Flash and Gary:
Flash: If you are using a Big Bore with the Marlin micro-groove barrel you will never get it to shoot cast, no matter how hard they are, accurately. I just do not think there is enough room those teeny tiny rifling grooves to grab the bullet and impart a proper spin. Also, find the Beartooth Bullet website and read the results of their experimentations with cast and gas-checked bullets. It will facinate you.
If you are stringing vertically make certain your barrel or the magazine tube is not resting on whatever type of a rest you are using. Hold the forestock as you would in the field when benching. If your vertical string still exists, then try one particular load at a time. One powder, one charge, one bullet, and shoot for group. If all your loads perform the same and continue to string vertically you may need to bed the forestock or at least relieve it where it may impact either the action, barrel or magazine tube.
Gary: how the hay did you get Montana Rifleman to give you anything other than a 1:24 twist. That's what they told me they use for their 444s. I had asked about a 1:18-20 twist as I had read that twist helps stabalize heavier 43 bore loads. But, I gotta brag a bit Gary: I was out last week with 26" Winnie and at a hunnert yds grouped 1 and 3/8s of an inch with two different gas-checked loads in 300 grains and one jacketed load of the same weight. It was mostly the rifle my friend, not me. But, two different powders, one liste dto provide 2200'/sec, the other 2300'/sec and a jacketed 300 grainer at 2300. All hit to poi and I thought those were some pretty good groups.
Now, sitting in my closet is a Timber Carbine with a 1:38 twist and an 18 3/4 inch long micro groove barrel and at the local store is a Black Shadow with the same rifling and twist but 20 inch barrel. Before taking either of those two out for any accuracy work I will lap both barrels and Pachmyer (de-accelerate) those stocks. They should both perform about the same but not as well as the Montana barrel or Harpy's 1:12 twist early production Timber Carbine.
Gary, I also had that concern about the 444 but thought - hay, wait a minute. There should not be any difference in a jacket or a gas-check bullet's performance. The gas-checked bullets I have used never leaded and I had wondered if the lead would first take to the grooves and be enhanced or supported by the gas check and would the gas check then take hold and scrape or clean out any lead deposits left by the front bands of the bullet? I have noticed no additional fouling after using gas checks.
However, I'll let you know how this works out with those two micro-groove barrels I will shoot later this summer. If they don't shoot gas-checked bullets as accuratly as I want them to they are either going to the Montana Rifleman or someone else for rebarreling but I would have to talk with Harpy and a few others to determine if I want anything other than a 1:24 twist. BTW, what is a 5A contour? Mikey.
