Measuring to the lands

[Mikecr]

I use the tools linked above:
-R-P Tool
-Sinclair 'Nut'
-BGC
-Wilson micrometer top seating dies

I don't average anything. Every round I load is verified well under 1thou off of logged CBTO.
Where I'm using custom BR bullets, I just set the dial, seat, verify, repeat for the next round.
Where I'm using factory bullets, I short seat 1thou, measure, adjust the die mic, turn 180deg, reseat, verify correct. When this is taking a lot of effort, I break out the BGC, match up enough bullets, and then my seating goes like custom bullets.

In my experience best seating window is well under 10thou in width. So if centered, I have +/- 5thou. Never in my life have I seated so bad as to miss this.

 

[bob4]

I use the tools linked above:
-R-P Tool
-Sinclair 'Nut'
-BGC
-Wilson micrometer top seating dies

I don't average anything. Every round I load is verified well under 1thou off of logged CBTO.
Where I'm using custom BR bullets, I just set the dial, seat, verify, repeat for the next round.
Where I'm using factory bullets, I short seat 1thou, measure, adjust the die mic, turn 180deg, reseat, verify correct. When this is taking a lot of effort, I break out the BGC, match up enough bullets, and then my seating goes like custom bullets.

In my experience best seating window is well under 10thou in width. So if centered, I have +/- 5thou. Never in my life have I seated so bad as to miss this.

Nice explanation Mike. Although I'm simply hunting, why would't I want to make the best ammo I could. BGC may be in my near future.

Yes, you are good.

Most people that say they seat their bullets .005 off the lands (for example), are only taking an educated guess like yourself. Usually by averaging 5-10 sample measurements.

If you're a couple thousandths off on your measurements, it's not a huge deal. Your accuracy window for bullet seating depths are .030-.040 wide.

If you haven't read it yet, read this: http://www.longrangehunting.com/foru...r-rifle-40204/
(It doesn't matter if you are not shooting Berger bullets, it still applies).

Just remember what your end goal is. Is it to know your true COAL down to the .001 of an inch? I would assume not. Your goal is mostly likely the same as mine, to reload more accurate ammo for a specific rifle.

Take a look at that link I posted. It's probably one of the best stickies on this entire forum. Hope this helps.

Thanks ,this was sort of the answer I was looking for.

And I have a good starting point. I also did 130. off but that's on another page and was nothing to look at. .090 wins for a start.

 

[Bart B]

bob4, from a ballistic statistical point of view, I think those three groups are equal in size. A three-shot group's size tell the shooter that 19 out of 20 of them will be anywhere from about 40% as big to about 245% larger. If the first 3-shot group is 1 inch extreme spread and you shoot 19 more of them, they'll typically range from about .4" to almost 2.5"

Take your favorite .22 rimfire to the range with 60 rounds ammo then shoot twenty 3-shot groups. See if each one's within 10% of the same size. If you shoot all 20 groups on top of a backer target, you'll have a 60-shot composite showing the real accuracy you can count on virtually all the time shooting that rifle with the ammo selected. It'll be bigger than the largest 3-shot group.

My basic rule for accuracy testing is, if several groups with the same shot count have more than a 10% spread in size, none of them represent the accuracy I can count on at least 90% of the time. The biggest one is close, though. Which is why I shoot at least 20 shots per test group. 30 is better. I want to know where all my fired shots will land relative to the aiming point; not just 5% of them which a 3-shot group shows.

 

[engineer40]

Which is why I shoot at least 20 shots per test group. 30 is better.

Hey Bart, I understand what you're saying in your last couple of posts (statistically)...

But I don't really understand what you're saying?

When testing different powder weights, bullet seating depths, different powders and bullets; it's not feasible if you are shooting 20-30 shots per test group. Please enlighten us. Thanks!

 

[engineer40]

I use the tools linked above:
-R-P Tool
-Sinclair 'Nut'
-BGC
-Wilson micrometer top seating dies

I don't average anything. Every round I load is verified well under 1thou off of logged CBTO.
Where I'm using custom BR bullets, I just set the dial, seat, verify, repeat for the next round.
Where I'm using factory bullets, I short seat 1thou, measure, adjust the die mic, turn 180deg, reseat, verify correct. When this is taking a lot of effort, I break out the BGC, match up enough bullets, and then my seating goes like custom bullets.

In my experience best seating window is well under 10thou in width. So if centered, I have +/- 5thou. Never in my life have I seated so bad as to miss this.

Mikecr, I have read many of your posts over the last year or so on this forum and I am often humbled at your level of attention to detail. (Please take that as a compliment.)

When using high quality bullets my reloaded ammunition is almost always within .001 inch of the seating depth that I intentionally set my dies to.

I still stand by my original comment that MOST people do not know their true COAL/CBTO of their chamber down to the .001 of an inch (with the bullet they have choose). And many of us can still tune our ammo to shoot sub .25 of an inch at 100 yards.

That's what I was trying to get across to the original poster as to not complicate things anymore for him.

 

[Mikecr]

I'm not trying to complicate things for our OP.
What's great about doing things right, is that they're usually easier.
The tough part is gaining understanding to do things right.

I don't have to average a bunch of hokey readings, and I **** sure don't have to average 20-30 shots per change. With a cleaning rod method I can find touching lands COAL & CBTO in about 10min. One measure, and it's right every time. But it doesn't matter what my land relationship(xOTL) is.
What matters is producing tested best seating depth(CBTO), with every round.
This is not complicated. It's simple.

We could skip straight to Berger's seating testing to find best coarse CBTO. Can do this during fireforming of new brass. After powder testing(at best coarse CBTO), we can tweak seating just to shape grouping. Done. Log it. Now make every round match this -for the life of that barrel.

 

[Bart B]

Bob4, if you're handholding your rifle against your shoulder as it rests on something atop a bench, I think the real accuracy of it with that ammo is much better than your groups show. Us humans tend to degrade a rifle and ammo's accuracy quite a bit. We don't hold the rifle exactly the same like a machine rest does. Nor as repeatable as one fired in free recoil. It's my experience observing people shooting their stuff from the traditional (not benchrest match free recoil type) position holding on to it shoot much smaller test groups slung up in prone such as what's now used in F-class matches. Same with my own tests.

Anyone believing one few-shot group represents what the size of several with that load will be should review the following results from the 2015 NBRSA Nationals:

2015 NBRSA Nationals Complete Results

Check out any given competitors smallest and largest groups fired for aggregate scores; specifically the match winners. Note how much bigger the largest one is compared to the smallest one. No competitor's groups in any aggregate match (average size of all groups fired) are within 10% of the same size. And sometimes, the smallest group fired is not part of any winning aggregate. There's a spread of two times to several times larger from the smallest group shot to the largest. Rarely is the first group shot the smallest of all of them.

If anyone can shoot their stuff in groups of any size that all have no more than a 10% spread across them, I applaud them. I've yet to see any proof of that.

Regarding bullet jump distance to the rifling. I've measured throat advancement across several .308 Win and 30-.338 Win Mag barrels and one .264 Win Mag barrel over their accurate life. "Life" is when average accuracy test fired group sizes get about 50% bigger than when the barrels were new. That's Sierra Bullets' standard for their test barrels used to measure their stuff's accuracy to meet their specs. Here's the average numbers for throat advancement in my barrels:

Seventeen or so .308's: .001" advancement for every 40 shots. Total after about 3000 rounds, .075". MIL SPEC throat erosion gauges in the barrels used in Garands went in about 1/3rd inch further at that round count than when new. They're tapered at .010" diameter per inch of length of the gauging head. Gauges went in about 1/10th inch further in for every 1000 rounds fired.

Four 30-.338's: .001" advancement for every 15 shots. Total after about 1300 rounds, .085".

One .264: .001" advancement for every 7 shots. Total after about 640 rounds, .095".

.

 

[woods]

Begin with a soild method for COAL(to a bullet tip); WOODS describes the R-P tool here, which is the cleaning rod method:
Reloader's Nest Forum - OAL
This give you cartridge base to a bullet tip.

Couple of pics had gone away since 2009, fixed it

 

[Bart B]

Hey Bart,

When testing different powder weights, bullet seating depths, different powders and bullets; it's not feasible if you are shooting 20-30 shots per test group. Please enlighten us. Thanks!

It is if you shoot a lot of ammo.

Consider this 270-shot test group of the 1965 lot of Lake City M118 7.62 National Match ammo at 600 yards:

Inside circle's 6 inches, outside is 12. Mean radius is 1.9 inch, Extreme spread is about 10 inches.

That group is a composite of 18 fifteen-shot, or 27 ten-shot groups, or 54 five-shot groups or 90 three-shot groups; if you choose to look at it other ways. Which series of 3, 5, 10 or 15 shots fired in sequence for a group is the smallest" Which is the largest? One thing's for sure; all the few-shot group centers are not at the same place relative to the point of aim which is at the middle of the rings.

I have no problem testing 20 or 30 shots of a load for its accuracy I can count on.

That aside, I've never worked up any load for a new barrel except for a .264 Win. Mag. Just used with the match winners and record setters use and got the same accuracy testing they do; sometimes better. Never considered the smallest group fired of any I've fired with less than 15 shots in it.

Here's two 15-shot groups with two different loads, each shot from each fired alternately. I think it shows what a 30-shot group with each is reasonably capable of. The last one of each load had 28 or 29 shots fired before it was. 10-ring's ten inches. 190's (black dots) shot with once fired cases with turned necks full length sized, 200's (red dots) shot with unprepped new cases. Each load's group is under 5 inches.

 

[bob4]

Bob4, if you're handholding your rifle against your shoulder as it rests on something atop a bench, I wouldn't put my shoulder to such abuse with as much as I have loaded for the 300wm.
.

I do use a lead sled but you're right, the human factor is always there. Then toss in a bit of buck fever and the shot groups average goes ballistic. I feel I am at the point when I know if I've pulled a shot. And it happeneds from time to time. Put all this together are reasons I look to make the best ammo I can. Good thread lots of helpful info.