Finding CBTO at Lands

[DirtNap35]

I picked up a new rifle and was attempting to find the CBTO at lands using a modified case from Hornady and their OAL gauge. Typically when doing this I find I only need to supply very minor pressure to the rod to move the bullet and then stop when i immediately feel any type of resistance back. When I say minor pressure I mean very minor pressure to move the bullet.

This rifle it's completely different. Once I insert the oal gauge/modified case into chamber, loosen the lock screw to move the bullet I notice I have to provide significant pressure to attempt to even move the bullet. Once it does move forward I can feel the stop from the lands. There is no way this can be normal. You almost think heck I'm already at the lands but know that's impossible because I have the bullet so far back in the case, then all of a sudden it will slip forward. Do I have an issue with the modified case being concentric or maybe the even the chamber?

 

[slv hunter]

It sounds like the case mouth is to small or not concentric as you said. Try moving the bullet in and out of the case with your fingers. You may need to true the case

 

[Mikecr]

What a terrible method..

 

[Koda_]

Ive experienced this and have found it can depend on the bullet, like ones with cannelures or other features. Also might help to deburr the neck ID on the modified case.
Move the bullets by hand and if any resistance then expect to use more firm pressure to find the lands, as long as your consistent is what matters, the lands will grow out a few thou after 100rds anyways.

 

[Gregg C]

Personally, I find it better by far to seat a bullet in a sized case, long, strip the bolt, and then move the bullet in the seating die till the bolt drops . A tiny bit of resistance, and average it out from a few times( I use10) . I then back off .020, cause I don't like jamming.

 

[DirtNap35]

Personally, I find it better by far to seat a bullet in a sized case, long, strip the bolt, and then move the bullet in the seating die till the bolt drops . A tiny bit of resistance, and average it out from a few times( I use10) . I then back off .020, cause I don't like jamming.

Agreed. I won't be using the Hornady gauge again

 

[DirtNap35]

It sounds like the case mouth is to small or not concentric as you said. Try moving the bullet in and out of the case with your fingers. You may need to true the case

The bullet seems to moving freely in the modified case. I ended up using another method to find my measurement, but now I'm concerned on why I had resistance to move the bullet. If the case isn't concentric then my bullet is rubbing side of bore? Would you say it's the modified brass more so then the chamber not properly cut.

 

[Jester896]

Was it a new rifle or new to you rifle? If it is new to you, have you looked in the chamber? A carbon ring could add a little pressure to the mouth.

 

[FEENIX]

The bullet seems to moving freely in the modified case. I ended up using another method to find my measurement, but now I'm concerned on why I had resistance to move the bullet. If the case isn't concentric then my bullet is rubbing side of bore? Would you say it's the modified brass more so then the chamber not properly cut.

You need to determine/troubleshoot your issue before proceeding. Otherwise, you will frustrate yourself while wasting time and effort.

I make my own modified case fired from the chamber and have no issues using the Hornady tool. I have been using the straight and angled since they came out. I have other means to check CBTO, though. My GS made me a tool using my chamber reamer for my .338 Thor wildcat.

 

[jeb405]

I got a lot of variation in measurements trying the Hornady tool, most likely user error but error none the less. I now use the Loctite method, except I use fired brass and just make a small imperfection (dent) in the neck for minor friction. I believe it is one of the 3 methods in Gavin's video.

 

[DirtNap35]

Was it a new rifle or new to you rifle? If it is new to you, have you looked in the chamber? A carbon ring could add a little pressure to the mouth.

New rifle. 0 rounds down barrel

 

[drabdrew]

Make a modified case out of a fired piece of brass. Way more accurate than using the hornady modified case. Although I started with the hornady for years and it worked just fine. It's also really hard to jam too far into the lans by hand so I wouldn't worry. I normally push pretty hard after it stops. Also to remove any variables hit your chamber/throat with a nylon brush and make sure there's no debris causing the bullet to stick

 

[DirtNap35]

You need to determine/troubleshoot your issue before proceeding. Otherwise, you will frustrate yourself while wasting time and effort.

I make my own modified case fired from the chamber and have no issues using the Hornady tool. I have been using the straight and angled since they came out. I have other means to check CBTO, though. My GS made me a tool using my chamber reamer for my .338 Thor wildcat.

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GS said to run my modified case through my sizing die. I'll give that a try and if that doesn't work go buy a new modified case. If that doesn't solve issue I would have to assume it's the chamber. I should add this is a +P chamber but GS that it wouldn't matter.

 

[FEENIX]

GS said to run my modified case through my sizing die. I'll give that a try and if that doesn't work go buy a new modified case. If that doesn't solve issue I would have to assume it's the chamber. I should add this is a +P chamber but GS that it wouldn't matter.

Instead of buying a new modified case, make your own from brass fire-formed from your chamber (as previously noted in #9) using a bit/tap; I got mine from Amazon for $10. Or have your GS do it for you. However, if your chamber is bad, it does not matter what tool or method you use to measure your CBTO.