How can I remedy this problem?

I finally had a chance to get out and fire the new Uberti 1849 Colt pocket revolver.
Have a problem with the gun and thought I'd bounce this off the forum to see what you folks might recommend.
I swapped out the factory nipples for TRESO bronze nipples.
On firing, the hammer gets blown back and the spent cap flies back and drops down into the base area of the hammer. The cap then blocks the hammer from falling properly on the next shot. Many times its so firmly embedded I have to use a thin screwdriver to wedge it out so the gun can be inverted and the spent cap can fall free.
Tedious as all get out as it occurs on almost every shot.
The powder charge doesn't matter. I went down to 6 grains and it still does this.
Is there a way to stiffen up the hammer spring?
Change to different nipples?
Any other ideas?

Yes. The factory nipples center hole is quite a bit greater in diameter than the TRESO nipples.

What powder and caps are you using? What powder charge?
GOEX 4Fg. Charge ranged from 6 up to 15grns.

Are you using pure lead balls or alloy/wheelweight balls?
Pure lead balls. .321caliber.

Is this a factory new gun or one that someone else has owned and just "new to you?"
Brand new gun.

Normally, Treso nipples and Remington #10 caps solve most cap fragment problems. If you are using caps that don't fit snugly on the nipple, it makes them easier to cause problems.
Exactly what I use on all my other C&B's. Treso nipples and Remington #10 caps.
I refuse to use CCI as they blow apart and jam everything.

Are you sure it is blowback gas that is pushing the spent cap off the nipple, or could the spent cap be dragged off the nipple on your next cocking stroke? There may be a burr on the hammer that is catching the cap and pulling it back off the nipple.
Positive its blowback because after the chamber is fired the hammer doesn't go all the way down onto the fired nipple. The spent cap is mushed down near the hammer pivot.

Most factory hammer springs are plenty strong enough to hold a spent cap on the nipple, that's why I asked if someone else had used this revolver before.
Brand new gun. I actually bought two at the same time. Only fired one today. On both guns the hammer seems a little weak on cock back for about 1/4in or so then the heavy spring pressure takes over.

If you are using alloy balls that are harder than pure lead, it will increase chamber pressure, and therefore gas blowback, as the powder charge fights to push the ball into the barrel.
Pure lead balls. They're so loose sometimes they come back out of the chamber stuck on the tip of the loading ram. I tried some Hornady .315's and they're uselessly too small. I've got some .330 00 buck balls I've cast out of pure to try next.

Not trying to talk you out of having a cap rake installed by Mike, just thinking of all possibilities as you requested.
It may come to that as the guns are useless like they are.

What BigBore45 suggested. Before spending any money, test it with the original nipples.

The factory nipples have larger flash holes than the TRESO nipples.
Won't this cause even greater back blast?

Is this your only Colt?
How strong does the hammer pull feel to you?

No. I have several others. Walkers, 1860, ROA.
All of them run much better with TRESO nipples vs. factory nipples.

The problem gun is the itty-bitty 1849 Pocket model in .31 caliber.

Mike Bellevue over on the Youtube shoots 12grns of 4F in his 1849 Wells Fargo(which has the identical cylinder as the Pocket Model). He doesn't mention which nipples he uses in his gun.

The hammer pull seems weak seems weak for about 1/4inch then stiffens up as it is drawn back.

I'll try 3F and see what happens.