Originally Posted by
lengthofpull
Hello all,
Long time reader, first time poster here. I am getting ready to have the kind folks at Rainier build me a "precision" upper and I have a few questions first. I have used the search function here to answer most of my questions but I have a few other items I haven't found anything on. If anyone could point me in the proper directions that would be great.
This is going to be a 20" Lothar-Walther SS barrel, Vltor MUR upper, and Apex rifle length hand guard. I have no need for iron sights and will be using a 4.5x14 scope on it. I will be shooting no further than 600 yards with most work done inside of 400. I have no plans for suppressor use.
Targets will be sage rats, coyotes, 12" steel gong and whatever targets i staple to a piece of plywood to try and outshoot my old man/his 223 bolt gun.
1. On a precision upper, what recommendations can be given for gas block selection? There will be no iron sights on this gun so I have no need for a rail. Just get a decent low-profile one?
A pinned block is preferred over set screws for reasons of durability. If you do go the set screw route for whatever reason just make sure the barrel is dimpled for it. Rocksetting the GB can also help if you use set screws. Getting a rail that covers the GB is an added layer of protection. But really, there is no reason you have to do any of this. Just get it pinned. I had an issued MK12 (set screw GB) turn into a single shot on me after taking a nasty fall on rocks.
2. For a muzzle device I am looking at the Vortex. I am not sure I believe that it "helps align exiting barrel gas to improve accuracy with all bullet types" but I am willing to have an open mind if someone presents data. A question I have for folks who have the vortex or other open prong style muzzle devices is do you find that foliage gets stuck in it when you're tromping through the woods? I want something that just does flash suppression, at this time i am not interested in a comp or break.
I've only run the Smiths on MK48's and M14's. On the 48's there was obviously no observable difference in accuracy (it's a MG). Flash suppression was impressive.
However, on the EBR's we were able to notice a moderate POI shift at 200m+, depending on whether or not you let the Vortex stop vibrating before taking another shot. In other words, POI was different based on whether the Vortex was still doing its tuning fork act from the previous shot or not. Disclaimer: those 14's were not accurate to start with and exhibited unpredictable behavior, so I cannot attribute the POI shift to the Vortex with absolute certainty. But the phenomenon was conceivable enough for us to switch back to the standard FH
3. The barrel comes with a matched bolt, however I believe (not sure) it is a DPMS which i am not thrilled about. I have a spare daniel defense bolt and I am going to do accuracy comparisons with both to see if the matched bolt offers any substantial accuracy gains. If this is the case is bolt carrier selection as critical as bolt selection from a reliability standpoint (assuming the key on the carrier is staked properly).
Headspace is set when the extension is put on the barrel. Acceptable headspace is between 1.4646" and 1.4706." The point where a rifle becomes "unsafe" is 1.4736''. However, the Army uses 1.4730'' for an extra 0.0006'' of safety. A matched bolt simply means that they are checking headspace with various bolts and finding one in a healthy range. I don't know the exact extent to which this effects accuracy, but unless you are shooting from a rock solid platform, indoors, there is very little chance you will notice a difference. There are certainly a lot of more important factors when it comes to knocking out the X ring. I would personally use the "matched" bolt that comes with the rifle and keep the DD as a spare if that one goes, instead of switching back and forth...unless doing a comparison is something you just really want to do.
Thank you for your time.
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