Well, what prompted all this was not undrilled movie prop guns, but guns sold with vents drilled and intended for shooting, hunting and re-enacting.
Here are quotes from two of the sellers' sites:
From MVTC:
"Can these be fired with shot?
A: Yes. Many of our customers hunt with these. Others target shoot. Others just shoot blanks in reenactments. The barrels are made of D.O.M. steel just like the "big names". The breechplugs are threaded and tight."
"Are the barrels proofed?
A: No. Here in the US, there are no proof houses. I checked with SAAMI as to their reccomendations about proofing. ("Sporting Arms and Ammunition Manufacturer's Institute", the organization who sets standards for such things)
Here was the response:
"SAAMI is currently working on setting standards for muzzleloading guns. There is no proof standard at this time... Cartridge guns are proofed at 130% to 140% of service load pressures. Where and how proofing of muzzleloaders will be done is not yet set."
What does this mean? It means that here in America, there are no standards to proof barrels to, nor proof houses to do the testing. In countries where there are proof laws and proof houses (like the UK and Germany), these routinely pass proof testing.
If you really, really want a muzzleloader to be proof tested, we can perform that task for a fee of $50. The gun barrel will be measured, test fired with double the service load (far in excess of Italian standards that are only 130% of service load) and measured again. The barrel will be marked with our stamp and you will get a copy of the test report. We keep a copy of the test report on file here. "
From Veteran Arms:
"Veteran Arms, LLC uses the “traditional” method of proofing which involves visual and mechanical inspection of each piece, the remote firing of the weapon with a charge of 160% of the recommended maximum load, cleaning, and final inspection."
"This February, Veteran Arms, LLC subjected one of its off-the-shelf musket barrels to an "Extreme Integrity Test." The barrel (.69 cal.) was removed from the stock, inspected as usual, and then fired with our regular 160% proofing charge (130 grains of BP + 1 oz of shot). No problem. In an attempt to achieve structural failure, the powder charge was subsequently increased in increments. We worked our way through live loads backed by 200, 300, 400, 500, 600, and 700 grains of powder. No problem. We finally got impatient and decided to load the barrel with 10 times the maximum recommended powder charge plus 2.5 times the shot. There was so much powder and shot in the barrel that the ramrod stuck out approximately a foot! Upon firing, the noise was extremely loud. The result: no bulges, no cracks, nothing. The barrel was completely unharmed. Of course, this information is not intended to encourage anyone to exceed the recommended load in their musket. It is intended only to illustrate what our barrels may be capable of withstanding and to dispel some myths which have circulated on the internet regarding the safety of Indian made products. "
Back to Bill in Oregon here:
Obviously, these statements are being made by importers/retailers who want to sell their wares to those of us interested in historic arms that meet a certain budget point, so the words must be taken with a grain of salt. Still, these folks seem comfortable with the quality of their guns.