And cap sizes don't mean anything. CCI "No. 10's" are not the same size as Remington "No. 10's", nor are the "No. 11's".
Mykeal,
While it is technically true that CCI and Remington caps are not the "same size" (that is as in how they measure), it isn't true they won't fit the same tubes by size. In other words, a tube that accepts a Rem #10 Cap will normally accept a CCI #10, and the same is true for #11 caps.
You should know this, Remington has chosen one Internal Diameter and affects the fit by changing the skirt length. CCI has chosen to primarily vary their Internal Diameter with minor changes to length (probably due entirely the manufacturing tolerances they will accept internally).
Since tubes are tapered either method will work, they just have to be pursuing some derived nominal tube they have adopted internally to manufacture their caps to. What I mean by adopted internally, is that there isn't an industry standard for either tubes or caps. Where we are today is the result of 181 years of production and a convergence of sorts as to the standard #10 and #11. We should also include the RWS 1075 and RWS 1081 caps in that group.
In addition there are European sized caps now available from Sellier-Bellot, they call them the 4.0 and 4.4. This can be confusing to many people who are used to European primers being sized by diameter the primers are listed by diameter:
4,4 (4.4mm) = .173" Which is close to the American nominal diameter of Ø.175 for small primers
5,3 (5.3mm) = .209" Which is close to the American nominal diameter of Ø.211 for small primers
Most of us know that European primers (including shotgun primers) tend to run small.
The (4,0 and 4,4) make sense for percussion caps if they are talking about height. If they are making a common internal diameter and then varying the skirt length 'a la Remington then it does make sense.
4,0 (4.0mm) = .157"
4,4 (4.4mm) = .173"
Those lengths are similar to the current (2010 production) Remington caps which measure:
2010 PRODUCTION
.CAP_....__I.D._....._Height_
Rem10.... 0.166" ....0.183”
Rem11 ... 0.166” ....0.154”
They are even closer to my 2007 Production measurements
2007 PRODUCTION
.CAP_....__I.D._....._Height_
Rem10.... 0.166" ....0.175”
Rem11 ... 0.166” ....0.154”
If you look at the petals that form the skirts on the Remington caps it is easy to see how these would vary from lot to lot. These are Remington caps:
For those of you who might be a bit confused about all of this let's consider a standard factory Uberti tube:
Now let's look at how Remington and CCI caps will fit on this tube. First the Remington caps.
You will note both caps have been placed on the tube until the I.D. of the skirt begins to have a light interference with the taper of the tube. This tube accepts Remington #11 caps. You could force a #10 Rem cap on, but a #11 fits.
These are CCI caps on the same tube.
Again both caps are paced on the tube until there is a light interference fit. Once again notice how the CCI # 11 cap fits but the CCI #10 is too tight and sits proud.
All of these models are derived from measured caps and measured tubes. From this one can see how a #11 Remington Cap will have the same relative fit as the CCI #11 even though they contact the tapered tube at different points and even though the priming compound is of different thickness on the two brands.
The thickness of the priming compound controls how high off of the face of the tube the cap will fit. This is a consideration for some people who have low clearance between their tubes and the recoil shield. In that case it would be wiser to choose Remington over CCI (RWS also has thicker priming compound and sits higher).
So while there is no "common size" by measured geometric shape, there is a common "size" for fitting purposes.
To add to the brouhaha, there are aftermarket tubes that are specifically targeted to certain sizes of caps. For instance the Treso tubes are designed to accept Remington #11 caps. The same is true for other manufactures.
Regards,
Mako