Bolt Life?

[26 Inf]

If you have a couple quality AR's and the appropriate 5.56 ammo for them set aside,

I really don't get the obsession with shooting 5.56. There are plenty of .223 rounds that are better suited for SD or HD and plenty of training ammo that matches those velocities.

Additionally, you don't have to worry about pitting or putting a hole through your plates at .223 velocities - 100 or 200 FPS @ 100 yards does make a big difference in that respect.

[ABNAK]

I really don't get the obsession with shooting 5.56. There are plenty of .223 rounds that are better suited for SD or HD and plenty of training ammo that matches those velocities.

Additionally, you don't have to worry about pitting or putting a hole through your plates at .223 velocities - 100 or 200 FPS @ 100 yards does make a big difference in that respect.

It's not an "obsession". Look at the FBI for instance: their load is essentially a TBBC but it is loaded to 5.56mm pressures. I would note that no military in the world that I know of which uses the .224 bullet has it loaded to .223 pressures. There must be a reason.

Nothing wrong with quality .223 fodder. Speer Gold Dots and Federal Fusion come to mind first. I suspect they are near the higher end of .223 pressures (weak stuff like Tula/Wolf/Brown Bear being near the bottom). You rarely hear of malfunctions with those good .223 rounds but stories abound concerning the weaker and cheaper foreign stuff.

Bullet performance *generally* improves with additional velocity and certainly effective range does. It also tends to improve function, albeit with a little more wear over time, unless of course the porting is adjusted accordingly.

[lysander]

It's not "5.56 mm" or ".223 Remington" ammunition.

The overall SAAMI specs defined for the two are pretty close, and that alone doesn't cause the problems under discussion.

It's the actual port pressure.

That is not a standardization point for SAAMI. A varmint load tailored to light bullets with a fast propellant versus a heavy match bullet with a slow propellant are going to have very different pressure curves. And the light varmint load might be extremely popular by bolt action guys. (ARs aren't the only users of .223 ammunition.)

Just like with any gas-operated weapon, the AR works better with a certain range of propellants and bullet weights, The M1/M14 community understood this for years, and in the past just avoided certain factory loads. Now, you see all sorts of "fixes" for your M1 or M1A/M14 so they can handle high port pressure....

Adjustable gas blocks, multiple buffer weights, multiple springs, all of these are "fixes" to the fact that port pressure in SAAMI ammunition is not standardized, and really can't be as 1) standardization is voluntary, and 2) it would negatively affect bolt gun performance.

[ABNAK]

It's not "5.56 mm" or ".223 Remington" ammunition.

The overall SAAMI specs defined for the two are pretty close, and that alone doesn't cause the problems under discussion.

It's the actual port pressure.

That is not a standardization point for SAAMI. A varmint load tailored to light bullets with a fast propellant versus a heavy match bullet with a slow propellant are going to have very different pressure curves. And the light varmint load might be extremely popular by bolt action guys. (ARs aren't the only users of .223 ammunition.)

Just like with any gas-operated weapon, the AR works better with a certain range of propellants and bullet weights, The M1/M14 community understood this for years, and in the past just avoided certain factory loads. Now, you see all sorts of "fixes" for your M1 or M1A/M14 so they can handle high port pressure....

Adjustable gas blocks, multiple buffer weights, multiple springs, all of these are "fixes" to the fact that port pressure in SAAMI ammunition is not standardized, and really can't be as 1) standardization is voluntary, and 2) it would negatively affect bolt gun performance.

Okay, but the pressure (wherever it originates or is dispersed from) is the issue, and ports control it to a large degree, i.e. whether the round is loaded hotter or the amount of pressure coming from the port is the issue. That tighter or looser regulation of pressure is what can cause accelerated wear or malfunction issues (like you said spring strength, buffer weight, adjustable gas blocks, and special BCG's address this one way or the other).

Example: the Hodge Defense barrel has an ever-so-slightly smaller gas port than most 5.56 weapons, and is a mid-length to boot. It was made that way to handle the relatively hot M855A1 on a regular basis. Having personally tested some high-end 5.56 pressure rounds---M855A1, Mk318, and Mk262---with an LMT Enhanced BCG I had about a 20% failure to lock back on the last round. That was the only "malfunction", otherwise it fired/fed/extracted fine. I switched to a standard BCG and it locked back every time. I'll bet my paycheck that if I had tried most .223, especially the garbage steel-cased foreign .223, failures to lock back would have been the least of my issues. So in the case of this particular barrel the port size was regulated to "tame" a specific round by limiting the amount of pressure delivered to the action.

You are one of our engineering whiz-kids so debating this kind of science is waaayyy out of my lane. I think we're talking semantics here though. Pressure and how it's delivered (regulated by the variables we mentioned) does indeed have an effect on wear of parts, specifically the bolt. A rifle set up to shoot .223 should have no issues cycling 5.56. However, a steady diet of 5.56 will likely increase wear on parts over time if all the variables were left unchanged, correct?

[lysander]

Okay, but the pressure (where ever it originates or is dispersed from) is the issue, and ports control it to a large degree, i.e. whether the round is loaded hotter or the amount of pressure coming from the port is the issue. That tighter or looser regulation of pressure is what can cause accelerated wear or malfunction issues (like you said spring strength, buffer weight, adjustable gas blocks, and special BCG's address this one way or the other).

Example: the Hodge Defense barrel has an ever-so-slightly smaller gas port than most 5.56 weapons, and is a mid-length to boot. It was made that way to handle the relatively hot M855A1 on a regular basis. Having personally tested some high-end 5.56 pressure rounds---M855A1, Mk318, and Mk262---with an LMT Enhanced BCG I had about a 20% failure to lock back on the last round. That was the only "malfunction", otherwise it fired/fed/extracted fine. I switched to a standard BCG and it locked back every time. I'll bet my paycheck that if I had tried most .223, especially the garbage steel-cased foreign .223, failures to lock back would have been the least of my issues. So in the case of this particular barrel the port size was regulated to "tame" a specific round by limiting the amount of pressure delivered to the action.

You are one of our engineering whiz-kids so debating this kind of science is waaayyy out of my lane. I think we're talking semantics here though. Pressure and how it's delivered (regulated by the variables we mentioned) does indeed have an effect on wear of parts, specifically the bolt. A rifle set up to shoot .223 should have no issues cycling 5.56. However, a steady diet of 5.56 will likely increase wear on parts over time if all the variables were left unchanged, correct?

Not disagreeing about the mechanics of operation.

I was pointing out the one cannot force the "ammo makers to keep up". There are more things out there that shoot .223 and 5.56 than just the AR, and not all of them will perform best with ammunition tailored to the 12,000 to 15,000 psi pressure nine inches from the breech face that the average AR likes*.

In the past, people that shot gas operated stuff knew that some ammunition didn't have the "oomph", necessary and just avoided it, and that was that. Now, with the internet, someone using ammo less suited to the rifle (be it foreign or domestic), can get on the internet and bad mouth your company. And, if you are a start-up, or a small company that could kill you, so you have to do something, namely make it work.

______________________________
*The AR was made for ammunition that was designed to give the maximum velocity possible for the give bullet weights, and thus relatively high mid-barrel (port) pressures. You best accuracy loading for a lightweight varmint bolt gun may not be the absolute maximum you can squeeze out of the cartridge, and so will have lower pressures.

[26 Inf]

I would note that no military in the world that I know of which uses the .224 bullet has it loaded to .223 pressures. There must be a reason.

Yep, the need to penetrate enemy helmets and armor at range.

[lysander]

I would note that no military in the world that I know of which uses the .224 bullet has it loaded to .223 pressures.

However, the US Army back in 2013 issued TACOM maintenance advisory message 05-038, which prohibited the use of British 5.56mm, except for training only. Some of the gripes were increased fouling, and lower than US spec port pressures.

[GrumpyM4]

However, the US Army back in 2013 issued TACOM maintenance advisory message 05-038, which prohibited the use of British 5.56mm, except for training only. Some of the gripes were increased fouling, and lower than US spec port pressures.

Some years back there was a lot of that on the civ market.

Worked fine in civ over-ported barrels. Was iffy in GI spec barrels.

Burned through a lot of it over a couple of years.

[MistWolf]

...Just like with any gas-operated weapon, the AR works better with a certain range of propellants and bullet weights, The M1/M14 community understood this for years, and in the past just avoided certain factory loads....

...In the past, people that shot gas operated stuff knew that some ammunition didn't have the "oomph", necessary and just avoided it, and that was that...

Folks could save themselves a lot of money, time and aggravation by simply paying heed to these words. I put a lot of trigger time on a Garand and an M14 before I got my first AR and understand this principle well- just use the right ammo for the rifle. Trying to tune an AR to run reliably on a wide variety of ammo is an exercise in futility. What's ironic is folks worried about "accelerated wear" using "hot ammo" in their AR. Once an AR is set up correctly (say for example, with a 14.5" barrel, H2 buffer and a .0625" gas port) it will run reliably on a wider range of ammo than an Garand or M14. Run a few rounds of the wrong type through a Garand or M14 and the op rod will be bent and the rifle redlined. Run the wrong ammo in an AR, it just hiccups and if it stumbles, rubs a little dirt on it and keeps going.