Hints, Tips, and general information
Welcome to the Home of the 6.8 SPC - 68forums.com.
Page 1 of 3 123 LastLast
Results 1 to 10 of 26
  1. #1
    68Forums.com lifer
    Join Date
    Mar 2014
    Location
    still in Colorado for a while
    Posts
    5,272

    Default Hints, Tips, and general information

    Someone suggested a thread that covers general basic knowledge and troubleshooting of the AR chassis style rifle. I thought that I could start a thread and all of the long time members that have gained their knowledge through a hands on approach can add general knowledge for the beginners to reference.

    There are a lot of stickies here and great information spread all over this website, but sometimes its hard to find the information you are looking for through the search function.

    I think the best way is to post links to other stickies and websites that are filled with proven knowledge already, then we can add other specific things that might have been missed later.

    To start, I'll post a few links to helpful information on troubleshooting and things of that sort, I think some basic build knowledge would be helpful, maybe torque specs for a first time builder would help and things of that nature. Lets try to limit this to just facts and keep opinions out and maybe this thread can eventually become a sticky for all to reference.
    Last edited by Texas Hog Man; 07-07-2015 at 12:14 PM.

    LUCK
    is the residue leftover when you subtract chance from preparation.



    Mil-Spec means that it meets the lowest specifications that the military will accept. Do you want mil-spec parts?

  2. #2
    68Forums.com lifer
    Join Date
    Mar 2014
    Location
    still in Colorado for a while
    Posts
    5,272

    Default Hints and tips from AR15Performance.com

    SHORT STROKING PROBLEMS- build tips
    First things first- THE BUILD.
    When building seal the gas tube into the gas block(permatex gasket sealer or blue loctite will work). Make sure the gas tube is right side up and pinned properly. Remove the rear set screw of the gas block. Look down through the hole and make sure the gas tube is not obstructing the port in the top of the gas block. If it is drill it out, most will allow a 9/64" bit without damaging the threads at the set screw. When installing the gas block on the barrel use the same sealer to cut down on gas leaks. Place the rear set screw hole over the dimple in the barrel. Tighten the front then install the rear set screw and tighten it. Careful with the loctite the screws are very small and allen wrenches strip easily.

    Continue the build. When finished from the rear run a patch with solvent on it through the bore to remove excess oil and any dirt or grit that may have accumulated in the bore during transit and building. Run a dry patch through to remove any excess solvent or oil. Next clean the chamber AFTER cleaning the bore to remove any junk that was splattered into it when cleaning the bore. A 28ga bore mop spun by a drill works well. You can use JB or Iosso bore paste but make sure to clean all of the grit out or the cases may stick.
    ETA- The Melonite treated chamber may get sticky when heated up the first time. You can clean the chamber with a good solvent or polish lightly but do not try to remove the black surface or refinish the chamber.

    Oil the bolt tail and rings, drop of oil in the hole on the side of the bolt oils the ejector pin. Install in the carrier with the extractor on the right side looking from the rear. Work it back and forth in the carrier a few times. Oil the rails on the carrier.

    With a mag in the rifle and no ammo in the mag, pull the charge handle to the rear. Does it lock back by hand?
    If not check the follower in the mag to see if it will push the bolt catch up. There have been problems with the "BAD" ambi levers. If the bolt and carrier do not travel rearward enough the buffer or spring could be too long or the screw in the stock could be preventing the buffer from traveling back far enough. Is anything binding when you pull the carrier back and forth by hand? I found a carrier key installed with one side up on the rail of the carrier from the factory.


    TESTING- place 1 factory round in the mag, chamber and fire it while holding the stock firm to your shoulder. Does the bolt lock back? If not it is short stroking.
    When first testing newly built uppers and rifles always use factory ammo, Hornady 110-120gr. We use 120gr Hornady loads to set the gas port sizes with a standard carbine buffer and spring.
    If the rifle shorts strokes when shooting factory ammo start checking things on the rifle. If it locks back on factory ammo but does not with the handloads then there is a problem with the handloads.



    Short stroking

    Be sure the rear set screw of the gas block is in the CENTER of the dimple in the barrel, that is why the dimple is there.
    Short stroking could be caused by low powered ammo such as Remington when talking about the 6.8, in the 6.8 it is also common to see short stroking with light bullets 80-90 gr and fast powders using light published loads since many in reloading manuals produce 45-50000 psi. With the 6.8 and the fast rifle powders it burns it is best not to use a H2, H3 or hyd. buffer or aftermarket springs. IF you want to use heavy buffers or springs you will need to drill out the port in the barrel to function with the heavier/stronger parts.

    Keep everything lubed up well for the first 200 rounds but, DO NOT put a heavy coat of oil in the chamber or barrel, always run a dry patch through to remove excess oil.

    Port sizes for 6.8. If you are able remove the gas block and look at the soot ring(soot left on the barrel by the large hole of the gas block)
    It should be completely around the gas port in the barrel. if it is not make witness marks with a sharpie to the rear of the port and align the gas block with it. While you have the gas block off check to see if the gas port in the barrel is clear, sometimes when they are drilled a small flap of metal is left hanging and when the first bullet passes it shoves it back into the port. On Mid length 6.8 systems using a car stock and buffer the port should be .076"-.078"(5/64) in diameter, rifle should be .093-.096. You can slide a 5/64" drill bit in a mid length to check and 3/32" in a rifle length to check. If you are building using an A2 rifle stock and buffer you will need to open the port up apx .004". Some new light bullet loads are even slower than before, those and Remington need a larger port to function. You can drill them out .004-.006" larger just be careful not to ding the barrel on the far side of the bore. IMO you should not drill ports or do anything else that is not reversible as a first attempt as finding a cure
    . If you have an adjustable gas block drilling the port out a little larger isn't a big problem, just adjust it back down to obtain a 3-4 Oclock ejection.


    If you are using handloads be sure your size die is squeezing the base down to .417-.420. Most chambers are .422 in dia at the base, some dies size to .422 and a semi-auto needs at least .002 clearance to chamber and needs .004" to be reliable when hot and dirty.

    If the rifle in question is older the gas tube could be clogged, remove the gas block and tube assembly from the rifle and try spraying brake cleaner through the tube to remove powder residue. Be sure the gas tube is right side up.

    Make sure the gap in the gas rings on the bolt do not line up.
    .078=5/64
    .082"=#45 wire size bit
    .086=#44
    .093=3/32
    .096=#41

    The chamber hardness will prevent anyone from removing any machining marks with a bore paste. Bore paste will remove the black and shine or make the surfaces sllicker but anything short of sandpaper run at 2000rpms for a few minutes will not remove any machining marks or grooves.

    To test accuracy- Load 28.6gr AA2200 behind the Hornady 110gr HPBT to 2.26" then see below.
    .................

    LUCK
    is the residue leftover when you subtract chance from preparation.



    Mil-Spec means that it meets the lowest specifications that the military will accept. Do you want mil-spec parts?

  3. #3
    68Forums.com lifer
    Join Date
    Mar 2014
    Location
    still in Colorado for a while
    Posts
    5,272

    Default chamber gauges explained

    refer to this thread to see info on chamber gauges : http://68forums.com/forums/showthrea...ield-explained

    LUCK
    is the residue leftover when you subtract chance from preparation.



    Mil-Spec means that it meets the lowest specifications that the military will accept. Do you want mil-spec parts?

  4. Remove Advertisements
    68Forums.com
    Advertisements
     

  5. #4
    68Forums.com lifer
    Join Date
    Mar 2014
    Location
    still in Colorado for a while
    Posts
    5,272

    Default where to Zero my scope

    Why a 200 yard zero.
    Why a 200 yard zero for hunting with the 6.8

    As most know, we specialize in the 6.8 SPC II at Ironworks Tactical. It is an excellent round for hunting in a lightweight profile rifle such as a MSR/AR15. I often get the question asked, “What range do you zero your rifle at”? I zero at 200 yards, which brings up another question, “why”? Like many people I do like to understand why it is I am doing something, not just do it because someone told me to.

    The 200 yard zero for the 6.8 is not because of the 50/200 yard zero that many people use in the 5.56 as this doesn’t always work out this way in the 6.8 or even the 5.56 with varying loads. For instance my load (all my hunting loads are hand loads) using the 120gr SST by Hornady ammo is almost 1” high at 50 and dead on at 200. Both my Barnes bullet loads do in fact work with the 50/200 yard zero but there is so much more to why I do this zero than just that simplicity.

    A precision long range shooter knows their DOPE (data of previous engagements) for their rifle and they use hold overs for varying distances. As a hunter we don’t always have that time or proper training, also many of us aren’t taking the kind of range shots that these professional sharp shooters are doing requiring the adjustments. So I simplify this by using my 200 yard zero method.

    When I zero my 6.8 at 200 yards, I know that the total max deviation of the arc of my bullet (120 SST for this scenario, the other bullets do similar but slightly different deviations) is 2.4 inches high then it hits dead on at 200 and at 250 yards it is 4 inches low. That is a pretty heavy arc which is why I chose this bullet over the 95TTSX or 85TSX which are much flatter shooting. My total deviation from 0 to 250 yards is 6.4 inches. The average animal (deer, pig) that I hunt have roughly an 18 inches chest profile. So if I hold dead center with my cross hairs I still hit a kill shot in the heart lung region without worrying about holds. At 300 yards, which is my max range I am comfortable shooting with my 6.8 is an automatic hold of crosshairs on the ridge of the back because the drop is 10 inches. This still gives me a good 8 inches or possibly more below point of impact so nearly a center shot into the chest.

    My 95TTSX load is literally 2.5 high, 0, 2.5 inches low at 250. That’s a total deviation of 5 inches on an 18” target. It is simple and works leaving out the need to try to Kentucky windaging it. All you need is a known trajectory. The best way to accomplish your known trajectory is to zero at 200, and then get some target shooting/practice in at 50, 100, 150, 250, and 300 to create a DOPE book. Do not making any adjustments to your optic simply hold dead center and measure the deviation of the group from center. Of course a ballistic calculator will give you the info as well but nothing is as accurate as shooting the known distances.

    Written by Brett C
    Ironworks Tactical

    LUCK
    is the residue leftover when you subtract chance from preparation.



    Mil-Spec means that it meets the lowest specifications that the military will accept. Do you want mil-spec parts?

  6. #5
    68Forums.com lifer
    Join Date
    Mar 2014
    Location
    still in Colorado for a while
    Posts
    5,272

    Default over gassing & shoting tips

    Over-gassing barrels will kill accuracy
    Before drilling out gas ports check everything else. The number 1 most common mistake made by builders is not aligning the gas block over the port in the barrel. With AR15Performance barrels it is simple...install the rear set screw of the gas block in the dimple. You don't need to measure from the shelf to the back of the block like many posts here say, some have a .265" back space and some have a .298" back space. It is a simple thing to align, stick the rear set screw of the gas block in the dimple on the bottom of the barrel.
    If a barrel is over-gassed the carrier will start moving while the bullet is still in the bore. The movement of the carrier will shake the rifle and destroy accuracy.
    If you find yourself with an over gassed barrel install an adjustable gas block and tune it.
    TBC

    Shooting tips. Lots of ways to shoot, lots of opinions. ARs are not bolt guns, sometimes it takes shooting a different way.
    DO NOT shoot off of the hood or bed of your truck or car, use a good rest and rear bag.
    Pull the stock firmly into your shoulder.
    Squeeze the trigger and hold it back(follow through)
    Higher power ARs with short barrels may need some front end control to obtain the best accuracy. Try placing your left hand out on the forward end of the handguard pulling into your shoulder and down onto the rest. (written By AR15performance)

    LUCK
    is the residue leftover when you subtract chance from preparation.



    Mil-Spec means that it meets the lowest specifications that the military will accept. Do you want mil-spec parts?

  7. #6
    68Forums.com lifer
    Join Date
    Mar 2014
    Location
    still in Colorado for a while
    Posts
    5,272

    Default other hints and tips from ar15performance.com

    LOTS of good info on this page from H : http://www.ar15performance.com/tips .... and this page to http://www.ar15performance.com/6_8___six5_misc_info

    LUCK
    is the residue leftover when you subtract chance from preparation.



    Mil-Spec means that it meets the lowest specifications that the military will accept. Do you want mil-spec parts?

  8. #7
    68Forums.com lifer
    Join Date
    Mar 2014
    Location
    still in Colorado for a while
    Posts
    5,272

    Default Torque Specs

    Please correct my numbers or information if they are wrong

    Barrel Nut: 30-80 ft pounds.... the proper way to install a barrel is to use a receiver vice block, grease the threads on the receiver with Aeroshell 33MS or other similar grease, tighten the nut and loosen it 3 times or more to make sure the threads are seated. It is also recommended but not always necessary to lap/square the receiver before barrel installation to make sure the barrel is square to the receiver. The barrel can be bedded to the receiver using Blue loc-tite on the barrel extension to receiver union (DO NOT use loc-tite on the barrel nut threads). Tighten the nut to 30-80 ft. pounds making sure to index the cut-outs on the barrel nut to receiver (for proper gas tube alignment) if necessary. If you buy an aftermarket free float tube (handguard) make sure to refer ONLY to their installation instructions for torque specs as many use different specs than the MILSPEC nut does)

    Muzzle device: (compensator or flash hider)... the muzzle device really doesn't need much torque to keep it on, once again the proper way to install or remove the muzzle device is to use a barrel vice (or wood blocks) to hold the barrel from rotating, install your muzzle device of choice (and crush washer or peel washer if necessary) and torque to manufacture specs or 20 ft. pounds. Some aftermarket muzzle devices used for suppressor quick connect may use rockset or other "cementing" to keep from rotating...make sure you follow the manufactures recommendations

    Receiver extension tube (buffer tube) castle nut: This one seems to get a little fuzzy, but if I remember correctly the torque spec is around 35 ft. pounds. It is recommended to NOT use loc-tite on the castle nut, but to properly stake it once torqued to spec.

    If someone can add the proper torque specs for scope mount rings and bases that would be helpful, as I always just guess on those, I'm pretty sure its only around 15-25 INCH pounds though
    Last edited by Texas Hog Man; 07-07-2015 at 01:17 PM.

    LUCK
    is the residue leftover when you subtract chance from preparation.



    Mil-Spec means that it meets the lowest specifications that the military will accept. Do you want mil-spec parts?

  9. #8
    Moderator
    Join Date
    Dec 2011
    Location
    NE Georgia
    Posts
    8,100

    Default

    I would add a few tips: When installing a muzzle device, especially when a crush washer is needed, clamp the barrel in a barrel vice or make a couple hardwood blocks with a hole drilled through the center for a makeshift barrel vice. Don't try to crush a crush washer with the upper supported in a holding block. We have seen several sheered alignment pins and even cracked uppers from this. Lock down the barrel and not the receiver. Second, always start with a standard buffer and spring. Some barrels are overgassed and a heavier buffer may solve the problem but until you try out the standard weight you will not know. If you go directly to a heavy buffer or buffer/spring combo, you may be causing problems instead of solving them.
    01 FFL, NRA, GOA, NAGR
    "This nation will remain the land of the free only so long as it is the home of the brave."
    ~Elmer Davis

  10. #9
    68Forums.com lifer
    Join Date
    Mar 2014
    Location
    still in Colorado for a while
    Posts
    5,272

    Default

    Quote Originally Posted by Woodstock View Post
    always start with a standard buffer and spring. Some barrels are overgassed and a heavier buffer may solve the problem but until you try out the standard weight you will not know. If you go directly to a heavy buffer or buffer/spring combo, you may be causing problems instead of solving them .
    Beat me to that one.....always start with stock equipment and check for proper function with FACTORY ammo (not reloads) ......can someone add the "ejection pattern" picture for people to reference...I can't remember what thread its in

    LUCK
    is the residue leftover when you subtract chance from preparation.



    Mil-Spec means that it meets the lowest specifications that the military will accept. Do you want mil-spec parts?

  11. #10
    68Forums.com lifer
    Join Date
    Dec 2012
    Location
    North Georgia
    Posts
    1,501
    Last edited by Rascally; 07-07-2015 at 05:58 PM. Reason: unwanted space insertion.
    "In every generation there are those who want to rule well - but they mean to rule. They promise to be good masters - but they mean to be masters." — Daniel Webster


 

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •