Smith & Wesson M&P 5.7??????

[Fotis]

So I have the FN 5.7 x 28. A while back I had no experience loading with it. I ran a Q/L for it. Spoiler alert it does not work!
Anyway simulation said xx grains of Lilgun would push a 40 gr V-max to 2K fps! Long story short I tried it and the neck separated and stayed in the chamber! In the FN I got neck separation because the case is not sealing and staying in the chamber long enough due to blowback design.

Would the new gas operated smith with the locking/rotating barrel be better suited to slower powders for better performance due to the delay in unlocking?
A good analogy would be the 10/22 mag being chambered for the 17 HMR---did not work out because the action opened before the power charge of LIL gun was completely burned. Savage solved this with the Savage A-17 with the delayed action opening patent.

Am I correct in my thinking or off completely?

[Toprudder]

In my mind, the locked breech design would work.

[Fotis]

So you think I am thinking it out correctly?

[panzermk2]

locked breach will not work with 5.7.


There other in depth conversations in the re loading area about QL just not working for the 5.7

Delayed gas SHOULD be perfect for the 5.7 IF S&W has made a quality fire arm.

[Grantness]

Let’s assume it can accommodate hotter loads / new powders… now you have to worry about keeping your ammo separated.

[Fotis]

Let’s assume it can accommodate hotter loads / new powders… now you have to worry about keeping your ammo separated.

I'd sell the fn

[panzermk2]

Meh honestly the FsN can handle loads well into primer popping, neck separating 65k,. I really would not worry about it.

While the S&W uses delayed gas blow back they are also using a rotating barrel with lugs. This system mirrors the lug design used in the Sig Arms Mauser M2 pistol.

This area has me the most concerned. If the S&W pistols fails it will be with the barrel lugs. The lug system is inherently heavier than any other system. It adds a great deal of complication to make work in a small carry pistol. Complicated metallurgy also. I really question S&Ws ability to keep the tight specifications needed, metallurgy needed and at the current price point. I suspect we will see reports of barrel lugs shearing or slides cracking along the races the lugs run in.