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Thread: whats involved in making an ar-15 6.8spc??

  1. #1
    Boolit Master Oklahoma Rebel's Avatar
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    whats involved in making an ar-15 6.8spc??

    what parts and work are needed to change a 5.56 ar-15 to a 6.8 spc? do I need a whole new upper, or do I just need a new barrel, bolt, and magazine? is this something an amature can do? also, when building the original 5.56, after it iis assembled, what is involved, if anything, in headspacing it? I admit, I am not 100% sure what this process includes, I have just heard people talking about doing it. is it necessary in the ar-15, I typically hear about doing it in bolt/lever actions. thanks for putting up with the "dumb" questions! have a good'un!- Travis
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  2. #2
    Boolit Master Boolit_Head's Avatar
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    That is it barrel, bolt, and magazine to change over. From 5.56 to 6.8 the muzzel threads will change from 1/2 x 28 to 5/8 x 24 so you will need a new muzzle device too. Since you are asking about a amature doing it I assume you are not familliar with assembling a upper. It's easy enough to put the parts togeather but hit or miss if they will work well if you don't pay attention to some details. Might be best to get someone to help with it. It's not however a smith only function. Renting a go/no go gauge set would be a good check but most of the good quality barrels can usually be trusted.

    Might want to watch a few upper assembly videos on youtube?
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  3. #3
    Boolit Master Oklahoma Rebel's Avatar
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    I basically know how to assemble the upper, so that's ok, but never done it, I couldn't think of the go-no-go guage, but I was trying to ask if I needed to get one of those. do they measure the distance between the chamber and bolt to make sure it will lock over the cartridge rim? also, will gun shops rent out those gauges? basically, I am doing my first ar15 build, but only have book knowledge, not hands on experience, but I want to do it all myself, I am waiting on a easy jig gen 1 to get here, because I have a 80% forged aluminum lower. thanks a lot!
    An armed man in a citizen.
    An unarmed man is a subject.
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  4. #4
    Boolit Buddy
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    Bolt, Barrel, and magazine are the only parts you need if you are building the same configuration. For example, carbine length gas and standard wt barrel.

    Here is the question, are you planning on keeping the 5.56/.223 and going back and forth between it and the 6.8? If so, you need a complete upper. It isn't worth it to continually change out parts.

  5. #5
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    The correct way to do this is to have the correct gauges. You strip the bolt of both the ejector and extractor. We're talking that the bolt is out of the carrier. You don't need the barrel in the upper receiver to check the headspace. You check and see of the bolt will turn and lock the lugs up with the go gauge. You then try the no go gauge if the bolt turned and lock the lugs with the go gauge. Usually when you buy a barrel, they either come with a bolt and are headspaced, or you send your bolt in.

    For further assembly if your receiver is a flattop you don't have to have the receiver block. You can clamp your receiver in your vice providing the jaws are law enough (that is no puny little vice) and you have jaw damage protection such as lead, brass, or hard wood like oak. You grease up the threads on the receiver tenon and also on the face of the barrel flange (facing the muzzle). If your barrel is very tight trying to go into the receiver heat your receiver with a hair dryer on hot and the barrel will slip right in. I not only like the receiver clamped in the vice, but I also clamp the barrel too and this insures the barrel doesn't try to turn when tightening the barrel nut. You'll need a torque wrench and barrel nut wrench. You torque the barrel to 38 foot pounds, then back it off, torque it again to 38 foot pounds, and back it off again. The third time is the finally torque. This sets the threads. If your gas tube holes line up you are lucky on the first time. If they don't you keep torquing until you get the first set of holes to line up. You never back off to line up the holes. Once you get them lined up you are finished tightening the barrel nut and aligning the gas tube holes. Don't worry what the value of the final torque is to align the holes. Next install the gas block and remember the gas block does not go all the way up against the stepped shoulder as they misalignes the gas port holes bey .030 inch. Some barrels have a dimple on the bottom of the barrel directly across from the gas port hole and the gas block, even if it is the clamp type with have a hole you can see through to line up with that dimple. The blocks with the set screws the screw towards the rear is used to align everything. Make sure too that the gas block is straight up and down and that the gas tube is dead on 12 o'clock. If using the original AR15 front sight/gas block the same 12 o'clock applies to that and if you're going to use the original style handguards you have to install the metal that metal that front of the handguards anchor into before you install the gas block. That's where that .030 inch comes into play, that's the thickness of that metal anchor. So now you see why if you're not using original handguards why you don't have the gas block up against the stepped shoulder. Next oil up your bolt/carrier groups, install the charging handle and bolt/carrier and ease it forward into the barrel extension. It should enter without binding and lock up. If it doesn't something is not aligned meaning the barrel. Backing up some you can install the gas tube on the block before mounting the block or you can do it after it was installed. Check the bore for oil, grease, or other debri, clean it if necessary and you're ready to install the upper on the upper, install the free float tube forearm or the originals and you're ready to test fire. Don't forget that after you checked that headspace to reinstall the ejector and extractor.

    VZ

  6. #6
    Boolit Master Harter66's Avatar
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    There are 4 gas lengths available .
    Pistol , carbine , mid and rifle . 6.8 SPCII is available in all 4 . A barrel length isn't always related to a gas length . 16" is available in carbine and mid 18" is available carbine ,mid and rifle even 20" is available as a mid .
    Not all 6.8 barrels are 5/8-24 some are 1/2-20 .

    There are also heavy barrels available that have other than .750 gas block steps .

    Key description words like MilSpec and H-bar will help ensure you get .750 gas block step even if you don't get M4 profile with M203 cut .
    Like everything else you get what you pay for in AR barrels .
    There are light years between the bargain buy M4 and an ARP bbl . I just installed a 20" rifle gas 5R replacing a Mossy or Williams barrel and ... ..... .wow ....... Words don't really have a way to describe the difference in a short way .


    Go here for 90% of all AR questions to be answered quicky and clearly and for everything you ever wanted to know about the 6.8 SPC .
    http://68forums.com/forums/forum.php
    In the time of darkest defeat,our victory may be nearest. Wm. McKinley.

    I was young and stupid then I'm older now. Me 1992

    About that rally point, the soap and mail boxes fall on blind eyes and deaf ears,the ballot box is manipulated,it would seem we are fast running out options....

  7. #7
    Boolit Master Oklahoma Rebel's Avatar
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    ok, I understand all of that, and how to use the go- no-go, thanks for the details vzerone, I bought my whole upper as a kit, basically all in pieces, except the bolt is assembled and the gas block is mounted. so I think I just need to double check with the guage, and as far as everything else, I believe I understand. if I run into any troubles, I will let you guys know! as far as the 6.8spc, if I do that, it would probably stay that way. I was thinking about that for hogs, but with the all-copper barnes X bullets, I think the 223 should do for the "eating" size hogs, and I will whip out the 44 super Blackhawk for the big tuskers! thanks again guys!
    An armed man in a citizen.
    An unarmed man is a subject.
    A disarmed man is a slave.

  8. #8
    Boolit Man
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    Quote Originally Posted by Oklahoma Rebel View Post
    ok, I understand all of that, and how to use the go- no-go, thanks for the details vzerone, I bought my whole upper as a kit, basically all in pieces, except the bolt is assembled and the gas block is mounted. so I think I just need to double check with the guage, and as far as everything else, I believe I understand. if I run into any troubles, I will let you guys know! as far as the 6.8spc, if I do that, it would probably stay that way. I was thinking about that for hogs, but with the all-copper barnes X bullets, I think the 223 should do for the "eating" size hogs, and I will whip out the 44 super Blackhawk for the big tuskers! thanks again guys!
    Bring the 45-70 with an ***-whoopin' big boolit and load for those big tuskers!

  9. #9
    Boolit Master Texas by God's Avatar
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    Welcome to the Dark Side. No one puts together "just one" AR! I think it's cool you are doing the 80% route. My cousin is up to twenty something hogs with his 6.8 using Hornady V-max 110 grs only. I'm not bashing Barnes, I don't think they are needed.


    one AR

  10. #10
    Boolit Master Oklahoma Rebel's Avatar
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    lol, if my finances allowed it, I would have multiples of almost every gun I have! now the v-max is their varmint bullet, correct? does he do head shots? if not, they make it through the shoulder intact? and one more question, for hunting hogs, with either the sks or ar15, using cheaper ammo, like wolf or prvi, do you guys prefer the soft points or hollow points? they seem pretty even in accuracy, in my sks, that is.
    An armed man in a citizen.
    An unarmed man is a subject.
    A disarmed man is a slave.

  11. #11
    Boolit Master Harter66's Avatar
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    I worked up the NOE 279-124 FP .
    FC cases
    CCI #41
    H322
    75/25 WW and tamper seals of 20-1+copper @ 130.5 gr lube and check .
    I sized them .280 for my .270.277 with the body remaining .279 .
    These run 20 bhn but act like like 16 on target .

    I closed the FC 115 FMJ groups by about 1/2" .
    The load ran 2050 fps in a 1-10 twist 16" slightly over gassed .
    This comes up a little short on the 1000# @100 yd .
    In the time of darkest defeat,our victory may be nearest. Wm. McKinley.

    I was young and stupid then I'm older now. Me 1992

    About that rally point, the soap and mail boxes fall on blind eyes and deaf ears,the ballot box is manipulated,it would seem we are fast running out options....

  12. #12
    Boolit Master Texas by God's Avatar
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    He shoots them behind the shoulders mostly. My brother shoots an SKS and prefers the soft points. The only deer I've lost was shot with a Wolf 7.62x 39 hp behind the shoulder. All I found was a piece of rib bone. I looked for two days and found his skull the following spring. Now someone else may have perfect results with them but I didn't.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check