Sinclair bump gage ?s

[bdh308]

I just recently purchased one of the Sinclairs bump gages for 308 win that attatches to your calipers. I guess Im a little confused on what kind of measurements Im looking for. The measurements will take place with Lapua brass while using a Redding body die. Anybody got some education on this or numbers I should be looking for this paticular cartridge? Rifle is a Remy 700.

 

[Wheres-Waldo]

Re: Sinclair bump gage ?s

A bump guage is designed to give you a measurment indicating the position of the shoulder.

The point of it is to give you an accurate reading on how far you have "bumped" the shoulder back during sizing.

What you want to do is meaure a fire-formed, unsized round.
*Record that number*

After sizing, measure again to determine how far back you have bumped the shoulder.

As to how far back you should go....
I used to "Partialy Size" all my .308 brass, which is to say I didnt touch the shoulder at all, and would FL when it had a hard time chambering.

 

[dragonjr45]

Re: Sinclair bump gage ?s

I've read that for benchrest, you should bump your shoulder back .002". I believe they suggest a little more for hunting rounds

 

[bdh308]

Re: Sinclair bump gage ?s

Thanks guys. I was hoping for someone with some experience with this paticular tool and maybe some similar numbers to go off of. From what I understand when chambering becomes a problem is the time to check for shoulder bump. The instructions that came with the gauge were pretty vague. I can measure one case and get a number, measure another case and get another number but really it doesnt mean anything unless I have some sort of standard measurement to refer to.

 

[Fuzzball]

Re: Sinclair bump gage ?s

The reference number you're seeking is the fired case length to the shoulder, none of us can give you that length, it's part of what your nice new gage is meant to tell you.

To obtain best case life due to the least stretching, don't move the shoulders back at all. Use your gage to measure and replicate the fired vs. sized shoulder length with your FL die. Try that for function, it should work fine, juat as smoothly as it would if you were re-chambering a fired but unresized case.

If for some reason that doesn't work/chamber as easily as you wish, then move the shoulders back a couple of thou.

You will find it's impossible to precisely repelicate ANY such case measurements consistantly. Variation in case springback is the reason, small variations in the brass alloy. There are small case hardness differences even in the same case box/lot and due to the number of times it's been fired. So, do your measuring and resizing using the shortest fired cases you have, then, on average, the rest should be okay too.

 

[bdh308]

Re: Sinclair bump gage ?s

Thanks Fuzzball...that makes a little more since. So using a once fired case as a gauge for the gauge is what Im after. Thanks again gentlemen for the help.