View Full Version : cast boolits weight tolerances?
05-23-2007, 10:12 AM
I'm a rank newbie to the CB ranks, Have some good experience with .45ACP and cast boolits reloading and want to try the CB in my militatry rifles. What is a reasonable expectation for weight variation with cast bullets? I have purchased different calibers from different sources and see a great variety of weights, i.e. up to 8 grains of difference for the same batch of bullets. Is that normal? Can some of you veterans give me an idea of what is a standard deviation for cast boolits?
Thanks for your help!
05-23-2007, 10:23 AM
After spending countless hours sorting boolits by weight, I finally came to the conclusion that a good visual inspection is all that is needed. What I did learn is that my non-reject boolits weigh within 1% of the norm. For a typical .30 caliber rifle boolit of 180 grs., thats 2 grs. of variation. Pay close attention to the boolit bases, that is the most likely spot for a flaw that will affect weight and uniformity, and is the easiest flaw to miss during the inspection.
An interesting experiment is to use some reject boolits and compare groups and POI with acceptable ones. There is surprisingly little difference.
05-23-2007, 10:31 AM
That is correct for all play and most hunting guns. For competition, the air bubbles get you fairly consistently, and depending on where the bubbles are amounts to what your grouping accuracy will be. If the bubbles are mostly centered, then OK for all circumstances, but the problem remains to decipher where the bubbles are. If they are more towards the edges, the grouping accuracy will wane more severely. The only practical measure is to shoot that batch after holding the weight variation to less than 0.25 percent for a BR match. ... felix
05-23-2007, 12:35 PM
Thanks Guys, I appreciate the information. I try for 1/2 grn or less with copper bullets for BR shooting so hopefully I can get similar results with cb. As to the bubbles or voids in cb, now realize I'm green as a gourd about cast boolits, but could you apply a high frequency vibration to your mold when it is cooling to drive out entrapped air or fill voids?
05-23-2007, 12:41 PM
Eight grains? Hokey smokes, Bullwinkle!
I weigh match boolits only to a 1% max tolerance - that's +/- 1.0 grains for a 200 grainer. Since I started doing that several years ago when I got an electronic scale, flyers have reduced to near zero. If one goes wide now, I am pretty much certain it's me. If I were shooting BR I would go with Felix's recommendation - 0.25%.
I regularly shoot my rack grade 03A3 in the high 90s (lots of 98s with Xs) on the SR21 at 100 yards. Groups are almost always under 3 inches with an ocassional group going under 2 inches. So, to me weighing a match boolit is worth the extra few minutes of work.
I also weigh just about all of my .22 boolits. Other than that, visual inspection while casting, lubesizing, and loading catch all I want to cull.
05-23-2007, 12:47 PM
Tackdriver, whar'yat? Fer y'all what ain't Okies, "whar'yat" means what town do you live in.
If you are anywhere near Coweta, come on out to Oil Capital on any 2nd Saturday for mil bolt match. Shooting starts kinda sorta promptly at 9 a.m. Fifty record rounds, off the bench plus sighter and bbl warmers.
05-23-2007, 12:51 PM
No, no! With BR swaged condom (jacketed) bullets, weight is not important unless you are talking more than 300 yards for the smaller calibers, and perhaps more than 600 yards for the larger calibers. The importance for these bullets is how they "feel" when swaged into final form. This is why you go to custom bullet makers for competing in jackpot BR matches. The feel must be consistent, making for the "hardness" at the lands consistant. Think ignition, ignition, ignition for this kind of accuracy because properly swaged bullets are inherently more concentric and have zero bubbles. Cast boolits by default will never be as concentric and the bubbles add to the errors. You measure weight in cast bullets in order to "find" those individuals with the biggest holes. ... felix
05-23-2007, 01:17 PM
The lightweights, yes. Those with the most air bubble or trash spot which is a different density from the alloy. Only problem is that if the boolit looks good, you have no relatively inexpensive way of knowing where that spot is under the surface short of destructive testing. Really it doesn't make any practical difference where the spot(s) is, because if it's there, it needs to be culled.
I remember one batch of boolits a while back that were just all over the place on weight. By chance I saw what appeared to be just a tiny spot on the base of one. Turned out to be a pin hole leading to a void. Checked some more by filing the bases down. Found lots and lots of irregular tiny voids. Only thing I can contribute that too was some kind of a venting problem. Never has happened since, at least not to the degree that it is noticeable.
Felix, come to think of it, that batch of boolits may have been one of the copper babbit experiments - you know how that stuff 'sheets' when in pours.
05-23-2007, 02:00 PM
Sundog, I live in the North end of Owasso. I get to occasionally shoot at the mil-match at Red Castle Gun Club. However, due to events with the G'kids, I am there on a erratic basis! I may get an opportuity to go to the Oil Capitol Club one of these weekends, Thanks for the invite.
I really appreciate all the input you guys have passed on, obviously this is a great site for learning!
05-23-2007, 02:25 PM
Corky, if the bubbles (voids) are uniform, then there is no problem for our purposes. We will never know how bad they are until we shoot them. But, that is true for any boolit. ... felix
05-23-2007, 08:18 PM
Geez Louise, Sundog! You're shooting an 03a3 in the 90's on the SR21? You sure know how to hurt a guy. I got an 83 once, back in the old days when I could see 100yds, but now if I can just keep 'em in the black I'm happy. Still shooting the same 03a3 but with a "C" stock.
05-24-2007, 10:51 AM
Hydraulic, yeah, and a shooting buddy who uses boolits I made does just about as well with his 03A3. My 03A3 came from CMP early on during the mass sell off. It looked like **** when I got it, but after finally getting down to bare metal and wood, well, by golly, the thing was a brand new rifle. Not a wear mark on it anywhere! I consider myself very fortunate, indeed! Not the best wood I've ever seen, but the thing is a real shooter.
Tackdriver, if you've never been to Oil Capital, you will be impressed. We have 35 covered fired points all with 100 and 200 yard target boards, and well spaced. Nice thing about the match is we all shoot the same firing order. No squading, no waiting. Besides the every 2nd Saturday, we also have a 4th of July match, what ever day the 4th falls on - Wednesday, this year.
edited: the mil bolt match is every 2nd Saturday (4th Saturday is high power, Mar - Oct).
05-25-2007, 07:02 AM
I do about the same as sundog with my Rem. 03A3 ( he can vouch for it cause my gun club bet the pants off his last year in the state mil bolt match).
My best score on the SR21 is 298 16X with one target being 100 6X, with cast of course. Shoot in the 90's with X count on a regular basis.
05-26-2007, 08:36 AM
How far are you boys from Tulsa? I make it down to Wannamakers show twice a year and have a daughter (the lawyer) in OKC. It's getting to where I have too much to mow in the summer and too much to shovel in the winter, so we're kind of looking at a possible relocate to the Tulsa area. A rifle range like that would be a real plus.
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