Help me figure out Chamber Size

[Steve Blair]

I always use the appropriate caliber expander on new cases, even if not neck turning. My usual target is for neck ID .002-.0025" under bullet diameter. For caliber .30 and 7mm, diametral clearance should be .004-.005". You could either leave the cases as is or take a light skim to somewhat uniform them.

 

[Endyo]

I always use the appropriate caliber expander on new cases, even if not neck turning. My usual target is for neck ID .002-.0025" under bullet diameter. For caliber .30 and 7mm, diametral clearance should be .004-.005". You could either leave the cases as is or take a light skim to somewhat uniform them.

Thanks Steve. Those are good solid numbers for me to work off of. It's good to be getting a consistent message. I'm very much in the ballpark of those measurements.

Luckily I have a force seater. I was going for the lightest seating force possible initially. I'm still testing but it seems a high seating force seems more forgiving.

 

[dkhunt14]

In some guns that is true. I use more tension then most but I shoot most in the lands and don't want the bullets to slip. Matt

 

[Endyo]

I've heard some will go with a light tension and jam into the lands with the intent of seating the bullet further back and getting a consistent seating depth based on actual ogive to lands.

I read here on these forums that Whidden supposedly does this. I thought that was interesting since this compensates for throat erosion and ensures that the bullet will still be sat "to the lands" as the barrel erodes assuming that tension is light enough.

Are there any negatives to the bullet slipping as you say Matt?

 

[dkhunt14]

Yes, if you have to remove an unfired round, you run the risk of flooding your chamber with powder and leaving the bullet stuck in the rifling. Not pleasant in the middle of a match. Also, a bullet seated with only very light neck tension will tend not to go as far into the lands as you might want it to.

This answers it. Matt

 

[Joe R]

I have a print of my sprinkler system that no longer bears any resemblance to the real thing because things have changed over the years.

As many have already stated the fired brass contradicts the print. Which do you think is telling you the truth? I'll bet a dollar against a nickel it's the brass. My advice is forget the print. The print reflects a single point in time, the chamber is now different.

Joe

 

[22BRGUY]

Yes, if you have to remove an unfired round, you run the risk of flooding your chamber with powder and leaving the bullet stuck in the rifling. Not pleasant in the middle of a match. Also, a bullet seated with only very light neck tension will tend not to go as far into the lands as you might want it to.

Really good point. If you do choose light neck tension, just always remember to point the barrel straight up if you need to eject, and do it slowly to avoid the powder nightmare.
Also, Cerro Safe has worked well for me to make chamber casts but make sure to lube the chamber and throat area well and have a long wooden rod, preferably oak, to knock out the chamber cast from the muzzle end.