bad groups, double rifling marks? 480 cast

[Gallahad]

Well I have tried several loads with 375 gr lbt bullets in this 480. hardness is 22 brn. bullets were sized for 480.  my best group of 3 was with 9.5 grs. of unique. no pressure signs, and mild report. 950fps. about 1 1/4 inches at 10 yds. still not happy i tried to recover some bullets, and finally got 2. these things penetrate like crazy. after inspection, it looks like there are 2 sets of rifling marks on both bullets, overlapping. one set of marks is just offset, but imprinted over the other.The bullets were from different powder loads. It looks as though the bullet was following the rifling, and slipped forward about 1/16 of an inch and caught the rifling again. THIS GUN WAS JUST MAGNAPORTED, and I hadent shot it before. bought it new. does the porting have anything to do with this?  I've never seen this before, and think it's causing my grouping problem.

[Badnews Bob]

Whats the bore size? have you slugged the bore? Could you be useing undersized bullets for your bore? I would be checking that first then looking somewhere else.

[Lloyd Smale]

my guess is undersized bullets and to hard of an alloy. Now i like Hard bullets. But to use them  you have to have them sized to match your gun. I size most of my 475 bullets to 476. Do you have any leading in the barrel? Another thing you could try is using a softer alloy. 22bhn isnt needed at that velocity. If a bullet is fitted properly it will give great results but a softer alloy may be more forgiving. Try wws with a little tin. Bottom line is if you are actually having a bullet strip through your rifling about the only thing that can cause that is being undersized or having an alloy to soft for the velocity your trying to shoot at and in your case your alloy is hard enough for any handgun velocity and even any rifle velocity up to 2000 fps.

[Gallahad]

sized to .476.  very very little leading. don't cast myself, got these from montana bullet works.

[Luckyducker]

I haven't had the priveledge of loading for the 480 but would sure like to.  Having said that what you need to do is either push the slugs harder to cause them to obturate the bore or use softer cast bullets.  You can only push them so hard before reaching excessive pressure levels and when you have found your "max load" for this firearm, if results aren't satisfactory, you will have to try a different/softer slug.  I had this problem shooting cast slugs in my Blackhawk 41 magnum.  I ended up shooting the same full power load that I had for jacketed bullets but they work.

[Lloyd Smale]

are you sure that bullet wasnt just deformed from impact? where do you live? do you get snow. Shoot into snow and then recover your bullets. Snow is a great bullet stopper that doesnt damage bullets. You could do the same thing by taking a 5 gallon bucket and filing it with finely crushed ice and water made into a thick slush.

[Gallahad]

I had considered bullet deformation, and recovered one that almost looked good enough to re-shoot. all 4 recovered showed same marks.  I will try different bullets before I call ruger. I had come to the conclusion that it may have been a poorly machined forcing cone. I have pushed these 375 grainers up to 1220fps. which is far from max, but results were same. Thanks a lot, when Im able I will update. God Bless all.

[TEXXAS]

Gallahad - Were the double rifling marks only on the front half of the rifling marks? It's common for a bullet to resist starting to spin as it starts into the rifling. I have seen plenty of bullets that have a double mark at the front that tapers to a single mark before it reaches the back of the bullet. Also look as see if the marks are the same all the way around. If cylinder allingnment is off one side will be different, as in a larger spread in the marks.

Chad