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Thread: .30-06 headspace

  1. #21
    Boolit Grand Master

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    Quote Originally Posted by M-Tecs View Post
    The Hornady Headspace Comparator does exactly what it is claimed to do and it does it very well. Hornady calls it a COMPARATOR for a reason. It was not designed as a direct measurement tool unless used in conjunction with a actual standard like a headspace gauge. If you want direct measurements get a headspace gauge to zero your comparator or get the RCBS case mic. That does give direct measurements.

    https://www.keyence.com/ss/products/...sic/method.jsp

    https://extrudesign.com/comparator-types-uses/
    ^^^^^^^^^^^^^^ this is correct answer
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  2. #22
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    While there is a ton of good information in these posts-- I see one thing not mentioned. The "headspace" for a 30-06 case is the distance from a datum point on the shoulder to the face of the bolt. What this means, is that if you fire full loads the case will stretch to fit the chamber. Once this happens, the case is custom to that rifle. Then, if you only neck size from then on, you do not have to concern yourself with headspace.
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  3. #23
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    Quote Originally Posted by Hick View Post
    While there is a ton of good information in these posts-- I see one thing not mentioned. The "headspace" for a 30-06 case is the distance from a datum point on the shoulder to the face of the bolt. What this means, is that if you fire full loads the case will stretch to fit the chamber. Once this happens, the case is custom to that rifle. Then, if you only neck size from then on, you do not have to concern yourself with headspace.
    If you only neck size eventually the shoulder will move forward enough that the rounds will not chamber. You have to push the shoulder back a couple thou every once in a while.

    Tim
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  4. #24
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    Tripplebeards, well the 1903A3 would have been ok with the original bolt except the barrel wasn't in the greatest shape. Gun shows back then were a great place to pickup spare parts especially new A3 barrels. I was kinda stupid when I had the A3 rebarreled as I didn't have it D&T for scope bases. Kinda regret that now. So when I sent out my 1917 Enfield barreled action this time I had it D&T for scope bases. Still may send out the A3 one of these days. Frank

  5. #25
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    Quote Originally Posted by dtknowles View Post
    If you only neck size eventually the shoulder will move forward enough that the rounds will not chamber. You have to push the shoulder back a couple thou every once in a while.

    Tim
    Not with many cast bullet loads. Not had to partial or FL size my cast bullet cases with most all of my cartridges. Not even my 30x60 XCB cases which have been fired 7 - 9 times with loads running 48 to 50,000+ psi. I have lost count of the times the cases have been fired in my match .308W and 7.62x54R rifles with just neck sizing. They still chamber easily.

    With many cat's sneeze loads the reverse usually happens, the shoulder gets set back after several firings.
    Last edited by Larry Gibson; 09-20-2020 at 09:19 AM.
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  6. #26
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    Quote Originally Posted by Larry Gibson View Post
    Not with many cast bullet loads. Not had to partial or FL size my cast bullet cases with most all of my cartridges. Not even my 30x60 XCB cases which have been fired 7 - 9 times with loads running 48 to 50,000+ psi. I have lost count of the times the cases have been fired in my match .308W and 7.62x54R rifles with just neck sizing. They still chamber easily.

    With many cat's sneeze loads the reverse usually happens, the shoulder gets set back after several firings.
    Good observations Larry. It does not always happen and yes the shoulder can get pushed back by the firing pin strike and primer protrusion.

    The shoulder moving forward does depend on the pressure, amount of time at pressure and how springy the action is.

    TEK
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  7. #27
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    Just for the record, it's the explosion of the primer that drives the case forward, not the firing pin strike itself.
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  8. #28
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    Quote Originally Posted by dtknowles View Post
    If you only neck size eventually the shoulder will move forward enough that the rounds will not chamber. You have to push the shoulder back a couple thou every once in a while.

    Tim
    Perhaps yours do-- but not mine. Been using the same brass for over 8000 rounds in my M1 Garand without trimming and they all still chamber. Even my newest brass has over 10 reloads.
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  9. #29
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    Quote Originally Posted by Hick View Post
    Perhaps yours do-- but not mine. Been using the same brass for over 8000 rounds in my M1 Garand without trimming and they all still chamber. Even my newest brass has over 10 reloads.
    Not saying this is the case with your loads but the bolt closing force on an M1, M14 and and AR have enough force to push the shoulder back when chambering. This isn't as true for sizing the body but it takes very little to push the shoulders back. When I first started shooting High Power a buddy had a State DCM rifle that had excessive headspace by about .011". I built him a Match M1A that was .0005 over minimum. While I didn't recommend it he fired several hundred loaded rounds about .008" long in the shoulder with zero issues. I've seen AR's push the shoulders back .002" or .003" long for the chamber.
    Last edited by M-Tecs; 09-20-2020 at 10:24 PM.
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  10. #30
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    Quote Originally Posted by dtknowles View Post
    If you only neck size eventually the shoulder will move forward enough that the rounds will not chamber. You have to push the shoulder back a couple thou every once in a while.

    Tim
    If they are always fired in the same rifle how is this possible?
    You mean they "grow" after you remove them from the rifle?

  11. #31
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    Quote Originally Posted by elmacgyver0 View Post
    If they are always fired in the same rifle how is this possible?
    You mean they "grow" after you remove them from the rifle?
    Yes, actually the growing happens when the round is ejected. When the round is fired the bolt face moves backward, the chamber and brass is stretched forward, the steel chamber sees only elastic strain but the brass is plasticly deformed, it is taken past its elastic limit (if the pressure is high enough). When the pressure goes away the steel chamber relaxes back to its unpressurized length but the brass doesn't putting the brass in compression. When the brass is ejected the compressive force is removed and the brass goes to an uncompressed state. We are talking tiny amounts of permanent growth that if the pressures are high enough can build up over time.

    Have you ever had to trim your brass because it got longer from firing? Hopefully the rifle's chamber does not permanently change shape but the brass is permanently stretched with each firing. The less you size it back down the less it will grow but if the pressure is high enough it will still grow. How high does the pressure have to be? That depends on the strength of the gun. Stronger guns will see less stretch on their brass. Actually if the pressure is high enough you can stretch the gun, that is one way a gun will get excessive head space or be shot loose.

    Tim
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  12. #32
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    Quote Originally Posted by Hick View Post
    Perhaps yours do-- but not mine. Been using the same brass for over 8000 rounds in my M1 Garand without trimming and they all still chamber. Even my newest brass has over 10 reloads.
    We are not talking about trimming we are talking about the shoulder moving forward if you only neck size and don't full length size. I am surprised that you have not had to trim your brass. Do you measure them, do they not grow at all? If your brass get too long you can jam the neck into the throat, pinching the bullet causing higher pressure. This will happen before the round is so long that it won't chamber. But then again, if we are talking about cast bullet loads, that is a different animal.

    I have never actually had a round that would not chamber but I would feel greater pressure required on the bolt handle to close the action and take note to push the shoulders back on the next loading.

    I use bushing neck dies that don't form the body or shoulder. If you partial neck size using a full length sizing die backed off it can push the shoulder forward faster than neck sizing dies.

    Tim
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  13. #33
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    Tim is exactly correct. This is most noticeable on guns which lock up at the rear of the bolt. The entire receiver stretches and then snaps back, compressing what is essentially a brass spring in the chamber.
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  14. #34
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    Quote Originally Posted by dtknowles View Post
    We are not talking about trimming we are talking about the shoulder moving forward if you only neck size and don't full length size. I am surprised that you have not had to trim your brass. Do you measure them, do they not grow at all? If your brass get too long you can jam the neck into the throat, pinching the bullet causing higher pressure. This will happen before the round is so long that it won't chamber. But then again, if we are talking about cast bullet loads, that is a different animal.

    I have never actually had a round that would not chamber but I would feel greater pressure required on the bolt handle to close the action and take note to push the shoulders back on the next loading.

    I use bushing neck dies that don't form the body or shoulder. If you partial neck size using a full length sizing die backed off it can push the shoulder forward faster than neck sizing dies.

    Tim
    I measure them every fall as shooting winds down. In the beginning, when I was full length sizing they did grow, but since I switched to neck sizing (about 6000 rounds and five years ago) I see no growth. Since it is a Garand, I do not load beyond typical WWII ammo velocities. Maybe that's why I am not seeing this problem. Maybe this also has to do with the comment made by USCRA112-- the Garand locks at the front of the bolt, not the back-- so maybe there is not enough receiver stretch to let the shoulder move forward.

    Edit: After thinking about this and the (honestly) good advice I find here, I went back this evening and pulled out my Lyman 30-06 case gauge and checked my 500 oldest 30-06 cases that I have been reloading year after year with only neck sizing. Every single case was still in spec (both shoulder and case length). I can only conclude that if some firearms stretch the cases even when neck sized, my Garand isn't one of them.
    Last edited by Hick; 09-21-2020 at 10:51 PM.
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  15. #35
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    Quote Originally Posted by Hick View Post
    I measure them every fall as shooting winds down. In the beginning, when I was full length sizing they did grow, but since I switched to neck sizing (about 6000 rounds and five years ago) I see no growth. Since it is a Garand, I do not load beyond typical WWII ammo velocities. Maybe that's why I am not seeing this problem. Maybe this also has to do with the comment made by USCRA112-- the Garand locks at the front of the bolt, not the back-- so maybe there is not enough receiver stretch to let the shoulder move forward.

    Edit: After thinking about this and the (honestly) good advice I find here, I went back this evening and pulled out my Lyman 30-06 case gauge and checked my 500 oldest 30-06 cases that I have been reloading year after year with only neck sizing. Every single case was still in spec (both shoulder and case length). I can only conclude that if some firearms stretch the cases even when neck sized, my Garand isn't one of them.
    I think you have three things working for you, first the front locking bolt, second the moderate chamber pressures and third the slamming motion of the action might be setting the shoulder back during chambering. Since the stretching is only a tiny bit each firing then the action only needs to set the shoulder back a tiny bit to compensate.

    Tim
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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check