Bridging the Gap

[light1984]

I am looking for a higher powered optic to replace my 4x ACOG on my LWRC IC-SPR. I've got my sights set on the Leupold MK6 3-18. I know "bridging the gap" is a no-no with rings, but the does the same hold true for a one-piece mount such as the ARC or Spuhr mounts? I know Spuhr offers a cantilever mount, but I'm leaning towards the ARC mount, or possibly Bobro. Here is a crappy cell picture of the rifle currently. Thanks for any input.

Josh

 

[jasonfaz]

You definitely want a cantilever mount. Especially if you prefer to run that rifle with the LWRC compact stock fully collapsed like you have it in the pic. The MK 6 has a huge amount of eye relief. I'd highly recommend either the Bobro with 2" of forward offset or the Larue with 3" of offset. The MK 6 also has a significant variance in eye relief as you adjust through the variable magnification range. I have the same type of set up and ended up using a monolithic upper for the build instead of your traditional upper + rail so I didn't have to worry about that gap. The other thing you'll notice is that all the 34mm cantilevered one-peice mounts are high as fu*k. I went with a 1.18" Spuhr with 20 MOA cant. Just about perfect height, but no cantilever 34mm one-peice mount exists with a CL that low. So you'll have to decide whether a higher CL or running your rig fully collapsed with a shorter OAL is more important and go from there.

 

[light1984]

I didn't even think about it, but I cant bridge the gab because the top forend piece comes off to get to the piston parts. So ill have to go cantilever. The Spuhr cantilever is a 1.46 centerline if i remember right and that or the bobro are the cantilever mount I'm leaning towards. You don't have any cheekweld issues with a 1.18 CL? My ACOG sits at 1.53 and it is near perfect for me height wise.

 

[jasonfaz]

Nope, but I use a PRS and CTR on the particular rifles my MK6 rides, which both have very different cheek welds than the LWRC stocks. The mount also has a 20 MOA cant that lifts the ocular up slightly. I run the LWRC UCIW kit and the Compact stock on a couple rifles with Elcans that have 1.5" CLs and with that enhanced cheek weld I have no problem at all. When you think about it, a 1.18" CL is right in the ball park of what CL would be on high or even extra high rings. So it's not really all that low.

Being a piston system, is your top rail height raised compared to a standard height DI gun? I know POF is, wasn't sure about LWRC. They don't appear to have anywhere near the additional height that POF rigs do. If that's the case though, then it would make a lower CL even more important IMO. My goal was to get my CL as close to the bore as possible while still being comfortable to shoot with a natural line to the eyebox right when I get cheek weld. I have a skinny, tiny head and the lower mounts have always been better for me to accomplish that with a variety of stocks...

 

[bill_van]

Years ago, I worked at a shop in the same area as LaRue.... we were in contact with them on a daily basis. I do remember them saying to never bridge a gap even though the rail was FF. I see that you are not able to with your current forend but just thought I'd throw this info out in case someone else had the question. Cantilever is the answer when a forward placement is required.

 

[jasonfaz]

...and I think you'll need more than an inch of forward offset the Spuhr gives you. The MK 6 has over 5 inches of eye relief at min magnification. It drops to a little over 3.5" at max magnification. The range of that variance in eye relief throughout the magnification range is easily the biggest downside to the MK 6 IMO, the point being that at 5" at minimum mag you'll definitely need more than 1" forward offset - even more so when you take into account the length of your stock. I certainly need it.

 

[light1984]

Bill: thanks for the input, you all are exactly right, cantilever is the only way to go.


Jason: As to the LWRC rail heights, they are the same as a standard DI gun. Thanks for the info on the variable eye relief. I had no idea it went up to over 5 inches. You are definitely right about the forward offset, I will need more than 1". I did some measurements on the LaRue SPR-S mount with a 2" forward offset and that puts my eye right at 4" from the optic based on where I usually run my stock position. Only thing about the LaRue I don't like is the locking screws being at the top. I feel that it would obstruct my view of the turrets. So I guess I'm looking at the Bobro mount. That seems to be about my only option. Thanks again for the insights.

 

[jasonfaz]

Sure thing. Larue makes one that has a 3" forward offset if you think you'll need more (LT139), and if you don't need the QD, JP makes an awesome cantilever mount with a 2" forward offset at $225. I'm planning on ditching my Spuhr for the JP actually just for the extra inch of offset.

 

[light1984]

That JP mount is really clean. I like that, looks to be a lot lighter too since it has no QD parts.

 

[tickled pink]

I'm going to have to compare the MK6 to my Bushnell AR/223 4.5-18x40mm scope. The Bushnell IMHO is clearer, sharper and has better contrast than my Leupold scope. I can easily see the .223 bullet holes on my targets at 100 yds. The clicks are very close to and as accurate as my Vortex 6-24 PST FFP MOA scope. The Parallax adjustment numbers are spot on for all ranges also. I also put a Custom Turret Label on the elevation turret also which gets me out to 900 yds. All I have to do is range the target then turn the turret to the distance on label hold for wind and shoot. No computing necessary.