Greetings and salutations,
Being a bit of a Black powder nerd..er..."enthusiast" for over 20+ years using both a Lyman Great plains flintlock (actually me first BP fire arm) and a Lyman Great plains Pistol and I recently picked up a GPR in percussion.

But there is something odd about it that makes me lift an eyebrow (in my best spock-like imitation) the hammer on the lock has quite a bit of front-to-back slack around the tumbler while the pistol and flintlock are (even after all these years) rock steady with no looseness at all.

I'm sure this can't be normal.

All so, what is the best touch hole dia for a GPR flint?, about a decade ago the original liner was replaced by a gunsmith and ever since then it's been a crap shoot if I get ignition or just a flash..I measured and the hole is slightly less than 1/16" (1.5mm ) isn't it suppose to be 5/64" (1.9-2 mm) for optimal?

Peen or shim it with brass shim stock.

Factory size touch hole has always worked best for me when I got a good one.

I use the touch hole liners sold by RMC Sports http://www.rmcoxyoke.com/inc/sdetail...ements/6549/84

the Lyman they sell works good in my Lyman Flintlock rifles.

Don't know what the factory liner was, I trusted the smith to put the right one in. I'd of done it myself but didn't feel too confident in my abilities at the time.

its a screw, not very hard to install it with a screw driver.

I like my flash hole to be .050 - .055" in diameter. I take the original (flat face with screw driver slot) and drill a shallow "V" in it with a 1/8" or 9/64" bit. Not much. Just enough to funnel the flame to the touch hole. Works better than the flat face.

Muzzle loader.com was very good about doing an exchange on the cap GPR, the replacement is as rock steady as the flint...kudos.

I still couldn't get the old SS liner out to replace, but in the process ended up opening up the touch hole, greater than 1.6mm (.063", the original 1/16") but less than 2.0mm (.08", 1/12").

I'll try this and see how it performs, if not then in goes the new liner.

I'd try harder to get it out. At some point you'll have to when it wears out.

Too big a hole is as bad as too small a hole.

Too big a hole can cause some major problems as well. It actually verges onto a safety issue.

took flint out Sunday with the touch hole slightly enlarged (from 1/16 to 5/64) or >1.5mm but <2.0mm) and the difference was amazing!...even forgetting my 4f primer and using 3f, if it sparked it fired! (at least until the frizzen and flint got too sooty).

And to think of all those years of frustration when I wanted to chuck it off a cliff and get out of muzzle loading!