Above is the "protected" Li Ion battery that went into thermal runaway in my BB that Matt was talking about in the above post. I'm not sure if it vented flames, but it surely vented gas hot enough to scorch the pocket of my pants. Luckily I wasn't wearing the pants at the time this happened.
The precipitating factor causing the above battery incident was the fire button becoming compressed in the pants pocket. This caused a rapid discharge of the battery, causing the battery to stress, overheat, and vent. The protective circuit in this battery failed to stop this. This is why safe chemistry IMRs are now recommended over protected Li Ion batteries in mechanical mods. You lose battery capacity (mAh) using an IMR over a protected battery, but when all is said and done safety is more important than higher mAh's.
Ever since this incident occured, I've used nothing but AW IMRs (Li Mn safe chemistry) in all of my mods, regulated as well as my mechanicals. No type of battery is totally safe, but I feel safer with these than I would if using protected batteries.
As Matt was saying above. Drilling a hole in the bottom of the Silver Bullet may not accomplish much but put a hole in your PV. As seen in my pic above, a battery going haywire in thermal runaway can become distorted in shape and swell, blocking any access to a vent hole in the bottom of the mod. Batteries typically vent from the positive end of the battery, although both ends blew out in mine. The BB did what it was designed to do - vent the hot gases out the fire switch and the hot spring collapsed, probably preventing the mod from becoming a pipe bomb. The fire button continued to work for a couple of days after this event, but then stopped working. I had to send it in to Chad at AltSmoke to have the button and hot spring replaced.
If I were you, I'd leave your SB alone and not drill a hole in the bottom of it. If the mod designer (Chad) thought a vent hole was needed in the SB, I'm certain he would have designed it with one. Like the BB, the Silver Bullet's switch is designed to vent gas in the event of a thermal runaway.
Buy a new
HOT SPRING, they're cheap and its wise to have a spare. Make sure you use a high quality IMR battery like the red
AW IMRs. You might even consider using a
Vape Safe Mod Fuse for a second layer of protection. These are a thin battery fuse that attaches to the negative end of the battery via a magnet, but some folks might consider this overkill - I'm not one of those.
Using a
KICK in your Silver Bullet would offer short circuit protection, and also allow you to adjust your voltage like a regulated mod. This would go on top of your battery. These take up some room in the battery compartment, so you would need to
drop down a battery size to an
18490 IMR, or purchase a
Silver Bullet KICK sleeve in order to continue using the 18650 battery.

Silver Bullet with a Kick
Here's a blog that I've written on
Battery Basics for Mods: IMR or Protected?