Shoulder bump guage

[flopearedmule]

Hi
New to the group. I've been reading this forum for a few months now. Finding all kinds of good info....thanks everyone for all the input!
I learned how to chamber rifles a few years ago, and I've built a few for family members.
The last one I built is a .280AI for myself.
I have shot about 100 rounds in it now and starting to reload so I can do some load development.
I've been trying to read a lot, hopefully not duplicate a question...…..but,

Here's my first question....I'm wondering where on the shoulder do you guys measure a fire formed brass? In the picture, the fire formed brass measures around .450 right before the shoulder.
I made a guage with the ID .380 with a slight 45* bevel.
I'm thinking all I need is a reference number then bump the shoulder a thousands back?? Am I on the right track? I was going to make a guage out of the chamber reamer, but I loaned it out and haven't got it back yet.

I have more questions, but I have to start somewhere. I've always just full length sized and I want to start shooting more accurate, so I have to tool up with some better tools. I bought a good set of full length redding dies and redding press with the competition shell holders.
Thanks

 

[dmoran]

That will work just fine, and like you say, it's just a reference number. Nicely made !.!.!

Welcome and good luck with your endeavors.

 

[Paul Hilgedick]

Yes, what you are looking for is a reference number. The gage you made should work, however when you get the reamer back run it in the gage. It will give the correct angle for the shoulder. When I chamber a barrel I use the stub I cut off to make my gage. This way I keep the info from the mfg. in case there is a problem with the barrel.

 

[chromatica]

RCBS Precision Mic (case gauge) will give you the measurement you want. They make a 280 Remington Mic but I haven't seen a 280AI. The upper half of the clamshell comes to rest at the designated datum on the shoulder for the cartridge. I suspect that the 40 degree shoulder of an AI case will displace the micrometer readout, but I believe relative changes could be accurately measured. That is all you need in order to measure the setback of your sizing dies.

 

[piie]

RCBS Precision Mic (case gauge) will give you the measurement you want. They make a 280 Remington Mic but I haven't seen a 280AI. The upper half of the clamshell comes to rest at the designated datum on the shoulder for the cartridge. I suspect that the 40 degree shoulder of an AI case will displace the micrometer readout, but I believe relative changes could be accurately measured. That is all you need in order to measure the setback of your sizing dies.

Doesn't the AI version of a cartridge have shoulders that "pivot" on the same datum (which is why you can still chamber a "normal" version of the calibre in an AI chamber)?

 

[dgeesaman]

Doesn't the AI version of a cartridge have shoulders that "pivot" on the same datum (which is why you can still chamber a "normal" version of the calibre in an AI chamber)?

The Ackley version of a cartridge is approximately the same where the shoulder meets the neck. That point isn’t really a datum. The AI different on all other points of the shoulder.

I have a 6BRA and I’m using the Hornady shoulder gauge for generic 6mm cartridges. It touches the shoulder at one point about halfway down but it’s working just fine. While I agree a gauge that’s cut to match the shoulder angle should be a better fit, I can’t identify any inferiority with my current setup.

 

[paperpuncher]

I bump .002"

 

[butchlambert]

I use the same thing as Paul Hilgedick. I make one for each different chamber that I cut.

 

[Webster]

Hi
New to the group. I've been reading this forum for a few months now. Finding all kinds of good info....thanks everyone for all the input!
I learned how to chamber rifles a few years ago, and I've built a few for family members.
The last one I built is a .280AI for myself.
I have shot about 100 rounds in it now and starting to reload so I can do some load development.
I've been trying to read a lot, hopefully not duplicate a question...…..but,

Here's my first question....I'm wondering where on the shoulder do you guys measure a fire formed brass? In the picture, the fire formed brass measures around .450 right before the shoulder.
I made a guage with the ID .380 with a slight 45* bevel.
I'm thinking all I need is a reference number then bump the shoulder a thousands back?? Am I on the right track? I was going to make a guage out of the chamber reamer, but I loaned it out and haven't got it back yet.

I have more questions, but I have to start somewhere. I've always just full length sized and I want to start shooting more accurate, so I have to tool up with some better tools. I bought a good set of full length redding dies and redding press with the competition shell holders.
Thanks

On a few blueprints I have looked at they give a data base line from the head face to half way up the shoulder. Anywhere near the mid-point of the shoulder should work. Your looking for change not a specific number at some exact location on the shoulder.

 

[butchlambert]

Just make a gizzy like Paul suggested with the same reamer. All you need and the measurement of the gizzy means nothing.

 

[Dusty Stevens]

Here is an example of a gizzy as butch talks about here. No problem to make one from a stub as you chamber a barrel.

 

[butchlambert]

That will work.

 

[Dusty Stevens]

heres the one harrels supplies with their dies. Even simpler

 

[flopearedmule]

Thanks everyone! I know now I just need a reference, and when I get my reamer back I'll make a new one.

 

[Ccrider]

Your bolt will let you know how much to bump.

 

[butchlambert]

Your bolt will let you know how much to bump.

I wouldn't trust that. In the old days I believed that and bumped my "shoulders" until it chambered and extracted fine. A big mistake. My problem was at the big end of my brass and not headspace. So to size the base I was seriously pushing my shoulders back. Use a "Gizzy" for your headspace measurements. If you still have a problem, check the diameter of the base of your brass. Make or use a small base die.

 

[Ccrider]

I wouldn't trust that. In the old days I believed that and bumped my "shoulders" until it chambered and extracted fine. A big mistake. My problem was at the big end of my brass and not headspace. So to size the base I was seriously pushing my shoulders back. Use a "Gizzy" for your headspace measurements. If you still have a problem, check the diameter of the base of your brass. Make or use a small base die.

I hear you. I see a difference in bolt feel between sizing needed at the base (bolt click) and shoulder needing to be pushed back a little more (right bolt close). When I say little, I mean .0005 increments.

 

[flopearedmule]

I wouldn't trust that. In the old days I believed that and bumped my "shoulders" until it chambered and extracted fine. A big mistake. My problem was at the big end of my brass and not headspace. So to size the base I was seriously pushing my shoulders back. Use a "Gizzy" for your headspace measurements. If you still have a problem, check the diameter of the base of your brass. Make or use a small base die.

Make or use a small base die.

What the heck is a small base die?

 

[dgeesaman]

Make or use a small base die.

What the heck is a small base die?

A die that keeps the bottom of the brass from growing.

Ideally your regular-use full length die has a small base effect so that the brass always stays well sized at the base of the chamber.

David

 

[butchlambert]

Make or use a small base die.

What the heck is a small base die?

Actually they make dies with a smaller diameter to size brass that is smaller than normal after it is fired.
That is the reason I spec my reamers about .003 larger at the base.