Tom asked me to put this in a trip report on the Collective after I sent him a note about the rope so I decided to have some fun with it. The combination of predicted warm weather , sun and no wind in the day coupled with just freezing temps. at night and the supermoon was too good to pass up. The High Spur area of the Roost is relatively isolated because of bad roads but is very beautiful. My son wanted to bring 5 of his fit, athletic 20 something friends along to do the Northeast Fork of High Spur Canyon. I chose a 60 something ex-NOLS instructor from the 70's with no technical canyoneering experience as my friend. And did I say wouldn't have to carry any ropes? NE ForK of High Spur is a relatively benign canyon described by some as just walking down a canyon with a rappel at the end. Its a bit more than that with 1 pothole (depending on recent weather) a couple of down-climbs that can be rappelled and the last drop is about 80 ft ending in 60 ft of free. It was a good choice for our group as I had done part of it before and 5 of our group were near noobs to total noobs with no technical rope experience. The corkscrew slot in the second half is very dramatic and compared by some who know to Antelope canyon as a photographers destination. The first half of the canyon if you do the full thing, is a couple of miles through beautiful narrows that occasionally may get your pack off. Nothing very challenging but aesthetically pleasing and we went through very quickly. We rapped the one down-climb in the upper part and the two in the lower to get the beginners some experience dealing with ropes and devices and setting some best practices leading up to the last drop. We had fun working through the one pothole which was knee deep and not a problem but getting 8 people through is still a bit of fun logistics. We had decent light for the corkscrew slot. Rapping the last drop before the free rappel. This can be down-climbed. Last rap, view from the top. The last rappel has at least two large blocks for anchors, one close to the edge and one 15 feet back and lots of room to safely work. Eddie, an expert climber and canyoneer had deployed my 200 ft Canyon Fire 8.3 mm as doubled on the mid-point and biner-blocked as most were rapping doubled on ATC's but a couple were going single on Critr2's. As rappels go this one is easy and a good first free rappel of some length. The first 20 ft are down a couple of ledges then a walk down a 60-70 degree slope followed by a very abrupt horizontal undercut leading to 60 feet of free. The rope had been carefully checked when bagged 2 weeks before and was looked at careful when deployed this day, the first usage since. First person rapped double on an ATC and began bottom belays. Second went single line on a Critr2. He spun slightly. No one went fast, bounced , etc. The third person went double on an ATC. As did the fourth. After the fourth Eddie called up that it looked like there was a nick in the rope so we pulled it up to (This picture taken later). We were somewhat taken aback as we now had one 120 and an 80 connected by a core shot and still four people to get down only one of whom was prepared to pass a knot. The most noob of the group was already unhappy with the situation and when she saw the rope her heart sank. Of course there was more than one way to skin this cat but since we also had a 100 ft 9.2 mm with us and a noob who wanted to either turn around or be lowered we re-rigged for a lower off of the other anchor block using a munter and as well a separate belay with an ATC off the original block. OK it was overkill but this was my first core shot. The lower went smoothly (mostly eyes closed) Lower in progress. I went last doubled on a Critr2 and observed that in many places the edge of the undercut was extremely sharp. Force per unit area tends to win in those situations. In this photo of the rappeller right after the single , we can barely see the core shot above the edge in this case as the rope is pulled up as he starts. (red arrow). In the next photo of the fourth rappeller we can see the core shot now below the edge as we had shifted the rope between rappels to distribute the wear. Both guys rappelled double right over it and didnt notice. The hike out was beautiful and long, with the short day we got back to camp at twilight. All happy but doing a bit of pondering. Next day the old people went off to attempt the NW Fork of Big Springs and the kids left. Fast forward 2 weeks and the football of either kind is over so i decide to turn this core shot over to the Seat of the Pants Institute for Cordage Testing, Back of the Envelope Lab. I have been thinking quite a bit about people rapping over the core shot and even though I found an old post from Tom Jones about no one wanting to go with him because his ropes had too many core shots, I was curious what it would take to break this thing. Even though there was a beautiful white tuft of core strands poufing out, it appeared that damage to the core was extremely limited. Probably less than 1 or 2 percent. The sheath had retained 8-9 mm of its originally 26 mm circumference. I had about 15 cm of rope left on one side and 10 on the other. I attached these to a Ropeman on the top and a Petzl Basic below. I attached 70 lbs below it, set up a Z-rig and hauled up the weight. I got up to 154 lbs and the weight was still all on the remaining now about 4 mm of sheath. The core was still puffed out. I lowered the weight then pulled back up until about two thirds of the weight was off the ground and almost immediately the core took the weight with about 2 very stretched strands of sheath remaining. I added 7 gallons of water to now have 212 lbs (getting close to my weight). The last strands of stretched sheath broke and the sheath pulled off the core. Still no core damage. I knotted both ends of the now free core, reattached to the ascenders and loaded it up with 212 lbs. It has been sitting there for 3 hours now, no the worse for the wear. Conclusions: While I wont be purposefully rappelling over core shots, these things do happen even when you are using high quality material that you have checked and deployed carefully in locations where many before you have ventured. It was not a random event. The very sharp edge while not everywhere on the lip is definitely present. In the case of the cutting of the sheath and the 2 who rappelled over the cut sheath, going double does appear to have defeated Force per unit area. These high quality ropes are really well made but not "overbuilt". Built right. The sheath is really strong. Addendum: The standard set of weights in th the Seat of the Pants Institute for Cordage Testing, Back of the Envelope Lab.