Torque the Gas Block Screws?

Discussion in 'Mini-14 Forum' started by KMO, Aug 2, 2010.

  1. KMO

    KMO New Member

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    When I first heard about tightening the 4 gas block screws to a specific torque setting, I couldn't think of a logical reason for doing so. My previous expereince with torque settings was limited to automotive projects, and I didn't understand the application for firearms. A couple of metal-worker friends explained the technical benefits to me, so I purchased a torque screwdriver from Ridge Equipment Co. It was a used Sturtevant Richmont Roto-Torq torque screwdriver, & has a 2 to 36 in./lbs. torque range with a 1/4" hex drive. I set it at 30 lbs. & tightened the 4 screws in a rotating pattern to keep the air gap consistent on the gas block halves. I did this concurrently with the reinstall of my trigger assembly received back from masterPsmith. I took this 196-series Mini-14 out to the range & set up at 80 yards (space limitations). My first three shots hit bullseye (on the crosshairs) and were overlapping. The next two were within 1/2 inch of the first three. This rifle was previously the least accurate of the three Mini-14's I currently own. It was OK before, but it's unbelievable now. Setting the torque was an important part of this improvement. Other keys to accurizing this Mini:
    - Mo-Rod
    - .040 ID gas port bushing
    - trigger job, as mentioned
    - Wolff extra power recoil spring
     
    Last edited: Aug 4, 2010
  2. masterPsmith

    masterPsmith New Member

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    Most people would be surprised what a Mini can do when properly set-up. Great job.

    Jim....
     

  3. M14sRock

    M14sRock New Member

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    It never ceases to amaze me how such a simple thing as screw torque can have such a dramatic effect. Most gun owners never even think about it.

    Mini's rock.
     
  4. livesnearcostco

    livesnearcostco New Member

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    Could someone explain to me why even gas block torque makes the Mini more accurate? Does uneven torque cause the barrel to whiplash more during shooting? Does a hot barrel just flex more before the bullet leaves, or does it tend to statically point in one particular direction when hot due to uneven pressure from the gas block? Does a Mo-Rod/Accustrut/HarBar work by damping oscillation? (The fact that the target Mini has an adjustable weight suggests it's barrel harmonics and not static heat warping, but maybe both are going on?)

    I am fairly new to my 583 series Mini-14 and enjoy shooting it. Group sizes at 100 yards with a scope and shooting off of sandbags ranges from 2" to 5" with cheap ammo, depending on ammo and how hot the barrel is. Sometimes I get a nice tight 1.5" group with a flyer 3" away. This is with the Wilson combat buffers front/rear and a mild DIY trigger job that reduced trigger pull from 6.5 lbs to 5.5 lbs.

    In my last outing I switched from the stock gas bushing to 0.050" so the brass doesn't fly as far but that didn't seem to improve accuracy much. I tried to tighten the gas block screws evenly but one was stiffer than the others so hard to know if I got the torque even. Plus the aftermarket bushings were slightly longer than the original one (about 7mm vs. 6.7mm), so it's possible the gas block was not sitting evenly on the barrel. With this setup, it seems that as the barrel heats up, the shots move up and to the right, whereas with the original setup the shots just moved up.

    I've now put in the 0.045" bushing and turned it down to be a hair shorter than the original (about 6.6mm), and also the stronger Wolff recoil spring, but haven't shot it that way yet.
     
  5. COSteve

    COSteve New Member

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    Uneven torque on the gas block means that you have uneven pressure and stress on the barrel which can affect harmonics and 'steer' the barrel while it heats. Even clamping of the gas block reduces induced stress.

    As to your group sizes, the next thing I would do is get decent ammo. The cheap commie junk and cheap imported ammo isn't made to the same consistent standards as the more expensive ammo so expecting good accuracy out of poor ammo is fruitless.

    Would you put cheapo regular gas in your race car and expect it to run as well as premium, high octane gas?
     
  6. livesnearcostco

    livesnearcostco New Member

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    Steve, thanks for the tips. I did try re-torquing the gas block screws more evenly and went back out with some Winchester Matchking 69-grain HPBT ammo [not Hornaday .223 match ammo (either 67 or 75 grain, have to check the box)]. It did seem more accurate but I was shooting at 50 yards instead of 100 and the 2nd day it was less windy and not raining. :D

    Let's say the cheap Federal ammo was 3-5" groups at 100 yards (rain, gusty winds) while the Hornaday match gave 0.75-1.5" groups at 50 yards (no rain, light breezes), which should translate to 1.5-3" groups at 100 yards. But I also figured out the 2nd day some of my trigger pulls are moving the gun around a bit even with front on sandbags. Maybe I need to try it in a Lead Sled to eliminate the human variability.

    I want to find out how accurate my Mini can be with the good ammo then mostly go back to shooting the cheap ammo for fun. Here's my rough ammo cost breakdown:
    Nice "match" ammo: $1.00-$1.50/round
    Regular "cheap" ammo: $0.50/round
    Walmart cheap Federal/Perfecta ammo: $0.37/round
    Bulk reloaded ammo: $0.30/round

    Edit: BTW by "cheap" I mean any .223 or 5.56 ammo I can buy for $0.50/round or less. It's usually Winchester NATO 5.56, PMC, Fiocci, Federal bulk pack .223, American Eagle, Aguila (made in Mexico), or Perfecta (made in Spain?). Someday I'll learn to reload my own ammo.

    Looking at my 50-yard targets with a ruler, I shot 3 to sight-in (after removing and replacing the scope) then 4 3-shot groups resting the rifle on sandbags. The group sizes were decreasing, probably because I was getting better at pulling the trigger without moving the POI.
    • Group 1: 1 7/8"
    • Group 2: 1 1/2"
    • Group 3: 1"
    • Group 4: 11/16" (just under 3/4")

    If I can replicate the accuracy of the last 2 groups at 100 yards, that should be 2" or 1.25" groups, and would make me fairly happy.
     
    Last edited: Mar 9, 2016
  7. Misfire51

    Misfire51 New Member

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    By cheap ammo we are talking about the commie stuff , Tula , wolf poly coated, and other combloc ammo. I consider good ammo to be PMC , Wold Gold , Fiocci , Remington 223 , Aguila , Perfecta, any of the ammo's that are brass cased and boxer primmed . My 583 tactical doe's not like American Eagle in the black box, It will eat all the 5.56 ammo in different grains . The ammo that my gun shoots the best is the Wolf gold .223 brass cased and boxer primed so that is the ammo that I stock pile the most . You just have to try different ammo to find which ammo shoots the best from your gun. Every Mini is different and has different likes and dislikes. It just takes alittle time.
     
  8. livesnearcostco

    livesnearcostco New Member

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    Got it I haven't tried any Berdan-primer, steel cased, or Russian-made ammo yet. And it turns out my "match" ammo was Winchester .223 match with 69-grain Matchking HPBT bullets for $1.50/round, not Hornaday. The Hornaday match ammo (at $1.00/round) is what I expect to buy for my next accuracy test and I got mixed up.

    By American Eagle I did mean the stuff in the black box. Haven't seen the Wolf gold locally but I haven't checked very much LGS's.
     
    Last edited: Mar 9, 2016
  9. Misfire51

    Misfire51 New Member

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    Apparently your gun is new . Personally I would break it in on some inexpensive brass cased boxer primed ammo , say 55 grn before I started dumping expensive match grade ammo thru it. I usually put 2 or 3 hundred rns down the pipe to make sure the gun functions properly before I dump a bunch of cash into any gun. But hay , thats just me.
     
  10. JTJ

    JTJ Well-Known Member Supporter

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    If you want to shoot the cheap Russian ammo get the Wolf 62 grain HP. Usually can be found for .25 a round. It is copper and lead not bimetal like the 55 grain crap that is hard on barrels. Also legal for hunting.
     
  11. livesnearcostco

    livesnearcostco New Member

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    Thanks guys. Gun is 2 months new but had already had about 300 rounds through it, probably about 6 visits to the range and average 50 rounds per visit. I have not seen the Wolf 62 grain HP yet, but I wasn't looking very hard. Will see if LGS or Bass Pro shop has it. Don't hunt yet but maybe someday.
     
  12. COSteve

    COSteve New Member

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    Unfortunately, while US Mil XM193, 55grn ammo isn't cheaply made, it is not as accurate as premium commercial ammo. The Army's design requirements don't require high accuracy just consistent manufacture and high velocities. It's usually better than the cheap commie ammo but not as accurate as it could be.

    The Mil XM855, 62grn green tip ammo is even less accurate as it has a steel penetrator in the middle. Because manufacturing variances don't absolutely place the dynamic center of the steel penetrator in the dynamic center of the bullet, it wobbles in flight which lowers accuracy so it makes a poor round for shooting groups even though it's a quality military round.
     
  13. livesnearcostco

    livesnearcostco New Member

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    Steve, thanks! I hadn't thought about NATO ammo in that way but what you said makes sense. I put the regular recoil spring back in, put on a TrueShot Technologies strut, and lightened the trigger pull to between 4.5-5.0 lbs. (Trigger pull was originally about 6.5 lbs, then 5.5 lbs.) Hope to take it to the range soon.

    Edit: got a short session at the range today and accuracy seems to be better. The gun still was stringing up and to the right while warming up but the groups seemed smaller. At 100 yards my worst groups were 3.5" and my best groups were 2". Previously I think my groups ranged from 3" to 5", so maybe the barrel strut reduced group sizes by 30% (but I also changed recoil spring back to stock).

    Only fired about 70 rounds today. Was lots of fun. The PMC seemed more accurate than the American Eagle or Freedom reman. I brought some Hornaday match ammo but didn't have time to test it. My trigger technique is still rudimentary and might be adding to the group sizes. Need to borrow a Lead Sled to find out, or maybe rest the rear of the stock on sandbags too.

    583-series Mini-14
    100 yards, 5-shot groups
    Simmons 8-point 3-9x40 scope set at 7x
    Front of stock resting on sandbags
    Sunny, about 70F, very little wind
    Trueshot Technologies 5.5" barrel strut
    0.045" gas bushing; original recoil spring; front & rear Wilson 1911 buffers
    Trigger pull weight 4.5 to 5 lbs (DIY trigger job)
    Ammo: Freedom Munitions reman; American Eagle black/white box; PMC Xtac -- all 55 grain
     
    Last edited: Mar 19, 2016