M&P 5.7

[zaitcev]

Nope, it's fully locked, just like AR-15 or M1 Garand. The action only starts moving once the bullet is past the gas port. However, this is an understanding based on the animation in the official announcement video. I don't understand just what prevents the whole action from recoiling with the bolt thrust. There must be one or two more lugs somewhere, missing from the animation.

In case anyone is interested, here's the patent US20220120524A1:

https://patents.google.com/patent/US...Corp.&sort=new

The production gun has some small differences, for example the rifled part of the barrel no longer extends into the tube. But the important part is, the tube is fixed to the frame. However, and I didn't handle the gun to check, the barrel and slide, while locked together, are free to move slightly relatively the frame and tube. Therefore, the gun could operate as a recoil-operated gun with a rotating barrel, if there were enough recoil. But there weren't. Therefore, the gas tapped into the chamber between the barrel and tube assists the unlocking, rather than being solely responsible for it like on M1 Garand. Well, I wasn't wrong about the breech being locked. But I think now that it's more proper to classify the action as "gas-assisted".

[spyderco monkey]

It's also a fine 'kit gun' cartridge. 5.7 is 6.5g per cartridge vs 12.6g for 9x19, so it is 1/2 the weight. And the straightwall body allows the cartridges to be stacked very densely.

The result is a 50rd box of 5.7 weighs as much as 25rd 9mm, and fits into a small box not much larger then a box of .22lr. From memory (traveling) a box is about 3.25" x 1.6" x 2". You can easilly fit 100rd into the pocket of a cargo pant or jacket.

Just to follow up on how compact and light 5.7 ammo is, here's a pic I took years ago of my 'grab n go' 5.7 setup.

FN FsN, 6 mags, 510rds, accessories, all fits into a lunchbox sized bag weighing less than 10lbs.



For going on a road trip, the whole setup can be tossed into a backpack of carry on wheelie bag, without either taking up too much space of making a bag conspicuously heavy.

[zaitcev]

One amusing physics-related oddity about the 5.7 is that its blowback (an integral of the bolt thrust) is as powerful as 9mm, but the recoil is much lower. So, a gun designer needs either a massive slide like on HiPoint, or a special trick that amplifies the recoil (like the accelerators of all 3 competing pistols). Still, those are not only options. I think a long recoil could work. Same goes for a full-on gas operation. I am sure that a delayed blowback would work too (see CMMG Banshee in 5.7). For various reasons neither of these looks very attractive in a handgun. But there's one other option: Pedersen hesitation locking. Its advantage is, it harvests a pre-determined amount of the blowback energy. So I'm quite sure it could be tuned for 5.7. The next company that considers a gun in 5.7 ought to give it a good look. It's not unduly complex, and it's compact enough for a handgun.

[fly out]

One amusing physics-related oddity about the 5.7 is that its blowback (an integral of the bolt thrust) is as powerful as 9mm, but the recoil is much lower. So, a gun designer needs either a massive slide like on HiPoint, or a special trick that amplifies the recoil (like the accelerators of all 3 competing pistols). Still, those are not only options. I think a long recoil could work. Same goes for a full-on gas operation. I am sure that a delayed blowback would work too (see CMMG Banshee in 5.7). For various reasons neither of these looks very attractive in a handgun. But there's one other option: Pedersen hesitation locking. Its advantage is, it harvests a pre-determined amount of the blowback energy. So I'm quite sure it could be tuned for 5.7. The next company that considers a gun in 5.7 ought to give it a good look. It's not unduly complex, and it's compact enough for a handgun.

"New, from Remington...the R57" is something that no one wants to hear. That is an interesting thought, though. It makes one wonder...

[HeavyDuty]

I have to admit needleguns like this interest me, but it’s academic - I don’t see myself as getting one. And add me to the list of people asking “why?”

[Jim Watson]

But there's one other option: Pedersen hesitation locking. Its advantage is, it harvests a pre-determined amount of the blowback energy. So I'm quite sure it could be tuned for 5.7. The next company that considers a gun in 5.7 ought to give it a good look. It's not unduly complex, and it's compact enough for a handgun.

The initial setback of the Pedersen breechblock is equal to the thickness of the .380 case head, such that there is no unsupported case wall while the chamber is still under pressure.

How well will that work with the long skinny 5.7 instead of the short stubby .380?

[PNWTO]

The price of the FN is ultimately what kept me away, but these are getting into the impulse range for me.

Same here.

However, I will never stop kicking myself for the time when, fresh off the plane with an account full of combat pay, I didn't pick up a NIB PS90+FiveseveN combo that a store was selling... for $1150.

[TGS]

I have to admit needleguns like this interest me, but it’s academic - I don’t see myself as getting one. And add me to the list of people asking “why?”

My guess is that it's a relatively cheap outlay to have something in the catalogue that a military can call up and order X number of.

In the last 5 years we've seen a shift back to concern over near-peer conflict and conventional warfare, not just by the US but our NATO partners as well. So, if I were a gun company, I'd want products on the books to fill that need if such arises. The only reason 5.7 was basically dead on release is because the collapse of the Soviet Union when it was released, and following focus on low intensity conflicts with people who generally weren't wearing body armor.

As the west focuses back on conventional war, the desire for these cartridges may reemerge.

[zaitcev]

The initial setback of the Pedersen breechblock is equal to the thickness of the .380 case head, such that there is no unsupported case wall while the chamber is still under pressure.

How well will that work with the long skinny 5.7 instead of the short stubby .380?

That is a valid point. I thought it was guaranteed to work because P90 was blowback operated, and thus permitted a significant case movement. Therefore, a smaller initial setback should be safe.

[Jim Watson]

While I once owned a real Remington PA51, and think it was a brilliant end around of the Browning patents;
like Will Rogers, all I know about the FN is what I read on the internet.
What I read was that the blowback is brisk enough that the shoulder is blown forward as the case backs out of the chamber. Resizing by the few who bother takes care.