Shoulder Bump measurement

[mtnelkhunter]

Hello all, I am a new reloader and working on developing my first load in 300WSM for a custom hunting rifle built by black canyon customs. I am using a L.E. Wilson cartridge case gauge and the wheeler method and wanted your input on my findings.

If I take a once or twice fired case and measure it in the case gauge I get about 2.111" - these cases will all still close in the bolt without too much resistance (firing pin and ejection plunger removed). Using an RCBS matchmaster FL sizing die if I bump it back such that in the LE Wilson case gauge I get 2.105 and above it's a stiff close - stiffer than not resized at all. If I continue to bump back to 2.102 I get a nice gravity bolt drop. My question - what gives? That's .009" that I am bumping back - my thought is that either the sizing die or the case gauge isn't at the same angle as the chamber and so is perhaps not contacting the middle of the shoulder or some such situation.

Am I good to go just bumping back to get that bolt drop and just use the measurement as a guide or should I be concerned and look into either perhaps first a different comparator set up or (hopefully not) a different sizing die?

Thanks!

 

[cajun]

I don't think the case gauges are accurate for shoulder bump. Get the hornady or similar comparator where you can measure the shoulder directly. It is not uncommon when sizing for the measurement to grow before you push the shoulder back enough. I think that is what you are seeing. I don't care for the way you measure with the wilson gauge.

 

[YZ-80]

It is not uncommon when sizing for the measurement to grow before you push the shoulder back enough.

True. I use the Sinclair shoulder bump inserts and typically bump .002 too .003". I check every sized case by chambering it. I like to feel a tiny bit of resistance when cramming the bolt. Don't know if it's right or wrong but works for me.

 

[mtnelkhunter]

I don't think the case gauges are accurate for shoulder bump. Get the hornady or similar comparator where you can measure the shoulder directly. It is not uncommon when sizing for the measurement to grow before you push the shoulder back enough. I think that is what you are seeing. I don't care for the way you measure with the wilson gauge.

Okay good! I was hoping to hear something along those lines. I ordered the 420 hornady head space gauge insert to use with the hornady comparator body - a cheap but hopefully better way to see what's happening.

 

[cajun]

Okay good! I was hoping to hear something along those lines. I ordered the 420 hornady head space gauge insert to use with the hornady comparator body - a cheap but hopefully better way to see what's happening.

I use the Hornady set. Works fine.

 

[L.Sherm]

Unless your doing the Wheeler method which it sounds like you are on in my opinion you can't get an accurate measurement. I want zero resistance because if you dont then do you have .001- .002 resistance. I do .003 seating depth test and dont let my bump variances go more than .0005.
Variences stack up and thats exactly what I want minimized.
You have .001 bump, seating, bolt resistance etc. Next thing you know you could have .004-.005 in a loaded round, was that a flyer you couldn't explain?

 

[mtnelkhunter]

Yeah I am using the wheeler method in terms of bolt feel/fall. And maybe that's all I really need to know.

 

[L.Sherm]

If your doing the Wheeler method your good.
Whatever comparator you use and measure with just use it everytime.

 

[Mikecr]

If I take a once or twice fired case and measure it in the case gauge I get about 2.111" - these cases will all still close in the bolt without too much resistance (firing pin and ejection plunger removed).

So bump to 2.110-2.109 and see how it works.
Don't accept a crazy bunch of brass movement for setting headspace.. It's just a tiny shoulder bump, nothing to it.

 

[mtnelkhunter]

I don't think the case gauges are accurate for shoulder bump. Get the hornady or similar comparator where you can measure the shoulder directly. It is not uncommon when sizing for the measurement to grow before you push the shoulder back enough. I think that is what you are seeing. I don't care for the way you measure with the wilson gauge.

This turned out to be correct - using the case gauge was my issue. once I got the comparator body I bumped them back .002" and they were closing without any resistance. However - that .002" from fired to re-sized on the comparator registered completely differently on the case gauge. Once fired was probably .010" out of the case gauge and then .000" out once bumped back that .002". So, yeah don't use a case gauge.