doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Chamber length question?

Just bought a Lefever 20ga Nitro Special made in 1925.
How do you check the chamber length to know if you can shoot 2 3/4 in shells?
Thank you.

My Nitro Special 20s have all been 2 3/4"...Geo

Drew's method with the index card sounds interesting, will have to try it sometime. My method which I have used for some time is to use a 6" flexible scale. Doesn't really matter if it is a high quality machinist's scale or one you pick up at a home improvement center. Hold the barrel up & look into it till you see the cone as a shadow. Slide the scale in beside your eye keeping its edge against the chamber wall until the corner meets the shadow. Read the scale at the breech at that point. I have actually on several occasions found this method to be more accurate than the gauges due to variations in chamber dia.

On a 1925 20ga Id bet they are short chambers.....I think the factory switched to 2 3/4in late in 1926...

Back when they were cutting short chambers, shells were paper and the thickness at the mouth was about .025", or about .050 total thickness when considering both sides of the hull. The whole point of chamber length was/is, of course, to make certain the thickness of the hull did not impinge on the bore diameter

Nowadays the mouth thickness of premium plastic hulls is pretty thin, about .005, or .010 for both sides. Unless the forcing cone constricts more than .040 in that first 1/4", there should be more than enough room to safely use plastic hulls in old 2.5 or 2.75" chambers.

If you are superstitious or work on hearsay, , the above absolutely will not work. If the rest of you find fault with this logic, let me know.

No fault with the logic. Risk analysis rears often in my work and, contrary to Satchel Paige, any looking back is not in that direction.

In Actuality both Chambers cut intentionally shorter than the shells for which they were intended & shells loaded into cases which were intentionally longer than the chambers for which they were intended predate the plastic era with roots well back in the paper case days. In England in the late 1930's with the introduction of the fold crimp shells were intentionally lengthened with their "loaded" length being similar to the length of a roll crimped shell. It has been mentioned here many, many times the Parker Bros as well as some others makers intentionally cut their chambers about 1/8" shorter than the shells for which they were chambered & this while paper was "King". Until fairly recent times SAAMI specs for the 2 3/4" 12 ga chamber called for a minimum length to forcing cone of 2.6136" to a dia minimum of .798". A minimum dia of .764" was called for at a point 2.8079" from breech with a maximum length of an uncrimped hull of 2.760". Thus if a max hull were fired in a minimum chamber there would be .1464" of hull lapping into the cone. These specs were in effect well back into the days of Paper hulls. The important fact is that in the one case the shells carried a load which was compatible with the guns for which they were intended while on the other hand the guns were built compatible with the loads carried in the shells for which they were intended to fire.

The intentional short chambering, before the days of plastic wads, made sense. The paper case mouth, opening past the end of the chamber, provided some cushioning to the shot charge when the gun was fired. Trap shooters in particular found they got better patterns with slightly longer fired hulls in slightly shorter chambers. Of course there's no longer any reason for that, since the advent of the plastic wad.

I have a newly acquired LCS Longrange, 1927. Flats are marked for 3" shells and a drop gauge goes in exactly half way between the 2 3/4 and 3 markings. Pretty sure this a true reading, not heard of any tight chamber Fulton Smiths?

Best,
Mark