6.8 SPC accuracy question

Discussion in 'AR15/10 Rifles' started by Lyons7STW, Mar 22, 2013.

  1. Lyons7STW

    Lyons7STW Well-Known Member

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    I have a stag arms 6.8 SPC II 16" upper. Free floated barrel. DPMS lower with Timmney trigger.
    I have been shooting SSA 85 grain frangible and a 90 grain Speer TNT hand load. Both these shoot fairly well.

    The kicker is my cold bore shot is exceptionally good. But subsequent shots seem to move an 1.5"-2". And start a whole new group.

    I can only assume there is some variable in the bolt lockup between when I drop it manually and when it runs it's own cycle.

    Anyone have experience in this area?
     
  2. Lyons7STW

    Lyons7STW Well-Known Member

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    It if I could could fix this little issue without a new barrel/ matched bolt combo that would be great. It serves its purpose as you can see but more accurate is the goal
     

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  3. J E Custom

    J E Custom Well-Known Member

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    I have several rifles that don,t like the first clean barrel shot so I shoot a fowler, dry patch and they
    group well.(Some loads are sensitive to a clean oiled barrel) Also some bullets react differently to
    bore conditions. Try setting your zero after shooting one round and if that doesent work try a 110
    or 115 grain bullet with more body to engage the rifling.

    J E CUSTOM
     
  4. Lyons7STW

    Lyons7STW Well-Known Member

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    I probably did no phrase that correctly. I have tried the heavier bullets and was disappointed. The two listed are the best so far.

    I shoot a fouler first even in my bolt guns. It can make a big difference. The issue appears to be between first shot from a dropped bolt and cycled rounds. I am not cleaning in between.

    Thank you for the response
     
  5. J E Custom

    J E Custom Well-Known Member

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    Stranger things have happened in the AR platform.

    If this appears to be the problem, It sounds like you need to size the brass smaller. (Factory ammo for
    autos is small base sized.) with more head space and a smaller body for ease of chambering in a tight
    chamber. If your dies are adjuster all the way down you can grind .002 to .003 thousandths off the bottom of the sizing die or buy a small base sizing die. Hornadys New dimension dies will also do this.

    At one time all AR15/M16s had a forward assist button to help seat the bolt in battery, if yours doesn't
    you will have to size the brass a little more.

    Hope this helps.

    J E CUSTOM
     
  6. Lyons7STW

    Lyons7STW Well-Known Member

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    My dies are small base and I had considered this so I checked and factory ammo produced the same result. I think I will take it to a good smith and see what steps can be taken to true up the receiver face, barrel, and locking lugs. Then insure barrel nut is properly torqued.

    I am not as well versed on autos so I had to research and it appears there are some some steps to take and improve this.


    Does this sound reasonable?
     
  7. ICANHITHIMMAN

    ICANHITHIMMAN Well-Known Member

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    This conversation is a bit silly, how much deviation are we talking about at 100m, how fast are you shooting and what is your barrel profile? Also consider the magazine your using it may be a factor, I don't believe bolt lock up it the issue.
     
  8. Lyons7STW

    Lyons7STW Well-Known Member

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    Muzzle vel. On factory loads is 2828 fps. Hand loads book indicates 2900 Barrel is older model 16" stag 1 in 10 twist standard Contour.
    We are talking 1.5" deviation at 100 yds.
     
  9. Lyons7STW

    Lyons7STW Well-Known Member

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    I am using C products mags. I would like to acquire some PRI mags but at the moment it appears I would have more luck finding a unicorn or jackelope. Why would the mag be a factor other than seating depth and that would not play into factory ammo.

    I talked to a local AR builder and he suggested a heavier buffer to smooth out the cycle.
     
  10. J E Custom

    J E Custom Well-Known Member

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  11. IDbound

    IDbound Well-Known Member

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    Thanks JE for your insights. While I am fortunate not to have the same issues as the OP with the same setup, I did learn some interesting points to look for if things to go awry.
     
  12. Firearrow

    Firearrow Well-Known Member

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    I have first and third gen PRI mags. Love the first gen as they have a smaller feed lip, but the third gens are good too. If you can find the first gen and just pay the price for them. I have only had 2 or 3 FTF on the third gen's in my ARP.

    Try Chris. Last I herd he has some coming.
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