Insert for 32ACP in 12 Ga Darne

[Hasbin]

Do you think I could use a 2-3/4 adapter in one side of my old Fusil Darne Halifax SBS. It normally uses 2-1/2 (skeet loads because of its age) but I was wondering if the left side could take a 2-3/4 adapter for 32 ACP without looking for problems. Three questions come to mind 1) What happens to the extractor plate when you put an adapter plug in. I'm guessing it's a loose/snug fit like a shell and not meant to be a press-fit that pins down the extractor. 2) The chamber will take a 2-3/4 long shotgun shell but I cannot fire them because there is insufficient head room for the shell debris. Does this head space matter when using an insert? 3) Will a 32ACP generate more localized (pinpoint) pressure on the sliding breech and firing pin than the usual skeet load?
Looking forward to learning the answers.

 

[Sharptail]

Hasbin, I do not know the answer to your question, but I am stuck at home with a miserable virus and have nothing better to do, so I will speculate. Besides, anyone who shoots a Darne deserves some sort of an answer.

1) You are correct about the loose/snug fit of the adapter, it should extract just like a shotshell. You then use a small rod to poke the fired brass out of the adapter.

2) A 2 3/4" shotshell is only 2 3/4 inches long after it has been fired (or before it is crimped in the loading process). This will be a problem if the adapter is made to fully occupy a 2 3/4" chamber, it will not physically fit in a 2 1/2" chamber as it will run into the forcing cone.

3) A .32 ACP firing a 71 grain bullet at 1000 fps (pretty much max) will generate 0.35 pound-seconds of recoil energy. Assuming you are using 1 ounce of shot at 1100 fps for your 2 1/2" skeet load you will be generating about 2.49 pound-seconds with the 12 gauge shell. The surface area of the rear of the .32 ACP should be 0.10 sq. inches, the surface area of the 12 gauge shell close to 0.6165 sq. inches. Convert both to pound-seconds per square inch to compare and you get 3.5 pound-seconds per square inch for the .32 ACP, and 4.04 lb.-sec. per sq. in. for the 12 gauge. In my estimation you are not in any danger of damaging the sliding breech by shooting .32 ACP.

NOTE: I have never done this before, it is best that you re-do the logic and math for yourself !!!

Another question is that of accuracy, what good would it be if you couldn't hit anything? While 12 gauge chamber size standards are published, actual measurements of production guns can vary a bit. I think that an "off the shelf" adapter might have more "play" than you would be comfortable with (even if you could find one to fit the 2 1/2 chamber).

One answer might be to find a 4 or 5 inch long, 1 inch diameter barrel blank, take a cerrosafe casting of the Darne's chamber and give both items to a machinist who is good with a lathe. A custom fit and head space would not be a problem. The barrel should be long enough to burn most of the powder within it. The crown should be de-burred, a tumbling bullet would surely wreck a shotgun barrel. Have the finished product reamed for a .32 ACP chamber and blue the thing (or use a stainless steel barrel blank). Of course, this is probably much more trouble than you were thinking of and probably more expensive too, but I bet it would work.

Thanks for providing an interesting mental exercise. If you get around to doing this (custom or off the shelf) please let us know how it works out.

Sharptail

 

[gallen270]

why 32? there is a plethora of other calibers to choose. If you set on 32, use a rimmed round, like the 32sw or 32h&r. Also, dont expect alot of accuracy from a 'barrel' the lenght of a shotshell, like mentioned above, do a chamber cast, and have a machinst make an adapter with a 10'' barrel.

i have a 32acp insert for a 3030 bolt action, its quiet and great for shooting grouse.

 

[Sharptail]

Gallen270, I don't think you need a 10 inch barrel to get the most out of a .32. It is putatively going into a SxS with a bead sight, I don't think rifle-like accuracy is the goal in this case. Of course sufficient accuracy is needed for reliable short range shots on small game.

More importantly, the extra weight of a long barrel would destroy the wonderful balance and feel of the Darne, if carried for wingshooting as well as ground game. The shorter adapter will do this too, just to a much lesser extent. The lighter and shorter the adapter is, the less its effects on handling will be felt.

It is also easier to carry a shorter adapter in a pocket or shell bag, which is the way I would use the thing. Just pop it in when required.

I must be really bored. I'll shut up now.

Edited to add: I forgot the most obvious point - the Darne is a sliding breech, not a break action. A short adapter can be employed without removing the barrels. I really will shut up now.

Sharptail

 

[gallen270]

haha, ok you justified it

 

[ben hunchak]

I wouldn't mess with the Darne, too nice a piece to damage, one of the finest handling guns I've ever shouldered. Get some cheapo single shot and mess with that, or better still send me the Darne....are they still making them??

 

[Hasbin]

Gentlemen,
Thank you very much for your well considered comments.
I took some measurements with the breech slid all the way back, I could chamber a 3" long insert. The actual 2-1/2 shell diameter tapers from 20.03 mm right behind the flange to 20.00 mm at 2-1/4 where the crimp is. Inside the barrel, the actual bore doesn't begin until 80 mm in so I guess the insert could be up to 3" long.
BTW are these inserts rifled?
Why am I going with 32ACP? Because I have them around all the time anyway and they're relatively cheap.
Sharptail, whilst I wasn't able to find energy numbers for the two shells, I was able to use your assumptions and validate the square area comparisons to arrive at the same place you did. i.e. The .32 ACP imparts about 20% less energy per sq inch to the breech.