Someone please check my math.

[Cheeseybacon]

I'm in the process of ordering scope mounts for my Bohica FAR-50 .50 BMG upper which should have been here by now but has been delayed (grr). The scope rail on this particular upper is a fair bit higher than a normal flattop AR upper. Knowing this, the guy who makes these uppers advised me to get the shortest scope mounts that I could for the best cheek weld.

I've decided to get the Burris Xtreme tactical scope mounts and I am wondering if I can indeed get away with the shortest version that they offer. My scope requires 30mm rings and has a 42mm objective. The shortest mounts offered are a quarter inch (0.25") tall.

I took the scope mount image off of Optic Planet.com and modified it slightly so I could visualize the dimensions of everything a little bit better. The images below are NOT even close to being to scale, but I think the numbers should be correct. If I'm understanding everything correctly and I did my math right, if I were to use a 0.25" tall mount I will end up with a 0.35mm gap between my scope's objective and the rail on my upper.



The next size up that Burris offers is a 0.5" mount, which would give me 6.7mm of clearance if I'm doing my math correctly.



I guess the first question is: am I doing my math correctly, or am I way off?

Secondly, assuming my math is OK, is 0.35mm adequate clearance or would I be a fool to use a mount with such negligible space between the objective and the rail? I'm using an A2 stock with this beast and would like to avoid strapping on some kind of cheek piece if I can.

Lastly, has anyone had any experience with Burris Xtreme mounts? Am I asking for trouble using these mounts on a .50 BMG setup?

[arrrrgh15]

Hmmm. 0.35 mm isn't much.

I think your math is OK, but I'm wondering if the 42mm is the outer diameter of the scope tube, or is it the objective lense. Maybe Burris has a table on their website with the outer dimension of the bell.

If it's the outer diameter it looks like you'll just clear it, but you won't have any room for scope covers, etc.

Good luck with your .50 bmg upper. they look pretty cool.

[Cheeseybacon]

Aw crap... scope covers.... you're right, there probably won't be room for them.

Hmmmm, looks like I'll be going with the half inch mount then. Glad I posted this before buying anything.

[Cheeseybacon]

Well I ended up buying the "high" (1.125") Badger MAX-50 mounts. That will give me 7.575mm of clearance between my scope objective and the rail. That should be enough for a scope cover to go on without any problems too.

I hope I can get a good cheekweld...

[Tomcat088]

I was just about to mention aaaargh15 said, that the 42mm was probably a measure of the diameter of the object lense and didn't include the metal tube that holds it or scope covers. Not to mention, even if everything was what you originally thought, any small difference in specs from the rings or the scope would put you laying on the barrel. So you made the right choice.

Just so you know, there are other ways to get a proper cheekweld other than using a lower mount. You can also get a stock that has an adjustable cheek piece, or buy or modify pads that wil give you a higher comb so that you can get a proper cheek weld. Hope this helps and best of luck to you.

[arrrrgh15]

Fortunately for you the FAR 50 is bolt action, so you won't need to contend with the charging handle getting in the way of a cheek peice.

I think if you went with that magpul stock or even just added a padded cheek peice made out of foam and 100mph tape you'd be good to go.

That FAR50 looks pretty damn ambitious. I'm anxious to see how yours turns out. Be sure to post some good pics.

[Cheeseybacon]

Thanks for the suggestions guys. My dad just finished building a target AR not but a month ago and he really fought to get a proper cheek weld, which I guess is why I'm so worried about it. He went through two different sets of rings and a cheek piece before he finally got the cheek weld right. I'm trying to avoid using a cheek piece if I can, but who knows, I might end up with one anyway.

[Tomcat088]

I understand how you might want to stay away from a cheekpiece. On a bolt rifle I don't think it's nearly as much of an issue. With the design of the AR and the size of front objectives that many of us use, they're hard to get away from. Just remember that it's better to have to deal with a cheek piece and have proper cheek weld, than it is to be fighting with cheek weld and shooting terribly, but still looking cool. Hope it works out and just keep us informed.