Optimal means to measure chamber .... bullet seating depth

[mikecr]

Mike -- It doesn't matter at ALL which datum if the number you have is repeatable. You just take the number you have and find out where the best accuracy is relative to that number. For example if I have a number of 2.255 for repeatable "Hornady tool touch" and I find, by testing, that my best accuracy is at 2.2560 or five thousandths beyond that point -- that's all I need to know, because I can load my ammo to that length and confirm it with the calipers and comparator. You are discovering the ideal seating depth experimentally with your live ammo. You only need the Hornady reference to have a repeatable starting point. Your testing will reveal the most accurate overall length with your working brass.

This is what I said at post #20, in far fewer words.

But as to determining touching relationship, just because people want to I guess, the cleaning rod method is superior to Hornady's.
It removes both the case(shoulder to ogive), and pressure induced variances.
It takes a more direct route to CBTO at touching, and there is no averaging for 'repeatable' as I read about folks doing. It's one measure, done. Very quick & easy.

 

[Webster]

Mike -- It doesn't matter at ALL which datum if the number you have is repeatable. You just take the number you have and find out where the best accuracy is relative to that number. For example if I have a number of 2.255 for repeatable "Hornady tool touch" and I find, by testing, that my best accuracy is at 2.2560 or five thousandths beyond that point -- that's all I need to know, because I can load my ammo to that length and confirm it with the calipers and comparator. You are discovering the ideal seating depth experimentally with your live ammo. You only need the Hornady reference to have a repeatable starting point. Your testing will reveal the most accurate overall length with your working brass.

Can anyone comment on if it's more difficult to determine touch after erosion has worn down the leading edge of the land? Based on bore scope I am getting 0.008" erosion in the land per 1000 rounds. It's a varmint rifle. I am not going to measure or adjust COAL as long as it shoots small groups. If the groups get bigger our I get flyers I will just try 5 & 10 thou longer and see if it helps. Maybe measure COAL touch or a new barrel.
Scanning Electron Microscope images of a 6MM Rem bore with about 6-7 thou rounds. Very little rifling for at least 6". At neck, 1" in, 2" in. For comparison top photo a cross-section of a stub cut from the end of a new barrel.

I find it easier to get repeatable results with the Hornady/Stony point tool and the Wheeler method on a fired barrel, compared to a brand new one. The new barrels may have some burrs in the lands from chambering, and make it harder to get a good reading.

I use the Hornady and Wheeler methods and they will be the same within a couple thousands, but you have to let the target tell you the correct seating depth.

Measuring COAL is not precise. Measure the Cartridge Base to Ogive Length (CBOL) with the Hornady length gauge and seat you bullets according to your target results.

For oddball calibers, or to insure you have the case properly seated with the Hornady measuring tool, get a 5/16 X 36 tap and a letter L drill, and thread one of your fired cases.

https://www.amazon.com/dp/B0195UFBUY/?tag=accuratescom-20

Deleted my original reply due to getting pix in the way I wanted.

guys,
I have been reloading for a while now... but can never seem to get a reliable fix in the exact measurement of my bullet length to the lands ... so that I can optimize my bullet seating depth.

I've tried loose set bullets (dummy rounds) and then chambering the bullet then measuring OAL .... and more appropriately measuring the length to ogive ....... and doing this repeatedly ... but don't feel I get the right precision I need or the repeatability I want.

I have not bought a commercial measurement device.... but seems like that is my next go.


Any suggestions?

Deleted original reply due to photo problems.

General info: Shows why it may be difficult to determine touch after a good number of rounds down the barrel. No definite land or edge to catch the ogive. This was a 6MM Rem with 6-7 thou rounds down a SS Douglas barrel. Severe erosion. Scanning Electron Microscope images on a cross-sectioned barrel.



100X 25X 250X 250X

 

[mikecr]

Well, if you need to be into the lands(ITL) to reach your tune, then that's what you'll have to manage.

If developed tune is off the lands(OTL), then you will not likely have to chase erosion to keep your tune.
After all, why would it? Chasing lands would be increasing relative case capacity, lowering load density, changing neck tension, and how would all that get your original tune back?

 

[Webster]

Well, if you need to be into the lands(ITL) to reach your tune, then that's what you'll have to manage.

If developed tune is off the lands(OTL), then you will not likely have to chase erosion to keep your tune.
After all, why would it? You would be increasing relative case capacity, lowering load density, changing neck tension, and how would all that get your original tune back?

Don't really know but the time pressure curve would be altered if there is less resistance to the bullet entering the bore. Shooting is the only way to know. Of course if your shooting comp and the barrel had a thou shots you would trash can it.

 

[mharpster]

I know this is an old thread, but I am making a tool that addresses the many problems with the other methods/tools discussed in this thread. The tool is called the LTL Gauge. Please see the ad currently running on the Accurate Shooter website or visit www.deadcentersports.com for more details. Feel free to post any questions you have here and I will be happy to answer them. Thanks for looking!

Mike Harpster

 

[BoydAllen]

I don't like using a random fit all tool .its too easy to make your own custom tool . Larry

Larry,
I have heard this "The case needs to fit the chamber." repeated over and over. You don't. Measure a tight case head to shoulder and write that down. Next measure your generic case, the threaded one that Hornady sells, and subtract that number from the first one. At the answer to all of your measurements that are taken with the generic case. That is all that there is too it. The nice part of it is that you only need one tight case for each barrel to do a one time measurement. As long as you save the difference in your notes, you are good to go.

 

[fguffey]

Feel free to post any questions you have here and I will be happy to answer them. Thanks for looking!

Thanks for the invitation, before gizmos and all of the Hornady/Sinclair tools I made transfers, I used the transfers to transfer the dimensions of the chamber to the seating die. Once I installed the transfer in the seating die I adjusted the seating die to the transfer; once adjusted I had 'ZERO off the lands'.

It is not a matter of focus on detail but I am the fan of 'all the bullet hold I can get', it means nothing to anyone but it keeps me from starting over everyday. Other reloaders are infatuated with neck tension with no way to measure it.

F. Guffey

 

[Comrade Terry]

 

[DL1979]

I believe the best method to find TOUCHING land relationship is the old cleaning rod method. This from the muzzle, provides distance from bolt face to a bullet tip, while that bullet is lightly held against lands.
One version described at 6.5Grendel forum: http://www.65grendel.com/forum/showthread.php?7743-Determining-Maximum-Overall-Cartridge-Length
View attachment 1021522
In no way will knowing touching COAL, or any other land relationship help you in optimizing seating depth. This, because optimum seating depth is not a land relationship, but a tested best CBTO.

Really lol so how do you know...look it up on the internet from someone else’s rifle?
the reason for knowing the seating depth by finding the relationship to the lands IS FOR repeatability and CONSISTENCY.
Wild Guess could work too lol

 

[mikecr]

the reason for knowing the seating depth by finding the relationship to the lands IS FOR repeatability and CONSISTENCY.

All that matters is tested best CBTO, which is repeated without regard to land relationship.

 

[338 dude]

There's a video on here for that. A smarter guy than me can find it and post a link. Basically, you pull your firing pin and ejector from your bolt. Use a prepped case and seat your bullet long. Carefully push your bullet in, in small increments, until your bolt closes on the dummy round with very slight/ no resistance.

That is what I call the wheeler method

 

[Texas10]

I've been using the touch measurement I described above for a while, but now I'm becoming a convert to the hard jam test. The reason is that hard jam is a quicker way to find the furthest forward loading position that can be obtained, and of course, moves further forward as the barrel erodes. So if your particular bullet prefers to be held to a narrow jump or jam you can easily chase that as the barrel wears.

While performing both tests yesterday, I found the hard jam first, followed by the touch dimension. The difference between the two was .035". So loading to hard jam minus .025" yields +.010 into the lands. I prefer to start there and work my way back out in .005 steps.

As others have commented, this is only a starting point for load development, but whatever method you use, it should be repeatable and easy to do. The hard jam method does not require special tools to perform. Size the case, seat the bullet long , chamber and close the bolt. I use a cleaning rod inserted in the muzzle end to gently push on the bullet as I open the bolt to eliminate the possibility of the bullet being moved or pulled out of the case while extracting. I prefer light neck tension on some loads so this helps make measurements consistent.

Having a reliable tool to measure CBTO (case base to ogive) or as some prefer BTO (base to ogive) is essential for proper die setup. Be aware that there are no regulations or well defined guides governing the manufacture of these tools, so what measurement you get on your tool will not translate directly to someone else's tool, or even another tool you own.

FWIW: I dedicate a shell holder to a set of dies for this very reason, particularly if holding shoulder bump to a close dimension is required for best groups or precision.

 

[JEFFPPC]

There are multiple methods to find the intersection of the bullet your using to the lands. It doesn't matter what method you use as long as it is repeatable and you use the same method every time.once you have a base number. It is a matter of plus or minus in relationship to that base number that allows you to fine a seating depth. If what you measure as touch is off a couple of thousanths either way, it does not matter. Using the base you find to go in and out will get you were you need to be. My opinion.

 

[Richard Coody]

Lots of ways to find the lands. Pick your favorite one. It really just depends on how complicated you want to make it.

But just remember all you are simply looking for a datum to start seating depth test from. Doesn't really matter if it is touch or jam or any where in between. It is just a starting point.