M&P 40 accuracy

[GlenS]

I have to requalify with my duty weapon (M&P40) soon so I went to the local range to practice. First try I shot my usual 40 reload, 180 plated bullet (Renier) & 6 grains of Unique. At 25 yards ity looked like a huge shotgun pattern, some shots off the paper totally. Duty ammo, 180 GoldDots, did somewhat better but that is some real expensive practice ammo. Tried some reloads using 180 HAP bullets and 6 grains Unique. Not much better, some fliers off by feet not inches. Experienced alot of keyholeing.

Anyone else having a problem like this with the M&P40? I really like the pistol but I can't continue to carry it if I can't figues out the problem.

 

[OKFC05]

Did you try what I suggested when you posted this before?

http://smith-wessonforum.com/smith-wesson-m-p-pistols/249945-problem-m-p40.html

 

[growr]

not at all....my M&P .40 shoots extremely well in USPSA/IDPA matches..(it has over 15,000 rounds downrange). many times stacking one round on top of the other at 10 measured yards.

I too use 6 grains of Unique but am using Montana Gold bullets instead of Rainer's or Berry's

If you are key holing you might want to reduce your powder charge. Usually a keyhole is an indicator that you are driving the bullet too fast for the twist rate of the barrel. Essentially the bullet is skidding over the rifling...and not being stabilized.

Be sure to test over a solid rest at 10 yards first so as to eliminate and shooter induced error's. Also have another high level shooter or your unit armorer test it as well to eliminate shooter error as well. Use some factory ammo for this test and then move to your reloads..

Don't move the target farther back until you find the real problem. You should be able to put 10 rounds easily into 2 inches or less at 10 yards.

If it will not do so, get it to your unit armorer.

Randy

 

[growr]

OKFCO5 's diagnosis in his other post is dead on advice!
Randy

 

[g_conway]

Put the gun in a vice. fire 5 and see that pattern. I'm betting it's not the gun.

 

[Titegroups]

Sounds like your bullets are a bit too small in diameter. Measure them and try something a bit larger so the rifling gets a better bite on them.

 

[spricks]

I would also try a different backstrap. That can make a big change in results...cheap try for sure.

spricks

 

[GlenS]

I loaded the ammo hotter than before. In fact a max load according to loading manual. The group shrank dramatically. And the keyholing stopped. I think the result is called obstration, or something like that. The bullet actually expands to fit the rifling of the barrel.

 

[fltbed]

I've talked to many people with accuracy issues with the 9mm M&P 5" but you're the first I've heard of having problems with the 40.

I believe the word your looking for is obtruation. And yes, you could be getting that effect with your max loads.
The reason your getting keyholeing with your lighter loads (as Tightgroups mentioned) is your bullets are undersized. This is normally due to using an excessive amount of crimp and very common if your using a Lee Factory Crimp Die.
Make sure your expander die is flaring the mouth of the casing only enough to ensure you don't scrape any bullet material off the side of the bullet while seating. If you expand to much, you lose bullet tension and set back will occur.
Set up your taper crimp die to only remove the flair. Excessive amounts of crimp will score the bullet and swage it undersize for your bore.

As OKFCO5 mentioned in the other thread, plated bullets have given a lot of us problems with accuracy and fouling. Switching to a true jacketed bullet (like Precision Deltas or Montana Gold) not only solves these problems, their cheaper to.

Hope this helps.

Jeff