Will shooting a gas-checked lead cast bullet in a barrel which has copper fouling help to remove the copper fouling? Or will it just add to the fouling with a coat of lead over the copper? A guy in my gun club says the gas check will scrape off the copper fouling.

To get the best performance out of cast bullets, you need to get the bore as clean and smooth as possible. I don't know how much it will affect the bore, leaving the copper fouling in, because I did not do that with any of my barrels. I have always removed all fouling prior to shooting cast.

Once the bore is clear of all copper, and the cast bullets are prepared correctly, you most likely will have little to no fouling or problems shooting cast bullets.

I believe you are correct, my problem is getting the copper out. Repeated scrubings, alternating with Shooter's Choice copper solvent, aren't getting the barrel totally clean.

Wink
I'm not sure what copper solvents are available in France. I've had good luck using a product called Montana Extreme. It's my understanding that bore cleaners with high ammonia content do the best job of removing the copper. Another option that may help is JB bore paste, a very mild abrasive that helps in removing copper and powder fouling.
I will use Montana Extreme every 100 to 200 rounds fired, just on the off chance that gas checks are leaving some copper fouling behind.
Jim

Wink
Another thought or two.
One of my shooting, bench rest, buddies has had good luck using Kroil oil to clean out fouling. He will swab out the barrel with Kroil and let it set in the barrel for several hours. The Kroil will seep in between the copper and barrel and allow the fouling to be removed.
I've come across formulas using Ed's Red with ammonia added. I think it was on this site but maybe Beartooth and Cast Boolets sites.
Jim

Wink, the classic copper remover is something called "28% stronger ammonia". It should be available at a janitorial supply house even in France. If that name does not translate, just buy the strongest ammonia they have. I have always used it straight, but some folks claim that it works better if you leave a length of copper wire in it overnight before using.

It's very agressive so don't leave it in the bore long. Five minutes between swabbings is plenty.

Any of you guys ever tried the electoalysis methods like Outers Foul Out or the home versions of the same thing?

I did - just works fine - you are also using ammonia with those, though. I tried it on a .303 Martini-enfield with a crappy-looking bore, which I bought for the action. When I had finished, I had a decent, shootable bore - quite a difference (But now I need another action...)! Just heed the instructions though. But bottom line is the home-made electrolytical copper remover works.

Wink..You friend is 100% wrong! A gas check won't remove metal fouling and if you expect anything like decent accuracy with cast bullets, the metal fouling must be first removed.

Like you, I have not had good result removing metal fouling with either Shooter's Choice or Hoppes solvents for that purpose.

However...Sweet's 7.62 will do the job. How long it takes depends on how much metal fouling there is in the barrel. Sometimes it just takes few minutes and other times it takes hours or even days. I once had a military 6.5 Swede that took me 20 hours of work to remove the fouling with Sweet's. I spread the work out over a couple of weeks so it didn't kill me. There are a couple of things to remember when using Sweets.

1. Use your regular bore cleaner first to remove powder fouling.
2. After you have removed the fouling, clean once again with powder solvent to remove the powder fouling which was under the metal fouling.
3. There will always be some slight traces of metal fouling on the patch. Some metal fouling works into the pores of the steel. There is no need to remove this as it just makes the barrel slicker and does no damage. It is pretty easy to tell when you get to the "trace" amount of fouling left in the barrel.
4. Don't leave Sweet's in the barrel for more than 10 minutes as it does contain ammonia and it will damage the barrel steel and ruin a fine barrel if left to long.

I would avoid straight ammonia like the plague unless you are very careful and don't leave it in the barrel for any length of time.

I shoot very few jacketed bullets, but I always clean with Sweets after a regular cleaning to keep metal fouling from building up. That is the easy way.

I have no experience with electro-chemical cleaning, so I can't comment on that.

Good luck and good shooting.