View Full Version : Factors affecting diameter of cast bullet
What are the factors (in % or .001 of inch and in general rule-of-thumb) that affect the size of a cast bullet?
Some of these are obvious, but knowing JUST how much variation there is would be helpfull (as under group buys - when ordering a custom mould).
In general is the bullet going to be bigger or smaller if the mix is HOTTER?
In general is the bullet going to be bigger or smaller if the mould is HOTTER?
Isn't there a table of shrinkage percentage for common alloys?
Is there a difference in SIZE between techniques of pouring (dipper vs. bottom)?
01-29-2006, 07:05 AM
Go down the page a ways and there's some shrinkage stuff. sundog
01-29-2006, 08:17 AM
Sundog, THANK YOU VERY MUCH! One of the best sources of info I ever seen. I can see my ink supply dwindle here fast.
01-29-2006, 04:30 PM
I have learned that bullets will vary in diameter with the same mould and alloy, simply by holding the mould closed with varying pressure. This is NOT my discovery, but I did confirm it. The diameter difference is almost too small to measure with a good set of micrometers but it is enough to see the difference by weight.
has a "Locking mould holder" that replaces your regular mould handles. It will apply the same pressure to the mould blocks each time you use the mould. Kind of works like a "Vise Grip".
The locking mould holder is moderately expensive, very heavy, but it does make a difference when you are trying to make the absolute best bullet you can. Good bullet casters (serious cast bullet competitors) are finding that they are now able to hold tolerances to less than +or- .2 gr. They are also finding that their scores are better. Jim Borton, ASSRA SchuetzenMeister, last fall shot a ten shot group at 200 yards, witnessed, that measured .711" (not minute of angle but actual measurement). Understand, ASSRA rules require plain base lead bullets, only. NO gas checks. ASSRA's score target (German ring target) has a center ring (scores 25 points) that is 1.5" in diameter. It is shot at 200 yards and to obtain the score of the higher ring, the bullet must be half in the next higher ring to get the higher score. This means to score a perfect 250 (ten shots of 25 each) requires a ten shot group of no larger than 1.5" and perfectly centered. I have seen Jim shoot several 250's during actual matches. In the group matches (normally five shots for group) I have seen him shoot groups under .700". He is a believer in the Cabine Tree mould handles and I concurr.
Now, when I cast for quantity in pistol bullets, do I use the Cabine Tree handles? No, but if I want to shoot alongside the likes of Jim Borton, I do.
01-30-2006, 12:01 AM
..............I'll transport Tom's post from the 38-55 "Group Buy" thread, here:
I was just about to suggest the same thing as you, but you said it much better than I could.
Regarding the as-cast dimensions as they relate to the mold cavity dimensions. I have a Lee 375-250-RF mold that has had the bevel base reamed to produce a plain flat based bullet.
This morning I carefully measured the diameter of the mold cavity at the bullet base and (according to my averages using a dial caliper that I consider the accuracy level to be at 0.0005") the cavity measured 0.3835" when cold. after 25 castings I again measured the cavity and the measurements were consistently at 0.3845". The castings were from wheelweights with 4.5% tin added to produce a facimilie of the Lyman #2 alloy. The last five castings each measured 0.3835" at the base diameter.
This is the first time that I have tried to determine the casting dimensions as related to the mold dimensions and I realize that much more testing should be performed before adopting the conclusion that this one test implies. The implication is that, from an aluminum mold, Bullets cast from Lyman #2 alloy will be of the same diameter as the cold mold cavity.
According to ratios that were calculated from the shrinkage data found in Lyman's Cast Bullet Handbook, If the Lyman #2 casts at 0.3835" then:
Wheelweights should drop at 0.3829",
Pure Lead should drop at 0.3823",
Linotype should drop at 0.3922" This is larger than the hot bullet cavity measured.
This anomaly further points out the need for further testing to determine precisely the relationship between cavity size and casting size.
Someone with more sophisticated measuring devices than I posses is needed to enlighten our present knowlege concerning the relationships.
Perhaps the new thread you are going to start will shake some knowledge out of the bushes.
Where did, or how did you arrive at the .3922" figure for linotype? Was it a percentage increase over the Lyman #2?
At issue for comparison's sake among members here is measureing ability, alloy difference, casting temp differences (both alloy and blocks), and WHERE the cavity could be measured.
Taking the last first, it's going to be pretty simple in that measuring in the ID of a plain base boolits cavity base band would be the only viable place. Secondly we're going to have to accept a .001" variance, as most casters would have a dial guestimator accurate to a thou, even though it can split lines.
If the purpose of this thread is primarily for the Lee custom runs then the measurements would also need to be done on aluminum mould blocks? Alloy temps are going to have more of an effect on aluminum then iron or steel moulds, I would think?
Buckshot - Thanks! That was (obviously) my starting point and is good to have included in one convenient place.
You've added another variable - mould material - aluminum, ir'n, or brass. And you've raised the issue of the level of ability (equipment/person) to measure accurately. That raises the related issue of What level of change makes a difference? Which could well be addressed in another thread.
I assume from your handle that you're the Dale53 that posts on ASSRA forum, which means that you're into Schuetzen. Further assume that we haven't met but could have, as Charlie Dell lives about 30 miles north of me.
Good point on the closing pressure on the mould. It would be a simple matter to rig a fixture on the table with a toggle clamp to hold the mould closed. Then it could be used for all moulds.
01-30-2006, 01:37 PM
The percentages of expansion were obtained from the information published in the Lyman Cast Bullet Hand book and then applied to the measurements that were made from the castings produced with the Lyman #2 alloy.
The Lee 357-250-RF mold was used expressly because it is aluminum and also the diameter is nearly the same as the group buy mould that generated this discussion.
My old Mitutoyo dial caliper has been used for so long that, by being careful, measurements of 0.0005" can be made as accurately as the electronic digital caliper which reads to 0.0005". The dial caliper gets more use as the electronic will occasionaly lose its zero and does not inspire a high level of confidence in the readings.
It was also determined that varying pressure on the mold handles will easily cause a difference in the measurement of the mold base band cavity of 0.0005", So a large pair of vise grips was used to gently grip and lock the mold handles when the hot and cold measurements of the base band cavity were made .
I realize that these methods are, at best, makeshift and hope that we can eventually find and evaluate data obtained with more sophisticated measuring devices and methods.
02-05-2006, 01:39 AM
................We need some folks with aluminum moulds (preferably PB) to mike the base of the cavity and then dropped boolit's bases. Info needed is mould cavities base diameter, cast boolit's base diameter and BHN or alloy, or best guess as to alloy.
Doesn't matter if you're interested in this group buy or not. Merely seeking shrinkage info.
02-06-2006, 09:03 PM
Guilty as charged!
You idea may work well....
I consider Charlie Dell a VERY good friend of mine.
When I cast for Schuetzen, I will take ANY reasonable precautions to have as perfect a bullet as possible (if I were shooting in CBA matches with a bolt gun, I would do the same).
However, there is little need for that kind of precision when casting pistol or revolver bullets as is highly doubtful that the pistol or revolver will or can make use of this level of precision. I still work very hard getting really nice bullets, but I am happy with +or- .6 or .7 of a grain. That is relatively easy to do with normal use of a multi cavity mould (it will be interesting to see if I can maintain those tolerances with a "Group Buy Mould" - may not be able to). I do demand good bases and fill out for even pistol bullets (it may be overkill but I do it out of pride, I guess :razz:
However, I have a couple of TC Contender barrels that CAN use better bullets. I treat those like rifles.
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