Hello
I own a Darne R13 in 12 ga. and the mouth of the left chamber is .803 in. I am cutting down win.AA shells to fit the 2.5 in. chambers but the maximum allowed cartridge size at the mouth of the chamber is .810 and the actual unfired AA shells measure .806 in. or more. Obviously I can't chamber them. I have managed to swaddge down the AA shells to .803 in. but this makes for very hard extraction.
1. Why are Darne chambers so tight?
2. Is any ammo available to fit these chambers?
3. Should I ream the chambers?
Regards
DblFixer

Hello DblFixer
Welcome on your first posting

Can you post the proof marks?
Maybe a 2 inch chamber?

Have you called RST?

http://www.rstshells.com/store/m/2-12-Gauge.aspx

Welcome
Mike

What is the chamber size on the right barrel? Do you have trouble with that chamber?

I’ve never heard this exact complaint leveled against Darne guns, in general. It would be my guess that it was measured at the proof house, and passed spec. But, if you don’t have problems with the right side, it might need to be reamed, or, perhaps polished. Just me, maybe, but, I’d make them match, assuming the right side isn’t sloppy.

Best,
Ted

Pretty sure he is having problems with the ID of the hole, not length.

Best,
Ted

The left chamber is .806. Still a problem. The proof is 6.5 and crown over PT. and epreuve triple. Also has Hors Councours? and
three stamps. I have a 165 kb jpeg on my computer but can't figure out how to post it, The post image asks for a url?

By unfired, I assume you mean factory fresh, never fired. I have a French resizing die made by Manufrance over 50 years ago and as soon as I find my elusive dial calipers I'll measure the ID and compare with what you have. I was able to insert NIB Win. game loads into the die, but unfired Fiocchi hulls were a tighter fit. I also assume you have thoroughly cleaned the left chamber for potential plastic build up.

Email me the picture, and I will post it, here. Good clear shot of the flats.

Best,
Ted

Picture. Most of the flats, anyway:



That is an old gun. The 6.5 chamber marking, per our friend Argo’s research, puts it around 1910 or so production. Your measurements tell me it is a 12 gauge.

Did you measure the right side of the breech?

Best,
Ted

Right is .803 in. Left is ,806 in.

Yes by unfired I mean factory fresh. The chambers are clean and shiny.

You could easily polish 1.5 thou off each side of the right to match the dimensions of the left side. .003 isn’t much.
You might have to buy or rent a cylinder hone that will work between .750 and an inch. I don’t have one that goes that small, but, I’ve seen them.

Best,
Ted

Just this week I used a 12 ga. chamber Flex Hone to polish my 870 SuperMag's chamber. It had severe extraction issues and the chamber was rough as a cob to the view and touch. A generous poster in another forum sent it to me and it has been returned to him. There are short videos on YouTube that demonstrate technique. I used the specified lubricant for the hone. It took 1.5 minutes of use to smooth out the chamber. Brownwells has them. The Flex Hone consists of numerous abrasive pads on the end of wires that compress allowing entry and the rotation of the drill causes them to push against the walls.
https://www.youtube.com/watch?v=RzAm5Ni0QCw

What grit was it, Gil?

A brake wheel cylinder hone should work. They are cheap.

Stan, I don't recall exact but it was for polishing. The man used it on his SuperMag to correct the same issue as mine. I'll ask him for the model number and grit size. Gil

And about as fast as molasses in winter. I don't have the patience to use mine. I've tried and tried, and it seems to do next to nothing.

Thanks to all who made suggestions. I ordered a box of rst 2.5 in. shells but in view of the cost delivered to my location, I will ream the chambers so that I can shoot AA reloads.
Best wishes for the New year.

That sounds like the best solution, assuming, the gun fits you well, and you shoot it well when you do get a round chambered in it. I wouldn’t be in a hurry to alter a gun I knew I was going to get rid of.

Good luck.

Best,
Ted

Sounds like the stones on your cylinder hone may be loaded with metal particles Stan. The carborundum abrasive on brake cylinder hones is the same thing that the abrasive balls on a Flex Hone are composed of. Gil was wise to use the recommended Flex Hone oil because it helps prevent the stones from loading up with metal particles. It is probably no different than the honing oil that is sold for use with carborundum knife sharpening stones. Even those load up over time, and periodically need scrubbed out.

I've used brake cylinder hones in shotgun bores to clean up mild pitting, and I have used them to clean up pitted brake master cylinder bores. They aren't super fast, but they certainly get the job done in a reasonable and controlled manner. I know you are very mechanically inclined. Those who are not should be advised that going too far can ruin a gun.

I do like Flex Hones and have used them. I just wish they weren't as expensive as they are. I often find smaller cylinder hones at auto parts swap meets for a fraction of the cost.