Here is my tip on how to find ideal seating depth.

[tonysnoo]

James, I think it's very enlightening and very thought provoking. thanks!

 

[6MMsteve]

it's funny that the moderate load shot 5 flat groups or water level groups or whatever yall cal them

 

[Jpresley]

Confused...are those actual groups or an example of what to look for? not trying to be a jerk, just clarifying as some are interpreting things differently. I thought we were looking a penciled dots. Testing this method at multiple charge weights is really something I need think about. Thank you.

 

[jamesdmock]

Confused...are those actual groups or an example of what to look for? not trying to be a jerk, just clarifying as some are interpreting things differently. I thought we were looking a penciled dots. Testing this method at multiple charge weights is really something I need think about. Thank you.

It is simply an illustration of what to look for, There are no actual holes in the target, but the dots represent what one should look for. I have used this method with real bullets making real holes and it works. Sorry if there was any misunderstanding about what was presented. The dots are much smaller than 6mm holes. Good shooting...James

 

[Tim Singleton]

As James has said this method is used by most short range BR shooters it can be applied to any discipline just keep going for more jump if you know that's where the bullet barrel combo normally shoots

Here is an actual target using this method

 

[ebb]

I really appreciate this kind of help and information, Thank you James!! I only wish there were an abbreviated version, That was 63 shots on the paper. On many guns that isn't all that much, but on one of my barrel burners it is a significant portion of the barrels life (7RUM not as much my 6.5-284). I hope you don't think I am being ungrateful cause I had no clue how to get setting depth other than shoot groups and look for groups to get better.

 

[Tim Singleton]

I can't think of any more valuable way to expend 63 rounds
You have hard evidence that gives confidence in your system
Just loading and shooting with no method doesn't yield a lot of value

 

[Mozella]

......... snip...........Sometimes I shorten the method by starting with bullets at .005 off jam because I have not had luck with bullets at jam. .......... snip.............James

I've been advised that trying to test bullets at .000"; i.e. just touching is fraught with inconsistency. Here's why. The difference between a .010" jump, a .009" jump, and a .011" jump is bound to be small.

However, if you plan to test a seating depth of .000", it is likely that one round will be at just touching, the next might be actually jammed a thou or two, and the following round might have a little bit of jump because it's just clear of the lands. These three conditions are bound to produce more inconsistencies. That's why when I test seating depths I always skip over .000". In other words, I'm pretty sure I can't reliably seat a batch of bullets to EXACTLY the same length.

 

[grovey]

Does a load lose it's tunability with seating depth changes if your making a huge jump just to get to the lands with a light bullet ? I'm basically at mag length just to keep enough bullet seated so the case holds it.

 

[TZaun]

I've been advised that trying to test bullets at .000"; i.e. just touching is fraught with inconsistency. Here's why. The difference between a .010" jump, a .009" jump, and a .011" jump is bound to be small.

However, if you plan to test a seating depth of .000", it is likely that one round will be at just touching, the next might be actually jammed a thou or two, and the following round might have a little bit of jump because it's just clear of the lands. These three conditions are bound to produce more inconsistencies. That's why when I test seating depths I always skip over .000". In other words, I'm pretty sure I can't reliably seat a batch of bullets to EXACTLY the same length.

I have always stayed away from .000" because I've read the same thing. I usually do a +5 and a -5. I was testing some 180 VLDs in my 7 RSAUM and both +5 and -5 looked good. I went back and loaded up +6, +3, 0, -3, & -6. When I shot those the 0 peppered all over and the other 4 groups held together with a slight edge to the jammed side of things. Using Alex's method for finding the lands is so precise that in the past, if I would've tried 0, I wouldn't have seen the inconsistencies I do now.

 

[tonysnoo]

As James has said this method is used by most short range BR shooters it can be applied to any discipline just keep going for more jump if you know that's where the bullet barrel combo normally shoots

Here is an actual target using this method

Ok, Tim, James,

Is there a clear winner on the actual? It doesnt look as pronounced as James drawn example.

 

['Freak]

Lookin' like -.008"

 

[bsekf]

I am always looking for a way to do it with less barrel wear, but....... I test at 200 yards and have never seen anything like that. While testing, my groups will show 1-2 inches of vertical as the powder charge goes up. So, using this method, I would have 1-2 inch groups as I went from light to med. to heavy charges. I still think you have to settle on a powder charge before you mess with OAL.

I am always surprised how groups move around as you change the "jump".

Bill

 

[Tim Singleton]

Ok, Tim, James,

Is there a clear winner on the actual? It doesnt look as pronounced as James drawn example.

that particular barrel and bullet combo didn't like the hot load at any depth tested
It just doesn't offer as wide a powder window as I would like
I choose .011 off jam

 

[tonysnoo]

that particular barrel and bullet combo didn't like the hot load at any depth tested
It just doesn't offer as wide a powder window as I would like
I choose .011 off jam

Looks reasonable. Do you then play on both sides of the one hole powder charge to see how wide the node was? Do you then again jump up and down a few thou to see if the jump node is forgiving too?

 

[Tim Singleton]

Looks reasonable. Do you then play on both sides of the one hole powder charge to see how wide the node was? Do you then again jump up and down a few thou to see if the jump node is forgiving too?

As long as it holds together I don't mess with it much.
That load did shoot good at 28.8 LT at the match I shot that particular barrel in

 

[jimmymac]

I've been advised that trying to test bullets at .000"; i.e. just touching is fraught with inconsistency. Here's why. The difference between a .010" jump, a .009" jump, and a .011" jump is bound to be small.

However, if you plan to test a seating depth of .000", it is likely that one round will be at just touching, the next might be actually jammed a thou or two, and the following round might have a little bit of jump because it's just clear of the lands. These three conditions are bound to produce more inconsistencies. That's why when I test seating depths I always skip over .000". In other words, I'm pretty sure I can't reliably seat a batch of bullets to EXACTLY the same length.

There is a distinct difference between jam length and touch length. In your example, you are using touch length as your .000" reference point and seating deeper into the case results in bullet jump.

In James example shown above, he is not starting off at touch length. He is starting at jam. His bullet at his given neck tension will go no further into the lands when he closes the bolt. This is his jam length or his .000" length if you prefer. He will not jump bullets until he starts seating deeper than his touch length, which might be .005", .010", .015", .020", etc away from jam.

I'll use my gun for an example:

In my PPC using 68 grain Bergers and .003 neck tension the distance between jam and touch is a full .024". If I stay within that .024" window, I will never jump a bullet into the rifling because I'm in contact with the lands for that entire distance. The only way I can jump a bullet is if I seat .025" or deeper than my jam length.

For testing I did a graph similar to James and Tim. I started off at jam and seated progressively deeper until I got to .016" off of jam. It was pretty easy to see where things were falling apart as I got farther away, so there was no need for me to seat any deeper than that. I ended up at .010 because that's what the test told me. I never jumped a bullet, but that is pretty common in SR benchrest. I have no idea how other disciplines do it.

 

[tonysnoo]

This is all really cool info. I suspect that touch vs jam vs ??? would only concern those trying to duplicate someone else's work. What ever reference I use would need to be consistent through my seating test... same as which set of calipers I use, as one set of my cheapies doesn't match the other set exactly.

thanks guys for all your sharing... again proves this site is the place to be.

 

[Mulligan]

To find the ideal seating depth for a given powder and bullet a person needs to first find the jam for that bullet. Also, one needs to load at three different powder charges for each of the following seating depths. These should be a mild charge, a moderate one, and a hot load. These three loads are tested at different seating depths...starting at jam and then moving away from jam in .005 inch increments. (see picture below).

When one finds a 3-shot group that is in the same relative position with each powder charge (like those at .015 off), that is a great seating depth. After using this to find the best depth, one can tweak his best load by trying within the .005 inch window or within the .5 grain powder charge. Good shooting....James Mock
View attachment 1019593

This is good stuff James, thanks for sharing.
CW

 

[rockable]

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