doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Chamber Depth Measuring

Anyone have an accurate, but economical method for measuring? I know Brownell's has guages, but at $20 each, I don't want to order one for each 12, 16, 20 & .410. I've got some old doubles that I like to check depth. How about an appropriate diameter dowel? And, what do chambers ACTUALLY measure?

You can use a dowel, but it needs to be the proper diameter - so you'll need a lathe.

I've made a few gauges out of not wood but white PVC pipe. Measure the brass base of a shell and turn the pipe to that diameter.

KSTT Galazan has a guage that has 10 through .410 for about $35. They work well. The easiest and cheapest is to get the chamber diameter measurments and cut a flat piece of metal to the correct width. I'm at work now, but when I get home I'll look on my computer for the correct measurments. I bought one from Galazan.

The brass base may or may not give you the right size for a chamber gage. "Nominal" dia of small end of chamber is; 10ga =.841", 10ga mag =.838; 12ga =.798", 12ga mag =.797"; 16ga =.732"; 20ga =.685"; 28ga =.614" & .410 =.463".
Realize that the chamber body itself has a taper of .005" per inch so if a chamber happens to be only .001 undersize (not uncommon on older guns) the gage will show it at about .200" short. Thus if turning a gage I prefer to make mine about .002" below those nominal minimums. It may go a short distance into the forcing cone, but that is of no consequence.
Generally I just pick up my old 6" machinist scale & hold the bbl up towrd a light source, throwing the forcing cone to appear as a shadow. I slide the scale in beside my face watching till the gap closes between the scale end & shadow line & slide my thumb nail up against the breech, for reading. After a little practice this can be done with plenty acceptable accuracy, & is quite inexpensive. You can even pick up a usable 6" flexible scale at most any home supply store, doesn't have to be a Starrett or Brown & Sharp. They are about 1/2" wide though ao will have to find somethig else for the .410.

I've read on one of the posts, take a 3"x5" index card and roll it length wise into the chamber and let it expand to the chamber dia. and ease it into the chamber, when it stops going, mark the end of the card and try it again and see if you get the same mark. Pull card out and read length with a 6" scale or ruler

Galazans $35 brass set work fine. I have the Brownells ones and I always get the same reading.

We used a bore gauge recently -- a rod about 1/2 lenght of normal barrels, with three contact balls at 120 degree intervals, a dial micrometer and a distance scale in cm and inches on side. With it we could see the start and end of the forcing cone and the ID of the barrel for about 1/2 its lenght. When inserted from other end we could see the profile and lenghts of chokes, as well as the IDs of the upper 1/2 of the bore. A really wonderful tool!!

It belongs to a friend, don't know the maker or cost. He used to be an avid trap and skeet shooter, hence the bore gauge.

FYI, the chambers on my Husqvarna M48 are too tapered for his chamber gauge, with the gauge indicating they are only about 50 mm instead of the correct 65 mm. The chamber gauge fit nicely into the chambers of two M51s.

Niklas

The gauges are NOT fine for the reasons 2-piper explained above. If the chamber is oversize they go in too far, and if it is undersize, like a Super-Fox chamber, they don't go in far enough. Mastering the use of the 6-inch machinist's scale is the way to go.

Well, this is sounding more confusing all the time. And, even if I were to come up with an accurate method, I'm still not sure of the data. Example, my 16 ga. Trojan was made in 1921. Probably chambered for 2-9/16", right? So, is that what the chamber would measure? Or, is the chamber longer, to allow for the opening of the shell? And, of course, there's only 3/16" between that, and 2-3/4".

A 2 3/4" shell is 2 1/2" when unfired. It opens to 2 3/4" Same with 2 9/16ths and 3" and so on.