Hi all, I picked up a Christensen 308 AR upper and it has an integral 20 moa rail. I dont shoot at and suck at long range shooting.

Will the 20 moa rail put my scope adjustments too near the end of travel ?

Should I put the barrel into my existing 308 AR upper? It has a special barrel nut I dont have the wrench for but I am sure I can work around that.

The other issue is the C A  upper does not fit my existing 308 AR lower.


Original Post

What scope? The amount of travel/adjustment your scope has will be a major factor.  I have a Rem700 with a D.D.Ross 20 minute mount and with the scope I have on it (a Springfield Armory 6x24) when I zero’d jt at 100, I only had about 3 clicks before it was bottomed out.

A 30 mm scope usually has more adjustment than a 1”, and a 34mm has more yet.  (More room inside for things to move around.)

I am thinking I will try to transplant the barrel to the existing upper. 

I dont want to fumble around looking for lowers that fit this upper with a rail

that may not work for my uses. 

I emailed Christensen and they basically said " Dunno what may fit, no mil spec for 308ARs".

Maybe it's just me, but I'd keep the upper and just mate it to a new lower.

AR10s can be finicky as heck, and if I had one that worked just fine, I wouldn't play Frankenstein with it over a barrel.   You go from two known working uppers (assuming the CA is factory it should work just fine) to one maybe working rifle and a bunch of parts.  You also said you don't shoot at long range or are that big of a distance shooter - just things to consider.

I'd venture a guess that CA are probably built to DPMS spec so there are plenty of lowers out there to work with it.  What brand/spec is your current 308 AR?

Keep in mind, this is the opinion of one dude on the internet, so take it for what it's worth - just some thoughts for consideration.


Last edited by Knight

Thanks Knight. 

My current 308 AR is a S&W hunting version. I like that it is ambi, not that I need it but I like it. I think it is a reasonably accurate rifle.

I think I maybe dont have the patience for  long range precision shooting.  Perhaps a course would help that and getting good fundamentals.

Like Knight said. Find out what pattern they use for their upper, try to buy a lower with the same pattern.

While it does suck to not be able to slap it on a lower, AR10s are nowhere near as universal (parts wise) as 15s are.

20 moa should be fine for getting zeroed at 100. Closer than that you may have issues.

I wouldn't transfer the barrel, because then you're gonna have a whole heap of parts that will be even harder to put together, just IMHO.

The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants.

Your scope has 55 MOA of elevation so with a 20 MOA rail at mechanical zero you'll be able dial down 7.5 MOA and dial up 47.5 MOA.  A lot of scopes actually have more that their quoted elevation range.  You'll have no issues getting a 100 yard zero.  Leupold customer service can verify this also.

I am going to get the burris XTR ring so I can negate the integral MOA in this upper.  I will also try to find a lower that works with it.

Last edited by The Extractor

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