doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Lengthened forcing cones and proof

Arguing with the Piper doesn't usually work out too well...

Selective quoting.

Well I have been proven Wrong a few times but this isn't going to be one of them. Just for the record Chuck on the 28ga SAAMI drawing you posted we have a end of chamber diameter of .614". We then have a bore diameter of .545". There is then a cone connecting these two sizes having a 5� angle off the bore axis or 10� included angle.
Now I simply ask you to figure the length of that cone, I already have & know what it would be. Jut like to get your input as you seem to be saying all I have said is Wrong. I know you are capable of this simple calculation, would just like to here the answer though. "IF" it doesn't compute to be a "Modern Long cone" then an apology would be acceptable. If you can show me that it is a "Long Cone" then I will apologize.
Just to be sure we are on the same playing field I would consider a "Long Cone" would be a minimum of 3/4" long & really more on the order of 1" to 1�" Certainly cones of 3/8" to 5/8" have been around for well over 100 years.

I think you've unveiled a triad conspiracy. SAAMI, Manson, and Clymer have come up with a scheme to sell 100 year old reamers. SAAMI, first, puts out a drawing that has the ancient forcing cone angle. The Manson and Clymer then sell these 100 year old reamers with old forcing cone angles to fish like me. I'd rat them out to the reamer police, but clearly they have them on the dole too. Those dirty rats. They even put conflicting reference dimensions and erroneous use of geometric tolerancing in their drawings to throw us off.

Chuck;
Sorry to Burst your Bubble;
Using diameters of .614" & .545" connected by a cone having A 5� ANGLE from bore axis per the SAAMI drawing I come up with a length of .394336804".
Now you might like to work with a bit more precision than that, but that's as many decimal places as my little Casio calculator will work to. Plenty close enough for a TN Hillbilly. That is not as long a cone as Drew's chamber cast of a 1905 Smith shows nor what 1907 & 1935 Smith drawings show. I have not actually measured the cone length on any of my Lefevers but I can assure you they are no shorter than that.
That SAMI Spec cone is "Modern" only if you compare it to one of the rare very early guns with the chamber ending in an abrupt step rather than a cone at all. Even my pre 1865 W & C Scott pinfire has a cone & not a step.

Your 28ga LeFevers have got to be worth a fortune.

Obviously I do not have a 28ga Lefever. To the best of my knowledge Lefever only made "Real" shotguns IE nothing smaller than 20. The L C Smith drawings did not include 28 either. I only used the 28 because that is the SAAMI drawing you posted. The subject was actually about forcing cone lengths, not bore sizes.

I know I have seen Parker research letters stating that a gun was sent back to Parker to have the chambers lengthened from 2 1/2" to 2 3/4". Is there any documentation showing how this was performed, or has anyone taken msurements or chamber castings?
Also guns such as my early Parker 28 has documentation showing it was ordered with 2 3/4" chambers. (It is on a 0 frame). So I know the OD. would be thicker than a 00 frame. Possibly the chamber length request drove he need for an 0 frame. Has anyone seen an original 28 with 2 3/4" chambers on an 00 frame? ( I'll see what I can find out on the Parker site)
LC Smith built some 12 gauge Long Range, and Waterfoul guns with 3" chambers, were different barrel blanks used? Some comparison measurements between the 2 3/4" and 3" Guns might be interesting.
Finally I remember taking measurements of the OD of a number of my 12 gauge guns a few years back at 2 3/4 and 3" and as I recall there was very little if any change in the measurements. Also the ID of the bores and chambers were all pretty consistent. At the time and even now I struggle understanding how moving the chamber forward 1/4" could be so critical to the integrity of the barrel. It just seems to me that the wall thickness of the chamber and bore would not have changed much in a 1/4", and if the same ammunition was used the pressure curve measurements would just move forward a quarter inch.
I'm not arguing my point just attempting to better understand the impact to the integrity of the barrel.

Now, a little homework exercise...calculate the length of the "un-real" .410 shotgun chamber forcing cone below and provide your assessment of its relationship to "modern forcing cone lengths". (tip: subtract the dimension given for the length from the breach to end of the chamber, from the length given from the breach to the end of the forcing cone.)

Chuck;
Chamber dia = .463"; Bore dia = .410; Difference = .053";
.053/2 =.0265"; Co-Tan 5� = 11.43
11.43 x .0265 = .3029; Exactly what is shown on the drawing.
I definitely would "NOT" call this a Long Cone.
The cone length is shorter for the same angle in the .410 than in the larger gauges because there is less difference in chamber & bore diameters.

Ghostrider;
Normal taper for the chamber itself is about .005" per inch. The OD of the barrel at a distance from the breech equal to the chamber length is virtually always tapering more than this, so yes even moving the chamber end just �" will result in a thinner wall at chamber's end. In a heavy barrel this is often of no consequence, but in a very light weight barrel can become critical.