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

MontanaCreedmoor

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?
 
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.
 
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I do pretty good with my smaller calibers with the "light tension close the bolt" method. Readings are repeatable +/- .001. If the tension is too light the reading will not be consistent.

I know, it's not very scientific, but I'm calling it good enough for me. I usually seat .010" deeper that that and play around from there. jd
 
joshb said:
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 extractor 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.
Click to expand...

This will not guarantee a perfectly consistent distance Off The Lands (OTL) and will often produce a inaccurate measurement depending on the neck tension.

In measuring many bullets both SMK and Berger, I find that that Ogive on the bullet, which should represent the point that the bullet will contact the lands, varies anywhere from 0.001"-0.004" or more within a lot and greater between lots. As I load at 0.015" OTL this represents a 27% possible variation between loads.

Also, the seating die will contact the Ogive of the bullet at different points as there is variations in Ogive slope. A seating die that contacts the Meplat is almost useless for accurate seating, as this will vary greatly unless you are turning the bullets.

Another thing that will affect your distance OTL is the neck tension. If the neck tension varies between casings then the effort to insert the round will vary as will spring back. This is why I anneal every single firing before I resize my cases. This helps to ensure that the metal between cartridges has the same consistency before sizing, ensuring a more consistent final size.
 
joshb said:
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 extractor from your bolt.
Click to expand...

The extractor is left in place as it is needed to withdraw the cartridge; The ejector plunger is removed. As this can be a PIA on a bolt with an spring plunger ejector, a dedicated case can be made by cutting a circular recess in a case head to allow the plunger to fit passively when the case is locked onto the bolt face with the extractor then inserted in the action. I have two actions that I use this method with and it works very well and negates the need to chase a plunger and spring across the shop floor:rolleyes:.
 
rardoin said:
The extractor is left in place as it is needed to withdraw the cartridge; The ejector plunger is removed. As this can be a PIA on a bolt with an spring plunger ejector, a dedicated case can be made by cutting a circular recess in a case head to allow the plunger to fit passively when the case is locked onto the bolt face with the extractor then inserted in the action. I have two actions that I use this method with and it works very well and negates the need to chase a plunger and spring across the shop floor:rolleyes:.
Click to expand...

Fixed! Sorry! Not enough coffee after a late night!:( Great idea on modifying the case! :) I'm gonna use that! A real time saver!
 
A good way to keep your seating depth consistent is to sort Bullets with a comparator; Bob Green makes a nice tool. IMO, hunting for the exact seating depth and chasing the lands is isn't as important as all the rounds being a consistent length. Using .010 necks, I switched to seating the bullets .100-.200 long and re-setting all at the bench. This eliminates any need to re-sort or remeasure SD at the bench especially if your pre-loaded rounds sit for any length of time.
 
Not knowing what chamber or caliber you working with here is a simple way of checking .
Take a case and turn the neck Two thousand thinner . Seat the bullet long with the fireing pin removed Keep moving the bullet into the case till the bolt closes firm .
Remove the bullet and load the case with a mid pressure load and shoot it . Size the part of the neck and load it again shoot it again . Now you have a case that fits your chamber and neck .
With that done now you have a chamber all case for that gun only .
Seating depth is not a fixed number so you have to change it where you gun shoots best .
I jump all my bullets and use seating depth to lower my Es
But I tune with a RAS tuner
Good luck. Larry
 
gstaylorg said:
Get yourself a Hornady OAL gauge. Practice a little bit to get the "feel" of the bullet just barely touching the lands. Measure. Done. A well-trained chimp could use this tool without issue.
Click to expand...
I don't like using a random fit all tool .its too easy to make your own custom tool . Larry
 
gstaylorg said:
Get yourself a Hornady OAL gauge. Practice a little bit to get the "feel" of the bullet just barely touching the lands. Measure. Done. A well-trained chimp could use this tool without issue.
Click to expand...

I use this also and call it good. If someone wanted to know exactly they could use this tool to get
close. Then seat a bullet shined with steel wool 10k longer in a fl sized case. Chamber and look for land marks, seat deeper shine again and chamber and look for marks. Do this until the land marks are gone.
 
T-Shooter,
That method you gave the url for is BRILLIANT!!

Thank you so much.

I have used the bullet long in a loose case for a long time then changed to taking out the firing pin and ejector plunger and make small seating adj. till the bolt just closes. One is inaccurate and the other takes a lot of time!! Using the cleaning rod is just the ticket!
 
Of the available store bought tools, I much prefer Sinclair’s.

http://www.sinclairintl.com/reloadi...lair-bullet-seating-depth-tool-prod35491.aspx
Instructions .pdf
http://www.sinclairintl.com/userdocs/learn/Sinclair_Seating_Depth_Gage_Inst.pdf

If not same bolt body dia. as Rem, Savage, Win, and Ruger, measure your bolt and order the correct rod guide.


&&

http://www.sinclairintl.com/reloadi...ating-depth-tools/length-gauge-prod70272.aspx
Gonna need to order their “Special Case” fer each caliber you load, or DIY yer own special case.
 
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
CRmethod.jpg
MontanaCreedmoor said:
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.
Click to expand...
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.
 
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