08-16-2021, 02:27 PM
(This post was last modified: 08-16-2021, 11:16 PM by Oso Polaris.)
Klem - thanks again for patience and advise!
This is Klem's advise/explanation on "Lock-up Time":
"The case bulging is a worry but also points to the cause of the short stroking. It means the pressure is still too high when the case is being extracted. As the case is being dragged back out of the chamber it is no longer constrained by the walls and now free to expand like a balloon. The first part to be free as it exits the chamber is the web and that's why it is bulging there. As soon as the bullet exits the barrel pressure drops otherwise pressure will take the path of least resistance and blow those cases up in your face. Cases are thicker down at the web so will support more pressure but thinner towards the shoulders and mouth to expand and seal at the mouth. But even thick cases down at the web will expand if pulled out too early.
That is not a 'break in' issue, it is early unlocking and extracting that is causing your short stroking.
The bulge is not from the case firing early while not in battery. The gun is designed to prevent firing unless the bolt is rotated completely into battery. What is happening is the gun has been fired and the bolt is unlocking and pulling back early. This happens mostly in short AR barrels and gas systems. The original AR system designed by Stoner was based on a long 20" barrel with rifle length gas system. Over the years the barrels have become shorter and gas systems along with it. Gas is getting to the carrier sooner and unlocking before the pressure has fully dropped. This means cases are still gripping the walls of the chamber and being dragged out with a lot of friction and stress on the extractor. This extra friction means the carrier doesn't go all the way to the rear to lock back on last round. In your case the heavier buffer is robbing even more inertia and not even going back far enough to pick up a new round. If the pressure is too high while the case is being dragged out it also explains the bulging. There is your problem - early unlocking while the pressure is still too high.
The deal is, after the bullet has passed the gas port there must be enough dwell time for the gas system to energise and impart enough inertia to the carrier to do a full cycle. But, too much dwell time and the system remains pressurised for too long (which is your case). it's a balance which we have some control over with different weights of buffers, carriers, adjustable gas systems and recoil springs. A new gun tends to be a bit rough so that factors in as well (your gun also, but this is a lesser worry and it quickly wears smooth)."
This is Klem's advise/explanation on "Lock-up Time":
"The case bulging is a worry but also points to the cause of the short stroking. It means the pressure is still too high when the case is being extracted. As the case is being dragged back out of the chamber it is no longer constrained by the walls and now free to expand like a balloon. The first part to be free as it exits the chamber is the web and that's why it is bulging there. As soon as the bullet exits the barrel pressure drops otherwise pressure will take the path of least resistance and blow those cases up in your face. Cases are thicker down at the web so will support more pressure but thinner towards the shoulders and mouth to expand and seal at the mouth. But even thick cases down at the web will expand if pulled out too early.
That is not a 'break in' issue, it is early unlocking and extracting that is causing your short stroking.
The bulge is not from the case firing early while not in battery. The gun is designed to prevent firing unless the bolt is rotated completely into battery. What is happening is the gun has been fired and the bolt is unlocking and pulling back early. This happens mostly in short AR barrels and gas systems. The original AR system designed by Stoner was based on a long 20" barrel with rifle length gas system. Over the years the barrels have become shorter and gas systems along with it. Gas is getting to the carrier sooner and unlocking before the pressure has fully dropped. This means cases are still gripping the walls of the chamber and being dragged out with a lot of friction and stress on the extractor. This extra friction means the carrier doesn't go all the way to the rear to lock back on last round. In your case the heavier buffer is robbing even more inertia and not even going back far enough to pick up a new round. If the pressure is too high while the case is being dragged out it also explains the bulging. There is your problem - early unlocking while the pressure is still too high.
The deal is, after the bullet has passed the gas port there must be enough dwell time for the gas system to energise and impart enough inertia to the carrier to do a full cycle. But, too much dwell time and the system remains pressurised for too long (which is your case). it's a balance which we have some control over with different weights of buffers, carriers, adjustable gas systems and recoil springs. A new gun tends to be a bit rough so that factors in as well (your gun also, but this is a lesser worry and it quickly wears smooth)."