6.8 SPC sub folder

Discussion in 'AR-15 Discussion' started by Darth AkSarBen, Apr 2, 2010.

  1. Darth AkSarBen

    Darth AkSarBen Member

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    What about a sub folder in the AR-15 concerning 6.8 SPC II?
    Folks that build and shoot the AR-15 in 6.8 SPC aka 6.8 x 43 would be able to post questions and answers there.
     
  2. Jo da Plumbr

    Jo da Plumbr New Member

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    Not sure there are that many 6.8 guys here.

    I was thinking of a 6.8 build then took a look at ammo costs.:eek:

    May just do a second 223
     

  3. Darth AkSarBen

    Darth AkSarBen Member

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    I reload, so it is a bit cheaper to feed than the .308 / 7.62 NATO semi auto I had. It has 80% of the enrgy of the 7.62 NATO and only half the recoil as well. Great deer and Hog rifle!
    [​IMG]

    I built the lower and some of the upper myself at home. I also have a .223 that is completely home built both upper and lower. Every part, barrel, pin, etc I put in it myself.
     
    Last edited: Apr 2, 2010
  4. NavArch

    NavArch New Member

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    I do not yet work in 6.8 SPC; I am trying to do all of my homework before putting down the $$$. As part of that homework, I gathered the data in the attached table. (my apologies for not noting the source document) These numbers would indicate that some serious velocity drops occur when going to a barrel of less than 16 inches. Since kinetic energy is a function of the square of velocity, that would seem to be a problem. Take a look at the graph of this effect; muzzle energy drops from 1560 at 16 in. to less than 1400 ft-lbs at 12.5 in.

    You say you re-load. 6.8 SPC brass comes in either small rifle primer or large rifle primer varieties. Which do you use, and do you know which Silver State Armory uses?

    Thanks.
     

    Attached Files:

  5. Darth AkSarBen

    Darth AkSarBen Member

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    Silver State Arms makes brass in both LR and SR primers. I do believe that all of their loaded ammo is built using Small Rifle primers. Hornady also make brass and loaded ammunition in SR primers as well.

    Your chart is a mite bit conservative.
    I have personally shot 100 grain bullets at 2998 fps that I have handloaded and no pressure signs. I have recently shot some 110 grain Sierra Spitzers at 2780 average fps muzzle velocity, and with accuracy at around 3/4 " at 100 yards.

    Their are bullets in the 85 range that go well over 3100 fps. This would make a bit different kinetic energy.

    You might have gotten that chart from frfrogpad website with the following info:


    There are currently 4 known military variations in use or in test: according to some sources a "ball" projectile of open tip match construction with either 110 gr or 115 gr projectile, a tracer, a 97 gr AP round, and supposedly a blank round. The 97 gr AP round utilizes a solid copper bullet with bands cut around the outside and a hardened steel or tungsten penetrator inserted into the bullet. No designations are known at this time. The cartridge has performed well in barrels down to 10" and shorter. Typical velocities for the SSA 115 gr commercial load are given below.

    Barrel Velocity Change
    from 16"
    20”
    2561
    +36

    16”
    2525
    --

    12.5”
    2384
    -141

    10”
    2265
    -260

    7.5”
    2035
    -490



    --------------------------------------------------------------------------------
    Sorty that it scattered it around. These were from early "commercial" loads and they had to keep down the pressures as there were still rifles out there with the earlier and WRONG SAAMI chamber with the tight throat leade cut in the neck of the chamber. Recent changes in reamer design made it possible to boost the powder and performance of the 6.8 SPC with a newer designation of 6.8 X 43 or 6.8 SPC II chamber. Relaxed rifling in 1 in 10.5, 1in 11, 1 in 11.12, 1 in 12 and 1 in13 also contributed to lower chamber pressures to drive the bullet faster. 1:10, 1:11 and 1:12 are somewhat more common, but the others are a bit harder to find. Also the 1:13 does not do as well at stabilizing the longer 130 gr bullets as a 1:12 twist does.

    Here is a link to the frog pad's info: The 6

    This piece by HTR (Hi Tech Rancher) a very avid 6.8 SPC II shooter gives a lot of insight on what has been happening to the cartridge of recent. Today's State of the Art in 6.8 X 43 mm SPC - Sniper's Hide Forums

    One of the greatest reasons the 6.8 SPC shines is that when shooting in the shorter barrel M4 carbine, it does not give up as much energy as the 5.56 does. this is because of the cartridge and bullet being larger in diameter and the ratio makes it so that even in a 16" barrel it is near it's upper velocity and going to long, and bulkier to carry barrels of 20 -24" does not give you that much extra velocity.
     
  6. NavArch

    NavArch New Member

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    Thank you very much for the additional data and links. The numbers I posted were 5-shot averages of the SSA 2nd Gen 115 SMK OTM w/ cannelure (as labeled by the poster). Perhaps those were results from earlier versions of the round.