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Posted: 6/24/2008 10:23:07 AM EDT
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Okay, i've decided to build up an "SPR-like" upper. It will not be an exact clone, but I will use the SPR barrel as I like the 18 inch length and the profile. No brake or can, will run a vortex. Most likely will never see a bullet lighter than 55 grains, majority of rounds will be loaded with 60 grain V-Maxs or 77 grain Sierras or Noslers. I do have a couple of questions I hope you guys can help me with. 1) Twist. I'm planning on using a 1:7 twist. Any reason why I should go 1:8 instead? 2) Gas system. This is what I struggle with, Rifle or Mid-length? I'm leaning towards the rifle length system, for smoother cycling from what I understand. Any thoughts on why a mid-length would be better? Primary use will be 200-300 yard plinking and very limited varmint hunting. Thanks in advance. |
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I had the exact same dilemma - shooting 55gr and up (mostly going to be 75gr PRVI), for same application. I went with the CMMG 1:8 M18 barrel mostly on price, and got it in rifle length, since I was also planning on using it as a three-gun platform. CMMG is definitely worth looking into, since their M18 barrel lets you choose between Midlength, Rifle length, or doing a dissipator type setup, with a mid mounted lo-pro gas block, and rifle length mounted FSB. Would also depend on what type of optic/rail setup you were looking at for that - free floated obviously is going to make sense, if you're ordering a barreled upper, look into CMMG w/ a VLTOR MUR-1A (very well priced) and adding a rail system of your choice (DD Lite rail, LaRue FF, PRI CFFFT, MI FF Rail, or TROY MRF, - I went with an MRF-RX from TROY) OR, if you're going with stock handguards, normal FSB then CMMG's M18 Dissy (Mid gas, rifle FSB) but it sounds like rifle makes the most sense. I happened to get 1:8, which is a slight advantage because it's my only rifle, and 55gr will be practice ammunition, but that should be fast enough to stabilize the slower 75gr loads I'll be using... but if you are set on a 1:7, ADCO is the first place I'd look for a barreled upper, if not getting one of the White Oak Precision uppers (though middy gas) in 18" SS profile. |
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I recently put an upper together w/ an 18" White Oak SPR barrel from ADCO ($255) w/ a rifle length gas system and FSC556 compensator. the lower for this rifle has a fixed A1 stock. I was finally able to take it out this weekend, and at 10x on the scope the rifle never moved, I could practically watch the bullet (65grn Black Hills Match) all the way in. Cheaper Remington/UMC 55grn ran just fine too. I can't speak for a midlength, as I've never fired one, but I'm loving the rifle length system. I've heard that midlength may become important in very cold environments, sub 0 or worse, but I have the misfortune of living in Kalifornia and freezing weather is not a real concern out here. ETA: my barrel is 1:7 |
The heart of any rifle is its barrel. Accuracy rests with the three "B"s: barrel, bullet, and brass, in that order. An investment in a good barrel will not be regretted later. Compass Lake made the first SPR barrels for the military, if memory serves me correctly. Complass Lake makes a great SPR barrel, and will make it with the barrel blank you specify: Douglas Premium, Kreiger, etc. The Douglas Premium air gauged 1:7 is a tight shooting barrel. Matt and I have not noticed a difference between the 1:7 and 1:8 twist barrels regarding group size, in any bullet weight. Hornady 53 grain match consistently shoot extremely tight groups. Federal Match 69 grain rounds are tight shooters as well. Black Hills 60 grain surprised the heck out of us; it shot tight. V-Max shot tight, but less tight than the Hornady 53 grain match....still MOA or less though. We prefer a rifle length gas system on an SPR profile, because that is the original design and it works, and works well.............it aint broke. We went to the range a few days ago testing four new uppers for our customers. All shot very well, MOA or less. Neither of us could shoot worth a darn. I vertically stung MOST EVERTHING I shot, regardless of upper, rifle, distance, or ammunition. Horizontal distances were 0.5 to 0.75" MOA, but vertical was upwards of 1.25 MOA. I was just not on my game. It was hot, and I did not hold consistent shoulder pressure.......I just didn't hold tight enough.   The uppers tested.   
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Compass Lake has the SPR barrel specs and can make you one, bit real SPR barrels were and are made by Gene Barnett using Douglas blanks. As for mid-length vs rifle length: Rifle-length, no question. Middies are designed to alleviate the problems caused by carbine-length barrels. Pushing the gas port further down the barrel toward the muzzle decreases pressure and all the problems associated with it. Going from rifle-length down to mid-length, you are increasing pressure and will be accelerating wear on the gun. There are no pressure or reliability issues associated with the rifle-length gas system and if you are using an 18" barrel, you should go that route. |
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