I whole heartedly agree with Long Range Demon TacKac on most of his post but I would like to add some input on some points.
In tests done in laboratory conditions measuring pressure at three locations, Chamber, mid point and 1 inch from barrel muzzle, small arms cal. 14,17, 222, 224, 25, 243, 7mm, 30, 338, 8mm, 416, 50, pistol 22, 25, 32,38, 40, 44, 45, 50. The testing also included 20mm, 30mm, 40mm, 81mm, 105mm,155mm. Literally thousands of rounds were fired in the small arms cal.
"As bore friction is reduced the bullet may accelerate down the bore as if it has a lighter mass. This can result in secondary pressure spikes if powder is too slow for the bullets rate of acceleration."
Their was no sign of a secondary spike in pressure noted in any of the findings recorded in the testing we preformed from any of the small arms cal.
Throat erosion:
I agree with the listed causes of the erosion with the addition of one other cause that being the sand blasting effect of unburnt powder. Some of the barrels used had chrome lined chambers and were less likely to be affected buy any of the causes.
Less copper fouling:
In the tests we preformed copper fouling was less prevalent then in non coated barrels our tests used hand lapped and none lapped barrels the results showed there was a larger benefit to non lapped barrels. Their were two tests done with molly coated bullets one used clean barrels the other used barrels swabbed with molly diluted in alcohol and allowed to dry for 3 min. before firing. It was found that the velocity stabilized after the third round in the swabbed barrels and copper fouling was reduced and easer to clean out in these barrels.
Cleaning molly:
"Serious barrel damage can result from molly buildup (caking)….Molly usually builds up "rings" at certain points in the bore. If the build up becomes sufficiently severe bullets fired through the restriction will expand the bore at these ring points."
The build up of molly in barrels was a concern covered in the testing; it was investigated and tested for to the extreme. Barrels were checked with bore scopes at 10, 20, 25, 30, 50,75,100, and up to 500 rounds without cleaning, tests were done in 224, 30, 50cal. and 20mm on full auto fire with no bulging barrels or for that mater excessive pressure. ( heat expanding the barrel in auto fire may have helped reduce pressure) in unlapped barrels molly build up in rough areas was present but by the end of testing build up was minimal even in these barrels.
The Bottom Line:
The test did show extended barrel life in reference to extending accuracy if a barrel was shooting well I would set the barrel back and rechamber.
Molly has other benefits for the long range shooter which have not been covered in past posts. Here is a test anyone can perform for themselves. Load 20 rounds with your favorite load and use 10 molly and ten uncoated bullets. Fire the 10 uncoated rds. At long range 500 meters or more, then swab the barrel with molly and alcohol and allow to dry, now fire at the same target using the molly bullets, you will see a marked difference in bullet impact on the target. I believe we saw a 40+ inch difference at 1000 yards with a 308 165 gr. As well as less recoil which means less fatigue in long matches.
