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Discussion Starter · #1 ·
A few weeks ago I finished a 6.8 AR build. Started with dated but unused parts: Bushmaster lower, M1S upper and barrel (1/10 or 1/10.5) with SPCI chamber. Finished it off with all quality parts and a Leupold VXR w/HogPlex. Have taken it to the range twice. Shot 3 different 110 gr factory loads and a few different 110 gr hand loads. Approx 6" groups at 100 yards with all the different bullets/loads?! Disappointed and surprised. I took great care in assembling everything. Would have been happy with 2" at 100 yards, given the rather low power scope and my eyes. Thought maybe a problem with over-gasing so tried 4 different weight buffers and a few different buffer springs. No change, and it consistently throws brass at normal distances. Very frustrating. Chamber ream to SPCII is on the list of "to do's" but could that make that big of a difference? Maybe I have a bad barrel???

Thx
 

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I'd lose the M1S barrel (SAAMI chamber, inefficient land/groove ratio, Enfield 6-groove rifling) and replace it with an ARP barrel. You'll get less pressure and more velocity from ANY given load with that change. My ARP equipped 6.8 will net me sub 1/2" MOA six shot groupings at 100yds. off a bench/bi-pod when I'm doing my part.
 

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My first 6.8 upper was a Bushmaster 1:10 SPCI chamber 16" barrel. It shot 1" groups @ 100yds. Be sure your scope mounts are tight and the muzzle isn't damaged.
 

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Lots of things can make accuracy worse. A standard 6lb trigger is a big one. A plastic handguard. 1/2-36" muzzle threads.
That barrel likely has a carbine gas system.
 

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I've fixed several M1S uppers. Most of them had loose barrel nuts some how. Could take the gas block/tube off and turn the barrel nut 1/4 turn tighter.. the barrel would move In the upper receiver.. after seeing that a few times I started just putting mine together.

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my 20" SS midweight 556 Mod 1 sales barrel was a tack driver when i had it, sold it to a very happy new owner when i dumped all 223/556 and stuck with 6.8 for everything small critters to blackies.
was made by ER shaw, not sure who makes m1s's 6.8

+1, dump it and buy an Arp barrel
 

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Discussion Starter · #9 ·
Scope was mounted right: rings lapped and aligned, everything torqued properly, balanced. Same level of detail throughout the rifle on all steps of the build. Geiselle trigger, so no issues there. My hand loads were done with precision, everything short of turning the necks.

Now the good news: Went to the range today with some handloaded Nosler 130gr, H4198 hand loads, based on a recommendation previously to give 130s a try. I was absolutely shocked. With a relatively low power scope, and 5-7 mph headwind, was no problem holding a 1" groups at 100 yards. I've been slinging lead for a long time and it's been rare for me to go from difficult 6" groups (using a common grain bullet for the caliber--110gr) to easy 1" groups just by going to a heavier bullet. I more accustomed to moving .5" - 2" change with different bullets/loads, but not a full 5" under similar circumstances. But I'll take it! I'd feel pretty confident now plugging a pig or coyote at 100-200 yards.
 

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Lots of things can make accuracy worse. A standard 6lb trigger is a big one. A plastic handguard. 1/2-36" muzzle threads.
That barrel likely has a carbine gas system.
When I bought a gas tube from them at the gun show, here in Dallas, they told me 12.5" barrels aren't made with mid-length gas (6.8 ARP, 12.5").

They aren't idiots, but their barrels are generally carbine length.
 

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Scope was mounted right: rings lapped and aligned, everything torqued properly, balanced. Same level of detail throughout the rifle on all steps of the build. Geiselle trigger, so no issues there. My hand loads were done with precision, everything short of turning the necks.

Now the good news: Went to the range today with some handloaded Nosler 130gr, H4198 hand loads, based on a recommendation previously to give 130s a try. I was absolutely shocked. With a relatively low power scope, and 5-7 mph headwind, was no problem holding a 1" groups at 100 yards. I've been slinging lead for a long time and it's been rare for me to go from difficult 6" groups (using a common grain bullet for the caliber--110gr) to easy 1" groups just by going to a heavier bullet. I more accustomed to moving .5" - 2" change with different bullets/loads, but not a full 5" under similar circumstances. But I'll take it! I'd feel pretty confident now plugging a pig or coyote at 100-200 yards.
That makes sense. That barrel wasn't made for our normal loads. Congrats!

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What were your factory loads and your hand load recipes?

No reason a 1:10 shouldn't shoot 110gr bullets, my match gun is 1:10/6 groove and I run [email protected] very accurately.

-Alexander
 

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What were your factory loads and your hand load recipes?

No reason a 1:10 shouldn't shoot 110gr bullets, my match gun is 1:10/6 groove and I run [email protected] very accurately.

-Alexander
Maybe I'm talking out of my, uh, arm, but I thought the 6-groove barrels were the 270 barrels co-opted for use in an AR15.

I realize that the twist SHOULD have more to do with the projectiles than the grooves, but the 6.8, as I understand it, doesn't care as much about twist as other cartridges.

Every barrel is unique, but 6" is certainly a different level. I haven't used my chronograph on 6.8 loads yet. I've been searching for accuracy thus far.
 

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The rifling pattern is more important than the twist. 1:10-1:12 will stabilize 85-120gr bullets in the 6.8.

Traditional Springfield pattern rifling has grooves that are equal in width to the lands, 50/50. This is not ideal for the 6.8. My barrel even though a 10 twist 6 groove has lands half the width of the grooves, reducing engraving force and pressure which allowed me to chamber it in spcII.
 

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I forget that the ratio is relevant. Thank you. Your match rifle seems to be doing what most folks' SPCII rifles do. Still odd that it turns into a .410 with buckshot when you use the smaller projectiles.

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handloaded Nosler 130gr, H4198
Even with decent accuracy, that's not a good combination. H4198 is an excellent powder for 85-90gr bullets, but it's burn rate is too fast for anything heavier. H335, CFE223, or AA2200 are all a better match for the heavier bullets.

I'd lose that barrel and get something good anyway.
 

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Every rifle and bbl is unique to itself.

Sometimes things that shouldn't work are just the ticket.

It's always nice when a scatter pattern group comes down to a servicable group with just a single change . I had 1 once that went from 6-8x12 down to 3x5 with a primer change and best of all it allowed for powder adjustment of compressed loads of almost .25 in of OAL from mag length to single feed out to the lands .
(A used up sks with 200gr custom spire point ).
 

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Discussion Starter · #18 ·
A small error in what I originally posted. I started out with factory 115 grain (not 110 grain) bullets: Remington Express Rifle, Remington UMC, and Tipton. I also used my own handloads: 110 gr A-MAX, H335, and Win primers. The factory bullets and handloads all shot approximately 6" groups. When I decided to give 130gr handloads a try my choices were Nosler ballistic tips and H4198. Interestingly Hodgdon does not list H4198 on their website as a 130 grain powder for 6.8s. Instead I used Hornady's Reloading Manual (8th Edition), which does list H4198 for 130s in 6.8s. Also, interestingly, the recoil seemed quite a bit softer, even though I went with a mid-level of powder recommended by Hornady. Without wind, and with a higher power scope, I really think I could have shot under an inch. I'm using a Leupold VXR (1.25 x 4 power) with a rather heavy Pig Plex reticle, intended for shorter range shots. Regardless, the loads worked and I'd feel very comfortable hunting with it.
 

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Factory Remington 6.8 ammo is known for being weak, and oft times lacking accuracy. Pitbull posted up pix once... of Remington bullets being SO non-concentric, it isn't even funny.

I've never had issues with Remington's hunting ammo over the years with my .30-06 bolt action... but I wouldn't use their 6.8 ammo for anything but mag dumps to see whether my rig would eat/feed that crap.
 

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A good trigger and ARP barrel is what made my groups smaller. My PSA 6.8 barrel ain't too bad either. I prefer Timney triggers. But ALG's Combat trigger with updated JP springs is a cheap substitution.
 
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