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Mark Barrett

Hello,

I read in Nathans reloading book, page 258, paragraph 4: "Thick necks can cause problems by trapping projectiles, resulting in pressure spikes and destroying accuracy. To check whether this is effecting your rifle take a fired case and try to pass a projectile through the case mouth. The projectile should pass relatively easily."

After firing my new 7mm-08 barrel the fired brass does not allow the bullet to pass thru until the 3rd shot. This happens after I have thoroughly cleaned the rifle copper free and polished the throat with a maroon poly, followed with the pad coated with autosol metal polish. The minimum SAMMI chamber specification is has a neck diameter of 0.316" and my loaded ammunition neck diameter is 0.309". The rifle is fairly accurate with 3 shot groups averaging about 0.65 inches with an occasional flyer about every 3rd group that opens the average groups to about 1".

Fired brass outside neck diameter is 0.315, which from reading countless internet gun blogs on this subject indicates that the chamber is cut to about .0.316' as the spring back of the fired round should be about 0,001".

So it seems that from 0.309" unfired loaded ammo neck to 0.315" is quite a lot of room for the bullet to not be trapping the projectile. Am I overlooking something? It seems that the necks should have 0.007 thou to expand to meet the neck chamber wall.

I shoot with a lot of experienced shooters and an old high reputation barrel maker that agree that a bullet should pass easily though a fired case neck. However in a famous bench rest shooter, Tony Boyer's: The Book of Rifle Accuracy, page 149 paragraph 1 states: After you have fired cases 3 to 5 times, you should be able to insert a bullet into them before sizing. If your necks are too thick, this will probably not work." He is using bench rest tight chambers with about 1 or 2 thou clearance between the loaded cartridge and chamber neck, which may be the reason it takes 3 to 5 shots to pass a bullet through a fired case neck.

I have the tools to turn the necks and kind of like doing it as it makes me feel like a pro, but I don't want to be a phantom fiddler and potentially f-up the brass.

Any insights into this topic would be greatly appreciated.

Thank you,
Mark Barrett