What is my Brass telling Me

[Retired shooter]

Specifically What is my Brass telling Me about Rifle Chambering
Hello to All
From all You RSGs ( Real Smart Guys) and or ( LEGs Lotta Experience guys) Get your mind back on reloading.
Have read similar previous threads 2011, 2019, and latest 2024.
Details as follows Gas gun, approx 350 rounds through it.
New 6.5 Starline Grendel Brass , Formed to 6 ARC ( new 6 ARC brass not available then), Shoulder bumped back approx .030 Verified with two different gages. Same as factory brass. FL sized without expander ball. Neck sized with bushing and expander mandrel, .002 NT Case length trimmed to 1.490 + .000 - .002 .

After first time firing ,Max powder charge for gas gun per Hornady 11 th edition . No over pressure signs. COAL 1.486-1.487. Shoulder datum long( pushed forward .012/.014). Again verified with two different gages. Same results with New Factory brass. Will be annealed before reloading.

Question, is that much shoulder movement standard, seems to be considerable brass movement back and forth.
If shoulder is moving forward, how is OAL getting shorter? Regardless of manufacture will all brass perform this way..
Bottom line does rifle chambering seem to be out of tolerance for this much brass movement. Fire Forming. Barrel manufacturing company states used a standard reamer for chambering.

Thank you to all, that are still reading.

 

[TTE]

Well, I'm not one of the more experienced guys, but here goes.

Not familiar with the cartridges you mention, however when fire forming, if the shoulder angle/case body/neck length is different, brass shrinks, at least in the stuff I have reloaded for when fire forming.

In a gas gun, IMO ..... .002 NT is not quite enough.

That's my $0.72 worth (up from $.02 due to inflation)

 

[Coyotefurharvester]

The factory brass/ammo you reference is likely on the minimum end of SAAMI ammo specs, your actual rifle chamber could be on the maximum end of SAAMI chamber specs. Fat chamber, brass can "shorten" when fired. I usually use the spent primer method(couple different case) to determine sizing die setting. I size my AR brass for cold winter function(chambers without FA) seems like 0.0035-0.004 bolt face clearance is very reliable and doesn't produce case separation issues. I have a Lee factory crimp die as a final step for AR ammo.

 

[fisherman987]

If your numbers are truly accurate and not due to a misplaced decimal point, then if you are bumping the shoulder back .030 as opposed to .003 you would be way over bumping the shoulder.

 

[Retired shooter]

If your numbers are truly accurate and not due to a misplaced decimal point, then if you are bumping the shoulder back .030 as opposed to .003 you would be way over bumping the shoulder.

Decimal point is correct for pushing shoulder back on new 6.5 Grendel brass to size it to 6 ARC. ( roughly .030) . And approximately. 030 trim for length. Worked with micrometers, & calipers many many years, not saying I may have had mental fog @ the time I posted. Try using Swiss mics, and read them. Some on the forum know what they are.!

After firing the shoulder is moving forward .012 / .014 The FL sizing die I use just barely gets the shoulder back to specs.

To all a good evening.

 

[swd]

Are you sure the new brass needs the shoulders bumped .030”? A lot of brand new brass is very short so using that dimension is very possibly the problem. I have seen new brass of various cartridges as much as .014” short of go gage. You should have the headspace checked. If it’s in spec then the new brass dimension is the problem. Or just bump the shoulder of the new brass .020” instead of .030” and go with it since your die still gives you the shoulder bump you need. My educated guess is using new brass is giving you the wrong dimension to work off of..

 

[fisherman987]

Decimal point is correct for pushing shoulder back on new 6.5 Grendel brass to size it to 6 ARC. ( roughly .030) . And approximately. 030 trim for length. Worked with micrometers, & calipers many many years, not saying I may have had mental fog @ the time I posted. Try using Swiss mics, and read them. Some on the forum know what they are.!

After firing the shoulder is moving forward .012 / .014 The FL sizing die I use just barely gets the shoulder back to specs.

To all a good evening.

Sorry, I thought you were talking about finished product.

 

[47WillysGuy]

Decimal point is correct for pushing shoulder back on new 6.5 Grendel brass to size it to 6 ARC. ( roughly .030) . And approximately. 030 trim for length. Worked with micrometers, & calipers many many years, not saying I may have had mental fog @ the time I posted. Try using Swiss mics, and read them. Some on the forum know what they are.!

After firing the shoulder is moving forward .012 / .014 The FL sizing die I use just barely gets the shoulder back to specs.

To all a good evening.

Question, is that much shoulder movement standard, seems to be considerable brass movement back and forth.
NO! 0.030" resize is way to much. Head separation will soon happen, IE somewhere between the case shoulder and the case head end and soon. Think of it, the pressure in the chamber when you fire a round is around 50,000 to 60,000 pounds per square inch. The brass case conforms to the chamber because of this pressure, then shrinks slightly smaller than your actual chamber size. You should only squeeze the case back 0.002-.004 of an inch.

If shoulder is moving forward, how is OAL getting shorter?
That's because of the 50-60K pressure is pushing the case brass outward in all directions, pushing the shoulder forward but pulling the case neck back.

And when you full size cases the for the next load, you'll find that the cases may grow a few thousands different from the firing. That's because the die squeezes the case into a smaller diameter, and the case neck moves upwards.

Hope I'm not confusing you!

If you want to know what's happening with your brass, take readings:
CNK=Case Neck ;; CHS = Case Headspace

CNK Dims, Fired (.2949)	0.2949
CNK Dims, Sized (.2875)	0.2875
CNK Dims, Loaded (.2895)	0.2895
CNK Thickness (0.0124)	0.0124
CHS Dims, Fired (1.5558)	1.5558
CHS Dims, Sized (1.5546)	1.5546
CHS Dims, Loaded (1.5320)	1.5546
Case Gage, Fired (0.0053)	0.0053
Case Gage, Sized (0.0003)	0.0003
Case Gage, Loaded Primed (-0.0011)	0.0000
Primer Pock Depth (0.1226)	0.1226
Case Length, Fired (1.9042)	1.9042
Case Length, Sized (1.9060)	1.9067
Case Length, Trimmed (1.910)	0.0000
0.200 line Dims(0.4698)	0.4708 goes to 0.4698 on FS

 

[gunsandgunsmithing]

Just set your dies to bump 3x fired brass back .003. If you're setting your dies per the instructions that die makers send with them, yes, you are likely over working your brass. They do this so that reloaded brass will presumably work in ANY SAMMI chamber. You are in control of how much you bump the shoulders back though.

 

[gunsandgunsmithing]

Question, is that much shoulder movement standard, seems to be considerable brass movement back and forth.
NO! 0.030" resize is way to much. Head separation will soon happen, IE somewhere between the case shoulder and the case head end and soon. Think of it, the pressure in the chamber when you fire a round is around 50,000 to 60,000 pounds per square inch. The brass case conforms to the chamber because of this pressure, then shrinks slightly smaller than your actual chamber size. You should only squeeze the case back 0.002-.004 of an inch.

If shoulder is moving forward, how is OAL getting shorter?
That's because of the 50-60K pressure is pushing the case brass outward in all directions, pushing the shoulder forward but pulling the case neck back.

And when you full size cases the for the next load, you'll find that the cases may grow a few thousands different from the firing. That's because the die squeezes the case into a smaller diameter, and the case neck moves upwards.

Hope I'm not confusing you!

If you want to know what's happening with your brass, take readings:
CNK=Case Neck ;; CHS = Case Headspace

CNK Dims, Fired (.2949)	0.2949
CNK Dims, Sized (.2875)	0.2875
CNK Dims, Loaded (.2895)	0.2895
CNK Thickness (0.0124)	0.0124
CHS Dims, Fired (1.5558)	1.5558
CHS Dims, Sized (1.5546)	1.5546
CHS Dims, Loaded (1.5320)	1.5546
Case Gage, Fired (0.0053)	0.0053
Case Gage, Sized (0.0003)	0.0003
Case Gage, Loaded Primed (-0.0011)	0.0000
Primer Pock Depth (0.1226)	0.1226
Case Length, Fired (1.9042)	1.9042
Case Length, Sized (1.9060)	1.9067
Case Length, Trimmed (1.910)	0.0000
0.200 line Dims(0.4698)	0.4708 goes to 0.4698 on FS

He's forming brass to a 6 ARC which is nominally .030 shorter than the grendel brass he's forming them from. That's why he's pushing it back .030 but his fired brass tells him he's going a little too far, for whatever reason. Lots of tolerance stacking going on here when all he should be looking at is HIS fired and sized dimensions.

 

[Doom]

It is a misconception to view the shoulder as being pushed forward. As pressure rises the case expand radially and into the bolt face tending to pull the original shoulder back and the pressure expands a portion of the existing shoulder to the case body diameter and a portion of the nest into the shoulder. This process makes the COL (overall length) shorter on the fired case with new material in the new shoulder and the Datum dimension (base to shoulder) longer. .

 

[TimW]

It sounds like you could decrease the amount of shoulder setback before fire forming. I have seen factory cases that are actually slightly below the min SAAMI spec but many are at the min for catrdige spec to ensure chambering.

At least after the intial fireforming you could go to the standard 0.002" shoulder bump or what I do is the stripped bolt test on the fired case and then set shoulder bump 0.002 off that reading. I use the same bump in my ARs.

 

[bozo699]

He's forming brass to a 6 ARC which is nominally .030 shorter than the grendel brass he's forming them from. That's why he's pushing it back .030 but his fired brass tells him he's going a little too far, for whatever reason. Lots of tolerance stacking going on here when all he should be looking at is HIS fired and sized dimensions.

Thank God someone finally read his post correctly!….
Wayne

 

[fkimble@charter.net]

Bozo, I was too busy laughing at the folks who did not comprehend his post. By the time I quit laughing gunsandgunsmthing had just replied!

Frank

 

[bozo699]

Bozo, I was too busy laughing at the folks who did not comprehend his post. By the time I quit laughing gunsandgunsmthing had just replied!

Frank

Sometimes I just shake my head……
Wayne

 

[Retired shooter]

He's forming brass to a 6 ARC which is nominally .030 shorter than the grendel brass he's forming them from. That's why he's pushing it back .030 but his fired brass tells him he's going a little too far, for whatever reason. Lots of tolerance stacking going on here when all he should be looking at is HIS fired and sized dimensions.

Thank you Sir

As the saying goes ( The Devil Is In The Details) most times on this forum people do not give all the details, creating longer discussions. This time I may have included too many details, and people not reading or understanding the process.

From years of being around machine work, and fabrication I know very well about tolerance stack up.

So from posts 9 thru 15 , if I am understanding correctly, just move the shoulder about .002 /.003 back, and see if the case will chamber easily. Do not be concerned about getting back to Sammi specs. Just form to the rifle chambering.

I was trying to get case length and shoulder datum back to factory specs, although I know those specs are not 100% repeatable. Again tolerances + / -

Thank you!

 

[Doom]

Thank you Sir

As the saying goes ( The Devil Is In The Details) most times on this forum people do not give all the details, creating longer discussions. This time I may have included too many details, and people not reading or understanding the process.

From years of being around machine work, and fabrication I know very well about tolerance stack up.

So from posts 9 thru 15 , if I am understanding correctly, just move the shoulder about .002 /.003 back, and see if the case will chamber easily. Do not be concerned about getting back to Sammi specs. Just form to the rifle chambering.

I was trying to get case length and shoulder datum back to factory specs, although I know those specs are not 100% repeatable. Again tolerances + / -

Thank you!

Yep, set the shoulder back 0.002" and you should be fine.

The SAAMI specs are for Max Cartridge and Minimum Chamber dimensions. This is to insure that a factory cartridge will fit in any chamber and the pressure will not exceeded established pressures. Based on Tolerances the headspace clearance for the ARC with factory ammunition could be 1.201 (Chamber Max) -(1.190-.007) (Cartridge Min) or 0.0171" which is a lot. Setting the brass back that much for reloading will drastically shorten the life of the brass.

 

[Retired shooter]

Yep, set the shoulder back 0.002" and you should be fine.

The SAAMI specs are for Max Cartridge and Minimum Chamber dimensions. This is to insure that a factory cartridge will fit in any chamber and the pressure will not exceeded established pressures. Based on Tolerances the headspace clearance for the ARC with factory ammunition could be 1.201 (Chamber Max) -(1.190-.007) (Cartridge Min) or 0.0171" which is a lot. Setting the brass back that much for reloading will drastically shorten the life of the brass.

Thank You.!

 

[gunsandgunsmithing]

Thank you Sir

As the saying goes ( The Devil Is In The Details) most times on this forum people do not give all the details, creating longer discussions. This time I may have included too many details, and people not reading or understanding the process.

From years of being around machine work, and fabrication I know very well about tolerance stack up.

So from posts 9 thru 15 , if I am understanding correctly, just move the shoulder about .002 /.003 back, and see if the case will chamber easily. Do not be concerned about getting back to Sammi specs. Just form to the rifle chambering.

I was trying to get case length and shoulder datum back to factory specs, although I know those specs are not 100% repeatable. Again tolerances + / -

Thank you!

Sounds like you are on the right track now. FWIW, I've seen factory brass well below sammi min, so if you were using that in your determination of say .030 shorter than X, then that's likely where a lot of the stacking variable came from. But the main thing is I think you're on the right track and I doubt there's a chamber problem, but it's still possible...just not very likely. If you're already familiar machine work, you fully get what I'm talking about and can see how fast the numbers change. Just focus on
YOUR fired and sized brass. About .002-.003 push back from fired to sized is cool, using brass that has been fired a few times to get a consistent place to start. Good job!

 

[Retired shooter]

Sounds like you are on the right track now. FWIW, I've seen factory brass well below sammi min, so if you were using that in your determination of say .030 shorter than X, then that's likely where a lot of the stacking variable came from. But the main thing is I think you're on the right track and I doubt there's a chamber problem, but it's still possible...just not very likely. If you're already familiar machine work, you fully get what I'm talking about and can see how fast the numbers change. Just focus on
YOUR fired and sized brass. About .002-.003 push back from fired to sized is cool, using brass that has been fired a few times to get a consistent place to start. Good job!

Have always used printed data, and or blueprints for fabrication, machining, or assembly work. Had been told numerous times to load back to factory specifications in regards to case sizing. Never gave it a thought to just bump the shoulder a couple thou. Never to old to learn. It's a wasted day if we don't learn something new.

Thank you Sir
To All a great Evening!