Front flip-up BUIS problem...

[xamsx]

I just received my BUIS from MI in the mail today for my DPMS Sportical 7.62x39. Got the rear sight on with no problems.. it was when I mounted and tightened the front sight on my railed gas block that I realized something was wrong...

YouTube - Railed Gas Block - Front BUIS Problem

I'm thinking the dimensions of the railed gas block aren't mil spec? Cause the allen head screw is tightened all the way and there's no way the base of the sight and the plate can get any closer together. They're slabbed together as tight as possible. The gas block is the original that came on the AR when I bought it.

Only solutions I can think of would be to buy a new railed gas block that IS mil spec, or return the front sight (if I even can.. I bought these as a package deal) in exchange for the one that's made for mounting on a railed handguard, as I just ordered a carbine length Daniel Defense Omega rail a couple days ago that should arrive any day now...

Kind of annoying DPMS put these railed gas blocks on all their Sporticals. What flip-up sight did they expect people to get that would work with them? Gah.

Any easier routed solutions that could be slipping my mind?

 

[jd4320t]

Would the sights be different between a 223/556 and 7.62x39?

 

[IndyGunworks]

Would the sights be different between a 223/556 and 7.62x39?

No a picatinny rail is a picatinny rail.... chances are your gas block is not in spec, or the sight is out of spec. go online and get some dimensions of what they are supposed to be and do some measuring to see which one is messed up.

 

[68kidd]

I own a DPMS SPORTICAL. I put a PRO MAG PM 138( flip up)on mine and it works fine. You can find them from about $55 and up. I think i paid $45 for mine at a local gun shop. Their site list them for $100 , but you can find them cheaper. Here is a link to some , i can sure you can find more if you search.

ProMag 138 Flip Up Front Sight Picatinny Rail Flat Top

 

[Dog1]

Looks like the gasblock is out of spec. Call DPMS in the morning and tell them about it.

The rail dimension should still be the same, be it a .223/5.56 or 7.62x39 AR.

 

[remymartin]

Something is surely out of spec. Rail is rail. Btw the fsb is backwards. No biggie though, my buddy runs his like that on a CMMG block with no problems. Just stick some newspaper in there for Now.

 

[xamsx]

Yeah, looks like I'll be making a couple calls in the morning..

Thanks for the input, everyone.

Something is surely out of spec. Rail is rail. Btw the fsb is backwards. No biggie though, my buddy runs his like that on a CMMG block with no problems. Just stick some newspaper in there for Now.

Yeah, I was thinking the same thing when I went to install it. You'd think it should fold to the rear, but then it'd be hitting the handguard (or quad rail) without folding down all the way. I checked on Midwest Industries' website to be sure and it states the front gas block model should fold to the front.

 

[jd4320t]

Wow, if that is out of spec it is WAY out of spec!

 

[Airborne33]

The part that tightens down the the rail. I don't know the name of the piece. Did you make sure it isn't flipped upside down? It might not "bite" down correctly if it is. BTW I'm obviously not talking about the screw, but the piece of metal that the screw pushes in to tighten it.

 

[Airborne33]

wait.. nevermind.

 

[xamsx]

The part that tightens down the the rail. I don't know the name of the piece. Did you make sure it isn't flipped upside down? It might not "bite" down correctly if it is. BTW I'm obviously not talking about the screw, but the piece of metal that the screw pushes in to tighten it.

I know what you're talking about, and yes, I made sure it wasn't upside down.

 

[xamsx]

Well, called Midwest Industries this morning and told them the deal.. Before I could tell them I think it might be my railed gas block, the guy I was talking to said he'd send a replacement out to me today. He then said if this 2nd one doesn't work, it's my rail, and I agreed.

MI are great people to do business with.

Comparing the front sight I received with the picture DPMS has on their website (Online Store — DPMS: AR-15 Rifles, Parts and Accessories.), I notice a couple very small differences in the base (primarily on the sides, where the sight would 'bite' the rail).. But those differences could be exactly why this is happening.
We'll see, I guess.

 

[jd4320t]

What about DPMS? Have you contacted them?

 

[jblomenberg16]

What happens if you put the front sight on the upper reciever rail? Looks like the rear flip up mounts correctly.

If the front sight goes on and locks up solid, then you have a gas block issue.

If it rattles around you have a front sight problem.

Obviously, you probably won't be able to shoot it that way, but it will tell you if you have a sight or gas block issue.

 

[jd4320t]

What happens if you put the front sight on the upper reciever rail? Looks like the rear flip up mounts correctly.

If the front sight goes on and locks up solid, then you have a gas block issue.

If it rattles around you have a front sight problem.

Obviously, you probably won't be able to shoot it that way, but it will tell you if you have a sight or gas block issue.

Great idea. Try the rear sight on the gas block rail too.

 

[xamsx]

What happens if you put the front sight on the upper reciever rail? Looks like the rear flip up mounts correctly.

If the front sight goes on and locks up solid, then you have a gas block issue.

If it rattles around you have a front sight problem.

Obviously, you probably won't be able to shoot it that way, but it will tell you if you have a sight or gas block issue.

Haha, kinda funny I come back to see someone suggested this, cause I actually tried it not long after I last posted my little update in this thread this afternoon and I'm now 100% sure it's a sight issue.
Swapped the 2 sights and the rear sight on the gas block was tight, with no play (as it was on the receiver), and the front sight on the receiver still jiggled around and wasn't snug at all (as it was on the railed gas block). I was foolish for not trying this in the first place!

I then took off both of the sights and compared the bases and noticed the opening on the bottom of the front sight post (where the picatinny rail would be) looks a little more roomy than that of the rear sight's...

Rear:

Front:

(Sorry for the blur.. My stupid camera didn't wanna focus for the front sight like it did for the rear)

See what I mean?

 

[jblomenberg16]

Haha, kinda funny I come back to see someone suggested this, cause I actually tried it not long after I last posted my little update in this thread this afternoon and I'm now 100% sure it's a sight issue.
Swapped the 2 sights and the rear sight on the gas block was tight, with no play (as it was on the receiver), and the front sight on the receiver still jiggled around and wasn't snug at all (as it was on the railed gas block). I was foolish for not trying this in the first place!

I then took off both of the sights and compared the bases and noticed the opening on the bottom of the front sight post (where the picatinny rail would be) looks a little more roomy than that of the rear sight's...

Rear:


Front:

(Sorry for the blur.. My stupid camera didn't wanna focus for the front sight like it did for the rear)

See what I mean?

Glad you got it figured out, and props to MI for sending you a replacement. Hope it fixes the issue!