Am about to complete a buld of a 20" flat top rifle w/ YHM LW 4 rail, and IOR M2 scope. Have read some concerns w/ short eye relief for these scopes and was wondering if anyone had any experience w/ putting their BUIS in front of the scope (so I can maximize the real estate on the top of the reciever). Will be mounting scope in IOR high throw lever rings. With a rifle length free float tube, and the BUIS mounted forward (saw at the extreme rear of the tube), will the sight radius be about what a carbine radius is? BUIS will be a DPMS A2 fixed.

Thanks upfront.

could work but im sure you can get it mounted properly behind the scope.




eta. not the dpms fixed sight though.

Well, I'm sure you can't get a fixed sight to sit behind your scope.... so you either need a folding sight or one that you can move around and repeat zero.

The DPMS fixed will probably not repeat zero. The LaRue fixed will. Not much if any difference in price.

You'll have to sight in the BUIS in its normal position, then park it on the forward rail and sight in the scope. If you try to use the BUIS mounted on the front rail, it will be to far forward to get a good sight picture, and the sight radius will be to short. (Although the Candaians apparently run the fixed BUIS in front of the Elcan scope, but it is on the upper receiver, not on a handguard rail.)

All this also means, if you want to use your irons, you'll have to have some way of removing the scope too. A QD mount or a set of QD rings. This is because you'll have to remove your scope to use the irons properly. Even if you use a folding BUIS you'll need that type of system.

Before I got a LaRue Mount for my Compact ACOG I had mounted my ARMS#40 in front of the scope.

Once the scope is removed and the BUIS raised, the sights work well enough for a backup sighting system.

the dpms rear WILL repeat zero.  with a red dot i might try it in front, but with a scope itd be too far forward.  the farthest forward ive run it is on the front of the receiver on my short stocked carbines.  just keep it with you in case your scope goes tits up.  i take mine off my 308 all the time, as well as the front, and still can hit at 200 and 300 yds.  just make sure you put it on the same every time, either to the rear or front of the rail slot.

THX all, the rail will be a free float, so I shouldn't have to worry about "wiggle", and the rings I'm using will be ARMS 22Hs, the IOR rings are out of stock at SWFA.

IIRC, D&L or something similar commonly mount their rear BUIS infront of scopes on their rifles.



Mike

Those D&L sights are not aperture sights though, they are essentially pistol sights, notch and post. I think the problem with moving a standard AR peep sight forward is that the rear aperture starts to get really small as you move it away from your eye. You could open up the rear aperture to compensate for that though.

Mike

Quoted: .... I think the problem with moving a standard AR peep sight forward is that the rear aperture starts to get really small as you move it away from your eye. ....

Which is why you use the Large aperture.

(photo of the rifle where I used the forward mounted BUIS).  The ARMS #40 deploys with the large aperture immediately available.

Quoted: Quoted: .... I think the problem with moving a standard AR peep sight forward is that the rear aperture starts to get really small as you move it away from your eye. .... Which is why you use the Large aperture.

Right, but then haven't you essentially made the large aperture the small aperture and no longer have something equivilant to the large one? I was taught that the large one is the one you want for close quick shots and if I'm transitioning to my BUIS, I'm probably going to have some of those shots coming up. ;)

Of course it's all a preference thing and I haven't tried this, so I may be exaggerating the effect somewhat. If it works for you I have no problems with that.

Mike

Quoted: Right, but then haven't you essentially made the large aperture the small aperture and no longer have something equivilant to the large one? I was taught that the large one is the one you want for close quick shots and if I'm transitioning to my BUIS, I'm probably going to have some of those shots coming up. ;)

You use what you have.  Small aperture sure beats NO BUIS.  Besides I didn't have any large apertures on my old M16A1 and it still did the job.

Quoted: You use what you have.  Small aperture sure beats NO BUIS.  Besides I didn't have any large apertures on my old M16A1 and it still did the job.

Agreed. I didn't know that they had A1's with a single aperture. I joined up (Army) in 86 and we had A1's but I believe they had 2 apertures. Learn something every day. Now I can go home.

Mike

Quoted: Quoted: You use what you have.  Small aperture sure beats NO BUIS.  Besides I didn't have any large apertures on my old M16A1 and it still did the job. Agreed. I didn't know that they had A1's with a single aperture. I joined up (Army) in 86 and we had A1's but I believe they had 2 apertures. Learn something every day. Now I can go home. Mike

So did mine - but they were both the same size (small).  The only difference was height.

Whoah...hey guys, I just wanted to know if it was a viable solution for my setup, didn't want to start ANOTHER pissing match about who's way is better...mods please close this thing

I would keep the BUIS behind the scope for many reasons, as has been stated above.

Keeping the proper sight radius, keeping the "ghost ring" larger aperature usable as designed (which is 0-200, small hole is for beyond 200) and most flip up rear sights are designed to work in the rear-most rail notch (especially the DPMS style).

If it were me I would trade that long EOTech for a shorter model and move it forward, ahead of the rear BUIS.

Quoted: IIRC, D&L or something similar commonly mount their rear BUIS infront of scopes on their rifles. www.dlsports.com/home/ar15_eotech_02_med.jpg Mike

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Not to hijack the thread, but let's take another step.  What would be a good folding rear BUIS to accomocate an EOTech with a PVS-14, both mounted directly to the flat-top?

Quoted: Not to hijack the thread, but let's take another step.  What would be a good folding rear BUIS to accomocate an EOTech with a PVS-14, both mounted directly to the flat-top?

Troy would be my first choice, ARMS #40L (the thin one) would be my second choice.

Quoted: If it were me I would trade that long EOTech for a shorter model and move it forward, ahead of the rear BUIS.

No need to trade it for a shorter model.  Just get a decent BUIS and it will fit behind the EOTech.  The above photo is from a manufacturer that sells BUISes that are meant to be foward.

The only time I'd consider putting the BUIS forward (as I have) would be to mount a scope (magnified optic) that had short eye relief (like the 3x Compact ACOG as shown above) OR if the only BUIS I had was non folding (like the LaRue or the Canadian C7A1 BUIS).