Some people use strips of lead tape on the barrels. Some may bed lead or Mallory metal slugs into the forend. Or place weight in the butt stock.

 

I ordered these after reading a couple of posts about adding weight. I have used the lead tape, but these are certainly heavier. The adhesive is designed to stay on the rim of a tire, so I would imagine they would stick to the bottom of a barrel. I haven't used them on a barrel yet, but have puts blocks of them in a BT99 butt stock and am happy with the results.

1/2 oz. Wheel Weights

Amazing deals on this 1/2Oz Wheel Weights at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

 

JMO but I'd be cautious about adding too much weight if the gun already handles and balances well. Or if you do add weight add to both ends to keep the balance close.

My AyA #2 is reasonably light at just a bit under 7lbs and I find on clays an 1150fps 1oz is very pleasant to shoot and very effective even on loooong targets, 1250fps 1oz not so pleasant. Field loads I don't put enough thru in a day to notice the recoil.

 

I’ve added weight to the stock before, but as noted it can mess with the balance. I’m a bit reluctant to go for one of the tape solutions because of the adhesive.

I was hoping for something more like a dummy barrel or some cylindrical magnets that would mount under the barrels under the rib, but it seems like maybe that’s not thing.

 

I know a guy who uses magnets. I think they are called "cow magnets". The move a little, but not more than an inch or two and are easily slid back into place.

 

I don't believe that you said what gauge you are shooting. What kind of recoil pad does it have? They make mercury filled cylinders that you can put in the buttstock to counter the recoil. You might want to check them out. There are a lot of things you can do that would be better than weighting the barrels like you are planning to do. Good luck.

 

How about a weighted handguard?

Weighted Brown Leather Handguards

Leather Handguards Leather over spring steel made to slip over the barrels of double guns to provide a better grip on splinter-type forends, protect hand from hot barrels, and add barrel weight to improve accuracy. Unlike most other handguards on the mark

connecticutshotgun.co

 

If you reload, 3/4 oz shells are an option. That’s what I shoot in my light SxS guns. Also makes a nice dove and quail load.

 

Actually those "cow magnets" are exactly what I was thinking of. https://www.tractorsupply.com/tsc/product/producers-pride-ringed-ferrite-magnets-3-pk-9803-19