For most people, the following test will be as interesting for the methods used as it is for the conclusions that were reached.
Understanding Extractor Lift
Alternate link to presentation
This presentation was initially shown in May of 2003; the “other comments” page would seem to be especially prescient in light of all the “improvements” that have been made to the AR platform in the years since. Some I fully support, such as midlength gas systems (especially for 16″ barrels), while others (such as poorly engineered “piston conversions”) I do not.
The following sentence is also quite interesting:
“Case extraction and ejection successfully occur as long as the case is held against the bolt face by the residual chamber pressure while the extractor lifts and returns to position.”
Although it is easy to put together an AR-15 from an amalgamation of random components, it seems lost on many that the AR-15 is a system that must work in harmony. The AR-15 is more than the sum of its parts. Many commercial manufacturers have taken it upon themselves to “improve” the system in order to make it work with cheap ammo, or be cheaper to manufacture, or simply because they do not understand why something was done a certain way. Such actions can reduce the service life of the weapon and compromise reliability.
Any examples?
Oops, don’t have PPT. Won’t open. Haven’t found an online presentation.
Nonetheless the comment about residual gas pressure keeping the case against the bolt for the extractor to lock back on? Very interesting. It sounds like the extractor actually lifted during firing, which could only happen once the bolt is unlocked and away from the lugs.
I’ve been taken to task elsewhere for suggesting that residual gas force also operates the entire bolt cycle (as it does in all blowback actions,) but that’s a different subject. Getting a description of exactly what happens during the extraction/ejection cycle, with pressure graphs of loads on the bolt face, in the bolt carrier, etc. seems to be proprietary data.
Looking forward to ginning up some way to see the presentation.
Downloaded the free Microsoft viewer (duh.)
The experimental gymnasticator answers a lot of questions I had concerning the cycle of operations.
1) Residual gas pressure does exist and will hold the case against the bolt face.
2) DI operates the bolt cycle, not the residual pressure, unlike a blowback or delayed roller lock.
3) If the extractor lifts it will not pull a resistant case from the chamber – hence the reason for the SOPMOD extractor improvements on the M4.
Thanks for the link, many should view this to more fully understand bolt cycling.