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View Full Version : Pistol shooting 1" to 1 1/2 inch low. (Grant or Anyone, Help please)



RogerinTPA
07-29-09, 09:10
I have two M&P pistols with identical sights (straight eights). The M&P9c is dead on. The full size M&P9 is shooting an inch, to an inch an a half low from POA. To compensate, I have to hold high, or displace the front sight by an 1/8 of an inch higher than the rear, in order to hit where I aim. I thought about having the FS shaved down and took it to a "smith" but he said there was too little material on the bottom to adjust. I called the manufacture, explained the situation and asked if they had a different size front sight for me to purchase. They said no, it's the only sight they offer. I saw some alternative sights at brownells, but I don't know the height/size measurement of my current front sight (#409 M&P Ledge Quick), to make an educated decision. Most folks say it's not a big deal, but it is frustrating to pick up any one of my handguns and know I can hit what I'm aiming at, then have to use a modified sight picture on this one. Anyone else with a similar problem using these sights? Thanks.

Roger

Robb Jensen
07-29-09, 09:34
Faster pistol rounds hit lower. You can change to slower ammo to make up for this or go with a shorter front sight.

I had custom fronts made for my M&P9L and M&P Pro because of this.
Kenny at Speed Shooter Specialties can make them for you.
My Pro has a .188" tall by .115" wide serrated front made from a Dawson blank. This works very well for me with 115gr FMJ and 147gr JHP subsonic match ammo.

Wayne Dobbs
07-29-09, 10:43
To determine what kind of sight correction you need use this formula:

Amount of impact error in inches multiplied by sight radius in inches divided by the range at which the group was fired in INCHES.

You don't mention what your range is, but if you multply 1.5 (error) X 6.5 (approximate sight radius) = 9.75 inches divided by 900 (25 yards) = .01 inches of correction needed.

Lots of folks, including gunsmiths will guesstimate this, but the formula has always worked for me.

TriumphRat675
07-29-09, 13:40
I thought my M&P 40 had gone TU when it went from dead on to shooting 1 inch low. I figured out the change was because I was using a few boxes of Speer Lawman practice ammo. When i changed back to wallyworld white box it went back to being dead on. Try a different brand of ammo and see what happens.

Surf
07-29-09, 15:29
As mentioned ammo can make a difference, but at what distance are we talking here?

RogerinTPA
07-29-09, 22:18
Very interesting responses. I never knew faster ammo would shoot low. Learn something new every day, but why is the 9c dead on? Shorter sight radius than the full sized? Thanks for the info gentlemen.

Robb Jensen
07-29-09, 22:26
Very interesting responses. I never knew faster ammo would shoot low. Learn something new every day, but why is the 9c dead on? Shorter sight radius than the full sized? Thanks for the info gentlemen.

The ammo is going slower out of the smaller gun.

ToddG
07-29-09, 22:28
I never knew faster ammo would shoot low


The bullet leaves the barrel sooner, meaning it leaves the barrel earlier in the upward recoil arc.
For tilt-barrel weapons, higher pressure ammo means the barrel takes longer to unlock (begin tilting). Unlocking too early can result in shots going high.

RogerinTPA
07-29-09, 22:30
Gotcha! Thanks again GotM4.

RogerinTPA
07-29-09, 22:39
As mentioned ammo can make a difference, but at what distance are we talking here?

15 ft. Ammo used is 115 grain wolf blk box, fouchi, and S&B.

Robb Jensen
07-29-09, 22:54
High pressure an high velocity are almost the same but sometimes you can have high pressure and low velocity and low recoil.

Case in point:
My old USPSA load:
9mm (9x19mm) 147gr JHP going 875fps makes 9mm +P++ pressures with very fast burning powder (VV N310) but feels like .22 Magnum.

Rider79
07-30-09, 03:04
Now you guys have me paranoid. I haven't noticed anything yet in my 19 with Warren 2 dots, but is this something I should be looking for? I've only shot practice loads so far. When Grant gets it in I plan on switching my carry ammo to RA9T or RA9B, and getting enough to test POA/POI in all my carry Glocks, but right now all I have is the Hornady TAP I've been carrying for awhile and not much of it.

ETA: Would I run into this with the RA9124TP? I'm considering picking that up instead since its in stock.

ra2bach
07-30-09, 03:36
Very interesting responses. I never knew faster ammo would shoot low. Learn something new every day, but why is the 9c dead on? Shorter sight radius than the full sized? Thanks for the info gentlemen.
actually, it was pretty common for a lot of people for the FS M&P to shoot low with the stock sights.

I never did get comfortable with the 3-dot sights and used a Sharpie to black out the two rear dots. magically, it started shooting to POA. you may want to try that or simply replace the sights altogether...

RemMan700
07-30-09, 13:51
heavier grain bullets will also leave the barrel slower and usually print higher then the same ammo but with a lighter bullet.

RogerinTPA
07-30-09, 18:37
actually, it was pretty common for a lot of people for the FS M&P to shoot low with the stock sights.

Not on my 4 M&Ps (FS45, FS40, FS9 &9c). I've been shooting them for a couple of years now, with over 3-5K rounds fired on each of them. They all shoot POA/POI with the stock sights, right up until I switch sights on the FS9. The .45 came with 3 dot trijicon sights from G&RTactical, and that too, shoots POA/POI.

ra2bach
07-31-09, 14:24
Not on my 4 M&Ps (FS45, FS40, FS9 &9c). I've been shooting them for a couple of years now, with over 3-5K rounds fired on each of them. They all shoot POA/POI with the stock sights, right up until I switch sights on the FS9. The .45 came with 3 dot trijicon sights from G&RTactical, and that too, shoots POA/POI.

roger that. in my case, it was a personal problem rather than a gun problem. something about the way those three white dots lined up just didn't work with my eyesight. once I blacked out the rear white dots, everything magically started hitting POA. but I have since changed out the sights anyway...