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Home of the 6.8 SPC - 68forums.com » 6.8 SPC Industry Partners » Bison Armory » New Uppers

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Old 05-08-2009, 11:30 PM   #1
carnaby
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Default New Uppers

Today is range day! I'm taking the following with me:



The first upper is the most basic, 20" with threaded muzzle, Phantom .308 FH, Bushnell 3-15x50 scope and rifle length gas system. The second one is the 20" unthreaded with intermediate-length gas system.



The first upper in this photo is an 18" with a Saylors Machine Phoenix FH and mid length gas system. The bottom one is an 18" with a TNW gas piston system and DPMS Levang linear compensator. I'm really looking forward to trying out the GP system.

Range report will hopefully follow soon.
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Old 05-09-2009, 02:37 AM   #2
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Quote:
Originally Posted by carnaby View Post
Today is range day! I'm taking the following with me:



The first upper is the most basic, 20" with threaded muzzle, Phantom .308 FH, Bushnell 3-15x50 scope and rifle length gas system. The second one is the 20" unthreaded with intermediate-length gas system.



The first upper in this photo is an 18" with a Saylors Machine Phoenix FH and mid length gas system. The bottom one is an 18" with a TNW gas piston system and DPMS Levang linear compensator. I'm really looking forward to trying out the GP system.

Range report will hopefully follow soon.
Looking forward to the range work.
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If you're looking to purchase a 6.8 SPC rifle, upper, or barrel, you should consider SPC II, and 1:10 or slower twist as the minimum acceptable specifications. There is no reason or advantage to purchase a 6.8 SPC product that utilizes the obsolete 6.8 SPC SAAMI chamber. The extra leade in the SPC II or similar chamber lowers pressures which is beneficial to the wear and tear on your firearm. Lower pressures at a given velocity, or increased velocities at a given pressure are the benefits of using the improved SPC II type chambers.
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Old 05-09-2009, 02:40 AM   #3
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looks nice, agreed on the range report.
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Old 05-09-2009, 04:38 AM   #4
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Just got back. Here's the results so far:

1. didn't spend much time with the piston upper as I was in a hurry and shooting at 100 yds didn't leave much time to sight in the irons sights. Three shots, cycled perfectly, move on to next upper (will come back to the GP on another day).

2. 18" barrels shoot great. Gas port is #45 (0.082"), all loads kick out right around 3-4 oclock, and accuracy is great. Most groups right around 1" without trying very hard or worrying about loads. Best group was 1/2" three shot with 85 gn Barnes TSX over 30 gn H322.

Also shot 110 gn Nosler Accubonds with H335. 29 gn and no pressure signs. 29.5 gn and primers were flattened. With 110 gn pro hunters I went to 30 gn H335 without any high pressure signs.

3. 20" barrel with intermediate length gas sysetem and 0.082" diameter port tends to short stroke on everything but loads using H335. I'm going to open up the gas port to a #43 and try again tomorrow. Accuracy is excellent as with the 18".

4. 20" barrel with rifle length gas and a 0.082" diameter port short strokes on everything, and won't even cycle. I'm going to open this one up to #42 (0.0935") and try again tomorrow.

So far so good, just need to find the gas port diameter that works for the 20" barrels. I'm headed back to the range tomorrow morning.
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Old 05-09-2009, 09:42 AM   #5
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I don't want to say I told you so, but I told you that you should use the Mid length gas system with the 20" barrels. LOL.
Sounds good though, although I'm surprised you had pressure signs with the H335 and the Accubonds.
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Old 05-09-2009, 10:17 AM   #6
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Sounds like pretty good results so far Carnaby. Did you ever decide on whether to go with a SPR profile for the 18 in bbl, so the OPS, Inc comp would work?
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Old 05-10-2009, 03:46 AM   #7
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Interesting thread - thanks for sharing the play by play. What would the advantage be with a mid-length gas port on a 20" barrel? Why not just use rifle length as designed?
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