457-340F now casts 460 after a little lapping

[BK7saum]

I received my 457-340 the other day. Finally cast with it night before last. Ended up with about 140 keepers. Only problem was they were 0.457" plus or minus a little.

Decided that wasn't good enough for my marlin so I broke out the coarse lapping grit as it was all I had.

Ended up lapping several times but now casts 0.460". One cavity is just a little wide at the parting line at 0.461". But that sizes right down. Weights are very close. I had to open up one cavity a little to get the weights closer. At first they were a half grain less. Now they are a couple tenths off.

Overall I'm happy with the progress and have a boolit closer to throat dimensions.

[bigboredad]

I have had great results with that bullet. However like yours mine cast at .457 too bad that can't get them to cast .460 right out of the box

[bgokk]

I have that mold and with WW it casts .459" I got lucky. Shoots great in my Marlin 1895.

[retiredPO]

Im Very Very new to this, and in the market for molds also.... and wanting to learn...so my question is why would you
expect a mold marked 457..... to cast 460.... should you like that it does what it says..... seriously, Im not being a smart
a..... are they supposed to give you bigger.....
thanks.

[BK7saum]

Not really. A lot of molds case groove diameter or just a little larger. However most of the time we want the boolit to fit the throat of the chamber or at least cast 0.002-0.003" over groove diameter. I already know that 0.460" boolits will chamber. And shoot well.
Past versions of this mold are known to cast 0.458" or even 0.459". Also, I had not lapped a mold before so it was kinda of an experiment.

Now that it casts 0.460", it is what I consider about perfect for my marlin 1895.

Does that clear up any confusion? Others here could say it better but its early and no coffee yet.

Brad

[btroj]

Actually most moulds cast to spec size or a bit larger, groove diameter has nothing to do with it.

Your mould did not produce undersized bullets, it was on spec. It did not make bullets the size you wanted but that is no fault of the manufacturer, you bought a mould that was spec'd smaller than you wanted.

The fact that other moulds cast different size bullets is not relevant. Yes, my 460420 mould makes a .460 bullet but it was spec'd to do so. Your mould was made to produce a .457 bullet and it did so.

We need to stop blaming moulds for making undersized bullets when they are the size they are supposed to be. Want a .460 bullet? Buy a mould to cast one.

[BK7saum]

Did I blame the mold or say it was out of spec? No.

Seems a lot of commercial molds are spec'd at nominal groove diameter or 0.001" over. What isaid only in a different way. I simply said I preferred a larger boolit and modified the mold to suit me.

Do you want to sell me a 2 cavity mold that will drop 0.460" boolits for less than $20?

$ is why I purchase the Lee. It cast at spec'd diameter. I never blamed the mold or Lee for it casting 0.457".

Based on responses of others that have a 457-340 that do cast 0.458" or even 0.459", I had hoped to be the lucky or rather unlucky recipient of an out of spec mold.

[BK7saum]

I did say "only problem was" In regard to diameter of 0.457, but that was in regard to my application in the 1895. I guess that could be taken as blaming the mold. That was not meant as a negative toward the mold.

[btroj]

But nominal bore size for a 45-70 is considered to be .457. Marlin makes big barrels.

I give you credit for making a mould work for your needs. How did the lapping affect the grease grooves? The grooves on the bullet aren't real deep to begin with and I wonder how the lapping altered the grooves.

[BK7saum]

I wish id kept the first boolits to compare. They still seem sufficiently deep but edges are a little more rounded. I applied the grit to the drive bands but I'm sure it migrated to the grease grooves a little as I lapped.
I am quite pleased with the outcome, and think that I made a good mold into a better mold for my application.

Thank you for your inquiry about the loob grooves I think that we sometimes forget there are a lot of negative things that can go wrong when we begin to make modifications to something

[btroj]

Lee grooves are small to start with, that would be my biggest concern. Lyman and RCBS grooves are at times too deep so less issue there.

In the end all that matter is how they shoot!

[BK7saum]

I plan to find out how they shoot in a couple of days. As of now I don't think that lube grooves are any appreciable amount smaller, although any lapping compound that migrates would have to wear on the mold in that area. I think I'm okay, but 26 inches of barrel will be the test.

[Dale53]

Congratulations on the O.P. for getting what he needed (takes more than a bit of skill to do that).

My particular Lee mould for that bullet shoots quite well in my Marlin 1895 with Ballard Rifling (one of the early rifles of the modern persuasion). With a scope, off a bench that rifle regularly gives me five shot groups around 1½" with that bullet. At the same time, I bought the Lyman 457643 mould. The Lee shot considerably better than the Lyman in my rifle.

YMMV
Dale53

[wmitty]

Marlin builds .46-70's...

[retiredPO]

Wow.... Im sorry I started something that could of got a bit heated.... but seems to of smoothed out nicely..... and I got to learn a lot,.... from my limited experience lee seems to cast exactly as advertised and others seem to vary more... it seems like from what Im reading,.... my best bet is to cast a little large and size to the gun......

[oldfart1956]

Folks this is one way to lap the mold without lapping the lube grooves shallower; after casting up the lapping boolits roll them in the lapping compound as you normally do. I'll assume you already have a nail/screw or whatever installed in the boolit nose/base depending on how it casts. Now chuck the boolit up in your drill and find a hacksaw blade roughly the thickness of the lube groove(s). While spinning the boolit at a reasonable pace ease the hacksaw blade into the lube groove and "lathe" the groove deeper. (this to accomadate the lapping compound over-run) Wipe the groove out with a bit of cloth, re-coat with compound and try to keep it out of the groove. When coating the boolit with compound you are rolling it on a metal surface to apply...correct? No compound gets in the groove this way. Also, after the first couple revolutions in the mold open it back up and clear the smutz off the mold faces and then procede. When I lapped a .459 mold out to .462 I ended up with lube grooves .003 deeper using this method. (a benefit in my case) Audie...the Oldfart..

[BK7saum]

Thanks Audie.

I have a 41 mold I'm thinking about opening up. Just a little bit. I'll try the saw blade trick next time around.

Brad.

[BK7saum]

Marlin builds .46-70's...

Why, yes they do. They cut 46-70 chambers in 457 barrels.

Now wheres that purple font?