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Thread: Case Gauges and Headspace

  1. #1
    Boolit Master 308Jeff's Avatar
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    Case Gauges and Headspace

    Back in 2008 when I first started reloading, I decided to pick up a 308 Winchester Lyman Case Gauge. I was loading for an LR-308, and I wanted to make sure my ammo was going to chamber properly.

    The vast majority of the brass I had was once fired LC that had been salvaged from military bases, and I assumed it was most likely M-60 fired.

    What I found out right away was that my resized brass would not seat flush in the Lyman Gauge when using a standard full length sizing die. I picked up an RCBS Small Base die and I could get the brass to seat, but even with the SB die I had to pretty seriously over-cam the press.

    One of the first things I noticed with my reloads was I was getting flattened primers even with starting loads. I wasn't seeing flattened primers with factory ammo.

    About I month ago, I decided to pick up and RCBS Precision Mic as I'm getting ready to start processing a bunch of 308 brass again. What I quickly found is that most of my previously resized brass is about .005-.008" below SAAMI specs. Eesh.

    Last night I set up my Redding Type S Bushing FL die using the RCBS Mic and found that I could quite easily resize to SAMMI spec. When I put that same brass in the Lyman gauge, it is noticeably above being flush.

    A little bummed that I overworked quite a bit of brass (and that I'm probably going to toss all of it after one firing), but I'm hopeful that I may have eliminated my flattened primer problem.

    What do y'all think about this?

  2. #2
    Boolit Master



    M-Tecs's Avatar
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    Flattened primers are common with long headspace. I find that my RCBS case mic's are one of my most useful tools.

  3. #3
    Boolit Mold
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    what is an LR-308?
    Is it a bolt gun or a gas gun. Reloading is different for each

  4. #4
    Boolit Master
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    LR-308 is usual nomenclature for an AR 10 from DPMS, but Armalite is a real turd about using the actual AR-10 name on them because they own the trademark. Then as everyone else started making them the LR-308 got more use on other brands then the DPMS.

  5. #5
    Boolit Master 308Jeff's Avatar
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    Correct. It is a DPMS gun.

    M-Tecs, now that I've used one, I'm in whole-hearted agreement. Recently picked one up for 223 as well.

  6. #6
    Boolit Mold
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    Does the gun have a match chamber or a standard chamber, is it 308 or 7.62 NATO?
    What is the chamber headspace?
    Case headspace should be at least .003 shorter. It is my understanding that an SB dies only reduces the diameter of the case, at the pressure ring, and not the headspace. A Lyman case gauge is not a case gauge it is a headspace gauge. If you want a case gauge I can recommend a Sheridan slotted case gauge.

  7. #7
    Boolit Man
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    I wouldn't toss the brass. Check it and see how it is after firing. There are certain differences between AR10 and LR series. Bolts, uppers, lowers, barrel extensions, mags. It's not just a name.

  8. #8
    Boolit Master
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    Quote Originally Posted by M-Tecs View Post
    Flattened primers are common with long headspace. I find that my RCBS case mic's are one of my most useful tools.
    +1 on RCBS case mic's. It really makes a difference when setting up sizing dies which if done properly increases case life and accuracy!

  9. #9
    Boolit Master 308Jeff's Avatar
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    It is my understanding that the DPMS 308's (at least the ones produced at the time mine was) have a match chamber. Unfortunately I don't have any fired brass at the moment to check where my actual headspace is at, but you can bet that will be the first thing I do the next time I fire the rifle. For now I set my FL die to resize to SAAMI (0 on the RCBS Mic) as all of the factory ammo I have checks out at that spec as well. You may be right on the SBC dies, mortyg. I can't say for sure. I have a Sheridan for my 300 BO, and I may end up getting one for the 308. Just going to wait and see how things work out now that I have the RCBS and I'm setting things up based on measurements from that.

    I may save the brass, WJP. Depends on where my chamber checks out after I fire some more rounds. I hate to throw out twice fired brass, but I have enough 308 to easily last me a lifetime.

    Thanks again for all your help, guys.

  10. #10
    Boolit Master lefty o's Avatar
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    not all gauges are created equal. example in 223 i have both a dillon, and jp enterprises case gauge and a case that fits perfectly flush in one is a bit below flush in the other.

  11. #11
    Boolit Master 308Jeff's Avatar
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    Quote Originally Posted by lefty o View Post
    not all gauges are created equal. example in 223 i have both a dillon, and jp enterprises case gauge and a case that fits perfectly flush in one is a bit below flush in the other.
    Not surprised by this. I'll keep using the Lymans I have for 9mm, 40 S&W, and 45 ACP. But for setting up rifle dies I'll rely on the RCBS Precision Mics or Hornady Headspace Comparator in the future.

  12. #12
    Boolit Mold
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    I load for an M14/M1A. In an M14 a fired case cannot be used for headspace measurements. The action is such that the case is still under some internal pressure when the case is being extracted and therefore the headspace is not a reflection of the chamber.

  13. #13
    Boolit Master 308Jeff's Avatar
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    Quote Originally Posted by mortyg View Post
    I load for an M14/M1A. In an M14 a fired case cannot be used for headspace measurements. The action is such that the case is still under some internal pressure when the case is being extracted and therefore the headspace is not a reflection of the chamber.
    Interesting. What do you do in a case like that? Just reset to SAAMI?

  14. #14
    Boolit Mold
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    They measure the chamber with a series of gauges. You have to disassemble the bolt and trial fit the gauges. At the point that the gauge won't fit and between the previous gauge is your headspace. The gauges are in .001 increments.
    In M14s, match chambers are on the short and fat side and basically 308 chambers.
    When describing headspace it is best to differentiate between the chamber and case headspace.

  15. #15
    Boolit Master
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    I only use L E Wilson case gauges for M1A's and my RRA .308, and like the Redding bushing dies.
    I stay away from Lyman gauges and most any thing else Lyman, there quality and customer service is not what it once was.

  16. #16
    Boolit Bub
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    The best gauge I ever used was made by Mo Defina in Connecticut. His gauges are highly regarded by the Highpower community for setting up X-course ammo. The last phone number I have is 203-775-1013.

  17. #17
    Boolit Master



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    Quote Originally Posted by jem102 View Post
    The best gauge I ever used was made by Mo Defina in Connecticut. His gauges are highly regarded by the Highpower community for setting up X-course ammo. The last phone number I have is 203-775-1013.
    Mo did a great job with them. I purchased my first one in 1992 at Camp Perry. Still can find them on eBay. Overall I prefer the RCBS.

  18. #18
    Boolit Master
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    I much prefer the Hornady case gauge. It will measure many different cases. I use it for a Hakim autoloader, pump guns, levers actions, single shots and bolt guns. You can easily set the shoulder location to the nearest .001 to fit your rifles chamber.
    You can make your ammo fit your chambers or a gauge if you have multiple rifles.

    Have both Forester and Wilson gages and none of them is a useful as the Hornady gage.

    I have checked both Wilson and Forester case gages with gunsmith chamber gages and they are an exact match.
    Last edited by EDG; 12-06-2017 at 01:42 AM.
    EDG

  19. #19
    Boolit Master 308Jeff's Avatar
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    If you're referring to the Hornady Lock-N-Load Headspace Gauge, yes it is a very nice tool. I happened to pick up a B350 bushing for mine yesterday to check the headspacing on my 300 Blackout brass. Compared to the box of factory ammo I have, I was happy to see all the processed brass I checked was between .000" and -.003".

  20. #20
    Boolit Master
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    Quote Originally Posted by 308Jeff View Post
    If you're referring to the Hornady Lock-N-Load Headspace Gauge, yes it is a very nice tool. I happened to pick up a B350 bushing for mine yesterday to check the headspacing on my 300 Blackout brass. Compared to the box of factory ammo I have, I was happy to see all the processed brass I checked was between .000" and -.003".
    The Hornady LnL will lie to you if you expect Saami numbers. The edges of the bushing bores have a small chamfer that causes the measurement to be too small. However the gage is excellent when comparing one round to another. Make up a max shoulder length case that barely allows your bolt to close. Save that case and use it for a gage. Your loaded rounds need to be .002 to .003 shorter than the chamber in an auto loader, pump or lever gun.

    If you slowly double or triple stroke your brass when sizing you can eventually learn to make each and every case read the same with the Hornady tool. Only a tool that measures in .001 increments can teach you that.
    EDG

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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