How to Measuring Seating Depth/Freebore?

[jiwilliams]

The smith' who chambered my barrel in 22BR made a seating / headspace gauge with the reamer.

I'm pushing a dummy round into the gauge. The bullet is under tension but can still be forced to move in the neck.

I then remove the dummy round and measuring the result. I can either grasp the case head and pull it out or insert a rod from the other end and push on the bullet until it releases the rifling.

Here is my problem.. when I pull the case out I get one OAL measurement but when I push it out I get another measurement about .010 less.

Obviously the difference of .010 from pulling the case out and pushing it out comes from neck tension on the case and/or rifling tension on the bullet.

Should I just split the difference and call this the true freebore and set my seating depth from this measurement? Is ther something lacking in my approach??

 

[billmo]

JW. You need to go with the actual measurement if you really want true COAL. You may be able to polish your gage a little on the inside and stop the "sticking" of your case inside of it. Hope this helps. Bill

 

[expiper]

HI Joe.....you prolly need a lil more tension on the neck....either use a smaller bushing or squeeze it with pliers or what ever ur doing....then the bullet will remain constant with gentle removal from your "gizzy"....rmember this is a handy lil tool for initial bullet LOAL...as the gun wears,aprox .003 per 100rds)...the gizzy will become less and less comparable...but can be used to interpalate an approximate place to start...
Once you get the ammo close ...try a dummy rd. in your rifle...see just what fits it!!!...You shuld see a mark on the bullet aprox as wide as it is long...or maby slightly longer ....this is usually indicating aprox. .010" of jam...this is where I,and lot-0-folks) have the best accuracy.
Feel how the bolt closes on a loaded rd...you shuld just notice it ...if the gun rocks ...you are prolly toooo long...
There you have a way to measure it....to feel it and ...to see it......all telling the correct length for that bullet in your chamber,,,,,,Roger

 

[Ackman]

A seating gauge like that is a good idea and one of those should be included with every chambering job. But using it with a standard case isn't the best way because there's too much neck tension.

Here's what works. First have a Dremel tool or one of the copies. They're not expensive and just about essential for messing with guns. You'll also use it for all kinds of other things. Necksize a new case, then inside chamfer. With a Dremel cutoff wheel, slit the neck lengthwise and go a little bit into the shoulder. Use a rattail file to smooth the inside burr. Now you have split neck case for checking distance to the lands. You might also drill the primer flashhole to where something a little bigger will slide in there to push the bullet out. Make one of these for every cartridge you shoot and keep it in the die box. Distance to lands will be changing as the gun is fired. After those first loads, get your measurement directly from the chamber and keep track of things. Comparing current gun measurement to the gauge measurement will tell you how much the throat has worn.

Adjust tension by squeezing the caseneck. You want it loose enough for the bullet to slide easily when it hit the lands and not jam into them, but tight enough it'll stay put and not move when measuring. Bullets can vary so don't don't go by overall length. What matters is seating depth and the relationship of bullet to lands. Use a seating depth gauge from Sinclair, I just call it an ogive gauge. There are a couple different types. Davidson attaches to the caliper beam with a set screw. That leaves one hand free and is by far the most convenient to use.

If you do seat into the lands, remember to fire every round chambered. When jamming the lands, unchambering an unfired round can easily leave the bullet stuck. It'll happen and not a matter of IF, but WHEN. Then you'll not only have a bullet in the throat but also a chamber full of powder. That gun will be out of commission until the bullet is removed and every bit of powder is cleaned. You'll hate when that happens, and especially if it's out somewhere shooting critters. For a varmint gun, stay out of the lands completely.

 

[jiwilliams]

Thanks all.. I'm going to give these suggestions a try this weekend.

 

[rayjay]

Here is what Ackman is talking about: