BUIS problem on an M4

[rebel]

A young friend of mine finally purchased his first AR. DPMS, 16 inch, lightweight barrel vanilla ice cream rifle. Imediatley started doo-dadding it-mag-pul stuff.I took him to the range yesterday for first shots with it. He had the mag-pul front sight on the handgaurd which I switched to the gas block. Even after adjusting all the way out, the thing shot 16" high at fifty. Just for shits and giggles, I put it on the handgaurd to raise it considerably and after shooting and adjusting ( bottoming out ) it shot a foot low. Even compared to another AR there with an A2 front and couldn't see much heigth difference. Quick fix-a small three lug riser on gas block? Anybody else run into this?

[FireF191]

What type of rear sight? Also, magpul states that the polymer sights CANNOT be placed onto the gas block due to heat.

[rebel]

Same mag-pul, I don't run them and did not have the packaging they came in, but that makes sense as they are plastic. Sounds like he needs the front sight on the hangaurd and riser the back, or whittle down the front post.

[GSO]

Glad to hear that you didn't shoot enough to melt the polymer.

The Magpul rear BUIS is made to regulate with the standard A2 front sight base. They then made the front flip up BUIS to match that height when mounted on a front rail the same height as the A4 (normal flattop receiver) rail. If the addition of the Picatinny rail to the handguard makes it higher than the receiver rail, then you would need a riser on the receiver for it to regulate properly.

Assuming it is 1/2" difference, something like this should work:

http://www.midwayusa.com/product/313161 ... inum-matte

[rebel]

Yep, what I figured. I only run stout metal flip ups on my stuff and never had a problem. But with different heigths of stuff folks are adding to rifles, you end up with all kind of different scenarios. I've got something he can run until he gets his own. Thanks for the Magpul siight/gas block tip-would have melted the bitch down if it had been dead on. As it was we only ran 20 rounds, and that was with breaks, cussing and switching the front sight around. Got 20 rounds of LC 223 to chop now

[-k-]

What kind of handguard is on it?

[kR-15]

I believe the DPMS rifles - especially the entry level ones (oracle for example) need a gas block riser for proper sight plane alignment on a front sight. The armorer at my LGS mentioned that when we were talking about sight planes and cowitness setups.

[rebel]

k-Not sure what model # handguard- short with bolt on rails. kr-15-slapped a small riser on the rear after moving the front back to the handgaurd and she shoots fine. Thanks for the input.

[kR-15]

k-Not sure what model # handguard- short with bolt on rails. kr-15-slapped a small riser on the rear after moving the front back to the handgaurd and she shoots fine. Thanks for the input.

Glad to hear it!! It sure feels good to put rounds on target after things get sorted out

[rebel]

He left me ammo-to sight in his rifle L.C brass makes good future blackout ammo.