doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Tapered chambers

Surely this topic has been covered before, but with all the highly technical discussions about wall thickness I couldn't resist.

My doubles of European manufacture apparently have chambers tapered roughly 1/2 of the length narrowing toward the cone. What is the purpose, is this a design feature of the paper hull era?

Reloading for these guns requires perfect crimping. No mushroom tops.

I once sent off the barrels of an older AYA with tapered chambers for a forcing cone job. Apparently the tool used cut the taper out. After, I noticed that shooting reloads of slightly worn hulls (AAs esp.) powder burns on the outside of the hull were common. I've wondered if the poorer seal was due to the removal of the taper.

I understood that there should be a slight taper on all chambers to aid ejection/extraction - but I may be wrong!!.
john

RC:
Most ALL chambers have taper. Do some internet research on your own and you will see that CIP standards specify this in almost every case. SAMMI standards are similar. Longer forcing cones only extend the taper.

Best, Kensal

Thanks, it makes perfect sense that the chamber would be smaller in the area where a perfect seal is critical. The guns I mention appear to have more taper in the chambers than, say my Win. 101, in which bulged or flat-topped crimped shells dropped right in.

Taper in a shotguns chamber has been in the area of .0045" to .005" per inch virtually since the dawn of the breech loader. Likely what you have is some undersize chambers, possibly cut with a reamer which was sharpened a few times too many without replacement.

Especially in years past chamber dimension tolerances were somewhat loose.

I have some dimensions which differ somewhat from these,rspecially in the 12ga, but will have to get my book out tommorow. They are found in Roy Dunlap's book "Gunsmithing" from the 50's-60's. He doesn't state his source, I always assumed they were SAAMI for the time, but couldn't guarantee it.

Interesting to note the if you take the choke diameters in relation to the lengths they all form a straight line. They could thus all be cut with the exact same reamer by adjusting the depth of cut, at least for the 12, haven't checked the other gauges.

I also note full choke constriction is .036" for both 10 & 12 Ga's, .026" for 16 & 20 Ga's & .020" for 28ga & .410

Here are the 12ga minimum chamber dimensios from the above mentioned Dunlap book. This book is a 2nd edition carrying copyright dates of 1950 & 1963.
Dia at forward end of chamber .798"
Body taper .0044" (Inc) per inch
Dia at breech .8095"
Length breech to cone 2.6136"
Cone angle (per side) 5�
A minimum dia of .764" is then called out to a point in the cone a distance of 2.8079" from breech. This calculates out to an exact 5� cone angle.

A couple of points this 5� cone would have a length of .394" for a difference in chambe & borer of .069" (.798"-.729")
Chamber dimensions are given in this book for 12, 16, 20 & .410. The 12 is the only one given a chamber length shorter than the shell's nominal length.
Max length of the loaded 12ga sheel is 2.53" for a roll crimped shell & 2.41" for a fld crimp one.

It is also noted the other three sizes do call for a body taper of .005" (Inc) per inch.