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

I use an internal dial indicator. You can see the the diameter change as you move it into the chamber. MSC used to have good ones for about $100. They will check chambers and chokes on everything but 410. The solid gauges can't account for in spec. varations.
bill

So then, a chamber measuring 2-3/4" IS for a 2-3/4" (nominal) shell?

kstt, you got it. Measure one of your 2 3/4" unfired shells it will be 2 1/2". The 2 1/2" is only 2 1/4" unfired.

"The brass base may or may not give you the right size for a chamber gage."

Agreed, my method is subject to some slop. But I have to wonder just where the bucks stops - I would bet that the Galazan's chmaber gauges are not perfect, nor are all shotguns machinined to the same tolerance. Certainly we've seen that to be the case with bore diameter, so I would not be surprised to see some variation in chamber diameter.

It would be easier if there were a definite shoulder, or register, to the end of the chamber but I see mostly guns with tapers which are much harder to tell where they actually begin.

There are 2 ways that will "Tell the enquiring mind whatis the True,Length of Chamber, length of forcing cone,& angle of forcing cone, exact size of Bore at end of forcing cone,diam. of chamber at Rim,and the taper from rim to start of forcing cone,(Length of Chamber)....Tools needed for No 1.Vise with lead 'Jaws'(so as not to damage the Barrels),Hacksaw. Hold bbls. vertical in vise,(make sure the forend"Loop" is clear of the top of the lead jaw. Find center of chamber, use hack saw to saw straight down through the center of the barrel, aprox.3.1/2",remove bbls, then hold in horizontal position,put 2nd saw-cut across radius of bbl.to meet 1st saw-cut, piece should lift off, and you will see the most perfect Half of a Chamber, in full profile. You can then use your 6" steel rule for the needed measurements!!!This is, of course T/inCheek,Gunshop Humour, I have done this to several Barrels, for Research/Development. They make excellent conversation pieces!..The 2nd method for acurate measurement of Chamber for length, Diam. Forcing-Cone length & angle. Is"Cerrosafe"(Brownells Cat'lg.#55.P27. 1/2lb $10.84+Postage.)or http://www.brownells.com)'Used the world over by Professionals & DIYs,100% accuracy)Please use care(& safety glasses) dont pour too quickly! Remember the Instuctions on the back of (If memory serves me)the Claymore Mine,"Not tobe taken Internally" !!!There is a photo of a breech-end of a pair of DBBLS.(Chapter 13 P76) S/Gun/Technicana,cutaway for the view of the inside of a chamber, with my brass 12b chamber gauge lying inside. Hope this answers 'a few questions'.Crossedchisles.

DT (Mr. Chisels) shows in his humorous post the fallacy of worrying much about the exact length of chambers on guns of normal chamber length. He sure isn't going to get caught worrying about 1/4 inch of plastic. The difference of length in a 2 1/2 inch chamber and a 2 3/4 inch chamber is 1/4 inch. I would guess that the first 1/4 inch of most forcing cones only shows thousandths in decreased diameter, maybe less than the variation in two different chambers. Sherman Bell's articles explaining such things brings us to the conclusion that there is very little pressure difference, if any, in 1/4 inch shorter chambers when shooting normal ammunition.

DT,I hope no one will try the "radical bisection" unless they have some of those useless old Purdey barrels lying around, in which case I suppose it would be OK. Bore gauge with graduations on the stem is said by Niklas to work; wall thickness gauge with similar graduations or perhaps a single hashmark representing the expected beginning of the change in gradient works for me. Whatever happened to the "mad biker" Wilhelm Gregor and the 20 hull in the 12?

jack

The very sharp step to the chamber was of course tried very early in the breech loading game & even quicker abandoned as totally undesirable. The cerro-safe method of course is the most revealing, but the 6" scale with a little practise is extremely useful & can be dropped (or clipped) into a shirt pocket & carried where-ever desired (mine is a constant companion). Chamber dimensions will not vary near the extent of bore dias, but ±.002/003" over the last 1¼ century or so is not uncommon. Some older chamber drawings called for about a 5° angle off the C/L for the forcing cone angle. On the approx .070" drop from chamber to nominal bore this would give a cone length of about .400". A gage +.003" from the juncture dia will stop .600" short, one -.003" will enter the cone .017". Of course on a longer cone (less angle) it will enter further, but becomes less critical. If one simply doesn't believe Burrard, Thomas or Bell on importance (or lack thereof) of exact chamber length, simply make your gage to -.003" from nominal dimension & if it enters to about the same length as your fired cases, "Live Happily Everafter", shotshells in chambers aren't precision fits.

And, just to keep things confused, many of our manufactureres (Parker Bros. and A.H. Fox Gun Co. for sure) held their chambers about 1/8 inch shorter then the shell for which they were intended -- ie 2 5/8 inch chamber for a 2 3/4 inch shell, or 2 7/16 inch chamber for a 2 9/16 inch shell, etc.

For some reason we always seem to want to make a hard job out of an easy one, every time this comes up. Look at the 3rd reply, from 2-piper. Using his measurements you can make very inexpensive chamber gauges from stainless steel rulers or any sheet metal wider than the gauge you want to measure. Rulers are nice because the already have the numbers down the side. Using tin snips, a grinder or a sander, narrow the rulers to the dimensions 2-pipes listed. Stick it in and read where it stops. This is the chamber length.
If you have no tools or no mechanical ability, Buy a set. PS, don't grind off the side with the numbers.