Hypothetical: What Still Needs Fixing?

[turnburglar]

I see people say it burns through bolts in 5,000 rounds. The issue I have with that is the Maintenance Schedule calls for replacement of the bolt at 10,000 rounds.

So who's right? Random internet users or the mandatory maintenance schedule?

Why can't both be right? 5-10k isn't a very large number to begin with. Some people would be replacing their bolt every year or two. That's hardly ideal.

I think the Arak bolt/barrel extension combo would be of benefit. But really why make these small changes? Why not just build a gun from the ground up that can handle the cartridge we want? The original ar15 was made for 222 rem, and now it appears 556 is pushing the limits of pressure and OAL.

Pick cartridge

Design gun.

[skp]

I see people say it burns through bolts in 5,000 rounds. The issue I have with that is the Maintenance Schedule calls for replacement of the bolt at 10,000 rounds.

So who's right? Random internet users or the mandatory maintenance schedule?

Seems like both could be right? The schedule calls for replacement at 10,000 but sometimes they fail at 5,000, presumably due to the hotter loads.
When was the maintenance schedule written anyway? Could have been a long time ago.

[sinlessorrow]

Seems like both could be right? The schedule calls for replacement at 10,000 but sometimes they fail at 5,000, presumably due to the hotter loads.
When was the maintenance schedule written anyway? Could have been a long time ago.

It's the most recent revision for the M4A1. Not sure on the exact date of the revision though.

[tom12.7]

To the OP,
There's a long list of issues that can be resolved with further development. Issues arise as the cost of development of them requires a profit to be made by their investment. The problem in doing so is in part due to modularity of the base rifle, everything snaps together like Lego parts. When you you make enough changes, the old parts no longer work with the new parts. The business is concerned about about building better "mouse traps" and "band aids" for the existing systems, because it's safer than than going into a platform that is at least initially proprietary to them and not compatible with the base gun.
An improved revision can be made without any doubt, take that as a given. No company would risk that investment right now, as "mouse traps" and "band aids" offer more profit and less risk, it's a no brainer.

[lysander]

Why can't both be right? 5-10k isn't a very large number to begin with. Some people would be replacing their bolt every year or two. That's hardly ideal.

I think the Arak bolt/barrel extension combo would be of benefit. But really why make these small changes? Why not just build a gun from the ground up that can handle the cartridge we want? The original ar15 was made for 222 rem, and now it appears 556 is pushing the limits of pressure and OAL.

Pick cartridge

Design gun.

The problem was the design of the case was insufficient from the get-go. The original military minimum estimate for effectiveness was a 55 grain bullet going 3300 fps at the muzzle, and required a max pressure of 50,000 psi. The .222 Remington was just a little too small to get that kind of performance, so Armalite moved the shoulder forward .017", and with selected powder loadings, 3300 fps could be reached while staying below the 50,000 psi limit. Springfield Arsenal suggested that the shoulder be moved forward another .030", so the case would be more versatile in powder choices to reach the 3300 fps speed and stay under 50,000 psi. But, Armalite did not feel like lengthening the magazine, so the longer case was quietly dropped. Then later it turned out that you actually cannot reliably get 3300 fps out of a .223 case and stay under 50,000 psi, so they bumped up the maximum allowable pressure, and then had to again when they went to the heavier bullet to keep the velocity up in the shorter barrel.

.222 Magnum (Springfield's suggested case) is more than capable of pushing a 55 grain bullet to 3300 fps with a wide range of powders and stay safety below 50,000 psi, also with the 62 grain bullet get 3200 fps and stay below the 55,000 Piezo/52,000 CUP limit of the original M193.

[Benito]

I'd like to see four particular improvements-
- Easier way to lock the bolt back without a mag
- The charging handle moved to a more convenient location
- A lightweight adjustable buttstock with a cheek piece like that used on the UBR
- The death of metal handguards

What's the issue with metal handguards? The newer M-LOK and KeyMod units are light and strong. Are you thinking of carbon fiber or something?

There are some very good suggestions listed so far.
Stronger bolts (reduced cam pin hole, stronger materials, etc), longer gas systems, not relying on the barrel nut to attach the handguard, etc. No argument here. Obviously a cost benefit analysis is required, but those would all definitely be beneficial in my view.

[BufordTJustice]

The problem was the design of the case was insufficient from the get-go. The original military minimum estimate for effectiveness was a 55 grain bullet going 3300 fps at the muzzle, and required a max pressure of 50,000 psi. The .222 Remington was just a little too small to get that kind of performance, so Armalite moved the shoulder forward .017", and with selected powder loadings, 3300 fps could be reached while staying below the 50,000 psi limit. Springfield Arsenal suggested that the shoulder be moved forward another .030", so the case would be more versatile in powder choices to reach the 3300 fps speed and stay under 50,000 psi. But, Armalite did not feel like lengthening the magazine, so the longer case was quietly dropped. Then later it turned out that you actually cannot reliably get 3300 fps out of a .223 case and stay under 50,000 psi, so they bumped up the maximum allowable pressure, and then had to again when they went to the heavier bullet to keep the velocity up in the shorter barrel.

.222 Magnum (Springfield's suggested case) is more than capable of pushing a 55 grain bullet to 3300 fps with a wide range of powders and stay safety below 50,000 psi, also with the 62 grain bullet get 3200 fps and stay below the 55,000 Piezo/52,000 CUP limit of the original M193.

I'm going to assume that there isn't much room to push the case neck any further forward in the 5.56 case without increasing the OAL of the case?

[1911-A1]

A lot of the debate seems to center around "It's a 40 year old proven design, we'd be stupid to abandon all that research and development. We should continue developing the platform."

and

"It's a 40 year old design. It's time to abandon it, take the lessons learned and develop something completely new."

[lysander]

I'm going to assume that there isn't much room to push the case neck any further forward in the 5.56 case without increasing the OAL of the case?

If you push the neck any further forward you start to leave the cylindrical portion of the bullet and get into the ogive.

That case design has reached the limits of its capabilities.

You can't push the chamber pressure up any more, the bolt design can't handle it, and the limitations of physics prevent launching any heavier projectiles at the same or lower pressures.

IF you want any further improvements in bullet performance, you are going to have to get a new case.

[MistWolf]

...the limitations of physics prevent launching any heavier projectiles at the same or lower pressures...

Not so. Increase the length of the leade and change the powder accordingly and you'll see an increase in velocity without an increase in pressure.

Bufford, to use a longer case, you'll need to redesign the mag to accommodate the extra length to see any practical gain