Help w/ Zeroing Irons on a 16" Barrel .308, using the MBUS Pro LR Sights

[TexasGuns]

I'm planning to zero my rifle tomorrow afternoon, maybe you can help? I'm using only irons tomorrow since I haven't an optic yet. These are my BUIS on an AR platform in .308 caliber. Will be using the Magpul MBUS Pro LR rear/front. Will likely shoot FGMM 168 gr. or other match grade. My plan is to get on paper @50 then zero @200 yards. Is that where you would start, what do I need to know? The rear has adjustment for elevation. There isn't much info on zeroing them for .308. If you have experience with zeroing these irons with .308 please let me know your finding(s) and maybe shorten my learning curve. I want to shoot @400 once I get dialed in and possibly try 600. Will be a fun day I'm sure! Thanks in advance.

 

[Trigger Monkey]

My understanding is that the BDC for the rear sight is a menagerie of bullets, barrel lengths, and muzzle velocities averaged into something that will get hits center of mass give or take 5" from 200 to 600 meters. I don't know if I'd trust the accuracy of that little BDC wheel necessarily, but it does give you some rudamentary elevation adjustment, which is nice. If you're shooting at targets ranged in yards you'll have to remember that the BDC is in meters so there won't be a direct correlation (e.g. 400 yards doesn't equal "4" on the wheel).

Below is target range in yards, conversion to meters, and my best guess for the sight setting and hold based on a full size IPSC without knowing the full ballistics of your rifle.

200 yds - 186 meters - "2" Dead On
300 yds - 274 meters - "3" Dead On
400 yds - 365 meters - "350 setting" Hold Shoulder Line
500 yds - 457 meters - "450 setting" Dead On
600 yds - 548 meters - "550 setting" Dead On

When zeroing, leave the BDC knob on "2", use the small aperture, make elevation adjustments with the front sight, and windage adjustments on the rear sight. I would zero about 1/2" high or so of center at 50 yards and confirm point of aim, point of impact at 200 yards. If you need to make small adjustments use the front sight for elevation, rear for windage still. After that start stepping out the distance, writing down the sight settings, where you had to hold on the target, and the results. Good luck.

 

[TexasGuns]

My understanding is that the BDC for the rear sight is a menagerie of bullets, barrel lengths, and muzzle velocities averaged into something that will get hits center of mass give or take 5" from 200 to 600 meters. I don't know if I'd trust the accuracy of that little BDC wheel necessarily, but it does give you some rudamentary elevation adjustment, which is nice. If you're shooting at targets ranged in yards you'll have to remember that the BDC is in meters so there won't be a direct correlation (e.g. 400 yards doesn't equal "4" on the wheel).

Below is target range in yards, conversion to meters, and my best guess for the sight setting and hold based on a full size IPSC without knowing the full ballistics of your rifle.

200 yds - 186 meters - "2" Dead On
300 yds - 274 meters - "3" Dead On
400 yds - 365 meters - "350 setting" Hold Shoulder Line
500 yds - 457 meters - "450 setting" Dead On
600 yds - 548 meters - "550 setting" Dead On

When zeroing, leave the BDC knob on "2", use the small aperture, make elevation adjustments with the front sight, and windage adjustments on the rear sight. I would zero about 1/2" high or so of center at 50 yards and confirm point of aim, point of impact at 200 yards. If you need to make small adjustments use the front sight for elevation, rear for windage still. After that start stepping out the distance, writing down the sight settings, where you had to hold on the target, and the results. Good luck.

That was very helpful, I'll try & follow those instructions. I have a laser rangefinder that'll help too. Thanks.

 

[thejeep]

You could also measure your sight height and plug your ballistics in to a calculator. Put in your desired zero range and see where the dope lines up at a closer range.

Using a sight height of 1.5” and a speed of 2600 and a 200yard zero, it says you should also be dead on at 25yards.

 

[Trigger Monkey]

Sight height on an large frame gas gun is going to be closer to 2.8". Plugging that into JBM with the above MV, although I think 2600 is going to be optimistic from a 16" barrel, it puts the close range zero closer to 47 yards.

 

[TexasGuns]

You could also measure your sight height and plug your ballistics in to a calculator. Put in your desired zero range and see where the dope lines up at a closer range.

Using a sight height of 1.5” and a speed of 2600 and a 200yard zero, it says you should also be dead on at 25yards.

Which calculator? I only have the earlier version of STRELOK.

 

[thejeep]

Probably any of them

JBM - Calculations - Trajectory (Simplified)

www.jbmballistics.com

 

[TexasGuns]

We shall see. I'm drinking coffee now, afterwards will load the truck with my favorite Guns & Ammo.

Today I'm going to focus on getting the irons done on this rifle I need to hit a 12-15" square at 400 yds. Then I can call it good for BUIS.

I'm going to try both the short range calculations & try the 200. Then I'll lob a 168 gr. in at 400 and listen for the ring of steel.
Thanks for the help men!

 

[TexasGuns]

@Trigger Monkey
In on steel 400 yards with the BUIS. Very satisfying!
Thanks for the help everyone.
TG

 

[Trigger Monkey]

Good to go! I'm glad it worked out.