I just completed my first AR.  It's a mega lower, with a del-ton 20" flat top upper.  I have a 3X9 scope on it.  Shot it today at the range.  It is shooting really good groups off the bench, but once taken off the bench and shot free hand or resting on the mag (prone) it's hitting about 4" low.  Is this due to fore end pressure?? and should I put on a free float tube.  Thanks.

no, but I shot a number of rounds both ways.  was able to hold the gun plenty steady to determine point of impact.  Also let a buddy of mine shoot. Same thing with him. dead on resting on the bench where there would be fore end pressure, and low without it.  Also resting the gun on the mag only, again no fore end pressure. low again.

It strikes me as odd that I would have it dead on, with the forend resting on a bag, and 4" low not resting on a bag.  I built it for coyote hunting where I may or may not have a rest, and I don't really want to have two impact points based on what's happening with the forend.  Do you think by putting a free float tube on it would help.  It would make sense to me, as then the only pressure would be on the barrel nut and upper receiver???

If you were using the sand bags at the end of the guard (muzzle side) then it may have caused some upward barrel deflection.  On the other hand, if the sand bags where placed at the receiver side of the front hand guard, then you have a loose barrel (saying the rifle was only rested, and not being pushed down).

Simple put, unless you were applying a lot of pressure on the barrel to tension pressure it, then it sounds like the barrel was not installed correctly in the upper, and the slightest pressure is going to case a shift in POI verse POA due to the barrel movement in the upper socket.

Also, you don't mention the make of the scope.  Most scope will not change there POA much as you get off axis to the view point, nor change there POA due to different types of vibration, But if you have a cheap unit, don't just write these off.


Now as for the Float tube for the rifle, not really a bad idea on a Coyote rig.  First shot will be off the bipod, then free hand if you miss to walk in the rounds.  If nothing else, the float tube gives a hang/attachment point for the bipod, and no matter how much tension you put into the front end (guard), the barrel will still print to the same POI until over heat/barrel excessive whip.

Thanks for the help, I think I'm going to put a a float tube and see what happens. Either way it's bound to help by either making sure the new barrel nut is propertly torqued or by eliminating the forend pressure it's gotta help.