Rule for load change switching jacketed to cast?

[tacotime]

If I have a good working load for a 45-70 with a 350 grain jacketed bullet and want to try a similar load for a 350 cast bullet in the same gun, is there a rule for adjusting the charge when switching from jacketed to cast on the same weight bullet?

[Larry Gibson]

No "rule", some quidelines though.  However it depends on the powder used.  There a plethora of loading data for the 45-70 using just about any powder that works.  Why guess?
 
Larry Gibson

[tacotime]

Because I have a decent working load for jacketed but can't get the same weight cast to work all that well so far using listed loads.  Though there might be a simple rule for adapting. 

[anachronism]

Not really. You're changing a major component, so you'll likely need to start at the beginning & do the normal load development program.

[mechanic]

One of the most basic rules for shooting cast successfully is to slug the bore, and be sure the bullet is large enough to engage and seal.  If you don't cast, you can still order from some companies in different diameters....such as .458,.459 etc.  Many off the shelf cast in my area are marked .457....too small for my BC.
 
That has been more fundamental to accuracy in my 45-70 than the load I used.
 
Ben

[watkibe]

I recently posted the same question on another forum: can I use data for a jacketed bullet with a cast bullet of the same weight ? I got lots of replies, some of which was very interesting stuff.
It turns out to be a complex issue. I have seen in print before that " lead has less friction than bullet jackets, so you will get less pressure with the same powder charge." I don't believe this is always true.
I spent some time looking through the 2nd ed. of Lee's "Modern Reloading" book, which has everybody's data side by side. I found several examples where cast bullet data used less powder than the same weight jacketed bullet. It's more about pressure, which is greatly affected by bearing surface. Some VLD bullets have comparatively little contact with the barrel, and lower pressure. Same way with how many grooves the bullet has. The Lee TL (tumble lube) bullets have many tiny grooves, and much more surface in contact with the barrel.
In lieu of a simple rule of thumb about what you can always substitute, I now use the rule "keep looking until I find published data to do what I want". Call Sierra; those guys have dozens of manuals, and they will look up loads for you - any bullet, not just theirs.

[.22-5-40]

Hello, tacotime.  Did you clean out all the jacketed bullet fouling from bore before you tried the cast?

[jlchucker]

As Mechanic says, slug your bore and work up a cast bullet load with the proper sized projectile.  This may involve, in the end, using a different powder than you normally use with jacketed bullets.  I use jacketed as well as cast in most all of my rifles, and have worked up loads, rifle by rifle, for all the bullets (boolits) that I load and shoot.  These days, my guns get mostly cast.  If I were you, if you've not done so before, I'd get a spiral notebook, and keep some records of my loads, gun by gun, bullet (boolit) by bullet, diameter by diameter, and powder by powder, so you'll be able to spend snowy winter days loading up your pet loads for everything you shoot.  about the only other thing I'd add is that if I've been shooting jacketed or cast ammo through any particular firearm, then wanted to switch to the the opposite flavor, I'd give my barrel a good cleaning, starting with a bore brush.  Some calibers (30-30 comes to mind first) and some rifles seem to digest both very well without the throrough cleaning step, but don't always count on it.