Does gas block settings on AR rifles effect Stand Deviation?

Discussion in 'Reloading Tips & Tricks' started by mdewitt71, Feb 24, 2018.

  1. Went out yesterday with a new 20" AR build and 5 different loads.
    3 Factory ammo loads and 2 hand loads and I can tell you none of them had good standard deviations numbers.....
    Lowest factory SD was 21.43 and this was IMI HPBT Match the other was 35 and 37.
    My hand loads (which usually run me 8-12 SD in other rifles before) was giving my 26 for one, 29 for the other.

    Now this is a brand new build, first time out...... It has an adjustable gas block.
    I was also shooting a LabRadar that isnt suppose to be affected by the weather even though it was raining.
    Just wondering if it might of been the rifle versus the loads?
  2. CRE10

    CRE10 No to Drugs Yes to Hugs

    Nov 18, 2013
    In a barn
    Did you notice where it was kicking the brass?
    WBF likes this.

  3. I did think of that but, I was using a brass catcher at the time.....
    I guess I will have to go out again and try it after chores are done and see how far brass is getting thrown.
  4. Wibb

    Wibb Senior Member

    Nov 20, 2007
    Seems like there may be more variables here. What is the barrel twist rate? What bullets are you shooting? Is this all brass you know the origin? I'm assuming this is optics on top? Everything torqued, tightened, no cant? As I'm sure you know there are lots of things that go into dialing in loads and the gun itself. Not all ammo agrees with all barrels. Hopefully that's not the issue.
  5. Why would an optic being torqued or not have anything to do with standard Deviation?

    I am chalking the first firing up to being a brand new build and new barrel/ gas block..... I have had this rifle out three more times and the numbers are dropping the more I get rounds down the barrel.
    Bob58 likes this.
  6. Wibb

    Wibb Senior Member

    Nov 20, 2007
    It wouldn't. I was reading this all wrong. You're talking about SD of your velocities, I was somehow thinking you were talking about your groups. That's what I get for surfing too late

    Still could be barrel and bullet related, but you'll be splitting hairs soon. When I'm dialing in that close I don't use my auto measure. I manually drop them and weigh every 5 loads, trickle as needed.

    Sorry for the confusion
  7. I didn't drop any powders... I have two 1500 Charge Masters and read out on GemPro scales to the .005 of a grain.
    My 22" bolt action .223 shot these same loads with a SD of 5 FPS in a 15 shot string.
    I think once the barrel and gas system get broke in on this new build, it will tighten up.
  8. Wibb

    Wibb Senior Member

    Nov 20, 2007
    You ever figure out what was going on with this? Did the barrel break in and tighten up or did the inconsistency continue?
  9. Yes, I just took the rifle out on it's 3rd range trip a few days ago and the SD numbers did tighten up from the very first trip.
    My Adjustable gas block was wide open too.... I was seeing ALOT of carbon and gunk in my chamber so I closed it off a bit.
    Hopefully will get it out again this weekend.
  10. Matt_in_KC

    Matt_in_KC Captain Obvious

    Jan 12, 2015
    Kansas City
    Just curious, was there anyone else shooting next to you on your first range trip? I have read that the Doppler signal can be affected by other projectiles down range when you are testing.
  11. No first range trip I was solo the whole day....
    IF people are having issues getting other shooters readings in their LabRadar they are setting it up wrong; for sure.
    I can tell you for a fact last Friday, I shot with 5 other gents at the same time 3 one one side and 2 on the other and my LabRadar was only picking mine up each and every shot.
    Matt_in_KC likes this.