On Page 14 of the S&W Safety & Instruction Manual for Revolvers it states the following:
"ALL SCANDIUM REVOLVERS FIRING MAGNUM AMMUNITION
WARNING: DO NOT USE MAGNUM® LOADINGS WITH BULLET WEIGHTS OF LESS THAN 120 GR. THIS WILL REDUCE THE POSSIBILITY OF PREMATURE CYLINDER EROSION."
It was explained to me that the burning characteristics of the powders used in the lighter bullet weight loads can increase the potential for erosion of the titanium cylinders inside the charge holes and on the front of the cylinder face. Once the surface layer of the titanium is breached the erosion can occur faster.
The bullet jump issue is explained on the same page of the manual regarding the Ti, Sc & PD revolvers.
"Before placing any of these reduced weight revolvers into service, perform the following test to determine the suitability of the ammunition you intend to use.
At a gun range or other suitable and safe location, prepare your revolver for firing by fully loading its cylinder with the ammunition to be tested. While pointing the firearm in a safe direction, fire all but the last round. Remove the empty casings and the last loaded round from the revolver’s cylinder.
Carefully inspect the loaded round to determine if its bullet has started to unseat (move forward) from its casing.(Figure 2) If it has, you should not use the tested ammunition in your revolver. Choose another projectile weight or brand of ammunition and repeat this test until you find one that DOES NOT UNSEAT under these test conditions. When you are finished, fully unload your revolver and secure it safely."
When I first took my M&P 340 to the range I tried it with a mix of a few different jacketed Magnum loads. I found at least a couple of them which exhibited some degree of bullet pull (slight unseating of the bullet) when checked in the recommended manner, and a couple which didn't.
That was in
my M&P 340, on
that day, using
those boxes/production lots of ammunition.
While I don't make it a practice to carry Magnum loads in my M&P 340 (although I'll use them during qualification and some practice), if I exhaust the remaining Magnum rounds in the boxes of ammunition which I checked with favorable results in my M&P 340, I'll perform the same tests once again with new ammunition ... even if it's the same make/bullet weight. Any variance in production regarding the sizing & crimp might change things in this regard and I want to confirm proper functioning with the exact loads/boxes/production lots I'm using. (I also test each +P load, for that matter.)
Now, something else which ought to be considered is the grip technique used by an individual shooter/owner. During one of my conversations with someone at the factory one time I learned that they had received a 360PD back for a customer complaint that it had exhibited bullet pull when he was shooting 158gr JHP Magnum loads. The gun didn't exhibit that issue when checked by the factory ... until they thought to try shooting the gun with a less-than-firm grip, at which time they could get some bullets to unseat themselves.
It seems that they didn't expect someone shooting these little pocket cannons would ever use anything less than a strong grip when shooting these hard-kicking little guns, and it may now sometimes be possible for someone to 'limp-wrist' one of these lightweight Magnum revolvers.
It was basically explained to me that it appeared that when a less-firm grip was used when shooting these little guns, it might be possible for the gun to move rearward under recoil faster than they had anticipated would occur when someone using a strong grip was shooting the gun. In those circumstances it might be possible for some bullets, depending on the crimp, to not be able to keep up with the rearward moving case when a less stable grip technique was being used.
I think these little guns are right out there at the very edge of combining a hard-kicking Magnum caliber in a diminutive ultralite gun in the hands of a human being.
If I want to shoot Magnum loads I'll use my Ruger SP101, or buy a Model 640, 649 or 60 and get larger grips.
I've repeatedly demonstrated that I can rapidly and accurately fire 2-3 shot strings on silhouette COM at reasonable defensive distances (1-10+ yards) using one of the Airlite Magnum J-frames ... but it's nothing I'd even remotely consider enjoyable.
FWIW, I really like my M&P 340. I replaced the Bantam grips with the stock Boot grips (which is supposed to add an ounce) and I can still notice it's lighter in my pocket holster than my 642.
I didn't buy the M&P for the Magnum chambering, though, but for the enhanced Scandium aluminum frame and the XS front night sight. Sort of an 'improved' 642/442, as it were. It works well in the role for me. Being able to occasionally use Magnum loads is a secondary benefit, and one which I seldom use outside of qualification and some practice. I simply prefer +P loads in mine. If they had offered the 642 with a blackened stainless frame and XS night sight I'd have bought it, instead.
That's just me, though.
