I have fire lapped my ruger 45 until the constriction was gone. The bore is now around .452 and straight. My cylinders were reamed to .4525 and after fire lapping are now closer to .453. My bullets after sizing through my star sizer are about .452. Using my LBT hardness tester the bullets are 25 BHN. I have seen pretty heavy leading at the back of the bore just in front of the forcing cone. I am pushing the 340 grain bullet from an lbt mold at 1000-1100 fps. I think my bullets might be a hair small (I don't want to shoot softer bullets I know this might help but I'd rather shoot one that fits the bore rather than relying on obturation.)

I just pushed a lead ball through the sizer die and it came out .451. The hard bullets come out .452. If I buy a .452 die from magma can I count on my bullets coming out a thousandth bigger? The guy at magma thought spring back would be limited to a few ten thousandths at most.

How much do your bullets spring back after a sizing?

Hard lead bullets will in fact spring back a little, but not much. I'm surprised you're getting that much difference. How big is the roundball to start with? If it's .454-.458", I'd whack it a few times with a hammer to get it well and truely oversized before you push it through the sizer. The soft roundballs should be accurate....

What are your loads? You might not be pushing them quite hard enough......

Lube? Gas check or no?

MattC, I too experiance the same problem when sizing bullets for my .500 S&W. Using straight linotype and a .500 sizing die, I get .501 bullets. I also have a .501 sizer and get .502 bullets with that one. I have to settle for the .500 die since no one makes a .499.

Remember that the mixture of your alloys will change the size of your bullets. The temperature of the bullets can make a difference as well. Meaning, make sure that they are cold before sizing and measureing.

The hornaday lead balls I used were .490 and the sizer die cut donuts, did several to be sure all came out 451.

I am using LBT blue lube and my bullets are gas checked.

The hardening cycle on the bullets I sized is complete they have been reading 25 for several weeks.

I wonder if I have throat erosion as I used more than 160 lapping rounds with clover 320 with no effect. THen I asked veral smith what he thought of that which of coarse he sold me a can of his stuff. About 80 shots later the constriction was gone. That is a lot of lapping rounds even though its a ruger stainless.

Too bad there isn't a way to slug only the throat or back of the barrel.

I'm surprised you got that much difference in the sizing of the different alloys, but that's good information. It does emphasize the need to use the correct hardness of lapping bullet, though!!!

Veral's book did mention that Ruger stainless revolvers may take upwards of 200 lapping rounds, as I recall, so you weren't too far off of the mark.

[QUOTE=MikeG]


It does emphasize the need to use the correct hardness of lapping bullet, though!!!

Yes, I guess the hard guys lap the whole barrel like a polish bob. Interestingly, the air cooled guys (12-14 BHN) spring back too, but only about 5/1000 (I don't have a micrometer only a caliper so I am interpolating. These are the same alloy and casting session just not water dropped.

The as cast size of the bullets is 454.

Matt- I agree with you that you need a little more bullet size. I've noticed a bit of springback in bullet sizing with harder bullets, esp. linotype and monotype, but nothing that was especially significant in my applications. If your throats are actually .453, that's where I'd be sizing bullets. I'm kinda hardnosed about bullet to throat fit because even a slightly off bore axis bullet can cause leading. Some people get away with it, but I never did. Star may re-bore your existing die out to the larger size. It wouldn't hurt to ask. ==Bob

I have often seen mention of what is perceived as "springback" of hard cast bullets. While the effect is the same, consider this. It has been demonstrated that a bullet passing down a barrel actually causes it (the barrel) to expand, sort of like a snake swallowing a rat. This, and the like expansion caused bu the propellant gasses is what allows a strain guage pressure transducer to work.

Usually a sizing die is even thinner than the barrel that the bullet will be shot in, and it isn't very well supported in the lubri-sizer body. This applies to any sizer, except for the Star type sold by Magma Engineering. What I am suggesting, is that rather than the bullet "springing back", which is highly unlikely, that in fact the sizer die is stretched to differing amounts depending on the hardness of the bullet.

Just for arguement sake, the end result is the same regardless.

I have found in my castings that it is always best to cast to size and not use a sizing die. This one of the reasons I like using some of the older orginal moulds to cast with. For example, my 44/40 shoots better with the older original Winchester bullet mould for that size. I cast, cool, lube my bullets in a cup cake pan and pop them out to reload when I am ready. The lube stays inthe grooves better that way too.;)

As you know, you can order dies to the size you want.

Alk, thought about that myself last night. The sizing dies are pretty thin.

May try to bore out a sizing 'die' of sorts out of a thick piece of scrap and see if I get the same results.

Alk, Hmm, that is an interesting point I'd have not thought of. I am experiencing this with a star sizer and the walls are fairly thick. Well, I hope magma sends me one with a springy steel die so it gets me the size I want. The die I am using is old star production. I'll let you know when it comes.

I just went down stairs and did a .490 round ball through a lee push through sizer. This is a beefy piece of metal. It measured .430. Next I did a 44 magnum 22 BHN bullet and pushed it through...reads 431. I'm thinking that water dropped wheel wieght must spring back a thousandth.