Cimarron 1878 Colt hammer double (formerly TTN) problem

[Poodleshooter]

I have a relatively new Cimarron hammer double 1878 Colt replica (no longer a "TTN", now some other PRC manufacturer) that has the awkward habit of occasionally disassembling itself when the action is broken at speed. Chiefly, the problem seems to be that the forearm latch doesn't go down all the way. This is easy to watch for when having fun at the range, but running at match speed I have to very careful not to let it pop loose or I end up holding a receiver/stock and nothing else.
I know how the forearm latch engages the lug on the barrel, via that small piece of steel shaped like a capital 'H' with one end closed up.
Does anyone have any commentary on how to better fit the entire latch/lug assembly? 
Much obliged for any assistance folks!

[Coffinmaker]

Thoroughly clean both the bearing surface of the fore arm latch and contact area of the barrel lug.  Either use some dykum or
candle/match smoke on the lug.  Close it up then take it apart.  The area where the soot has been disturbed needs to be carefully
relieved with a file.

Coffinmaker 

[Poodleshooter]

Thanks Coffinmaker.
Should I relieve the "forend lever bolt" (the closed end 'H' piece) or the barrel lug itself? Presumably the smaller, cheaper part (the forend lever bolt)?

Referring to the nomenclature per here: http://www.coltparts.com/pt_78shotgun.html

The forend lever bolt piece appears to be slightly -deliberately- ground at an angle on one side in the middle of the 'H', and flush on the other side. I can change engagement slightly by flipping the lever bolt over. When the squared up side engages the lug, it appears to lock up more consistently. The angled side appears to allow it to work loose. What I can't figure out is why the opposite surface of the middle crosspiece of the 'H' is ground down at all. That machining doesn't seem to serve a purpose that I can see...

[Coffinmaker]

I don't really understand where all your trying to make changes.  You describe a fore end latch that won't close.  There is an "L" shaped lug protruding down from the barrel.  It fits into the fore end iron.  The latch cams into the crook of the "L" and there is a spring and
plunger that stop the movement of the latch when it is in place.  Your stoning just a touch of metal inside the crook of the L so the
latch cams completely over into the fore end iron where the spring and plunger hold it in place.

As long as the gun lock up tight, leave the locking lugs alone.

Coffinmaker

[Poodleshooter]

Hi Coffinmaker,
I think I found the problem. If you remove the forend, there is a steel coverplate, screwed into the forearm wood. Remove that, and you have the latch assembly and a loose piece of steel that will fall free when the coverplate is removed: the aforementioned "forend lever bolt", which actually is the forend's engagement surface for the barrel lug, cammed into place by the latch itself.
After flipping that forend lever bolt piece over and reassembling with some light tapping, the forend snugged up against the barrel much tighter than it did when I first bought the shotgun (not long ago).
When time permits, I'll try to get a photo of this. This piece can easily be installed upside down, so a photo of it might be good for reference for anyone who takes their forend down for refinishing.

Thanks for your assistance.

[Abilene]

Glad you got it figured out!