Tough deal to have a gun blow up.
I have to say that I would never have to worry about the results of shooting a 40 cal Shield with a bullet holding a 180 gr projectile because I wouldn't have any desire to do so. That's like shooting plus P 38 special loads out of a baby chief for target practice. I know you can, but why? Because you enjoy pain? The gun is too light and too small to feel comfortable shooting that round at a pressure that would make the projectile perform well enough for why I would be utilizing a Shield in the first place (personal protection).
I suppose a too large of projectile may have been the first leverage point which then lead to a greater likelihood of a round with too high pressure. I doubt S&W advises not to use rounds with 180 gr bullets in the 40 cal Shield but it would interesting to see if SAAMI has specs designed specifically for guns within this platform.
I think everyone here would agree that a 4006 could handle significantly higher pressures than a Shield, so the ammo specs should be different just like they are when shooting a SAA Colt vs. a Ruger Blackhawk.
EDIT: Just checked SAAMI's velocity and pressure data and 180 gr is at the top of their measurements.
Obviously your not a 40 caliber owner. The 180 grain bullet is pretty much the standard weight bullet for this caliber and very common. Typical range loads such as WWB or Federal Champion feature a 180 grain bullet loaded to a velocity in the ballpark of 950 fps with SD loads using a 180 grain HP running at 1050 fps.
Per SAAMI the maximum pressure for the 40 S&W is 35,000 psi, which is the same as 9mm and 357 Magnum. There is no definition for a +P designation by SAAMI for the 40 caliber but the longer 10mm does feature a higher operating pressure of 37,500 psi. For the 9mm there is a +P definition and the operating pressure for that variant is 38,500 psi.
Problems specific to the 40 caliber that led to a mistaken belief found on the Net that this caliber operates at a higher pressure than other calibers are almost universally associated with semi auto pistols that have a feed ramp cut rather deeply into the chamber in the barrel. This results in an area of the case that is not supported. Early Glock 40 calibers featured this design feature and the typical result was fired cases that had a distinct bulge. This issue was seen so widely that brass that is bulged in the rearward portion of the case is referred to as being Glocked.
Of note, a feed ramp that is cut somewhat deeply into the chamber on a semi auto is usually a result of necessity. One result of making the barrel length shorter on a semi auto based on the Browning tilting barrel design principle is that as the barrel is made shorter the movement of the slide must also be made shorter. At some point the feed ramp must be cut deeper into the chamber in order for a fresh load to be fed into the chamber. As a basic rule of thumb chamber intrusion by the feed ramp starts to become necessary at the point of 3 times the overall length of the cartridge. BTW, typical OAL for the 40 caliber is 1.125 inch and 3 times 1.125 is equal to 3.375 inch.
Finally because Force is equal to Pressure times Area a larger diameter cylinder must feature thicker walls in order to contain a specific pressure than a thinner cylinder. This means that if a 40 caliber case has a wall thickness in the case head that is identical to a 9mm case that 40 calliber case will be more prone to bulging in an unsupported area. Which is what led to early Glocks in the 40 caliber bulging cases. Because Glocks were originally designed for the 9mm and were intentionally designed to have exceptional feed reliability. One way to achieve exceptional feed reliability in a mass produced semi auto is to use a "gentler" angle on the feed ramp. So Glock used a 9mm feed ramp angle on their early 40 calibers and they "Glocked" the brass. Note, SAAMI does NOT set standards for case wall thickness or case head designs, probably because they don't want to be liable.
So, look at the Shield for a moment. It features a 3.1 inch long barrel, a length below that 3 times OAL magic point that allows "full" case head support. So it's a certainty that the feed ramp intrusion in a Shield will be less than ideal and with some brands of cases it may "Glock" the cases. On multiple occasions we have seen reports of the 40 caliber Shield producing Case Head Ruptures. Reports of this different type of event being associated with the Shield are likely what led to the OP concluding this was a fault of the pistol.
So, let's cut him some slack there. However, we can blame him for shooting reloads he didn't make for himself with his own hands. The ONLY reloads I shoot are my own and I would not reload for the Shield due to the shorter chamber support this pistol features. Actually I won't purchase a 40 caliber Shield simply because I don't want to deal with the bulged cases that would result.
This incident bears absolutely
NO resemblance to that happens with a Case Head Rupture. Those events typically blow the magazine out the bottom of the grip and sometimes split the frame, they do not blow the barrel into shrapnel. I'm repeating myself but this was without any doubt at all the result of a
severe overcharge. Looking on the net for this particular reloader they claim to use "Hodgson" powder. It just happens that Titegroup is made by Hodgdon and I think it's very likely that is the powder used in these reloads. I think that it's also nearly certain that the ram on the reloading press was cycled twice while the shell plate was only cycled once. The result of that would be a case with 2 TIMES as much powder as intended with an end result of a very blown up pistol.
I also have a sneaking hunch that whoever produced this ammunition won't step up an admit fault, they will blame this failure on the pistol due to the Case Head Rupture events now well circulated on the Net. Hope I'm wrong about that but the "web site" for Military Ballistic Industries has a distinct fly by night appearance and I'll bet there is absolutely no way at all to "login".
