Author Topic: Cap Gun Primer: Percussion Caps  (Read 19459 times)

Mako

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Cap Gun Primer: Percussion Caps
« on: January 10, 2012, 03:33:15 PM »
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Cap sizing and the fit to the cones remains the most misunderstood part of percussion firearms usage.  Most shooters of single shot muzzleloading rifles and pistols do not agonize over the cap to cone fit the way that percussion revolver shooters do.  Even those revolver shooters that do not
« Last Edit: January 10, 2012, 06:56:52 PM by John Boy »

Mako

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Re: Cap Gun Primer: Percussion Caps
« Reply #1 on: January 10, 2012, 03:45:04 PM »
There are 5 caps in the #10 and #11 range commonly available today.  The RWS 1075 seems to be impossible to find these days and appears to have been "replaced" by the RWS 1075 Plus in availability.  The "Plus" cap is actually a "magnum" cap but will work for our purposes.   In addition to the five is an entry supplied by Hellgate for an RWS #55 cap, these are also called RWS 1055 caps and I will add to the data sets when I locate a package of them I squirreled away somewhere.



I have now measured:

    120 Remington #10 Caps from four distinct manufacturing lots, 20 caps from each package (two lots provided 2 packages)
    120 Remington #11 Caps from five distinct manufacturing lots, 20 caps from each package (two lots provided 2 packages)
    120 CCI #10 Caps from Three distinct manufacturing lots, 20 caps from each package (3 packages from one lot, 2 from another and 1 from a final lot)
    120 CCI #11 Caps from five distinct manufacturing lots, 20 caps from each package (2 packages from 2 lots, and 1 from two other lots)
    87 RWS 1075 Caps from one lot
    79 RWS 1075Plus Caps  from one lot



This is an image from models of the five caps in question, note how all of the caps are arranged to set the height as it would be relative to sitting on the cone face, this will give you some idea of the differences in priming compound thickness between the caps.



These side by side comparisons of the cross sectioned models will help you understand why some caps appear to be "larger" than others on the exterior, but are in fact nearly the same size internally or actually a bit smaller than another cap that might have an overall shorter outer height.

Construction differences are readily apparent between the three manufacturers.  The corrugated features show up as a ribs on the inside of the CCI caps, a ghost image of the corrugation shows through on the Remington caps, but are not measurable.  The Remington caps have the four "petals" left on them which is part of the forming process.  Actually all three styles of caps have these petals at a point in their forming process.  CCI and RWS trim the bottom of the skirt and finish them differently.  RWS applies an internal chamfer to the skirt to facilitate loading and CCI breaks the outer edge slightly.  Only Remington leaves the skirt as formed, this "as formed" condition often manifests itself with petals of slightly different length on the same cap (look at the photo of the Remington #10 cap as an example of this).

Photos in subsequent posts will show the internal features and differences described above.

The external heights are as follows:

The #10 Caps



The #11 Caps (note the RWS 1075s are categorized as #11 caps because they fit the same cones as caps marked as #11)






Mako

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Re: Cap Gun Primer: Percussion Caps
« Reply #2 on: January 10, 2012, 03:53:40 PM »
The Remington #10 Cap is the longest cap of the bunch.  This confuses people because it appears to be the "largest cap," when in fact it is the smallest or tightest fitting cap.  The tightness is due to the length of the skirt hitting the taper of the cone further down the body where the diameter is larger.




The two "important" dimensions are the Internal Diameter and the Internal Height.  These two dimensions will determine the fit on a cone.

Note the fold seam ("split") that appears at crotch of the petal which is an artifact from the forming operation. You can see also the superficial marking made by the roll tool that made the corrugations;  it shows through as a "ghost" image to the interior but is not measurable.  The Shiny material on the interior is the sealing compound used over the green paper bursting disk covering the priming compound.

Mako

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Re: Cap Gun Primer: Percussion Caps
« Reply #3 on: January 10, 2012, 04:00:26 PM »
The CCI #10 Cap fits the same cones as the much longer Remington cap.  The internal diameter is the smallest of the five caps and hits the tapered cone at roughly the same height as all of the other caps except for the Remington #10.   The smaller diameter makes the tighter fit on this cap.





The two "important" dimensions are the Internal Diameter and the Internal Height.  These two dimensions will determine the fit on a cone.

The ribbing actually shows through on the interior walls.  There is sealant from the bursting disk shows on the walls with a distinct line from the process.  The yellow colored Bursting Disk covering the priming compound appears to be a fiber and binder mixture instead of a paper disk.

Mako

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Re: Cap Gun Primer: Percussion Caps
« Reply #4 on: January 10, 2012, 04:05:22 PM »
The Remington #11 Cap has the same internal I.D.s as the Remington #10.  The difference is in the skirt length (Internal Height).  The shorter skirt doesn't extend as far down the taper of the cone and will fit on a larger diameter cone.  Compare the internal height and the I.D. between the three #11 style caps and they are very similar.  The Remington appears to be "smaller" than the other two #11 caps because it has a shorter exterior height; the difference is in the priming compound thickness.





The Remington #11 cap shares the same green paper Bursting Disk with the #10 version.  It also shows residual sealant on the inside.  The close up photo shows the cracks at the petal crotch that often pass entirely through from the exterior to the interior.

Mako

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Re: Cap Gun Primer: Percussion Caps
« Reply #5 on: January 10, 2012, 04:10:11 PM »
The CCI #11 Caps are very similar to the CCI #10 caps with the exception of the Internal Diameter.  The I.D.s and internal height are very similar between all three manufacturers.




The ribbing shows through on the interior walls.  There is sealant from the bursting disk shows on the walls with a distinct line from the process.  The reddish brown colored Bursting Disk covering the priming compound appears to be a fiber and binder mixture instead of a paper disk.

Mako

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Re: Cap Gun Primer: Percussion Caps
« Reply #6 on: January 10, 2012, 04:15:49 PM »
The RWS 1075 Cap is actually a #11 size cap (which means it will fit on cones that caps labeled as #11 will also fit).




The cap has a tan fibrous bursting disk and it it sealed with a clear green sealer.  The interior edge of the bottom of the skirt has been chamfered and this creates a "saw tooth" pattern along the bottom edge.

Mako

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Re: Cap Gun Primer: Percussion Caps
« Reply #7 on: January 10, 2012, 04:22:09 PM »
Some of the Factory  tubes have cones that are smaller in diameter and #10 caps fit snuggly on them while #11 caps will fall off (unless pinched).  I do not recommend pinching except in extreme circumstances, pinching can create its own set of problems.

This illustration depicts the two contact points for the two different #10 caps when they are fully seated on the cone.





Mako

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Re: Cap Gun Primer: Percussion Caps
« Reply #8 on: January 10, 2012, 04:26:17 PM »
Treso Cones are designed for #11 caps, the model is derived from measurements taken from 4 sets of factory fresh tubes (24 tubes).





Mako

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Re: Cap Gun Primer: Percussion Caps
« Reply #9 on: January 10, 2012, 04:33:22 PM »
Poor Cap fit:  There are three kinds of poor cap fit.  The kind that causes the most grief are caps fitting too tightly on the cones.  This causes high caps and inconsistent ignition.  This is an example of such a condition, in this case a CCI #10 cap has been placed on the cone and pressed down until it has exactly the same amount of interference a #11 Cap would have on the cone (roughly .003").  As you can see the cap sights proud and there is .047" of clearance between the priming compound and the cone face.



Some shooters will maintain they have no problems with "undersize" caps; they use a pushing stick and force a tight fitting cap down.  This is commonly done, but it often results in caps that are split before firing and they may even become loose at that point.  If the cap is not fully seated it often will not fire on the first hammer strike because the force of the hammer blow is used to seat the cap further onto the cone instead of crushing the priming compound between the hammer (top of the cap) and the face of the cone.
The second condition is a large cap on a small cone.  Some factory cones are better suited to #10 caps; if you "seat" a #11 cap on those cones you will not get a fit that will keep the cap in place.  Often the cap will fall free or back off under recoil from the previous chamber and by the time it reaches alignment for firing it is not seated.  Once again you may get a "soft" hit as the hammer attempts to drive it home.



The third condition is created by shooters using the technique of "pinching" caps to create a friction fit between the oversize cap and the cone.




Pinching caps creates a path for hot gases coming back through the flash hole on the chamber being fired to find a path directly to the priming compound.  When Samuel Colt was selling his pistols he was advertizing them as being "water proof."  We all know they weren't "water proof" but they were intended to be sealed at the rear.  He struggled with chain fires and rear

Mako

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Re: Cap Gun Primer: Percussion Caps
« Reply #10 on: January 12, 2012, 01:25:29 PM »
Pinched caps continued:

A reader sent me a message and asked if the castellations on the rear of the cylinders wouldn't prevent chain fires from the rear if a cap was in place.  They didn't understand how the hot gases could negotiate the tortuous path and make it through a small opening created by a pinched cap.

What many people don't know is that Colt's earliest designs suffered from chain reactions due to a closed breech design Colt originally touted as a safety feature and a protection to the caps from the elements.  Colt found his enclosed standing breech and on some designs enclosed blast shields on the front of the cylinders except the one aligned to the barrel, not only allowed chain fires, but exacerbated the problem. His later designs deepened the castellations and dropped the top of the cones below the surface of the rear of the cylinder. Even with these improvements the cloud of burning gas that actually comes back through a flash hole and envelops the entire rear breech area is much more than we imagine.

On August 29, 1839 Samuel Colt was issued a new patent for Improvement in Fire-Arms and in the Apparatus Used Therewith, included in his claims was a feature we now take for granted.  That feature was the reduced opening at the chamber end of a percussion tube. 




Prior to his design, tube through holes were either straight through or tapered in the opposite direction like a rocket engine nozzle as defined by the Robert Adams (Englishman) patent.  With single shot weapons the back blast wasn

Hedley Lamarr

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Re: Cap Gun Primer: Percussion Caps
« Reply #11 on: January 12, 2012, 01:34:42 PM »
This thread is for information only.
Please place all discussion on this topic here:
http://www.theopenrange.net/forum/index.php?topic=9094.0

Thank you!
Hedley Lamarr

"There's a special rung in hell reserved for people who waste good scotch." - Lt. Archie Hickox