doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com English .410 choke and bore markings

Can someone enlighten me on some choke and bore numbers on an English sxs .410? The right barrel has the number 405 and a decimal of 10.2 and the left barrel is marked 400 and a decimal of 10.8 Can anyone tell from these numbers what chokes this gun may have? Thank you!

It appears to have been re-proofed. The barrel marked .405 and now 10.2mm is now .4015 (+?) and the .400 now measures .425 (+?).

Are you sure you have got them the right way round?

Photos would help.

They indicate the bore diameters at 9 inches from the breech face and are nothing to do with the chokes.

I will send a photo when I get home tonight. Thank you

10.2 mm = .4016
.405 = 10.287mm
10.8mm = .425.
.400= 10.16mm
Does sound like numbers might be reversed. Could have been miss stamped at reproof which is unlikely but not impossible, or you just flipped them in your notes. Sounds like one barrel needed pits removed, and had to be reproofed after the job. Funny about the 10.2 being under sized for the other bore but it is the fit at 9” and a 10.3 plug converts to .406 so perhaps slightly too tight, hence the use of 10.2 plug. .405 remaining 10.2 is not impossible but going from .400 to .425 does seem like a lot. Barrels walls measured or wall thickness measured would tell you a lot.

Quickest way is to check the flats for markings. If not clear then, I’d measure bore diameter 9” from the breech to confirm bore diameter. Perhaps bore really just went from .400 to .405 and the other from .405 to .425. .0025 removed from one bore wall and .010 wall cleanup from the other.

Yes, I reversed the markings. Right barrel: 400 10.2 choke 7/8 Left barrel: 405 10.3 not 10.8. What does the choke 7/8 marking mean on the right barrel?

7/8 sounds like improved modified. But I can not recall seeing chokes marked on any British doubles I own. It might be marked choke and the 7/8 is not part of choke markings. Coming from me it is rich but pictures might explain a lot or confuse us even more.

My question is why would it be reproofed? Were the chambers altered from 2” to 2 1/2”? I ask because the bores sizes are almost original, certainly not out of original proof. Are the chambers 2 1/2” because 2” was more common before WWII I understand. If they made the chamber longer it would need reproof.

A picture of the Proof Marks would certainly help.

7/8 is a shot weight in ounces that is sometimes found on English 20 bore guns.

It is way too heavy for a standard load for .410. If remember rightly they were marked 3/8 for 2”, 7/16 for a 2 1/2” and 5/8 (or 11/16 ?) for a 3”.

Even with brass 3” cases and a Baikal to fire them in I don’t think Stan’s ambitions run to 7/8 oz in a .410”!

Stan would if he could. I might as well. Think of it as a 40-45 yards late season Dove killing machine. Of course he might need to load it with cordite and steel wads. Never underestimate the lengths that some of us will go to get 105% out of our guns. Because we all know the limit is the gun not the gunner.

The gun is a 3" gun. 76mm chambers

Could the 78 be 76?