New 357 barrel strangeness

[Pipian]

Re-barreled my rifle with a Kreiger 357 barrel with a 14 twist. I’m beginning to work up a load, but barrel slugs out at 356 and am wondering as to what weight and size lead Boolits, I might try first. I surmise that when I did my break-in with a box of 125s and they spiraled out for being too light. Any any good suggestions?

[charlie b]

Welcome.

Factory .357mag, 125gn loads? What distance are you shooting? They should not 'spiral out' unless they are undersize bullets. Seems like something is off.

A long time ago I loaded for a Marlin in .357mag and it liked the heaviest bullets that would function through the magazine. 158 and up. It did not like max loads.

[gwpercle]

Re-barreled my rifle with a Kreiger 357 barrel with a 14 twist. I’m beginning to work up a load, but barrel slugs out at 356 and am wondering as to what weight and size lead Boolits, I might try first. I surmise that when I did my break-in with a box of 125s and they spiraled out for being too light. Any any good suggestions?

What round is the new barrel chambered for ... Details are pesky ... but they matter ...
... A Lot !
Gary

[waksupi]

If the barrel is .357, you will probably need a .359 or thereabout bullet diameter. I would look at 180 gr. bullets for a rifle.

[Daekar]

Were the 125s factory or handloads? Cast or jacketed?
My experience with 357mag has been that some of the magnum powders do not work well with light bullets, and need something heavy for accuracy. When I loaded some Lee 358-158RF over Lil'Gun, even the lowest charge produced a shotgun pattern instead of a group, but that same powder with a 245gr bullet produced the tightest groups I have ever achieved in that rifle. The same Lee bullet loaded over Green Dot performed accurately, and so did a similar 125gr mold.
The usual advice for sizing in 38/357 is 0.359, if your chamber will permit it. My Henry likes 0.360 if I'm pushing things faster. I would not be concerned about pressure with cast bullets even if your bore is a smidgen smaller than usual.

The right boolit choice varies by intended use, but if maximum power and accuracy is the goal, I would go 180gr or 200gr.