Very old thread, but also high on Google list for hits, the subject of Randall model 18 strength is something many are curious about......
Let me tell you what i know by looking my early/mid 70's knife, about only difference today being the tang might be a bit shorter on newer....
The handle is 1" OD stainless tubing, with 1/8th" wall thickness X's 2, leaves a max of 3/4" ID....the tang is approx 1/4" thick and is pressed or beat into the tubing to degree tubing is distorted slightly top and bottom, leaving a max gap of 1/4" tapering to zero top and bottom of both sides....tang is approx 1 3/4" long...
This alone would be hard to come loose no matter the use, but there is more....the main area any loosening would start would be at mouth of tubing under repeated impacts, and it would take a lot of beating to distort the stainless thickwalled tubing......however, the blade has shoulders at start of tang, these shoulders rest on a guard made from 1/4" thick brass plate, and THEN the plate rests on the mouth of the tubing....total support against movement.
The blade is brazed to the guard on both sides with 172,000 psi shear strength silver solder at 1200deg F, then the handle tubing is brazed identically to back of guard after the press fit....Randall does not claim any, but i suspect with contact and solder wicking and flux, the tang also is getting soldered to inside of tube at base.....the gaps next to tang inside the tubing are filled with industrial epoxy to prevent any stored items inside handle from becoming stuck, the epoxy's only official function, although the rock hard epoxy would also prevent any lateral movement of tang, even were it not jammed inside the tubing with zero room to move aside from distorting/destroying the tubing itself....
In a nutshell, the handle will probably hold well past point blade would fail, blade failure much more likely than failure of 1" diameter stainless tubing with 1/8th" wall thickness...any reader here can probably envision simply the handle pressed onto tang and how hard it would be to intentionally disassemble shy of destroying either one, or both, in the effort....
I was a skeptic of design until i bought one, now think it is one of the strongest blade handle joints out there, over anything Randall makes, or most anyone else's, aside from an integral, and none of those are forged, and a Randall truly is hand forged, basic blank with tang done via air hammer, then bevels forged by hand with hammer.....mine has seen a lot of hard use and abuse, and i trust it completely, as much as i can trust any knife....
As for an update on how well they hold up, will not argue with original thread respondent referencing talking to Gary and him saying a couple per year that were heavily abused, but my own source, a 30+yr employee recalls only one where handle failed after gross abuse, and long time dealer of Randalls since the 70's doesn't recall any failures although he does remember the one run over by a tank and bent into a shallow u-shape and handle did not fail.
As for the handle uses?......it was designed for crashed helicopter or forward observer crew or passengers, much loved by Special Forces (and still is), to saw/hack way out of vehicle, and have emergency stash of meds/water purification tabs/etc if you were running for your life behind enemy lines and with only what was tied to your britches, with everything else left behind in burning wreckage. a worst case scenario emergency tool/weapon....often forgotten, the spear lashing points on guard were not for spear fishing or deer hunting....in jungles where we were at, there were tigers, and aircrew often only armed with .38spl S&Ws
