Ummm, your bayonet would be a bit stubby on a carbine gas system...
Yes, but that is why it is there....really.
Stubby? Yes, but the hoards in Haiti were sufficiently intimidated by "stubby" a time or two.
And Colt M4's routinely break/crack bolts...really. This ain't hearsay. This was extremely rare with the old 20in rifles but fairly common today.
M4's are also famous for the dreaded "bolt over base" malfunction that will ruin your day. I believe the high port pressure causes this.
Ummm, the USGI standrad issue M4 has a 14.5" barrel, the govt has never used a 16" barrel....really.
If the "bolt over base" is bolt bounce, that is why we have H and H2 buffers with loose weights inside, run a soldi buffer like the 9mm buffer and see what happens.
Having carried an M4 on a few continents, I never knew how long the damn barrel was, thanks.
You are correct that often a buffer change can fix all manner of problems.
Bolt-over base is when a piece of brass is extracted but doesn't clear the ejection port and gets lodged ABOVE the bolt and under the charging handle. If you pull the charging handle, it jams it harder.
A Leatherman MUT is the fastest way to clear this, without a proper tool, just beat the butt against the ground for inertia to unwedge the bolt.
