Thinking of getting a Mark IV for plinking. I was told, years back, that the bull barrels were more accurate, is this true? What model's are recommended and why?
A few years before Bill Ruger died he bought his own barrel making machinery. He now had a handle on the quality of his barrels compared to before when he sub-contracted out to the lowest bidder. This is why in the dead hand of the past you often had 1 Ruger rifle shoot amazingly accurate and the next 9 look like scattergun groups. In a TV interview before Bill died he said "I find it rather ridiculous that people go out and buy a custom made barrel for their 10/22 rifle when we now make the most accurate barrels in the world".
Heavy barrels (assuming a quality barrel) do shoot more accurately because the person can hold the gun more steady during the trigger pull and they heat up more slowly which causes less barrel vibration. Heavy barrels also vibrate less violently than standard weight barrels.
The longer the barrel the longer the sighting radius when used with iron sights and you have less aiming error. This of course does not hold true when one uses a scope or electronic sight which are standard equipment now for most competition.
Trigger pull often contributes to 50% of the accuracy of any weapon. When you have a heavy, rough, creepy trigger pull accuracy goes right out the window no matter how good a shot you are and no matter how expensive the ammunition you are shooting.
Quality of the ammo is also paramount to good accuracy. If you think a box of econo-grade blaster ammo like Remington Thunder Turd is going to outshoot the Kings Ransom price ammo like Lapua Midas or Eley Red Box Rifle match you are definitely on drugs.
A dirty, fouled and leaded barrel will not shoot accurately either, but improper barrel cleaning will ruin a match barrel faster than a cat can scratch his rectum.
Over cleaning can ruin a barrel as well. Recently in the past few years two of your top shooters sold off their prior match .22 rifles and the bores were so fouled it was a wonder they did not blow up but it proved one thing and that was that a good shooter using expensive ammo can go long periods between cleaning a barrel. It is just that trying to clean such a fouled barrel can be time consuming and you run the risk of ruining the barrel if you are not careful in the cleaning process. I might add that when these two guns were cleaned they shot every bit as accurately as when they were new. I might add one of the reasons these top shooters did so well was not that they had superior accuracy but they had superior skill in doping the wind. The Achilles heal of .22 rimfire shooting is the devil in the wind. Pick a day with a constantly shifting wind, even one as low as 5 mph and you may as well stop shooting and quit wasting ammo. Go play golf that day instead.