Measuring shoulder bump with coal vs shoulder comparator

[Nevrsummr]

When resizing cases do you use coal to measure how much the shoulder is being set back, or a shoulder comparator? Mainly for the initial setup of the die. Why do you choose this method?

It seems to me that coal would give you a more accurate picture of the bump. Shoulder comparators tend to hit a different spot on the shoulder depending on cartridge, and there can be some movement forward of the comparator contact point, so you might not see the full measurement of shoulder movement. But ive been wrong before. Lol.

 

[LaHunter]

COAL = Cartridge Over All Length (case head to bullet tip). This is independent of 'brass shoulder bump' and really not directly related to shoulder bump.
As far as precision reloading goes, COAL is really only useful to ensure your rounds will fit into your magazine.

Shoulder bump is a key measurement of brass sizing. You will need to measure this with a comparator type tool that indexes on the brass shoulder. This measurement is important so that you minimize overworking the brass, while ensuring that your sized brass will fit into your chamber. Many reloaders like to have .002 - .003 of head space (clearance) with their sized brass to ensure they will chamber every time.

 

[Nevrsummr]

Coal i was referring to would be without the bullet in this instance. Call it what you want.

Case overall length?

Anyway, wouldnt the oal of the case measure more accurately than how much a random line on the diagonal shoulder of the case has moved? Or am i all wet?

 

[Petey308]

It would only be accurate if the cases are trimmed the same. They can vary in length after sizing due to them stretching.

So using a good comparator, like the set from Short Action Customs, is best to measure shoulder bump and setting your dies.

Yes, comparators tend to vary, but as long as you use the same comparator each time, the point it's measuring to will be the same. It's the same reference point. If you used one comparator one time, abd a different one the next time, yes it would be a different measurement. Just use the same one and measure the same way and you're good.

 

[FEENIX]

COAL

CBTO

CBTO is what most reloaders measure and reference to the lands.

 

[Petey308]

How you trimmed your cases would also potentially vary things. For example, if you use a lathe style trimmer, it'll trim the case based on base to case mouth. If you use a trimmer like a Giraud, Frankford Arsenal, Little Crow, etc it indexes off the shoulder and only trims the excess from the shoulder to the case mouth. So getting a consistent shoulder bump is import with that style of trimmer

 

[Petey308]

View attachment 391304
View attachment 391306
COAL
View attachment 391305
CBTO

CBTO is what most reloaders measure and reference to the lands.

I think in this situation he's talking about sizing brass and the correct way to measure it to know the sizing die is set properly and producing the right amount of shoulder bump. Same concepts though as far as terms and caliper setup, just measuring the case vs bullet. So measuring without the comparator from case base to case mouth, or case base to shoulder with the comparator attached, but the headspace version and not the bullet insert.

 

[FEENIX]

I think in this situation he's talking about sizing brass and the correct way to measure it to know the sizing die is set properly and producing the right amount of shoulder bump. Same concepts though as far as terms and caliper setup, just measuring the case vs bullet. So measuring without the comparator from case base to case mouth, or case base to shoulder with the comparator attached, but the headspace version and not the bullet insert.

Yep, I was setting it up but forgot to attach the video by Jeff.



~around the 3-minute mark.

 

[Nevrsummr]

Thanks guys. Ill follow your lead.

 

[Nevrsummr]

Yep, I was setting it up but forgot to attach the video by Jeff.



~around the 3-minute mark.

Great video. No measurements needed. Ironically i have all the equipment to do that. Just need to be smart enough to put 2+2 together.

Thanks for your patience n help

 

[cajun]

In order to do that properly your bolt needs to be stripped. Also your still using a subjective measure as in feel. A headspace comparator gives you a number to go off and is going to be more accurate. Also you can measure how much your brass is growing on firing and control the resizing process. With the above method you have no idea how much the bump is. I had a rifle once with an oversized chamber and a die that was sizing way below minimum spec. The result was about 15 thou shoulder bump and a case head separation. The tool is cheap and well worth it.

 

[Taylorbok]

You can't measure bump off of case length, *** you push the shoulder back and size down the body the brass flows forward into the neck which is the whole reason you need to trim cases, essentially as you move the shoulder back the case will get longer, there is no way to determine the correlation nor is it consistent, you need to use a comparator and measure off the shoulder.

 

[VenatusDominus]

I removed the extractor plunger and firing pin from my bolt. I then bumped my shoulder using a Redding Type S bushing die and the Redding Competition shell holders. Starting with the .010" shell holder I sized the brass and checked the fit in the chamber. I worked my way down until the bolt would close with out tension (.006" shell holder for my particular chamber). I then measured the case using my headspace comparator to get the correct base to shoulder number to go off of. What I have observed is that if you do not anneal every time, you will get a different shoulder bump using the exact same press/die/shell holder set-up. This is due to a difference in brass spring back as the brass work hardens. I anneal immediately before bumping my shoulder and have found that this give the most consistent shoulder bump.

 

[Nevrsummr]

So, i followed the steps in the video and the instructions on the redding shell holder kit. Started with the .010 shell holder and with the die firmly touching the shell holder. My bolt closes the same tension with or without the sized case in it. Shoulder comparator reading before sized is 2.212 and after sized is 2.213 so the shoulder grew .001. Should i just call it good with the .010 shell holder? Or should i try the .008? I dont think i will be able to feel the difference. My ejector is removed from the bolt btw.