What to do when a molds nose is too small?

[zero]

I've got the lee 457-500-f mold, it casts 459-460 at the rings, which is perfect for my h&r, but it casts 451 at the nose, which is a bit small. With whatever alloy or load i use i get about 3" groups at 25 yards. Paper patched the groups are touching, but i've got a guy that wants some rounds for his 45-70, and i don't really want to give him patched rounds, he'll be using them from a guide gun. And my guide gun had lands of .454, and patterned like a shotgun no matter what i tried. So my question is, could i open up the nose a bit to get more bearing on the bullet? I've used tape to some success before in other molds, but would the nose being slightly out of round affect accuracy after sizing? Would a gas check help? Or could i patch and keep all of the patch inside the case?

[stimpylu32]

Please explain what you mean by .451 at the nose ? Are you talking about the the very end / tip of the bullet or just ahead of the driving bands ?
 
stimpy

[zero]

I mean ANY area ahead of the driving bands. The bands are the only part of it that even gets close to the rifling

[quickdtoo]

Properly sized bullets are the key, properly sized = big enough to fill the grooves. 

http://www.leverguns.com/articles/fryxell/microgrove-barrels.htm

There has been a great deal of concern over the years about whether or not Microgroove rifling would shoot cast bullets well. One group of folks says that Microgroove rifles can't hit a barn from the inside with cast bullets, one group says that Microgroove barrels shoot cast just fine just so long as velocities are kept below 1600 fps, and one groups says that Microgroove barrels shoot cast just fine at full throttle. The key to success with cast bullets in a Marlin with Microgroove rifling is to keep in mind that these barrels tend to have oversized groove diameters, and that the grooves/lands are shallow. Therefore, in order to get proper engraving (and minimize "slippage" of the cast bullet as it enters the shallow rifling), it is necessary that the bullet completely fill up the groove diameter of the barrel, and engage the maximum amount of the driving surface of the lands. Since Microgroove barrels are commonly oversized, this means that the cast bullet must also be oversized to effectively "fill up" the grooves. Other factors that also contribute to good accuracy with cast bullet in Microgroove barrels are the use of a GC bullet (which helps to provide a better grip and seal), and making sure that bullet are cast hard enough for the application (generally a BHN of 12 or more). It is also worth remembering that throats in modern rifles are almost always cut larger than groove diameter of the barrel (to insure that ammunition can chamber easily), and that best cast bullet accuracy is obtained by fitting the bullet to the throat, hence reinforcing the need for oversized cast bullets in Microgroove barrels (for example, the throats on my .30-30s run almost .311", so I size cast bullets to .310" for these guns).

[stimpylu32]

Cast bullets are a whole different animal than a Jacketed bullet , with jacketed , the bulk of the bearing surface engages the rifling while with cast , the driving bands are the part that engages the rifling . So nose dia. is not a factor with these bullets , you have other issues that are causing the poor accuracy .
 
Its either your powder , bullet or loading technique that this rifle just doesn't like .
 
stimpy

[Ranch13]

You don't really want the nose any bigger, it may be to big and lead the snot out of the bore now. It's a bore rider bullet and as such the nose is just supposed to ride down the bore, not fill the grooves.

[zero]

Hmm, ok. I just know that with my lee 405 mold, it may not have alot of overall bearing surface, but it does cover about 3/4 overall length and with this 500 it's less than half, and even less that contacts. I've tried quenched wheel weights predominantly, sized to about 458. Would a gas check help? I wouldn't mind trying to do some but i have no way to attach them to the bullet. And what about the other idea of patching just the groove area and keeping the patch in the case, might that work any?

[stimpylu32]

I see from Lee's site that the 457-500F is a Gas Checked bullet , are you using it checked or non-checked ? And if checked , are you using the proper sized check ?
 
stimpy

[zero]

I've been trying it unchecked, but i wouldn't mind trying a check. Like i said though i'm not sure how to get it on there, all i have is a lee single stage press. I've never really been able to find a clear answer on whether gas checked molds can shoot well without checks or not?

[45-70.gov]

some times a GC mold will work without the check  sometimes it won't


if it is a GC mold that would be my first choice to try

[stimpylu32]

zero
 
Most times a checked bullet shot without a check will not shoot very well , checks can be applied 2 ways , the best is to crimp them on while sizing the bullet , it just squeezes the check in place , the other way is to use a dab of glue to hold the check in place , this way is used when the bullets are shot " As Cast " with no sizing being used .
 
stimpy

[zero]

So just running it through a lee sizer with the check on the base should be enough to secure it? That may be why i never got my 303 mold to shoot well

[stimpylu32]

Yep , its that simple 
 
stimpy

[zero]

Alright, appreciate the advice, i'll give that a try. What about if the nose is slightly out of round(by like .002), will that throw it off very much? And by nose i mean the bore riding part ahead of the bands

[45-70.gov]

out of round??
might put screw into base of slug  mound in drill
apply lapping  carefully

[Jim Flinchbaugh]

Zero,
You need to lap out the nose portion of the mold. This can be done with lapping compound a bullet cast form the mold using lapping compound.
You'll likely have to lap, check the size, cast a few more at the new size, lap, cast a few more etc till you get it where you want.
You do want the nose to very lightly touch the lands- a "bore" rider as it where.
You're on the right track, if PP shoot well, lap it out or find a mold with a bigger nose. If you lap, when to size a few polishes with toothpaste
will shine it up for a nice finish