Why the difference? BUIS vs. .308 Carry Handle

[Rekrab]

While I'm still not finished with my basic build I've been looking around to score a deal on a carry handle for my LR-308.

Since I'm not cash-rich enough to put the optics I want on it yet, I'm looking for a basic Iron Sight set up to hold me over until I can put a nice Eotech or Trijicon on it.

First of all, I'm building a carbine, not a rifle so step back from your keyboard, I'm not building this as a bench rest long range shooter. Just something for fun.

Anyways!

While shopping I noticed a rather large price descrepency between the .308 Carrying Handles and the AR-15 Carrying Handles. I've been told this is because the greater recoil of the .308 round requires a heftier sight to take the abuse. I'm willing to accept this.

However! When I start looking at flip-up irons, everything is universal and I don't see any designed for the .308 round.

I'm confused and annoyed. Annoyed because there are only two companies that manufacture the .308 carrying handle (Colt and DPMS) and confused because I'm lost on back up iron sights.

I'm at the point where I'm saying "Ah screw it, I'll just buy a cheap-o Magpul BUIS!"

[C_1]

Well, if you plan on putting some optics on it, a flip up back up iron sight would be a good choice, rather than a carry handle sight.

[Rekrab]

This is true, I've just always loved the look of the carry handle.

[ar15barrels]

The deal is that a 308 carry handle is longer and a different height than an AR-15 carry handle.


Armalite first started producing AR-10's in an A2 configuration, using the very same front sight from an AR-15 and then making the receiver's sight height to accommodate that.
Now the AR-10 receiver (as well as all other 308 AR uppers) has a larger bolt carrier diameter to handle the larger 308 bolt.
Therefore, when you make a flattop 308 upper receiver, the top of the receiver is going to be taller (measured from bore centerline) than an AR-15 upper receiver.
AR-15 backup sights are all made to fit on a standard height AR-15 receiver and align to a fixed A2 front sight post.

So you have a difference between upper receiver rail heights caused by the different bolt carrier diameter.

When Armalite started producing flattop receivers, they first built them all with railed gas blocks and removable front sights.
They made those parts lower to keep the same cheekweld of an AR-15.

So, if you want to run backup iron sights on a 308 AR, you can use a standard rear backup sight, but you will not be able to use a standard gas block mount front sight.
The AR-15 rear sight will be higher when installed on a 308 receiver or with a flattop and a special rear sight that's lower than normal.
There is also an extended height gas-block-mount front sight made by Midwest Industries that solves this problem and lets you use standard ar-15 rear sights on a 308 flattop receiver.

If you have a fixed sight on a 308 barrel, it can only be used with an AR-10A2 receiver.
If you have a gas block on an armalite 308 barrel, it can only be used with Armalite's rail mounted gas block fixed front sight and carry handle, or with an MI rail mounted 308 gas block flip-up front sight and regular AR-15 rail mounted rear sights.
Lastly, if you have a full length rail system, you can use regular AR-15 rail-mounted sights on both the rail and the receiver as they are on the same plane.

[Rekrab]

Well that clears up a bit of the mystery Randall, thanks for the history lesson!

However, I'm still lost on whether or not I can just slap a BUIS and call it good. My initial reaction from your post is telling me "no" but I wanted to make sure.

Thanks for the help~

This is my upper by the way: http://www.dpmsinc.com/store/product...=1704&cat=1939

[ar15barrels]

re-read my post.
I edited it a few more times to fill in gaps in info.

DPMS complicates matters even more as they have made receivers and gas blocks in two different heights.
For your upper with fixed front sight, you will need a special 308 rear sight or carry handle that's lower than standard AR-15 parts due to the fixed front sight on the barrel.

[Rekrab]

Huh, well that's bizarre.

I've never seen any special 308 rear sights that are marked as being lower. I've only seen the special marked carrying handles. Is there a special designation I should be looking for?

[ar15barrels]

I've never seen any special 308 rear sights that are marked as being lower.

I have not either.
There are only carry handles.
You can cut the handle part off the front and end up with something like this:

[Rekrab]

Hahaha, Yeah, after dropping $130 on a carrying handle I don't think I'll be wanting to hack it up like that.

Thanks Randall you've been a huge help. Hopefully I can kick some business over to you one of these days. Like, if I ever decide to convert my Saiga and want a flash hider put on >.>

[C_1]

Would the TROY micro rear sight work? I dont know. Just a thought..

[ragenmoan]

I wondered if I was limited to only having glass sights for my DPMS LR308 upper receiver. It is the "smooth side" flat top receiver with no door or shell deflector. Using the DPMS free float hand guard as a reference point, the flat top rail is raised above the hand guard and the barrel block rail is level with the hand guard. Does anyone make an iron sight combination that will work for this DPMS LR308 smooth side upper receiever assembly? Maybe DPMS? I called them and at least 1 person said that it was OK to use standard AR15 BUISs! I did not get a warm fuzzy feeling from them....