Barrel Chamber - neck diameter ??

[cooperve]

If you don't know the neck diameter of your factory rifle (22-250 40XB) chamber, how do you determine the neck diameter? Is it as easy as measuring the diameter of a fired casing or is there neck shrinkage after firing? This is probably not the accurate/correct way to determine the diameter, but any idea how close this would be?
Thanks.

[Stephen Perry]

Set of pin gages will do the best at nailing down a chamber neck diameter. Find a gage that barely drags in the neck. Another way less costly. Take a fired case use scotch tape. Start wrapping small pieces around cases neck. Check to see if you get a touch on the tape when inserted, when it feels like a touch measure this with a .001 mic/caliper. Rough measurements are fine using a factory chamber.

Stephen Perry
Angeles BR

[ab_bentley]

If you have the ability to pull the barrel you could cast the chamber with CeroSafe, you could use the pin gauge like Mr. Perry stated, a fired case will give a close estimation of the diameter (about a .001"-.002" less than the acutall). MTC, Adam

[RareBear]

For chambers that launch .224" bullets, Varmint Al's website mentions adding .0013" to the fired case neck diameter to get the chamber neck diameter.

A side note here, my particular 22-250 fired case necks measure .254" at the case mouth and .256" at the rear of the neck, indicating a non-parallel or cone shaped chamber neck. Such a chamber neck as this might be problematic for pin gauges.

[Chuck Miller]

Well, I just take some fired cases, measure them to make sure there is a gereral consensus among them, subtract 1 thou and I'm done. Basically came on this method after years of taking and measuring fired cases from rifles with known neck diameters. As for .0013, I guess that's about as close to 1 thou that these old eyes can see.

[GeorgeL]

No, the case neck doesn't shrink after firing but it does spring back to varying degrees depending on annealing, brass hardness, etc. So, measuring a fired case is not a useful methd of determing chamber neck dimensions. The best method for most of us that don't have, or have access to, pin gauges is a chamber cast. And, no, you don't have to pull the barrel to make a chamber cast--I never have. Do a google search and you'll find out what you need to know to make a chamber cast using cerrosafe.

[long shot]

Originally Posted by GeorgeL

The best method for most of us that don't have, or have access to, pin gauges is a chamber cast. And, no, you don't have to pull the barrel to make a chamber cast--I never have. Do a google search and you'll find out what you need to know to make a chamber cast using cerrosafe.

I'm with ya George.

Aaron

[cooperve]

Thank you for the posted information. I will use the rule of thumb +.001 to .0013 until I try a cast chamber method.