Underpowered ammo velocities?

[Giggles]

What velocities would be considered underpowered when it comes to .223 / 5.56?

[Clint]

Velocity and port pressure are not directly related.
The powder burn rate can affect cycling greatly.

[markm]

Velocity and port pressure are not directly related.
The powder burn rate can affect cycling greatly.

Exactly. Bullet weight and powder burn rate can be combined/tuned to various levels.

[davidjinks]

Do you mean “Underpowered” in regards to affects on target? I.E. it lacks penetration, fragmentation, expansion etc...

What velocities would be considered underpowered when it comes to .223 / 5.56?

[TomMcC]

What velocities would be considered underpowered when it comes to .223 / 5.56?

About the only underpowered ammo I know of personally and have heard of from others is PMC Bronze. Out of my 20" when I had it, it would do about 2850 fps. That to me is underpowered. Even steel cased Wolf and Tula would do a bit over 3k.

[jsbhike]

Hodgdon data from 2001, but shows pressure vs. Velocity.20200604_192103_HDR.jpg

[Clint]

Peak pressure is really only a meaningful measure regarding failures.

The total pressure impulse (PSI x SEC) determines velocity.

The later portion of that curve determines available gas drive.

Hodgdon data from 2001, but shows pressure vs. Velocity.20200604_192103_HDR.jpg

[Giggles]

I’m asking in reference to internal ballistics not terminal ballistics. I was just wondering after I observed a tuned gun fail to lock back a bolt while firing PMC bronze, and it made me wonder if that ammo is considered “underpowered” especially it’s posted velocity on the box is like 2900 FPS.

[davidjinks]

To answer that you would need to find out the minimum velocity threshold of the particular projectile you are using.

An example would be; Speer Gold Dot 5.56MM 75 grain will penetrate and expand at a minimum of 1800 FPS. I made those numbers up because I don’t use that type of projectile/ammo.

I’m asking in reference to internal ballistics not terminal ballistics. I was just wondering after I observed a tuned gun fail to lock back a bolt while firing PMC bronze, and it made me wonder if that ammo is considered “underpowered” especially it’s posted velocity on the box is like 2900 FPS.

[mack7.62]

Speer Gold Dot is a good example, I don't think they even make a 5.56 load because it uses a bullet tailored to perform better at .223 velocity, same with the Federal Fusion bullet, you actually degrade performance if you push it too fast.

But to the OP's question in regards to PMC Bronze that round does have a rep for being underpowered.