Home » Articles » How to Break Rocks with a 22 Round: aka Microshaving

How to Break Rocks with a 22 Round: aka Microshaving


Microshaving / Rock Capping (Dangerous)

Buy at Amazon

Microshaving or Rock Capping is a technique used for splitting rock.  This works by discharging one of more .22 caliber nail gun cartridges (or blanks) within a drilled hole.

It is a useful method for splitting boulders into a manageable size.  It may also be used, albeit less effectively, to trim bedrock.

I learned about the technique from attending a briefing on the capabilities of a local cave rescue organization.

They use this to enlarge passages in order to remove hurt spelunkers.  However, microshaving is called rock capping in the united kingdom and is used their to widen passages while cave exploring.

This is inherently dangerous

This is an inherently dangerous activity as detonating blank cartridges inside a rock is unpredictable.  I do not recommend anyone actually use this technique.

However, in the event of some unforeseen future cataclysm, a thoughtful prepper may find a use for this that outweighs the danger to life or limb.

I got a couple of shrapnel injuries from my experiments in microshaving.  So unless I have a very substantial need to crack a rock without using explosives I will not be doing this again.  It scares me.

Why I am sharing

I thought long and hard about posting this, and leaned toward not sharing (which in the UK – capping is not talked about because they are afraid public attention will cause it to me legislated against).  In the end, I decided to post this because – I trust the intelligence of my readers, and I think information should be freely shared.

The basic technique is to drill an 8 mm or 1/4 inch hole to the required depth (about 8 inches), insert one or more cartridges into the bottom of the hole, and to explode the cartridges by striking the top cartridge with a firing pin. Although capping is an effective technique, it is also particularly hazardous when performed with the wrong tools, or incorrectly or carelessly with the right tools.

Some Hazards you need to be aware of

  • The caps can explode prematurely if inserted in the hole carelessly, and expelled with great velocity.
  • The firing pin can be ejected from the drilled hole at a velocity sufficient to penetrate flesh.
  • Fragments of rock shoot off in all directions, again at a velocity sufficient to penetrate flesh.
  • Gases from the exploded caps are noxious (although not produced in great quantity). They include oxides of nitrogen, oxides of carbon, oxides of lead, metallic lead and acrid fumes.
  • The sound of the cap exploding in a confined space can be sufficiently loud to damage the ears.
  • The larger lumps of fragmented rocks can fall on badly positioned limbs.


You can buy a complete microshaving kit from a well known cave rescue supplier for about $100 bucks.

  • Drill and bits: The bits should be marked so that holes are drilled for the correct length. This will normally be the length of the firing pin less the thickness of the capping mat.
  • Caps: These come in a variety of strengths, and the stronger ones are obviously more effective (such as the Black Hilti cartridges or Red cartridges from Spit – these have the advantage of being a slightly smaller diameter than 8 mm and easily slide into an 8 mm hole without risk of jamming). They should be transported in waterproof containers (such as pill boxes) which have been padded to prevent them from rolling around.
  • Slide Hammer: The best ignition tool is a long slide hammer with the firing pin fixed to the end. This allows the caps to be fired from a safe distance, and the weight prevents the firing pin from being expelled. The firing pin should be protected during transport, possibly with something like an ice-axe protector.
    • I used a 1/4 rod with a wedge ground into the end to ignite the rimfire cartridge and a pole driver to keep the rod from being shot out of the hole.  People have been speared in the chest from firing rods being shot out of the rock – once again


  • Capping mats: The pin should be inserted through a mat intended to contain the blast. The best mats are made of conveyor belt material, and should be a minimum of 1 foot square. These are effective at confining the blast without being damaged.
  • Blow pipe: To empty the hole of excess dust which could absorb the impact of the firing pin. – Any rock dust from the drilling will be shot straight up when the round is fired and can cause severe eye damage.
  • Goggles: To protect your eyes from any ricocheting fragments.
  • Ear muffs or ear plugs: To protect your ears from the sound of the ignition in confined spaces.
  • Gloves: To protect your hands from any ricocheting fragments.  I neglected this and received a nasty puncture wound

Did I mention it was Dangerous

It should be clearly understood that when used carelessly, microshaving is dangerous. Every attempt should be taken seriously, and undertaken methodically following established procedures.

Accidents will happen when the operator becomes too comfortable

  1. Drill a hole in the center of your boulder with an 8 mm bit to the depth dictated by the length of your firing pin less the thickness of your capping mat. This should be about 6-8 inches deep. The bit should be marked so no guess work is involved. Note that shallow holes are dangerous as the blast-back is a lot more severe. If the maximum depth of a hole that can be drilled in a boulder is, say 7 inches, the hole should be drilled to the full depth rather than half-way.
  2. Empty the hole of dust using the blow pipe.
  3. Insert the caps. For a smaller boulder, one will usually do. On a larger boulder two may be required. For bedrock three may be required, but no more than three should be used. In general, use the minimum number of caps – this will lessen the noise, the fumes, and the flying fragments.
  4. Ensure any helpers move well back, and the drill and bits are set well to one side.
  5. Ensure gloves, ear muffs, and goggles are all in place, and that your legs are not under the boulder. You should assume that an accidental firing is possible during the next stage, so you should be positioned as far from the boulder as possible.
  6. Position the protective mat so as to provide adequate protection.
  7. Push the tip of the firing pin through the capping mat.
  8. With the capping mat inserted over the firing pin, push the cap(s) gently to the base of the drilled hole. Treat gently so as to avoid premature firing.
  9. After warning any helpers, strike the firing pin firmly and sharply with the slide hammer, and firing should occur.

Failures May Occur

Rarely, a cap may fail to detonate. This could either be because the cap is dud, or because the hole is too deep for the firing pin to fully penetrate. This is potentially dangerous, as if it is left and care is not taken, it could be fired accidentally whilst drilling a second hole. In the first instance, another cap should be inserted as above, and a further attempt made to detonate the cap. If this fails, a second hole should be drilled such that it cannot intercept the previous hole, and the boulder split. Care should then be taken with the debris until the unexploded cap has been located.

It was legal at the time this article was written

As far as I know, microshaving is legal.  Mostly because it is unknown and nobody has written laws or regulations precluding it.  It is not blasting, and does not work well for moving a large amount of rock.  It is more like extreme chipping away of rock outcroppings.

I do not recommend you try this, especially since its highly unlikely you can have the help of someone experienced in the proper techniques, but I do recommend you think about the process because its another example how someone used their brain to re-purpose materials to solve their problems.

Leave a Reply