FORCING CONES

[edgarspencer]

This is a subject that comes up quite often. The Forcing Cone is the tapered section of the barrel bore, immediately in front of the chamber, The larger diameter being the end of the chamber, and that point, where many of the questions originate, is the Chamber Length. The point of these questions is, invariably, so the shooter knows what the appropriate length shells can safely be used in the gun.

Because of the knowledgeable members, we accept that Parker Brothers bored their barrels to dimensions based upon the theory that a certain amount of the shell, upon opening when fired, extends into the forcing cone, in order to form a (better?) gas seal.

I have several questions, and hope to learn from knowledgeable people, and not just opinions, are the following;
A, Did Parker guns, made prior to the introduction of paper hulls, even have forcing cones?
B, Was the amount of opened hull withing the forcing cone, on an unaltered gun, always the same. To answer this, historical data most probably is necessary,i.e. factory records, or hang tags.

After the full acceptance of paper shells, a variety of lengths were available.
I have guns with 2 3/8" chambers, which I accept as fact, were intended for 2 1/2" shells. Likewise, I presume those of my guns with 2 5/8" chambers were intended for 2 3/4" shells.

Dean recently spoke of one of his guns with a 2 9/16" chamber, so my question was what shell was that gun intended to digest.

I have a hang tag (but not the gun) which states the gun was intended to shoot 2 5/8" shells (see the attached image) so what chamber length would that gun have been bored?

Are there any others out there, that lay awake at night thinking about this stuff, or are they all still trying to understand quantum physics and subatomic particles?

[Dean Romig]

This is a subject that comes up quite often. The Forcing Cone is the tapered section of the barrel bore, immediately in front of the chamber, The larger diameter being the end of the chamber, and that point, where many of the questions originate, is the Chamber Length. The point of these questions is, invariably, so the shooter knows what the appropriate length shells can safely be used in the gun.

Because of the knowledgeable members, we accept that Parker Brothers bored their barrels to dimensions based upon the theory that a certain amount of the shell, upon opening when fired, extends into the forcing cone, in order to form a (better?) gas seal.

I have several questions, and hope to learn from knowledgeable people, and not just opinions, are the following;
A, Did Parker guns, made prior to the introduction of paper hulls, even have forcing cones?
B, Was the amount of opened hull withing the forcing cone, on an unaltered gun, always the same. To answer this, historical data most probably is necessary,i.e. factory records, or hang tags.

After the full acceptance of paper shells, a variety of lengths were available.
I have guns with 2 3/8" chambers, which I accept as fact, were intended for 2 1/2" shells. Likewise, I presume those of my guns with 2 5/8" chambers were intended for 2 3/4" shells.

Dean recently spoke of one of his guns with a 2 9/16" chamber, so my question was what shell was that gun intended to digest.

I have a hang tag (but not the gun) which states the gun was intended to shoot 2 5/8" shells (see the attached image) so what chamber length would that gun have been bored?

Are there any others out there, that lay awake at night thinking about this stuff, or are they all still trying to understand quantum physics and subatomic particles?

The chambers were predominantly machined the same, within a specific gauge and within a less specific time period, and that isn't the factor in the equation that would ever change. The thing that would change from one paper cartridge maker to another is the open length of the cartridge.
I would therefor say that due to this factor, the length of the cartridge that opened into the cone varied accordingly.



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[Dave Noreen]

This all gets really confusing. I find earlier hang tags even more confusing with these lines Length of Shell 2 5/8 Inches and then the next line Use Shell 2 3/4 Long?!? This gun targeted with 1 1/4 ounce --

96765

This gun targeted with 1 1/8 ounce --

96766

Later 12-gauge tags generally state Use Shells 2 5/8 Long if they were targeted with 1 1/8 ounce --

96767

96768

and Use Shells 2 3/4 Long if they were targeted with 1 1/4 ounce --

96769

96769

I have found that the vintage paper shells I've fired and checked for length were very uniform and right on for stated length. Not at all like modern plastic shells.

[edgarspencer]

Dean, I'm not certain that answers any of my questions. I'm not actually sure I even understand what you said. My questions are based on my assumption that the manufacturers stated cartridge length is the Opened length of the hull.
Also, there some point between the beginning and ending diameters of the forcing cone that matches the internal diameter of the hull (wad diameter)

[edgarspencer]

This all gets really confusing. I find earlier hang tags even more confusing with these lines Length of Shell 2 5/8 Inches and then the next line Use Shell 2 3/4 Long?!? This gun targeted with 1 1/4 ounce --

96765

This gun targeted with 1 1/8 ounce --

96766

Later 12-gauge tags generally state Use Shells 2 5/8 Long if they were targeted with 1 1/8 ounce --

96767

96768

and Use Shells 2 3/4 Long if they were targeted with 1 1/4 ounce --

96769

96769

I have found that the vintage paper shells I've fired and checked for length were very uniform and right on for stated length. Not at all like modern plastic shells.

Confusing? Ya Think? I just measure a Remington Kleenbore, Box labled 2 5/8", and roll crimped, it measures 2 3/8"
The attached shows a NPE which measures 2 3/4", and the same hull, loaded, fold crimped with 1 1/8 oz measuring 2 1/2"

[Garry L Gordon]

Based on those hang tags, I believe we may never know the answers to Edgar's questions. One could surmise from the earlier period tags...but that would just be speculation without any corroborating evidence.

These are incredibly interesting questions, but as someone who cannot by any measure be considered "knowledgeable," I'll stick to quantum physics and sleep better at night. In the meantime, I'll use the milder, shorter shells, enjoy my shooting, and continue to follow discussions like this with great interest.

Thanks for bringing this up!

[Dean Romig]

Factory forcing cones have been measured at between 1/2" - 3/4" long depending on gauge and the accepted standard for the time period. Ideally, that point should be at, or just a mere few decimal points before, the terminal end of the cone.

For example, an open 12 gauge UMC(or any other shotshell manufacturer) 2 1/2" shell might actually measure as much as 1/16" shorter or longer than the 2 1/2" prescribed measurement while Peter's(or any other shotshell manufacturer) 2 1/2" equivalent might measure plus or minus a slightly different length, while others might measure exactly 2 1/2" on the nose.





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[Austin J Hawthorne Jr.]

I've had two early lifters that had an abrupt step at the end of the chamber. To the best of my knowledge (which is admittedly limited) these were made prior to the introduction of paper shells and were intended to be the length of the brass cases then in use.

[Kevin McCormack]

You MUST MEASURE!!! Years ago I bought a pretty generic Ball type choke gauge suitable for measuring 12 and 16 gauge only, and a Galazan brass chamber insert gauge to check the 10-28 gauge spectrum. Both cost less than $200 total at the time (c. 1980). As I began to purchase more and expensive smallbore guns, I blew it out and bought Jon Hosford's Barrel Wall Thickness Gauge and his combo choke gauge, which ran into the upper 600s of dollars.

I did some interesting comparisons between the ball-type gauge and Hosford's dial gauge; readings varied along the true bore diameter readings and the choke run at the end of the muzzle readings per each instrument, but the measurements determining the degree of choke were always congruent in the final readings. Was the investment in the higher end instruments worth it? Based on the mistakes I avoided over the years by investing in good measuring tools, there can be no question.