SPR precision AR questions

[johnson]

I agree that the BCM upper and BCG are good choices but I disagree about the gas block. Although a 5.56 is not a heavy recoiling weapon the reduction of felt recoil makes for a very smooth shooting rifle with very nice follow up shots.

And it'd great especially with a suppressor.

Here's my AR and build list. I also have a thread in the custom build forum detailing why I selected the parts.
http://i.imgur.com/6qSblq1.jpg
16" SPR

The things I would change would be to go with the A5 system with heavy buffer and tune it with an adjustable gas block. I'd also like to try a Geissele NM trigger.

When rjacobs and I went shooting last year, my AR bolt didn't lock back on the last round with a custom 10rd PMAG that I was using. I used his Lancer L5 AWM mag and everything functioned fine. Last week while I was shooting, the same PMAG started working fine out of the blue. I still need to run it some more especially in other rifles to narrow down the issue but that's one reason why I want to go back to a buffer/spring system instead of using the JP Silent Captured Spring.

For the upper receiver, you would want something that fits tight to the barrel extension. My Mk 12 barrel had to be tapped in to the Ultramatch billet upper. The new BCM uppers are supposed to be a little undersized for a tight fit so that may be an option for you. The MUR receivers would be a great choice as well especially if you plan on hanging a suppressor at the end of the barrel. There are some older threads that talk about receiver flexing and bolt breakage and that's why VLTOR designed the MUR.

I got the Rainier upper receiver because it's supposed to be dimensionally correct with very tight tolerances. I've only sighted it in so far but with the receiver and Nightforce Unimount I have retained pretty much all of my scope elevation and windage looks to be dead center in the adjustment range. Being dimensionally correct may not aid in accuracy but it helps keep the bolt in perfect alignment with the extension.

I'm still needing to finalize the zero and will try to make it out to the range tomorrow to show how much shift I get with and without the 30P-1 attached.

Here's Wes Grant's (MSTN6) version of the SPR.
http://www.scout.com/military/sniper...pr-mk-12-mod-2

[Singlestack Wonder]

I agree that the BCM upper and BCG are good choices but I disagree about the gas block. Although a 5.56 is not a heavy recoiling weapon the reduction of felt recoil makes for a very smooth shooting rifle with very nice follow up shots.

The proper application of the correct buffer will accomdate that. Adjustable gas blocks are problematic if one wishes to adjust them more than once as carbon builds up in a short amount of time freezing the adjustment mechanism. On blocks without an adjustment screw detent, the screw tends to back out over time. Some attempt to loc-tie the screws. While this works, the screw is now non-adjustible and locks tighter further on due to carbon buildup. By choosing the right components, adjustiblew gas blocks are unnecessary. Blciks like the Noveske Switch Block are a different animal with only two positions, open and suppressed, and typically do not lock up due to the design. YMMV

[Singlestack Wonder]

And we don't see them on serious use use rifles...that's a clue.

[Fatorangecat]

You should look at the SLR sentry gas block. It is a pretty solid design. It does not require loctite and I have had no issues with it fouling out. I just close and open the adjustment screw periodically to be sure. I don't doubt the reliability of it but anything with moving parts can fail.

[CRAMBONE]

Go with a BCM SS410 barrel and BCM gasblock. No reason to have an adjustable gas block on an a 5.56 rifle. You will be very pleased with the BCM's barrel accuracy. While you at at it, go with a BCM upper receiver and BCG. It's never been proven that a Vltor MUR does anything better than a standard receiver. Great price and proven performance.

It looks cooler. Honestly that is the reason for some of the attraction I have to the Vltor. And I guess even though it's never been proven to benefit performance I would rather have the potential than not have it.

[Averageman]

I follow these threads with great interest as I am contempating one of these myself.
Thanks for posting this, I will follow it closely.

[CRAMBONE]

Ok I think I've decided on a Geissele Mk4 rail. I like the milled in front rails for possibly mounting night time stuff at a later date. Not sure on the gas block yet, but kind of leaning toward the Syrac. Also I posted these same questions on a local gun forum and you should see some of the replys.

[el_chingoton13]

Good choice. If you buy the rail directly from Geissele you get one of their gas blocks included. It's not adjustable but it could be useful.

[CRAMBONE]

Looking at the Rainier ultramatch 18" rifle gas barrel. They only come in 1-8 twist. I don't currently hand load and was looking to use a lot Mk262 due to it being plentiful and affordable. I've searched some and read a little on the heavier bullets in 1-8 twist barrels. Some say ya and some say nay. Does anyone have any good info on this barrel/round combination?

[Sqr]

Just finished another build with a 20" SS Jury Custom Barrel in 30 Herrett AR/RT. NEA grey coloured billet set coupled by Yankee Hill push/pull pins and a CMMG bolt carrier/ Colt gas key paired with a DD bolt. This is charged with a BCM large handle and held onto with MFT pistol grip along with a LUTH-AR MBA A2 stock. The upper is completed off with a 15" Diamondhead rail over a JP adjustable clamp on gas block. The lower is outfitted with an SP billet mag release, Magpul B.A.D. Lever and CMMG LPK.