Sight jump left-to-right when dry firing

[rdtompki]

We have four full-size M&P all with Apex DCAEK installed. All have about a 5 lb trigger pull. The gun with which I'm experiencing an issue has the stock trigger spring, but so do two of our other M&P. These are all recent acquisitions over the last year or so. When I dry fire the three of handguns the front sight is absolutely motionless. When I dry fire one of the .40 cal the front sight jumps left-to-right quite a bit. I've looked at the Apex videos and it may be that I need to adjust the trigger bar loop (I've e-mailed Apex), but I thought I would also reach out via the interweb.

I've looked at several threads that bring this up, but most discuss remedies related to grip, finger placement, etc. That's obviously not my situation. Would appreciate information from anyone who has remedied a similar issue.

 

[ScrapmasterFlex]

I do not think I can help you fix your problem directly but would like to share a bit of recent experiences that helped me some-

In June I think, I bought a LaserMax Genesis ... that is a micro-sized, rechargeable high-quality green laser. It was designed for subcompact semi-automatics to be rail-attached but works on any gun with a rail; it even has a remote switch you can buy for a long-gun. I am not sure what prompted it- to be honest, it came on an eBay auction that I was able to virtually steal it. I had recently bought a new Sig P226 MK25 and wanted a full-size light and green laser combo to put on the full-size rail on this full-size gun. BUT, they are $400 nearly, and this was a pawn shop that puts their inventory online. Someone bought it and received it one day and needed immediate money the next. they pawned it brand new in open box, the auction didn't generate much and I got it for like $60 bucks, awesome.

point is this. I put it on, and wound up doing a bit of dry fire practice. I noticed that I was having a HUGE hitch in my trigger-pull. You know how a lot of "novice" (right-handed) shooters pull the shots low and to the left? I was able to see myself do it big time when the laser was on the wall .... it was extremely easy to see my problem. Since then I have consistently practiced my aim , my hold, and particularly my finger position on the trigger and the entire squeeze, follow through, etc.

I have since moved the laser to a few different guns, with obviously different actions and triggers etc. And I had very different results- some were very pronounced one way, another gun had me jerk another way, and one was looking pretty darned good. So it re-enforced the idea different guns, with different systems/different triggers, can make you shoot differently.


None of this might apply to you, maybe it's a gun hardware issue. But it could very well be the way you shoot, the way you hold or squeeze the trigger etc. Just something to think about, don't mean to patronize you or anything, just something to consider.

 

[forrestinmathews]

I feel like it is a function of the disconnector. It is actually the rear of the slide moving. Mine does this. It doesn't affect where the bullets hit so I have learned not to care about it.

 

[MichiganScott]

If all of them jumped you could figure it's a grip issue. Since only one of the .40's does it, you can figure it's hardware. If it shoots as well as the others do, I'd ignore it. If it bothers you, sell it and try to find one that doesn't.

I've got three stock 9's and they all do it when dry fired. They all hit the target when actually shot, so I've never thought anything about it.

Tolerance stack can do strange things.

 

[Rastoff]

We have four full-size M&P all with Apex DCAEK installed.

The most common cause of this "jump" is trigger over-travel. However, the DCAEK is supposed to take care of that. So, I recommend you check your over-travel. If you don't know how to do this, I can give an explanation later.

I feel like it is a function of the disconnector.

It cannot be. The M&P doesn't have a traditional disconnector like you'd find in a 1911 or an H&K USP. It is more of a passive device and is not part of the sequence when doing dry practice.

The disconnector is this part of the trigger bar:

It serves two functions. First, it moves the striker block out of the way of the striker. Secondly, it functions as a disconnect. It operates as the slide moves toward the read. There's a cam in the slide that pushes on this and moves the trigger bar loop out from under the sear, thus disconnecting the sear from the trigger bar.

Here's a short vid on how the trigger works:
https://www.youtube.com/watch?v=5_RoDAOQGnQ

 

[robkarrob]

I think it is an over-travel issue. Dry firing only amplifies the problem. The other guns may have less OT and that is why you can keep the muzzle still on those guns. Unless there is a very evident issue difference in the actual pull, I would check the OT differences between the guns with no problem and the one that moves. You can measure the OT by placing an object, like a punch, behind the trigger, so the trigger stops moving right after the break (striker releases). Chances are you won't get a punch or similar that fits perfectly. Just roll some tape around the punch until you get it built up enough to stop the trigger movement. You can put a ruler up and then measure the trigger movement to fully back, after removing the punch.

I personally do not like excessive OT. All my guns have some type of stop to reduce the OT to a bare minimum. Minimal OT helps to reduce excess muzzle movement, helps to get back on target faster, and allows for faster trigger reset.

Bob

 

[Indynick]

Thanks for the explanation. I was experiencing the same issue during dry-fire, with my Shield, but not my 380 BG.

 

[thewittmp]

The most common cause of this "jump" is trigger over-travel. However, the DCAEK is supposed to take care of that. So, I recommend you check your over-travel.

Thanks for that tip. I have the same issue with my Shield, but not my FS40, BG380, or M&P22. To test, I put something (pen ink cartridge) behind the trigger just after where it breaks and my "jump to the right" disappeared.

 

[mikeasb]

Another vote for trigger overtravel. Both of my Shield 9mm's did it until I installed the DCAEK in them.

 

[rdtompki]

I "solved" my problem by swapping slides on my two 40 cal. The better trigger (short reset, no over-travel) now hosts the slide equipped with Dawson sights. This frame has a 5lb/10oz trigger pull so I'm going to put in an Apex competition spring kit which may reduce that by a pound or so. I really don't mind the actual pull as the break on this combination is very clean, almost no discernible creep. The other 40 will be my night stand/competition backup gun.