do it this way, how are you doing your seating depth increments to find your seating depth node and what is the deepest you've ever had to go off this hard jam CBTO reference point. My concern, once I did the measurements via WHEELER method, is this new CBTO distance was so much shorter than all my previous seating depth testing never pushed the bullet deep enough to see any jump vs this 'kiss' distance and thus left me wondering if I'm missing out in finding a more accurate depth that is much deeper than I ever tested.

 

[L.Sherm]

I start at .010 off and go deeper .010 at a time, fine tune .005 at a time