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Whats .001 of seating depth worth?

To add to this conversation, in regard to seating and the resolution we want out of a given ladder its about 60%-40% split meaning when you find your seating zone regardless of how lazy or freaky the platform is it will hold a +- of .001 total before migrating again 60% of the time with out a "true" .001 next to it. then 40% of the time at best you will have a .001 next to it that will plant in same quadrant with same size and general shape. Often I find i will have what I call a .001 on grouping sound .001 off grouping with kicked shots then back on .001 grouping sound again. i can shoot either side as a solid but if I shoot between them it will spit shots every time. over the course of a given season when we get platformed tuned and r_-verfy each match it will graph the same even if seating tune shifts slightly forward or back as season go's long the center will not perform either side as a solid will. as other have said just depends on what you need out of a given situation but in regard to long range BR every little detail can't hurt you but this one is a biggy LOL

Shawn Williams
 
Alex Wheeler said:
I like to post targets that are very good examples. And this one is a great example of seating depth at 1k at Deep Creek that Tom Mousel shot tuning before the match. We know +6 shoots and +4 blows up, have not seen +5 yet. Most likely the window is +6-+8 which is very normal for a Vapor Trail in this reamer. Just a good example of why keeping seating depth consistent is so important. View attachment 1353604
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alex, I,m alway a little more satisfied when I have a .001 either way side by side before migration proceeds. This tunes gave Tom some excellent targets through some very unfavorable conditions this weekend.

Shawn Williams
 
Alex Wheeler said:
You measure every case and if they are not, they get used for sighters, so yes the shoulder bumps are held to better than we can measure for record rounds.
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What tool do you measure headspace with? I have a Redding instant indicator. Tried it but had drifting of .003".
 
PracticalTactical said:
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.
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That question is one that every precision reloader needs to reckon for themselves: should I do (this extra measure of precision or preparation) because it’s actually affecting my groups, or because it *might* and I choose to control it just to be sure?

I do agree that this discussion could be about finding the middle of the seating depth window, or as Erik Cortina described very well, to stay at the long end of the window so that you don’t fall out of it due to throat erosion at an unfortunate time.

In any case it is a nice reinforcement to measure every round of a critical batch and sort/cull the high and low for sighters - because it takes little effort and it can matter.
 
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dgeesaman said:
That question is one that every precision reloader needs to reckon for themselves: should I do (this extra measure of precision or preparation) because it’s actually affecting my groups, or because it *might* and I choose to control it just to be sure?

I do agree that this discussion could be about finding the middle of the seating depth window, or as Erik Cortina described very well, to stay at the long end of the window so that you don’t fall out of it due to throat erosion at an unfortunate time.

In any case it is a nice reinforcement to measure every round of a critical batch and sort/cull the high and low for sighters - because it takes little effort and it can matter.
Click to expand...

In my own testing I found there was a predictable correlation between velocity spreads and accuracy as it relates to jump.

I found that more jump translated to poor accuracy and wide velocity spreads.

As it moved closer to the lands, there was a clear accuracy improvement as well as a reduced muzzle velocity spread.

There was also a point where everything started going the other way and accuracy started to suffer as velocity spread's opened up again.

Having said that, things got bad a whole lot faster from too long than they did from too short.

FWIW... In brief terms... I have pondered this with others around the F Class circuit and the camp fire theory is that pressure bleeds around the bullet if there is too much jump, but that is relative to the free bore length and diametrical clearance. Guys that tend to get away with significant jump are assumed to have a tight diameter free bore which cuts down on that blow by pressure loss.
 
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Toms said:
What tool do you measure headspace with? I have a Redding instant indicator. Tried it but had drifting of .003".
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you mean your brass is drifting on shoulder bump? You arent liking what the instant indicator is showing? do you anneal every firing? Some brass has a mind of its own. Are they fully fireformed? Anneal and repeat if necessary. Let them sit in the die for 30 seconds, they will come around, and if they dont. Do like Alex have a mound of scrap brass. LOL
edit
IMO if you want the easiest most accurate headspace tool....you are using it. If your brass isnt listening. I would look at anneal times, cleans dies can take headspace down over .001 with lube accumulation. I wont settle on anything less than .001 variance across all rounds. Most are .0005. They are foulers or trash.
 
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Toms said:
What tool do you measure headspace with? I have a Redding instant indicator. Tried it but had drifting of .003".
Click to expand...
I use the sinclair comparators or ones made from the reamer and get good results both ways.
I guess I should ask what kind of variation you guys are seeing? Seating is not very hard to hold to a +/- .0005 tolerance, same goes with bump if you have a good setup. You dont end up with that many sighters. If your bumps vary, you may need a new die or press thats stiffer, also even lube is important. Setting up cam over with the redding shell holds helps out springy presses. If your seating depths vary much, and you have good bullets, look at your neck prep. My loading procedure is about as basic as I can make it. Take a case as fired, lube with my finger, size, wipe off lube, seat primer, brush inside of neck, dump powder, seat bullet. I dont clean anything or anneal. Obviously you trim and chamfer when needed. I would suspect most guys have a far more complicated process, and I used to as well.
 
As an exercise , I measured each of these 100 sized cases for shoulder set back uniformity, 5 are out .001
Then I measured 1 case 11 times noting 2 times that my calipers displayed a difference.

Maybe my tools are not sensitive enough or I’m pretty close.
 

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I measure every case after sizing and keep them all within .0005 for both my 6 BRA and 300 SAUM IMP. The Prazipress is a big help there. Sometimes I need to size a case a second time to get it there.

I measure every bullet after seating and also keep them to within .0005" for my record rounds. I just started measuring the 6mm Roy's for OAL--like Roy told me to do. I will also begin experimenting with pointing and trimming.

With the Berger's I am currently shooting in my 300 SI, I am measuring and sorting them by BTO as well as base to seater stem. I will also start experimenting with pointing and trimming these.

I had a tuning disaster last Friday before the match. I had loaded two ladders for the 6 BRA and one for the 300 SI. I over adjusted my scope and put all my shots low off paper.

I wasn't terribly worried about the 300 SI. I did very well the last match and the 300s are forgiving. However, my 6 BRA LG has further to go. I managed to "borrow" some primers and loaded up a three group test: + .006, +.009, +.012. Like last match, +.006 shot well, but +.009 was out. +.012 started to come back. The +.006 was a 3" group--decent, but not yet where it should be on tuning day.

When @GlennK saw my target he asked why I didn't shoot .005, .006, .007. The answer was because in prep for this match I had failed to bug Glenn and @tom like I should have. You see not only are these guys two of the best, they expect you to bring your A game and expect to help you get it there.

Those are the two I bug the most about tuning. I also bug @Alex Wheeler about chambering barrels and @Northridge about match procedures. While either of those guys could help me with tuning, I gotta spread the peskiness around....... BTW, Alex's tip allowed me to finally cut a 5R chamber with nice straight rifling ends (vs U shaped).

But I digress. The key to consistently shooting small groups Deep Creek is testing very small changes, like .001" seating depth increments. To see those small changes everything else has to be up to speed--loading, tracking, and wind analysis.

So for tuning on Friday before the Aug Match, my 6 BRA ladder will be +.005, +.006, +.007, +.008. Maybe I should add +.004 as well--I'll definitely ask Glenn. I'll also have some vials ready to test .1 grain either side of my 30.9 charge.

For the 300 SI, I'll test what I meant to test last Friday: 61.6, 61.8, 62.0, 62.2. The 200 grain Berger Hybrids are very happy at +.021. I know .2 grains seems awfully small in a 60 grain charge--kinda like a .1 grain change for a 30 grain charge; but we do see these changes on target. And I know there is a 3 in my 300 SI HG--after all, I did that last year with a cobbled together 300 WSM using inferior brass but tuning it in .2 grain increments.

Also, I need to give just a little more 30 cal competition to my buddy @Throwin Lead.......
 
Alex Wheeler said:
I use the sinclair comparators or ones made from the reamer and get good results both ways.
I guess I should ask what kind of variation you guys are seeing? Seating is not very hard to hold to a +/- .0005 tolerance, same goes with bump if you have a good setup. You dont end up with that many sighters. If your bumps vary, you may need a new die or press thats stiffer, also even lube is important. Setting up cam over with the redding shell holds helps out springy presses. If your seating depths vary much, and you have good bullets, look at your neck prep. My loading procedure is about as basic as I can make it. Take a case as fired, lube with my finger, size, wipe off lube, seat primer, brush inside of neck, dump powder, seat bullet. I dont clean anything or anneal. Obviously you trim and chamfer when needed. I would suspect most guys have a far more complicated process, and I used to as well.
Click to expand...
Thanks Alex. I have a comparator that works ok. My press is a Bonanza coaxel press with Harrell's die. Seating with either Redding micrometer seater die or Wilson hand die. I tested loads at 300 yds. Three rounds each in 6 br 29,29.1,29.2,29.3 gr Varget 107 Sierra seated .010 short of touching. Group for 12 rounds was 1.195" verticle, 1.525 horizontal. We shoot 600 yard br, using 300 yard rapid fire target, 31/4" X ring 71/4" 10 ring. Shot 100 with 9X last shoot. Just trying to do better. Thanks Tom.
 
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