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

[QuietTexan]

There are two separate and distinct seating depth tests, and Berger recommends BOTH of them depending on the ogive profile. Berger recommends two ladders for secant ogives, on for bench and one for the field (where filling up an action with powder could be hazardous):

Target:
1. .010 into (touching) the lands (jam) 6
2. .040 off the lands (jump)
3. .080 off the lands (jump)
4. .120 off the lands (jump)

Field:
1. .010 off the lands (jump)
2. .050 off the lands (jump)
3. .090 off the lands (jump)
4. .130 off the lands (jump)

For Hybrid or tangent ogives start at 0.015" off the lands, and back out in 0.005" intervals.

 

[KsKevin]

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.

Looked back at my records on the Berger (VLD - so secant ogives), my initial development was tested at: lands, -0.040", -0.080", -0.120" which were CBOT lengths of 2.790", 2.750", 2.710", 2.670". Wheeler measurement indicates my kiss CBOT is 2.653" so all seating depths I've tested none have truly been jumped vs wheeler CBOT.

 

[QuietTexan]

Ok, in that particular case you would need to re-shoot, but 0.137" is A LOT of jam, and makes me question your Wheeler method test. Anything over 0.100" into the lands and you would either see the bullet set back into the case, a bullet heavily engraved with rifling, or left behind stuck in the bore if you open on a chambered round. Did you happen to notice anything like having to cam the bolt down hard to get them to chamber? I'd mock up a dummy round at 2.790" and load it and unload it to see what it looks like.

 

[KsKevin]

Which one shot the best? Bracket that at +/-0.010", if all those shoot well you're in the right jump range, so move on to charge and let the results on target guide you more than measurements on paper.

Best groups were -0.080" / 2.710" CBOT (which is jammed +0.057" according to wheeler measurement to kiss lands). All left me wondering if I'm leaving anything on the table which is what started this whole mess/thread.

Also, starting development of a new load for Berger 180g VLD (never shot this bullet before) which is what started all this rethinking of where to start on seating depth (hard jam or light kiss)... didn't want to have to test 18 differing seating depths.

 

[QuietTexan]

Sorry, I changed that because I read your post wrong, I thought you said they were all jumping, but you were saying that they were all jammed.

For VLD bullets I do the Berger test, bracket the best at +/-0.010", and move on. So far those loads shoot better than I do. So call it 35 rounds for seating depth testing today. 5 rounds to ladder the powder up to the 93% range, 35 rounds seating depth testing, 20 round powder ladder, and normally I'm there.

 

[KsKevin]

Sorry, I changed that because I read your post wrong, I thought you said they were all jumping, but you were saying that they were all jammed.

10-4.... you got it. I just want to start at the right place and test accordingly. the starting spots are just so **** far apart it left me scratching my head.

 

[QuietTexan]

Unpopular opinion maybe, but I breeze past seating depth testing on some loads. If I have a mag length limitation or some other restriction to where length can't be just anything, I'll seat at the SAAMI length, do powder, and then monkey very slightly with seating depth, just a couple of 0.005" changes to see if I can tighten up the horizontal.

This is why defining your end goal is important. If you want to make the smallest holes in paper or ring steel at 2000 yards, the sacrifices of single feeding or not being able to reliably unload a round are probably worth it. If you need to carry a rifle three days in a blizzard and unload it every night, then functionality gets in the driver's seat and who cares if your horizontal is 2" wider than you could make it with a jammed bullet, the vitals on a whitetail are the size of a basketball. Better to have the gun go off than an action full of powder.

 

[KsKevin]

So just did Eric Cortina's approach. Neck sized a one-fired case, loaded the Berger 168g VLD to 2.910" CBTO, imperial waxed the bullet, chambered it and had to jam bolt closed, pulled it out and measured. CBTO after chambering = 2.793" (hard jam). This is +0.140" longer than the WHEELER light kiss CBTO distance. That is a massive delta in terms of where to start and back to the question I raised in my orig post as to whether these Berger VLDs are so slender ogive do they result in this much delta in seating depth from jam to light kiss.

Nosler ABs go from CBTO of 2.861" hard jam to Wheeler light kiss of 2.821" --> delta 0.040".

 

[Ckleeves]

Do you have a bore scope? It sounds like there might be some carbon buildup in the throat giving you some false readings which would explain why your measurements keep getting shorter with increased round count.

 

[KsKevin]

Unpopular opinion maybe, but I breeze past seating depth testing on some loads. If I have a mag length limitation or some other restriction to where length can't be just anything, I'll seat at the SAAMI length, do powder, and then monkey very slightly with seating depth, just a couple of 0.005" changes to see if I can tighten up the horizontal.

This is why defining your end goal is important. If you want to make the smallest holes in paper or ring steel at 2000 yards, the sacrifices of single feeding or not being able to reliably unload a round are probably worth it. If you need to carry a rifle three days in a blizzard and unload it every night, then functionality gets in the driver's seat and who cares if your horizontal is 2" wider than you could make it with a jammed bullet, the vitals on a whitetail are the size of a basketball. Better to have the gun go off than an action full of powder.`

No issues on this front. COAL with the longer hard jam was 3.490" and still has ~0.150" longer for magazine fit

 

[KsKevin]

Do you have a bore scope? It sounds like there might be some carbon buildup in the throat giving you some false readings which would explain why your measurements keep getting shorter with increased round count.

i've wondered about that but do not have a bore scope. hard jam takes me back to measurements nearly identical to where I started though.

Had about talked myself into redoing everything based on WHEELER method thinking i've never seated deep enough to find optimal but this thread has me thinking I should stick to where I've been as Eric Cortina's approach reaffirms all my previous measurements as a proper starting point.

 

[KsKevin]

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.

Cajun - thank you. I'm going to use this approach as it has restored my confidence in methods (and saved my sanity ).

 

[fightthenoise]

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

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precisionrifleblog.com

This is the best method I've found. Measuring the distance to lands just tells you where the lands are. You want to know where the danger zone is (hard jam into the lands). Back off 0.020 or whatever from that point and do your seating depth test in 3 - 5 thousandth intervals. You will find a node

This is my favorite video on it

 

[wnc-coyote]

So I will admit, I just had to look up the wheeler method. Holy crap thats a ridiculous amount of work to find a number that really means nothing toward the end result.