youre better off just running down to your local drug store and getting a nail file. I dont know if you have any tools lying around, but I once used a metal file to score one, haha. Then I stuck the end of it in an emptied out disposable pen to snap off the top.
One of my personal favorites that has always worked well for me is the handy little wire stripper that you can get in the automotive electrical section at your local wal-mart. Because it's made to fit different gauges of wire, it'll fit around the neck of an amp and scour it nicely.
BJ- your idea is similar to mine. I wrap the amp as you described and hit the very tip-top with a small hammer (while amp is in an upright position) - amp being held against inside of sink. Ive never had or heard of any shards of glass being sucked up and injected in any way.
I have never lost an amp this way-the only way I can make that claim.
Personally guys, Ive broken a couple amps before using amp openers. The tooth/file in it will dull and your just trying to score it with what amounts to a butter knife-and bam!-it crushes. The way I do it Ive NEVER broken an amp. Or you can buy a shitload of amp openers and make sure you always use a new-sharp one.
My sister is a nurse and I saw her open an amp one time. Get a piece of cotton gause and put it over the top, then hold the bottom and bend the top from side to side. Always works for me, never broken an amp anyway.
I usually just snap off the top no problem but one time it didn't work so I open a drawer put the amp at the bottum so the very tip would hit the drawer when I closed it and then slammed the thing shut! Glass was everywhere even in my precious sauce so I was very careful not to suck that up! for the most part it works