Changing neck diameter in a chamber

[Rflshootr]

If someone had a 6.5 chamber reamer and wanted to chamber a barrel for an identical cartridge in 7mm and had a proper size machine reamer to open the neck diameter, what would be the best way to check the neck length/depth while the barrel was still in the lathe? Example: a 260 Remington to a 7mm-08 or a 6.5x284 to a standard 284 Win or any other combination of identical body cartridges.

 

[Mike Bryant]

If someone had a 6.5 chamber reamer and wanted to chamber a barrel for an identical cartridge in 7mm and had a proper size machine reamer to open the neck diameter, what would be the best way to check the neck length/depth while the barrel was still in the lathe? Example: a 260 Remington to a 7mm-08 or a 6.5x284 to a standard 284 Win or any other combination of identical body cartridges.

The reamer makers make piloted neck reamers that will just open up the neck or a combination with a neck reamer and a freebore combination. I haven't used them for opening up a chamber from a smaller caliber to the next sized caliber. I've mainly used neck reamers for opening up a tight neck chamber to a no turn chamber in the same caliber. However, the 6.5 reamers and the 7mm reamers use the same ID pilots. So, you can ream a 7mm barrel with a 6.5 reamer with the correct sized pilot for the bore and be fine. The only problem that I'd think that you'd run into when doing this is that you would have a sharp edge at the point where the shoulder meets the neck. When you look at the chamber print, there is a slight radius at that point that you wouldn't have when opening up the neck with a neck reamer to make a larger caliber. Whether that makes any difference, I don't know. I'm sure its there for a reason and is probably the same reason as radiusing the start of the chamber to enhance feeding. It's always best to have the proper reamer with all the dimensions correct for what you want to chamber.

 

[Rflshootr]

Mike I thought about that too. But since you mentioned the neck reamer......how do you check the depth to make sure you are far enough in or not too deep? Kind of the same thing I was asking with the other example.

 

[GeneT]

I opened a .300-221 to approximately .300 Whisper (to accept cases made from .223 without neck turning). I turned a couple neck-sized plugs and measured to the back of them. One to establish the baseline, one for the new neck diameter.

GsT

 

[Mike Bryant]

Mike I thought about that too. But since you mentioned the neck reamer......how do you check the depth to make sure you are far enough in or not too deep? Kind of the same thing I was asking with the other example.

I check the length I need to go off chamber prints. Watching the tailstock dial, I'll go in almost to depth and check the neck with a borescope. You should see a ring at the front of the neck where the neck diameter steps up from the original neck. When opening up a tight neck to a no turn neck, you can feel it when you get to the end of the neck if your are hand holding the reamer with a t handle. But, basically go slow and check your progress with a borescope. Probably won't feel a difference opening up a chamber to a larger caliber as you are already taking out so much metal.