Shoulder bump / headspace question

[Vandy321]

Novice reloader...

Virgin adg brass was .012 - .014 less than saami (zero) using the RCBS precision mic guage.

After fire forming at a minimum charge (seating depth test, mainly to fire form), case grew .007 and now measured .006-.007 under the zero on the saami headspace guage...assuming zero is saami minimum on that precision mic headspace guage, they have not expanded out even to min saami specs yet?

Assuming these may not be compeltely fire formed based off the light charge. Should I just load them up and shoot them again or take that .007 less than saami and bump it back .001 and maintain that headspace?

They empty cases still chamber fine in a stripped bolt.

 

[cw308]

From using a light load your cases aren't expanding and stretching to the max , one trick you could try is backing out a fired primer , chamber that case with the backed out primer and see when you chamber where the primer measures from primer to datum. Or you could lower your die to size the neck only . Or you could build up the back of a fired case until you feel alittle resistance on your stripped bolt . I ordered a Go Gauge for my 308 it measures 1.630 adding shims to the back or the gauge I found my chamber length from datum to bolt face was 1.632 , using that measurement in my RCBS Precision Mic I case size from zero on up . If you have a fired case that won't chamber you can lower your F/L die slightly untill your stripped bolt can close with a slight resistance. I found the stripped bolt method very accurate and reliable on both CBTD & CBTO . Only difference is ogive is adjusted by bolt lift . Datum on closure . Hope I didn't confuse things .

 

[Vandy321]

So if still .007 under saami and stripped bolt will still close on that fired brass, should I just shoot it again to ensure it has fully expanded and will no longer chamber a d bump after that?

I plan to shoulder bump with the Redding Body and the Comp shell holders (the 6 pack)

 

[Uncle Ed]

Below is a Colt 5.56 Field Gauge at 1.4736

Below is the same gauge in my adjusted and calibrated Hornady cartridge case headspace gauge. This gauge was reading .011 less than the Field gauge. So I loosened the red and silver sections of the gauge and placed a .011 feeler gauge between the two sections and locked them down.

Below is a fired case from my AR15 in the gauge, I then set the die up to bump the shoulder back .003.

The shortest new case I have ever found was .009 shorter than a GO gauge or minimum chamber headspace.

The Hornady gauge is used to compare lengths and without a headspace gauge to use as a comparison you have no idea where the GO gauge reading or zero is at.

Example below is my RCBS Precision Mic and with a .308 GO gauge in it it reads minus .0015 because this gauge not calibrated and only a comparator gauge.

Also if the cases you fired with a reduce load have the primers protruding, it means the cases did not stretch to fit the length of the chamber. Meaning the rear of the case did not stretch and contact the bolt face and re-seat the primer flush with the base of the case.

If you make a workup load starting at the suggested start load and work up to maximum you will find the start load cases are the shortest. Meaning you need a warmer load for the case to totally fill the the chamber to get a more accurate measurement of the shoulder location minus a little brass spring back.

If you want to find out how much shorter your new cases are than your chamber you can do it with a fired spent primer.

1. Measure the new case form the mouth to is base and write it down.

2. Next just using your fingers place the spent primer in the primer pocket. If the primer falls out with just finger pressure then push the primer against your reloading bench to start it in.

3. Now chamber this case and let the bolt face seat the primer and remove the case.

4. Now measure the case from the case mouth to the base of the primer and write it down. Then subtract the first case measurement from the second and this will be your head clearance. Or how much shorter the case is vs actual chamber length or headspace length.

 

[Uncle Ed]

Note, look at the chart below and at what firing the cases actually stretched when fired.

Example below, the top case started to stretch the third time it was full length resized and fired without adjusting the die for minimum shoulder bump .001 to .002.

With new excessively short cases I jam the bullet into the rifling with a mid-range load. This holds the base of the case against the bolt face when the cartridge is fired. Another method is creating a false shoulder by expanding the case neck and then reduce part of the neck back down to hold the bullet. This is a lot more work and the false shoulder needs to be adjusted to allow the bolt to close with firm pressure. Meaning the false shoulder is holding the case against the bolt face.

Below example of false shoulders, the "fat" section of the neck holds the case against the bolt face and prevents the case from stretching.

 

[cw308]

Great Post Uncle Ed

 

[Vandy321]

That's great!! I will try that out.

For subsequent shoulder bumps, is .001-.002 off of that length a good place to keep it? Hunting rifle, reliable feeding is key for me

Shooting a 300wm

 

[Uncle Ed]

That's great!! I will try that out.

For subsequent shoulder bumps, is .001-.002 off of that length a good place to keep it? Hunting rifle, reliable feeding is key for me

Shooting a 300wm

Vandy

.001 to .002 will be fine for your shoulder bump and remember there is some spring back of the shoulder after firing and again after case sizing. Meaning the harder the shoulder and neck area gets the more spring back you will have.

NOTE, I never had a single case head separation in over 48 years of reloading until I bought a surplus .303 British Enfield rifle. On a military Enfield rifle at max military headspace you can have .016 head clearance or air space between the rear of the case and the bolt face. So this means making sure the case headspaces on its shoulder and not the rim.

Below this Winchester .303 British case was full length resized with press cam over and fired three times and had a partial separation. This thinner Winchester case had .009 head clearance each time it was fired. I then found Prvi Partizan .303 cases had thicker rims, a larger base diameter and .010 thicker in the base web area.

Meaning not all cases are built Ford Truck Tough and you might have cases made by Chevy.

This is where neck sizing or partial full length resizing will extend cases life with minimum head clearance.

 

[J F Johannes]

That's great!! I will try that out.

For subsequent shoulder bumps, is .001-.002 off of that length a good place to keep it? Hunting rifle, reliable feeding is key for me

Shooting a 300wm

Uh Oh! That’s a belted magnum. Ed is going to have to revise his whole spiel.
Jim

 

[Vandy321]

Follow up question.

According to my RCBS Precision Mic...my cases are now .007 under the zero. I just tossed all my once spent primers from this brass so I cannot measure this go around.

That being said. My redding comp body die is bottomed out (I adjusted as I went, hoping to see a .001 shoulder bump) with no bump.

I'd pl planned on the redding comp shellholder to help, but the do not seem to work in my forster co-ax...

Is my only way to bump the shoulders is hope these expand on subsequent firings out past saami mins and the body die will bump them? Or if that doesnt happen, I have to grind the die body down in intervals until it bumps the shoulder?

 

[JFrank]

Ya could just fire them a couple more times before ya start worrying about headspace.

 

[Uncle Ed]

Uh Oh! That’s a belted magnum. Ed is going to have to revise his whole spiel.
Jim

Actually a belted case is nothing more than a rimed case with the "rim" moved slightly forward.

The biggest difference is the rimless bottleneck cases that headspace on its shoulder.

And well informed reloaders let all three types of cases headspace on their shoulder.

Besides I don't own any belted rifle calibers, and that's because the the .270 Win is the worlds best
non-belted magnum.

The second best non-belted magnum is a 30-06 loaded to the same chamber pressure as the .270 Win.

 

[J F Johannes]

@Vandy321 Do a search here for “belted magnum” , you will get plenty of info. Let us know after several hours of reading what ya think.
Jim

 

[Uncle Ed]

Follow up question.

According to my RCBS Precision Mic...my cases are now .007 under the zero. I just tossed all my once spent primers from this brass so I cannot measure this go around.

That being said. My redding comp body die is bottomed out (I adjusted as I went, hoping to see a .001 shoulder bump) with no bump.

I'd pl planned on the redding comp shellholder to help, but the do not seem to work in my forster co-ax...

Is my only way to bump the shoulders is hope these expand on subsequent firings out past saami mins and the body die will bump them? Or if that doesnt happen, I have to grind the die body down in intervals until it bumps the shoulder?

When you resize a fired case the shoulder is squeezed upward in the die. And if you partial full length resize the cases the shoulder will move forward without firing them again. Raise the ram and place a nickle on your shell holder and then screw the die down until it contacts the nickle and tighten the lockring. You may need to lower the die more if the cases do not chamber because the cases may have become longer than the chamber.

 

[JFrank]

Shoulder bumping is for fully fire formed cases.

 

[Vandy321]

The cases

When you resize a fired case the shoulder is squeezed upward in the die. And if you partial full length resize the cases the shoulder will move forward without firing them again. Raise the ram and place a nickle on your shell holder and then screw the die down until it contacts the nickle and tighten the lockring. You may need to lower the die more if the cases do not chamber because the cases may have become longer than the chamber.

The cases will chamber and after the body die, the reading on the precision mic gauge did not change, so I'm assuming shoulders didnt grow?

I guess I'm lost on (when its time) how to bump the shoulders with just a redding comp body die on a Co-ax press.

Even cranked all the way down to a slight cam-over, the die is not touching the shoulder. Assuming they have more growing to do. When it is time to bump shoulders, do I start with the die up pretty high off the shell holder and slowly adjust down as I measure till it finally bumps it .001?

Is there a better gauge to use than that RCBS prec mic to track shoulder movement?

 

[JFrank]

 

[Uncle Ed]

And sometimes Wilson case gauges are worthless, especially with rimmed or belted cases. Meaning he has a Precision Mic that will tell him more the a Wilson type gauge.

Below a new unfired .303 British case in a Wilson gauge showing how short the shoulder location is.

Below a fired .303 case in the gauge showing how much longer the British chamber shoulder location is than SAAMI standards. The case is resting on its shoulder in the gauge and case diameter or the rim is not holding up the case.

I prefer the Hornady cartridge case headspace gauge because of its speed. And if used with a large digital display it make viewing easy if you have chronologically gifted eyesight.

 

[Bindi2]

Ed you just showed that SAAMI specs for the 303 Brit are wrong which has been the major problem all along. Don't FLS unless you absolutely have to the dies are wrong, use a Lee neck collet die. As long as the bolt does not close on a 74 gauge you are good to go. Making a tight 64 is just as bad as a closure on a 74. Relax head space is in your head it is being used as a means to get rid of many serviceable rifles.

 

[Uncle Ed]

Ed you just showed that SAAMI specs for the 303 Brit are wrong which has been the major problem all along. Don't FLS unless you absolutely have to the dies are wrong, use a Lee neck collet die. As long as the bolt does not close on a 74 gauge you are good to go. Making a tight 64 is just as bad as a closure on a 74. Relax head space is in your head it is being used as a means to get rid of many serviceable rifles.

In 1914 the Enfield chambers were reamed longer due to a ammunition scandal and who was awarded contracts to produce ammunition. Much of this early war ammunition would not even chamber so the chambers were reamed larger in diameter and longer to the chambers shoulder to chamber the bad ammunition.

And since the British were still angry over our American disagreement with King George the Brits never told the SAAMI when it was formed in 1926 about the chamber changes. We got even and changed the rules of Cricket and Rugby and called it Base Ball and Foot Ball. Then the British got even with our changes and called Soccer foot ball and caused mass world confusion.

And at least you Ozmaniacs were smart and hired the American firm of Pratt and Whitney to setup your Lithgow Enfield plant. But sadly you cheated at Perth and took the Americas cup from us and Men at works song "Down Under" almost became your National Anthem.

You might remember me under another screen name at Gunboards Enfield forum and my free Enfield books and manuals. I miss all the fun I had with you Australians especially Dr Beers. I once asked him for Enfield pointers so he took a photo of his target pointing with his index finger. And I see Alan De Enfield likes to use all my old photos and images.