Bore diameter and groove diameter.

[Pat73]

For some un-Godly reason some of the rifle manufacturers are using .430-.431" bore barrels for the rifles they make instead of .429" like the revolvers have.
So you may have to deal with that also and use a .432 lead bullet to get good accuracy and velocity.
It won't hurt shooting .432" lead bullets out of a revolver in case you have a 44 revolver to go with your rifle.

Got a S&W 629 6 inchn barrel

 

[Pat73]

Blame SAAMI.

The SAAMI pistol specs for 44 Mag say .429" groove diameter. VELOCITY AND PRESSURE DATA (saami.org) (page 54)
The SAAMI rifle specs for 44 Mag say .431" groove diameter. VELOCITY AND PRESSURE DATA (saami.org) (page 143).

I've never seen a good explanation for the difference, but don't blame they rifle makers. They're just building to spec.

Wow. Thank you. Did not know this fact. But, why?

 

[gwpercle]

Since you have 12 groove rifling I would size cast bullets to .432 " . Check to make sure they chamber at .432" before loading a quantity .
It's been my experience that with multi-groove barrels (more than the usual 4 or 6 ) the larger bullets seal better . But .431" may work also ... a lot depends on how hard (BHN) the cast bullet metal is .
When using cast bullets use one with a Gas Check ...
...it just makes load development so much easier !
Gary

 

[Pat73]

Since you have 12 groove rifling I would size cast bullets to .432 " . Check to make sure they chamber at .432" before loading a quantity .
It's been my experience that with multi-groove barrels (more than the usual 4 or 6 ) the larger bullets seal better . But .431" may work also ... a lot depends on how hard (BHN) the cast bullet metal is .
When using cast bullets use one with a Gas Check ...
...it just makes load development so much easier !
Gary

Thank you. 200 gran rnfp is 15/16 bhn .429" and 240 grain swc is 19/20 bnn .4305"

 

[AJC1]

Thank you. 200 gran rnfp is 15/16 bhn .429" and 240 grain swc is 19/20 bnn .4305"

A softer bullet seals easier.

 

[gwpercle]

Thank you. 200 gran rnfp is 15/16 bhn .429" and 240 grain swc is 19/20 bnn .4305"

Give them a try ... it's all a balancing act with velocity - bullet hardness - proper lubrication and what phase the Moon is in and how you hold your mouth as cosiderations ...
Only shooting them will tell the tale !
Gary

 

[Pat73]

Give them a try ... it's all a balancing act with velocity - bullet hardness - proper lubrication and what phase the Moon is in and how you hold your mouth as cosiderations ...
Only shooting them will tell the tale !
Gary

With my 629, they are notbad at all. I will try them in my riffle.

 

[Barbaroja]

I’m playing this game right now with a .444 handi-rifle barrel. The only other 44 I have is a .44 spl flattop Blackhawk and that I size cast at .430 for. The .444 is slugging at .430 so I’m going to need to get a .431 and .432 sizer to try. I’m still going to load some of the .430 Bullets I have on hand to try but I don’t expect anything good from it.
Being able to size them the same would be great but it doesn’t look like it’s in the cards for most of us. Saving grace for me is I’m looking for a 320gn+ bullet to shoot in the .444 and have no intention of shooting them in .44spl.

 

[gwpercle]

I’m playing this game right now with a .444 handi-rifle barrel. The only other 44 I have is a .44 spl flattop Blackhawk and that I size cast at .430 for. The .444 is slugging at .430 so I’m going to need to get a .431 and .432 sizer to try. I’m still going to load some of the .430 Bullets I have on hand to try but I don’t expect anything good from it.
Being able to size them the same would be great but it doesn’t look like it’s in the cards for most of us. Saving grace for me is I’m looking for a 320gn+ bullet to shoot in the .444 and have no intention of shooting them in .44spl.

You might try increasing the size for the .444 Marlin with powder coating ,,, or
Another trick that might work is Patching the bullet , not with paper but Teflon Plumbers Tape on the driving bands . Do a search on the term "Teflon Tape Bullet Patching " an old Louisiana boy Clyde "Snooky" Williamson wrote a book and patened the idea . Basically it's a Teflon Tape wrap on a lubed bullet , a gas check is installed to cover the base and hold the tape wrap and the tape is gently heated to "shrink wrap" it in place .
Now you have a larger , Teflon jacketed bullet ... I'm not sure how much you can enlarge with the tape but it's a cheap and easy try .
The Marlin Micro groove barrels like the bullets on the fat side .
Gary

 

[Barbaroja]

Mine is not microgroove, fortunately it’s a later model with Ballard rifling and a 1:20 twist and they are already powder coated. I have a mold that drops at .432 I just don’t have a sizer for it yet. To that end I shot 20 rounds of .430 cast pc’d Bullets today with no leading to speak of, not much accuracy either.
No tricks needed, just going to do it right and size them for the barrel.