Upper receiver for SPR build?

[Fatorangecat]

Hopefully someone better qualified to answer comes along but tighter fitting upper receivers are thought to be more accurate. The same is said for thicker walled receivers like the MUR. The reasoning is that it creates a more rigid upper while firing or loading a bipod. Some people prefer monolithic rail systems for this reason. Most people are trying eliminate every variable possible but for me a quality free floated match barrel with a Geissele trigger on a relatively loose Colt upper produces very good accuracy.

[Antonio5005]

Hopefully someone better qualified to answer comes along but tighter fitting upper receivers are thought to be more accurate. The same is said for thicker walled receivers like the MUR. The reasoning is that it creates a more rigid upper while firing or loading a bipod. Some people prefer monolithic rail systems for this reason. Most people are trying eliminate every variable possible but for me a quality free floated match barrel with a Geissele trigger on a relatively loose Colt upper produces very good accuracy.

Thanks, yea I guess I never took that variable into account. I could see it possibly being an issue. Especially if you're trying squeeze out every last MOA that you can.

[Rogue556]

Hopefully someone better qualified to answer comes along but tighter fitting upper receivers are thought to be more accurate. The same is said for thicker walled receivers like the MUR. The reasoning is that it creates a more rigid upper while firing or loading a bipod. Some people prefer monolithic rail systems for this reason. Most people are trying eliminate every variable possible but for me a quality free floated match barrel with a Geissele trigger on a relatively loose Colt upper produces very good accuracy.

This has been my understanding as well from the research I've done, which was why I was curious about the potential benefits of using an upper other than the Colt (As it's the cheapest option). It will be used for 600 meters and under and the majority will be 300 to 400 meters on steel so I'm not sure how much difference it will make in my scenario. I'd be happy with anything 1 MOA and under with good ammo (The more accurate the better, obviously).

[Fatorangecat]

I went with an 18" WOA SPR barrel, MK8, SLR gas block, Vltor A5 and Geissele SSA-E and it is ridiculously soft shooting and very accurate. I don't have time to reload and typically just shoot BH 77gr. I don't remember the last time I shot larger than MOA off the bench. The WOA barrels really are just great barrels. Having been down this road though just pull the BCG and sell the whole upper.

[Rogue556]

Alright guys, I have acquired a few parts since my last post in this thread and still need some help choosing an upper receiver.

Parts list of what I have so far:

18" Centurion Arms Mk12 barrel

Geissele Mk4 15" MLOK rail

Geissele gas block

Geissele Super Precision 30mm mount

Nightforce NXS 2.5-10 optic

BCM FDE ionbonded BCG

BCM complete lower receiver.

(Still need Geissele SD-E, Surefire MB556, Magpul UBR, KAC BUIS, and Atlas bipod)

I'm stuck between four upper receivers currently. The Vltor MUR-1A, VLTOR MUR-1S, Larue Stealth, and standard BCM.

The only reason I haven't gone with the VLTOR MUR-1A is because I am wanting to run KAC 45 degree iron sights on this rifle and I know the brass deflector/forward assist gets in the way of that. I have not heard as much about the rigidity of the LT Stealth upper as I have about the VLTOR MUR uppers. If both are roughly equal than the LT is about $100 more expensive which seems a bit high considering the other options (I do understand the materials used are different, however). That leaves the MUR -1S and BCM. I'd like to keep the FA if at all possible but would still consider the MUR-1S if it seems the most logical choice. Last is the BCM upper which I know plenty have used with good results but with a heavy 18" barrel and suppressor (eventually) hanging off the end I know I could benefit from a more ridged design.. What do you guys think? Shell out the extra for the stealth upper since it seems to check all the boxes, or go with one of the others? If one of the others, than why?

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[Eurodriver]

Have you ever tried to shoot a rifle with an 18" barrel, a 15" Geissele rail and a 10x NF, with an Atlas hanging off the end at a 45* angle?

[Rogue556]

Have you ever tried to shoot a rifle with an 18" barrel, a 15" Geissele rail and a 10x NF, with an Atlas hanging off the end at a 45* angle?

Identical to that? No. I've used a mixture of the parts mentioned (besides the barrel. The SS barrels I've used were 16"). Rails on those guns were 12" C4 and 13" Geissele but not the Mk4 specifically. Bipods were both Harris (I have not used an Atlas. Decided to go that route based off of the praise everyone seems to have for them). Am I missing something? Is that too much weight that far out?

[Vegasshooter]

What he's saying is that with all the weight you have on the gun, turning it to a 45* angle to make up close shots probably won't be as easy or as fast as you think. IMO, if you're building the gun as an SPR, leave the 45* offset sight off. It's a scoped, distance gun, not an entry/home defense gun. I could see if you were using a 16" mid length with a 1-4 or 1-6x scope. That's a common "do it all", or 3gun gun. Since you're going with a dedicated SPR, let it be that.

[Rogue556]

What he's saying is that with all the weight you have on the gun, turning it to a 45* angle to make up close shots probably won't be as easy or as fast as you think. IMO, if you're building the gun as an SPR, leave the 45* offset sight off. It's a scoped, distance gun, not an entry/home defense gun. I could see if you were using a 16" mid length with a 1-4 or 1-6x scope. That's a common "do it all", or 3gun gun. Since you're going with a dedicated SPR, let it be that.

Gotcha. That makes sense. I hadn't really stopped to ask myself if I needed them. I suppose the BUIS train of thought stems from having multiple 14.5" and 16" guns with RDS. This being my first precision AR I was carrying that logic over, which obviously, wasn't well thought out on my end. I suppose that leads me to the MUR-1A and more money for ammo.

[Fatorangecat]

I would go with the MUR1A or the BCM. I think the upper receiver has less affect on accuracy than people think. I have an SPRish rifle built off a 6920 with a very sloppy barrel to receiver fit and it continues to surprise me every time I shoot it. I hung a 2" plate at 200 yards over the weekend and rang it with effortless boring consistency. I am however a fan off matching parts from a manufacturer. With a BCM lower and BCG I would go BCM upper.