I'm recently moved into a townhouse.  The townhouse's outer walls and the inner walls that separate this townhouse from the neighbors are of a cinder block construction.

What I was wondering about was the use of a 12-gauge for home defense.  Is there a high chance of penetrating cinder blocks with 12-gauge slugs?  What about 00-buck?

I was hoping to check the "Box of Truth" for info, but alas, I see that the website is no more.  Any info anyone can provided would be appreciated.

I would think the slugs would go through - I never tried.
You should be fine with the 00... In my experience they don't penetrate very much.

With 00, I'd be a lot more worried about angle  deflection off  treated cinderblock walls or the 00 coming back at me..

This is a trick question.  Usually every other core of a "cinder block"  (actually a Concrete Masonry Unit) is slushed solid with concrete and steel rebar.  In some cases all the cores are slushed solid.

If they are not slushed solid, I will guarantee a slug will go right through.  I decent whack with a hammer will cave in an unslushed CMU.  If they are slushed solid, there is no way a slug will go through, as you basically have 7 5/8" of solid masonry at that point, with rebar to support it.

There's also all types and sizes of block 4",6",8",10",12" hollows, semi solids, etc., the most common are the 8's (7 5/8" plus the mortar joint).

Quoted: There's also all types and sizes of block 4",6",8",10",12" hollows, semi solids, etc., the most common are the 8's (7 5/8" plus the mortar joint).

Forgot to mention that.  I guarantee the wall he is referring to is a 7 5/8" block wall both for fire separation and structural reasons.

Quoted: This is a trick question.  Usually every other core of a "cinder block"  (actually a Concrete Masonry Unit) is slushed solid with concrete and steel rebar.  In some cases all the cores are slushed solid. If they are not slushed solid, I will guarantee a slug will go right through.  I decent whack with a hammer will cave in an unslushed CMU.  If they are slushed solid, there is no way a slug will go through, as you basically have 7 5/8" of solid masonry at that point, with rebar to support it.

Guess I'll stick with the 00 Buck for now until I do more homework on this.  I really don't know if the cores of this place are slushed solid or not.  

If it helps any, the house is on the east coast of Florida so it's probably been designed with some features to withstand hurricanes.  If you look at the place from above, it looks like a symetrical cross.  If you then cut that cross into 4 equal quarters, each quarter would represent one townhouse in the unit.  I've heard someone mention that if it's not a DiVosta design then it's a copy of one.  Maybe someone is familiar with the design or construction of these types of buildings.

Oh, and one other thing of note.  The design is very "quiet" in that I've never been able to hear any noise from any of the neighbors.  Don't know if maybe that gives some indication of construction or not.

Actually that is very useful info.  When I get some free time I'll dop a little research on the Florida Building Code and let you know what i find out...they may very likely have to grout CMU solid.

The only actual test I ever read about was in an older book on combat shotguns.

In one chapter, the author ran a series of tests with shot, buckshot, and slugs against a good variety of wall construction, including wallboard, the old fashioned lath and plaster, and exterior walls of a number of types including brick and cinder block.

His bottom line was, no standard interior or exterior wall construction would stop ANY buckshot or slug, and not most larger shot, UNLESS the wall was brick or block construction.

In the pictured tests, 00 buck would spall the surface of the block, but not shatter it.
Slugs would often break the block, but not penetrate all the way through.

He also concluded that simply setting a cinder block on the ground and shooting it wasn't a valid test, since the blocks are mutually reinforcing, making them harder to shatter and penetrate.

His rather unique conclusion was, if you have verified intruders in the house in the middle of the night, simply slide off the bed onto the floor and shoot the shotgun right through the walls at where the bad guys are.  
The shot will sail right through the walls and hit the BG's.

His second conclusion was: Unless you have brick or concrete block exterior walls, don't expect the shot to stay inside the house.

Based on this, I'd say you're fine in a dwelling with a firewall made of cinder block.

I do question the use of shotgun slugs as an inside-the-house defense round.
The big advantage of the shotgun is the spreading "cloud" of shot, and the speed at which you can get it on target by "pointing" the shotgun.

The use of slugs turns the shotgun into nothing but a large caliber musket, which must be precisely aimed.

These days I mostly hear home defense discussions concerning how tight a particular load or gun patterns.

In a true inside-the-home gun you want just the opposite.
A good rule of thumb on shotguns is, the shot will spread "about" one inch per yard.
In other words, at 6 yards you'd have a circle of shot about 6-7 inches in diameter.

A 6 to 7 inch circle is not big, and it's VERY possible to flat MISS a shot inside the typical home.
Years ago, people used to make up shotgun shells with a spreader modification to make the shot open up faster for use inside.

In a "combat" shotgun, a tight pattern is good for those longer shots.
In a true Home Defense gun, the bigger the pattern at short range, the better.

Since my Remington 870 Police is a true inside gun, I opened the factory Improved Cylinder choke to a true Cylinder bore, and I selected buckshot loads that DON'T shoot tight patterns.

Especially in the case of shotguns, you have to do a "real world" assessment of what your MOST LIKELY situation is.

Will you MOST likely be shooting at a Bad Guy, or will you be "shooting past someone"?

If you run a very high probability of having an innocent bystander between you and an intruder, by all means you should take that into account when selecting gun and ammo type.

However, it's not too good an idea to base things on something that has a very low probability of happening, especially when you reduce your effectiveness in things that are LIKELY to happen.

Im not kidding when I give you this information on what you are looking for. Simple bird shot will work just for what you are asking. 6's, or 7.5s will go threw a wall of sheet rock but will not go through the next wall. At the ranges you are talking about it is perfect.My friend has first hand knowlage on this for he shot and killed a man in his gargae charging him with a hammer.Dropped him dead in his tracks!!! If you do not believe me go shoot a watermellon at 10 to 12yards and see what happend. Its very ugly.10 yards is 30 feet so think of the size of your town house...

Slug-O