Chamber Size Of DBBL Shotgun

[Lawman]

How can I know or measure the chamber size of a DBBL Shotgun (65mm or 70mm) ?

Lawman

[snIPer]

might be similar to this
http://indiansforguns.com/viewtopic.php ... highlight=

[Risala]

Check the barrel flats for chamber size.

HTH

Sanjay

[Lawman]

Hi Sanjay, what is barrel flat ?

Lawman

[Mack The Knife]

The lower flat part of the barrel/s at the breech end.

[Lawman]

Thanks.

Lawman

[Lawman]

Hi, I measured the barrel flat of my Astra DBBL gun to determine the chamber size. The flat portion measured 65 mm. I think this is the chamber size of 65 mm. But I regularly fire Astrum 70mm cartridges from this gun without any problem. Barrels are OK. Gun-Gurus, please advice should I use only 65 mm cartridges or Astrum (70mm) is OK ?

Lawman

[Risala]

If the chamber is 65 mm then fire only KF or equivalent from it,do not fire 70 mm cartridges,as pressures

generated may be higher than what the gun can take.

Sanjay

[penpusher]

Measuring the barel flats will not tell you which cartridge the shotgun is chambered for.The chamber length should be egraved on the barrel flats.It should either read as 2 1/2"(65mm) or 2 3/4"(70mm).There are some shotguns that were chambered for 2" cartridge.Most shotguns with 2" chambers used black powder cartridges.

[Lawman]

Hi penpusher, on the barrel flat the following mark is engraved "[12-70]" beside Gun Number and other marks. Is the aforesaid mark indicates 12 guage and 70 mm ?

Lawman

[Risala]

Yup,your 12 G has a 70 mm chamber,no problems with Astram's,KF,Magna's etc.

Safe shooting

Sanjay

[Lawman]

Sanjay & penpusher, thanks to both of you for your valuable informations regarding chamber size of DBBL shotgun.

Lawman

[sangi]

Apart from all of the above, which has created a new fear for me, and on going back to the thread in trepidition, not found an answer.
Was sanguine in the (misconceived) perception that my 12 bore DBBL BSA SXS,28" barrels, boxlock, non ejector(obviously?), fairly/ really old workhorse was a 2 3/4 chamber; not because of an eley alphamax fitting comfortably in it, but also because I have this(fatalistic ) attitude towards firing 70 mms in old english guns with paper thin barrels and prefer only 2 1/2. I have confidently replied to so many that it is 70 mm, that I too started doubting it!! Must have fired just 2 70 mm catridges in 25 odd years through her.
So checked it out, did not find the customary markings of 2 3/4 /70mm or 2 1/2 /65 and took a step back. A chord struck on seeing the 1 1/8 stamps and the old fuddled mind tried to dredge out something from those childhood days when one had to regularly qualify a 'viva-voce' from the old man of No 6, 1 1/16 ozs shot, how many pellets in the cartridge, how much lead for a duck at 35 yds and how many pellets in the 35 circle!! To cut a long story short, was there not a system of measuring chamber size based on 1 1/8 or 1 1/16?
Maybe just a question of very poor maths, but does 2 3/4 or 2 1/2 translate to 70 or 65 mm? Thanks to the gurus(and matematically inclined) in advance. Regards

[Grumpy]

2 1/2" = 65mm.
2 3/4" = 70mm.
3" = 76mm.

`1 1/8` only refers to the load that the gun was proved for - 1 1/8 oz ( 32.4 grammes ) of shot. Although any gun marked with such a proof load will have 2 1/2" chambers ( unless the chambers have been lengthened ) because 2 1/2" chambers were the British standard length - there is NO direct correlation between the chamber length and shot load. 2 1/2" Cartridges are available with shot loads of up to 1 1/2 oz ( 42 gramme ) and 2 3/4" cartridges are available with shot loads down to 24 gramme ( 7/8 oz ) ( - which is now the only approved load for ISSF Trap etc. )
It is a popular misconception that 2 3/4" cartridges are more `powerful` than 2 1/2" cartridges. They are not - per se. They`re just longer, and, as such, able to hold more shot. There ARE 2 3/4" cartridges that are more `powerful` than any 2 1/2" cartridge ( eg the 2 2/4" mini magnums ) but they have been developed because 2 3/4" is now the `standard` chamber length internationally - including British guns.

English guns have `paper thin` barrels ?
Oh yeah ?
Take a look at the breech ends. You might note that the chamber walls are a LOT thicker than `paper thin`and that the barrels are tapered. As far as pressure is concerned the important area is the first 8 inches or so. I routinely have the 2 1/2" chambers on British guns lengthened to 2 3/4" - including guns with damascus barrels. If the barrels are in good condition there is no reason why they shouldn`t pass the 850 Bar reproof. I have NEVER had a gun fail a reproof. That means that they can be used with ANY 2 3/4" cartridge EXCEPT the `mini magnums`. I have even had the chambers on a 2 3/4" ( No, not all British guns had 2 1/2" chambers - `Live Pigeon` - the original Trap discipline - and Wilfowling guns often had 2 3/4" chambers....routinely so not long after c 1900 ) wildfowling gun lengthened to 3 1/2" Magnum and the gun sailed through a full 3 1/2" magnum reproof which means that it can be used with ANY 12-Bore load. Not something that I`d recommend - the breeches have to be decidedly `meaty`, it dramatically increases the load on the hing pin and locking and the 3 1/2" Mag produces decidedly `stiff` recoil but the customer was a **** and insisted. Most Americans - shooters generally - aren`t so stupid .................................)
If you have a 12-Bore gun with 2 1/2" chambers and the barrels in good condition look for a competent gunsmith with a 12-Bore chamber reamer and have the chambers lengthened to 2 3/4" and the forcing cones re-cut.

Just to reiterate what has been said above - just in case there is any confusion :
The proof marks will be found on the barrel flats - the flat area under the breech ends of the barrels. The length of the actual flats will not correspond to the length of the chambers.

[Grumpy]

penpusher, I`ve never seen a 12-Bore black powder proved gun with 2" chambers. That doesn`t, of course, mean that they don`t exist but most 12-bore 2" chambered guns are the specifically designed lightweights and are nitro proved. I have one and probably use it more than any of my other guns.