Strange 223 "short stroking" issue

[Jicko]

I had a batch of 55gr 223 "short stroking" on me. (A round is fired, the bolt does not go back far enough to chamber another round. Or it is far back enough to hold the bolt open with an empty mag)

I couldn't figure out why. It is not the gun since Fed/LC XM193 and Fed AE223 runs fine.

I chrono'ed the rounds and the velocities are as expected and in between the XM193 and the AE223, so pressure should be ok.

Any idea where else should I look?

Components:
- LC/FC brass
- CCI #41 primers
- 55gr FMJBT w/c (lightly crimped too)
- IMR 4198 21.5gr (this sounded low, but Sierra's manual said 21.8gr is the max for this powder to yield 3100fps)
- COAL: 2.25

Rifle:
- Noveske 14.5"

[sleepur606]

I'm not 100%, but it could be a lack of lubrication in the gun itself.

Last time I was out shooting, my buddy had not lubed properly after cleaning, and the gun would fire fine and cycle the bolt, but it would not cycle far enough to chamber the next round. We were out in the desert and, of course, no one had any oil with them, so he pulled some ATF off his trans dipstick and it worked pretty good for a while.

This happened with Remington UMC and Hornady Vmax bullets. We both put about 50 rounds of UMC through it after the lube and it shot fine, but that quickly wore off.

Try that, might help.

[Jonathan Doe]

Maybe the gas port is too small? or recoil buffer is not the right kind?

[ar15barrels]

Is it a mid-length 14.5" barrel?
If so, the choice of 4198 is poor as that powder is a little fast to make a proper port pressure for a 14.5" mid-length barrel to run correctly.

Don't directly equate velocity with pressure and pressure with proper gun functioning as different powders make different port pressures and different port pressures change gun function, even though the net velocity may be the same.

Using your load data, quickload is predicting a peak pressure of 47,600 and 17,500 at a mid-length gas port and 2880fps from a 16" barrel.
Switching to 26.3gr of H335, quickload is predicting a peak pressure of 47,500 and 18,500 at a mid-length gas port and 2900fps from a 16" barrel.

[Jicko]

I think IMR 4198 is a poor choice.... but that is what i can find at that point...

It is a 14.5" carbine gas system noveske...

Again, the gun is not poorly lube or anything, since it does function with other ammo.... just this one batch... I would probably pick some other powder later, but I do want to figure out what happened to this batch... (but Sierra does list IMR4198 to be a working powder for their 55gr FMJBT)

So, Rand, can you help me predict the pressure with your quickload? I would like to get down to this... and at least have a conclusion the reason why these dun work while AE223 and XM193 does...

PS. does anyone know what powder do Fed/LC XM193 uses?

[EOD3]

I know this sounds silly but... Have you tried different magazines? What you're describing could result from a bad or improperly seated magazine.

[pc_city]

PS. does anyone know what powder do Fed/LC XM193 uses?

The tech manual data sheet for M193 calls out 28.5 gr of WC 844.

I think 28 gr of Winchester 748 will get you to where you'd like to be.

[Jicko]

I know this sounds silly but... Have you tried different magazines? What you're describing could result from a bad or improperly seated magazine.

Not a magazine issue, I tried multiple PMags and USGIs, and this happened on every one, and XM193 and AE223 worked with the mags.

[USN CHIEF]

Jicko, have you tried shooting the ammo with a different AR?

[Jicko]

Jicko, have you tried shooting the ammo with a different AR?

Yes, do the same with my SPR.

[buffybuster]

Not enough gas to cycle the action. IMR4198 is actually too fast to reliably run in an AR. I have done it but you have to load it to a the MAX for it to run reliably and even then the brass doesn't go too far.

A long time ago, I ran 21.5grs of IMR4198 and it barely cycles the action, 22.0grs (even though slightly above recommended max) ran OK. Thus, I don't use 4198 for AR loads.

[Sunwolf]

I use 4198 in bolt action only.

[Jicko]

Then how come Sierra list IMR4198 as one of their recommended loads for AR!?

http://accurateshooter.net/Downloads/sierra223ar.pdf

On page 6.


Now I know that IMR4198 is probably not the best choice... I just want to know if there is a way to use up my batch.... in a mid-length gas-system? or a rifle-length gas-system? or in a 24" barrel?

[buffybuster]

4198 would probably have the best chance of working in a carbine length gas system with a 16" barrel (not 14.5 w/ extension). In that configuration, the system is overgassed to begin with so there will be more time under pressure and with 4198 being fast and the pressure falling off quickly, there should still be enough gas to run the action.

As I said previously, the AR will run with 4198 but it's at the max load vicinity. Ruger Mini14 run just fine with as little as 20.0grs of 4198 (55gr bullet) but the AR's need more gas.

[ar15barrels]

Now I know that IMR4198 is probably not the best choice... I just want to know if there is a way to use up my batch.... in a mid-length gas-system? or a rifle-length gas-system? or in a 24" barrel?

A 24" barrel would probably increase the dwell time enough to make that powder work better.