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  1. #1
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    Default Small Base Dies Vs full length

    I've seen a couple of post through out the internet, that you don't get as many reloads with small base dies as you do full length dies. That they decrease the life of the brass. Is this true?


    Kip

  2. #2

    Default Small base VS full length

    Actually the small base die is also a full length sizer die. The difference between a small base and regular full length sizer die is that the small base die sizes the base of the cartridge case more than the regular die. How much more depends on the cartridge for which the die is made. Yes, the small base die does work the brass more and can lead to shortened brass life. I would start with a regular full length sizer die and only use a small base sizer die if it is really necessary. I only own one small base die. That is for my match chambered .308 bolt gun. I have to use it on cases that are once fired in another chamber (i.e. Lake City Match or M118 brass). New brass does not require a small base die to fit and once the brass is fired in rifle I can use a neck sizer die from then on. But that is a bolt gun. A semi-auto would require a regular full length die. I don't use small base dies for my Garands (I have 9) or my ARs (I have a COLT HBAR and a RRA NM). I can use the brass fired in either AR by running it through my RCBS regular full length sizer die. I can do the same thing with my Garands. Two of my Garands have tighter commercial chambers while the others have USGI chambers.

    Bill

  3. #3
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    Default Bill

    Thanks for the quick response. I've ordered RCBS small base dies that should be in this week for 6.8

    Which full length RCBS dies do I need to order? There are several different types. I will be reloading for 6.8. and I'm glad you responded due to you use RCBS full length. I have a Hornady LNL. And have only used Hornady pistol dies thus far. Hornady 6.8 full lenght dies are not available.

    Kip

  4. #4
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    Default

    Actually I the small base dies size the brass slightly smaller at the base then full length dies. Small base dies are to be used in semi autos for more reliable feeding and full length dies are more popular in bolt action as the brass is sized close to "spec".


    ETA:
    From Bucknrut
    I have a quick question while we are on the topic. I don't know anyone that uses a SB die, so is there anyone who could tell me the difference between the FL and SB sets? Are the Small Base dies just more accurate/precise than the FL dies?

    Response from Constructor
    The base diameter is about .418 or .004 under chamber spec. a regular FL is apx .420 or .002 under chamber spec.

  5. #5
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    Default

    I purchased a set of FL dies 1st and it didn't kick the base down enough and would stick in the chambers of both my AR's. Bought the small base dies and problem solved. Not every chamber is the same.

  6. #6
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    Default

    In the SAMMI and SPC2 chambers you don't need small base dies, whats the point of sizing your brass smaller than it was when new.

    Now the makers of the DMR chamber reccomend SB dies, must be the way they ream their chambers(probably just a way to get more pressure and still extract without issues) I'm not sure.

    I do know I have a SAMMI 6.8 1/10 twist barrel and I use regular LEE (Hornady New Dem. dies on their way this week) FL dies and just make sure I'm properly sizing my brass with the correct head space and OAL to prevent overpressure which is what causes the case base to swell. After all the base of a cartridge being to larger to extract is clearly a sign of overpressure and these guys are just getting around the problem by undersizing their brass instead of realizing the real problem to begin with.

    Load correctly and regular FL dies are all you need. JMO

  7. #7

    Default

    It can be true but it really depends on your chamber.

    Small base dies squeezes the walls of the case down to what the factory specs them to. But the area most all 6.8 cases fail at eventually is the case neck. It splits. Now if people were annealing their cases so that the necks were not the failure point it is possible it woudl be an issue. But even with that the main issue that causes case failures is how far you set the shoulder back from what it is after being fired. This is one of the things that causes that hologram looking line about a 1/4 of the way up from the bottom of the body. Given this info and the way the AR works the main thing effecting you case life as far as hand loading goes is how much you set the shoulder back. This is what givens you your headspace. You should keep this amount at about .003 for everyday rounds and if you are going for slow shooting top accuracy loads (not combat or your protection rounds) you can go down to .001. Even at 0 you are still technically sizing the shoulder as when the body is squeezed on the sides the brass has to flow somewhere and that is into making the case actually longer unless there is something pushing on the case shoulder which it then flows into the neck hence why you have to trim your necks every so often.

    IMO I think the Hornady Head space tool kit is a mandatory item if you plan to be reloading. When used with a caliper another mandatory tool it will allow you to measure the distance fromthe case bottom to the datum line on the case shoulder. This will allow you to precisely set how much your die sets the shoulder back. As I said above most will do well with a .003 setback. This will give you top relaiblity with but still not make the case have to expand too much. The more you set the shoulder back the more the case has to stretch and then be sized back down. This back and forth motion work hardens the brass and causes it to fatigue and that leads to failures. If you keep your loads below the max (no swipes) and use no more than this amount of set back you should not see any reduced life in your cases by using SB dies. IN 90% of the cases your necks will split before anything else doing this.

  8. #8
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    Default

    Quote Originally Posted by EWP View Post
    In the SAMMI and SPC2 chambers you don't need small base dies, whats the point of sizing your brass smaller than it was when new.

    Now the makers of the DMR chamber reccomend SB dies, must be the way they ream their chambers(probably just a way to get more pressure and still extract without issues) I'm not sure.

    I do know I have a SAMMI 6.8 1/10 twist barrel and I use regular LEE (Hornady New Dem. dies on their way this week) FL dies and just make sure I'm properly sizing my brass with the correct head space and OAL to prevent overpressure which is what causes the case base to swell. After all the base of a cartridge being to larger to extract is clearly a sign of overpressure and these guys are just getting around the problem by undersizing their brass instead of realizing the real problem to begin with.

    Load correctly and regular FL dies are all you need. JMO
    Small base dies do not size smaller than new brass. New SSA brass is .415 dia. , small base dies size to .418 and FL dies to .420 most of the time, some a little less some a little more.
    The SAAMI and SPC II chamber is .422, semi autos really need .004 clearance to be reliable when hot and dirty so that means .418. The DMR-C chamber is .423 or .001 larger than the SAAMI or SPCII.
    we did it to make sure the chamber is not small even after chrome even though the barrels are electro polished to remove the same amount that the chrome will replace.

    Companies that are known to make benchrest dies like Redding and Forster usually make them larger for bolt action rifles to aid accuracy, those are the ones you need to be careful with as they may not resized the case enough. RCBS and Hornady usually size brass smaller.
    What you need to remember is all machined parts have a tolerance of plus or minus .001. some as much as .005. If you use a company that designs the die to .420 and then goes large to .421 you may have issues. So we say for RELIABILITY it is best to go with small base dies, it is just like insurance that they will size the cases small enough to work when hot and dirty.

    ETA Dude! We have to stop doing this
    Last edited by constructor; 07-28-2009 at 02:31 AM.
    SIX5 -6.5mm on a 6.8 case
    Nexgen the lightest 308 AR coming mid 2014
    http://www.msrhunt.com/

    The 6.8 is the #1 choice for hunting deer and hogs with an AR15

  9. #9
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    H, I thought it was .418 for the cartridge base and .422 chamber base.
    Capt. Malcolm Reynolds: [on the ship's intercom] This is the captain. We have a little problem with our entry sequence, so we may experience some slight turbulence and then - explode.

  10. #10
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    Quote Originally Posted by joshuades View Post
    H, I thought it was .418 for the cartridge base and .422 chamber base.
    OOPs you are correct, I will edit those. 12 hrs in the shop, 2 hrs on the phone it is 1am and I am a walking zombie
    6 hrs and we do it all over again, what a life
    SIX5 -6.5mm on a 6.8 case
    Nexgen the lightest 308 AR coming mid 2014
    http://www.msrhunt.com/

    The 6.8 is the #1 choice for hunting deer and hogs with an AR15


 

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