Driving an AR, dry firing problem?

[Bravo 4]

Yesterday I had my DPMS built .308 out doing some dry firing practice (recent medical issue keeping from firing live ammo). I noticed that most of the time the crosshair would jump .2-.3 mils to the right when the trigger was tripped. It did this not matter how I drove it or what kind of rest I used. I thought it might be me so I pulled out two bolt guns and no problems at all. I have also done a lot of dry firing with my M110 and never noticed this problem. The only modification I've done to the DPMS was install a Chip McCormick Tactical Trigger. I will admit that it has given me fits trying to find a load that will group decently and consistently.
Any ideas?

 

[LouBoyd]

Is there a reason you don't use Snap-Caps? The energy of the falling hammer has to go somewhere. When firing live ammo much of the energy is absorbed in the primer as it is with a Snap-Cap.

Snap Cap 308 Winchester Polymer Package of 2

 

[Bravo 4]

Never felt the need. I dry fire all my rifles thousands and thousands of times and never had any issues with wear-n-tear. If you dry fire and the sights/crosshairs bounce off target there is an issue with you or your equipment...that's what I have been taught for years. I understand what your saying, but the sights shouldn't be moving off target!
Thanks for the response Mr. Boyd.

 

[Greyfox]

I have seen this with my AR10 type rifles. Unlike a bolt rifle, the hammer is hitting the rear of the bolt directly, especially when there is no round in the chamber to neither absorb the firing pin hitting the primer. There is also no cartridge in the chamber to take up any small tolerence in the bolt lock up. The inertia of the bolt getting hit directly by the hammer is magnifying the impact of your hammer. If it still does this when you put a dummy round in the chamber, check the alignment of the trigger assembly and whether the hammer is hitting the firing pin squarely and centered. Some trigger assembles have hammer springs that are too heavy. I use RRA Match and Geiselle triggers. They are perfectly aligned, and have good hammer spring tension.

 

[Bravo 4]

I was thinking that the hammer spring might be pretty stout. I will check to see if it is hitting square.
I might try the snap caps and then putting the factory trigger group back in.

 

[ICANHITHIMMAN]

I just got out my 5.56 rifle and did some dry firing it does not move so I'm not sure whats up. I would not think it should move. What kind of scope is it?

 

[Bravo 4]

The scope is a Falcon 4-14. I don't think that's the problem but I will check it. I did check the mount. Habit to check them before and after anyways.