Factory M&P chamber is huge!

[Flash74]

I got a false sense of security reloading for my M&P's. Everything I cranked out fed and functioned just fine with the factory barrels. I never got a case gauge since all my reloads would drop in and out when I used the barrel for a case gauge.

Once I got a Storm Lake barrel for my 9mm, I realized my reloads were not up to snuff. I had rounds that would not chamber at all in the Storm Lake barrel, could barely be pushed into a Glock 17 barrel, but would drop in and out of the factory M&P barrel. I have since refined my 9mm reloads and have had no issues making quality ammo that fits the tight chamber of the Storm Lake barrel.

I am experiencing this same thing again. I just got a Para P16.40 and tried my reloads for my M&P Pro 40 in its barrel. 10% of the rounds do not chamber without a strong push, 15% chamber but stick a little and will not spin and the rest (75%) drop in and out of the Para barrel. I tried the rounds that were really tough to get into the Para barrel and put them into the stock M&P 40 barrel. They would drop in and out of the M&P barrel.

It's time to refine my 40 loads and get a case gauge. At first I thought it might be the length of the rounds. I load to 1.160" for the M&P. I measured the Para chamber and found it could take at max a 1.190" loaded round. It definitely wasn't length. I turns out the rounds that were really hard to chamber were a touch out of round. It really makes a difference on how you sit the bullet on the case before seating it. When I load too fast the bullet might sit a little crooked on the case and I let the die collar (Hornady) straighten the bullet before seating. This made a bulge at the base of the bullet that couldn't be seen but could be measured.

If you are reloading for a factory M&P barrel you might find they don't work so well in another gun. Check your reloads!

[ParaGunner]

It's bulged cases from loose chambers. Try a u die or a bulge buster kit to resize the entire case.

[Flash74]

I do use a Udie. The "bulge" is at the bottom of the bullet after seating, not the bottom of the case.

[Forrest Halley]

I just use a Regular RCBS die. No trouble. Who knew?

[wgj3]

There is a balance between tolerance and precision. The slightly looser tolerances seem to insure greater reliability. I value this attribute greatly as I do very little precision shooting with my handguns...

[Flash74]

There is a balance between tolerance and precision. The slightly looser tolerances seem to insure greater reliability. I value this attribute greatly as I do very little precision shooting with my handguns...

Agreed, the balance is fine though. My 9mm with stock barrel would shoot 8" groups low and right at 25 yards. Dropped in the Storm Lake and had centered 4" groups. My 40 always shot 4" centered groups. I love the reliability, but wonder if the accuracy would have improved if I had better reloads.

Since my original post, I polished the chamber of my Para since it had a rather sharp transition into the throat. Just a little work with a felt wheel and some jewelers rouge. The rounds that stuck a little will now drop in and out, but the 10% that were tough are still tough to get in and out. A 10% failure rate us unacceptable, time to work on the reloads.

[shooterDrew]

I have found this same thing. I reloaded for my mp9 and it fed everything without hesitation. Tried those same reloads in my kimber 9mm and not having the same luck. The chamber on the kimber is much tighter and the rounds that work perfectly for the mp certainly don't enjoy the same reliability. Difference for me tho is I found the same performance from the stock bbl and a storm lake replacement barrel.

Sent from my iPhone using Tapatalk