7mm Wby Barrel Ordering - Headspace and Chamber Protrusion

[loudandproud]

I know this has been covered but I have not been able to find exactly what I am looking for.

I just bought a brand new M111 .300 win mag. I am planning on rebarrelling the rifle in 7mm Wby Mag. This is the first gunsmithing project I've done, and I am a newbie to reloading. That being said, I am a Mechanical Engineer and have a lot of experience build race engines and other tight tolerance work.

Today I called Lothar-Walther. I am looking at a SS barrel in 9" twist, 28" length, threaded for a muzzle brake and fluted.

When filling out the order form I notice the chamber protrusion measurement. When I inquired, the gentleman I spoke with stated that the proper chamber protrusion for my application was .135". Curious, I went home and measure my casing. The distance from them belt shoulder to the end of the casing (primer face) was approximately .215".

Could this be right?

If I set the headspace up off of the belt (correct for belted mags?) at .002" clearance, this will put my casing shoulder .080" off of the shoulder. Is this right??

Should the chamber protrusion be near equal to the distance I measured? Or am I missing under standing this whole thing.

Also, one the casings are shot the first time, what Is the proper way to set up the resizing die? Should I just have it bump the shoulder back a hair, or not at all?



Thanks for any help guys, this is my first savage. Really excited to see what I can do with this build.

[scope eye]

I am not sure but I think that's what you call free bore, and on a Weatherby there is a lot of it.

Tanks Dean

[Speedrat1]

Chamber protrusion.... that amount of the chamber that is not contained in the barrel. IIRC the headspace measurement on a rimmed mag is approx. .221 and the figure you were given was .135 so...... .221 - .135 = .086 which is the amount of the cartridge that will be outside the chamber to allow for the extractor to get into the extractor groove. :o

hope that helps!

[Speedrat1]

Also, one the casings are shot the first time, what Is the proper way to set up the resizing die? Should I just have it bump the shoulder back a hair, or not at all?



Thanks for any help guys, this is my first savage. Really excited to see what I can do with this build.

Got carried away with my "cute" reply and missed the second part of your question. My generally accepted way of working with headspace on the mags/reloading is.... new brassfire them to the chamber and I bump them a couple thou from then forward. With used brass it's a lot more variable.... I try to find a cartridge that will only chamber with a little effort, not shaving brass tight! I then bump it down a thou or so at a time till it chambers smooth and use it then as my "master" cartridge. I'm assuming in all this you have a way of accurately measuring the cartridges like the Hornady kit.

[loudandproud]

Do you have a link to this Hornady Kit?

Also... I don't think im understanding the chamber protrusion.

Any pics?

[KRP]

Chamber protrusion.... that amount of the chamber that is not contained in the barrel. IIRC the headspace measurement on a rimmed mag is approx. .221 and the figure you were given was .135 so...... .221 - .135 = .086 which is the amount of the cartridge that will be outside the chamber to allow for the extractor to get into the extractor groove. :o

hope that helps!

The belt is contained. The .135 is what a go gage will protrude from the barrel, which is about what the rim/extractor groove are plus a little bit(and some extra) for clearance between the bolt head/barrel. Factory bolt heads usually have ~.110 recess from the front to the face but they vary. With pre-fits they have to consider loose factory tolerances and add a bit of protrusion to make sure they will fit all rifles without bolt head/barrel interference issues since they aren't measuring the actual bolt face being used and chambering accordingly.

[Speedrat1]

no promotion of Midway, just for exhibit. This is what I use....

http://www.midwayusa.com/product/479704/hornady-lock-n-load-headspace-gage-5-bushing-set-with-comparator

[loudandproud]

The belt is contained. The .135 is what a go gage will protrude from the barrel, which is about what the rim/extractor groove are plus a little bit(and some extra) for clearance between the bolt head/barrel. Factory bolt heads usually have ~.110 recess from the front to the face but they vary. With pre-fits they have to consider loose factory tolerances and add a bit of protrusion to make sure they will fit all rifles without bolt head/barrel interference issues since they aren't measuring the actual bolt face being used and chambering accordingly.

Ok, so the belt is contained by a relief in the end of the barrel. Headspace is considered the distance between the face on this relief and the bolt face. Chamber protrusion is set by moving this relief deeper or shallower in the chamber. Chamber protrusion does not affect the distance between the chamber shoulder and the face that the belt sits on.

^^All this sound right?

How accurate should I expect the chamber to be size wise... from the belt shoulder to the shoulder?

Has anyone here ordered a barrel in a belted magnum... did .135" work?

[KRP]

Ok, so the belt is contained by a relief in the end of the barrel. Headspace is considered the distance between the face on this relief and the bolt face. Chamber protrusion is set by moving this relief deeper or shallower in the chamber. Chamber protrusion does not affect the distance between the chamber shoulder and the face that the belt sits on.

^^All this sound right?

Yes, pretty much. The belt relief is part of the chamber, protrusion is a matter of running the reamer in deeper/shallower. Headspace is the dimension from bolt face to the forward edge of the belt relief. The distance from the belt to the shoulder is a fixed dimension per the reamer.




How accurate should I expect the chamber to be size wise... from the belt shoulder to the shoulder?

Has anyone here ordered a barrel in a belted magnum... did .135" work?

I'd expect it to be accurate to SAAMI specs, unless you specify differently. LW is a German company though so maybe CIP specs.

I've never ordered a barrel for a belted mag. You could measure your bolt head and brass and order to fit. It seems as if LW is offering semi-custom chambering to fit your rifle/components.