mp 15, brand new with loose rail

[78Staff]

That's correct. Do not mount the front sight to a drop in rail/forearm. But, why Rastoff? I'm so glad you asked that young Padawan...

You got a like for the Padawan reference right off the bat

 

[sugerwater]

I use a Damage Industry Rigid Quad Rail. It's thinner then the delta ring side to side and is rock solid. With the rage being FF hand guards, quad rail have lost a lot of popularity. I'll keep mine anyway. Magpul MOE locks in pretty good but not solid.

 

[BluGrass]

That's correct. Do not mount the front sight to a drop in rail/forearm. But, why Rastoff? I'm so glad you asked that young Padawan...



No matter how tight you get the drop in forearm, there will always be a tiny bit of movement. If the front sight is on the forearm, it will move with the forearm and your Point of Impact (POI) will constantly be changing. Any movement of the front sight will affect the POI. So, if the front sight is attached to the barrel, it will be rigid and won't move with the forearm.



This is why an optic should be mounted to the receiver. The receiver is fixed to the barrel. Thus, the two move as one.



This is also why a free float forearm is such a good idea. Because the free float forearm is attached only to the receiver, any flex in the forearm won't affect the sights. Thus, when you put your forearm on a bag, rest or bipod, the rest won't cause the barrel to move like it would with a drop in forearm. However, if the front sight is affixed to a free float forearm, that forearm had better be rigid or any movement will change the POI.





Any pressure on the barrel can affect POI. I know the barrel seems very stiff, and they are, but they still bend if you put it in a rest. They only bend a tiny bit, but that is enough to change you POI a couple of inches at 100 yards. So, if you have a drop in forearm and want to use a rest, place that rest as close to the receiver as you can. This will reduce the lateral pressure on the barrel. This is why most bolt action guns have stocks that don't touch the barrel. The effect is the same as a free float barrel.

Thank you again Rastoff. I moved my front sight to gas block and my groups improved immediately. Didn't shoot a ragged hole in the bulls eye but hit it more than I was before. Breathing and consistent cheek weld are now what I need to work on. Thanks again

Josh


I'd rather die on my feet than live on my knees

 

[Rastoff]

That is an excellent report Josh. Glad we could help.