Cast bullet weight variance-how far?

[6622729]

Playing with my AR15 in 300AAC, I use the Lee C312-155-2R from a 6 cavity and like the results. Now I have time to fine tune a little. I made a sample run from just a single cavity of my 6 cavity mold to remove the potential that the cavities are not identical. I think I buy into the idea of casting from single cavity for best accuracy potential. I was actually impressed with how fast it went. Anyway, I weighed the 20 to 25 sample bullets and found a median weight around 149.7gr. I used a maximum acceptable variance of +-.3gr which caused me to cull 5 bullets. My absolute heaviest bullet was just over 150.0gr and the lightest was 149.3. How tight a tolerance makes a practical difference?

[stubert]

1% is ok by me.

[centershot]

That's pretty tight tolerance, no doubt they will fly true. But, your reject-rate is 20% (YIKES!). I cast the Lyman 311041, a 173 gr FP, and hold =/- 1.0 grain. Works for me, and as stbert said, 1% is good!

[petroid]

I have found increased accuracy by weight sorting boolits but I'm still hovering in the 2 moa zone, so there are other factors I need to sort out

[5Shot]

For group shooting I weight sort +/- .2 grains, but I don't cull those that fall outside the range. I separate them and use them in a different group. As long as they are all shot in the same group, they produce excellent accuracy. A sample size of 20 something is really small, so a high reject rate isn't unexpected. If you had a high reject rate with a sample of hundreds, then you have issues.

Overall bullet weight is a factor too - small bullets should have a smaller variance.

[dudel]

For group shooting I weight sort +/- .2 grains, but I don't cull those that fall outside the range. I separate them and use them in a different group. As long as they are all shot in the same group, they produce excellent accuracy. A sample size of 20 something is really small, so a high reject rate isn't unexpected. If you had a high reject rate with a sample of hundreds, then you have issues.

Overall bullet weight is a factor too - small bullets should have a smaller variance.


This ^^^^ You get accuracy (or repeatability) from consistency in components and technique. You could have a wide grain variance (with good bases, and no voids), and as long as you segregate them, load and shoot them together you POI should be consistent within the group (if you are doing your part, and the rifle is capable).

[6622729]

My 20% cull rate based on weight is mostly a function of pour technique and mold temp. I only made about 25 pours with a preheated mold so the temps didn't have a chance to settle down either in the mold or the pot and I had no rythem pouring just a single cavity. That will improve for sure. As for there being other factors that effect accuracy, I get that. I'm doing really well with 15.4gr of W296 and my other components from the 6 cavity Lee mold. The single cavity and weighing each bullet seemed the next place to get sorted out, pun intended. lol.

As someone mentioned, I didn't discard the 5 bullets that didn't land within the limits, I have a jar of bullets from my last session that is of all 6 cavities. I tossed them in there as they were good castings. I'll use them up for general plinking. If I see any improvement in accuracy using this sample single cavity and grouping the bullets by weight, it'll be single cavity casting for me from here forward.

[Mk42gunner]

Since I mostly plink and play around with cast loads in rifles, I am not concerned with the last little bit of sorting to the last few tenths of a grain. I will weigh a few boolits when I first get a mold, or when changing alloy lots; just to see how close to nominal the mold throws.

However, I can see the point, if the rifle and shooter are up to holding ½MOA groups.

You really need to check all six cavities from that mold, you might be surprised at how close they are. I would suggest marking the cavities so you can sort boolits easily after casting if there is a difference larger than your desired spread. Using one cavity out of six strikes me as being a very inefficient use of resources.

Weight sorting boolits is one place I can see using a digital scale.

Robert

[6622729]

Since I mostly plink and play around with cast loads in rifles, I am not concerned with the last little bit of sorting to the last few tenths of a grain. I will weigh a few boolits when I first get a mold, or when changing alloy lots; just to see how close to nominal the mold throws.

However, I can see the point, if the rifle and shooter are up to holding ½MOA groups.

You really need to check all six cavities from that mold, you might be surprised at how close they are. I would suggest marking the cavities so you can sort boolits easily after casting if there is a difference larger than your desired spread. Using one cavity out of six strikes me as being a very inefficient use of resources.

Weight sorting boolits is one place I can see using a digital scale.

Robert


I appreciate the comment about inefficient use of resources but I'm looking for removing variables so using one cavity and weighing each one is my best effort for consistency. As for a digital scale, I have the Redding model 1. I set it for 149.7 and can quickly determine weights from 149.2 to 150.2 without moving anything. I don't trust the digital scales due to drift. I use very expensive digital laboratory scales in my work and even they can drift.

[hutch18414]

I would suggest reading the "Consistency in Casting " thread by Goodsteel. Too bad he got banned.

[karlrudin]

I usually take my bullets that are poured in a session which average 200+ for 7mm. Separate them by bullet quality first, wrinkles, voids etc. Then check the bottoms. Then start weighing them. Size, gas check, tumble lube then weigh them again. Separate them to a 0.1 variance. Seems to help. I think my case is just OCD because I do my cases the same way. Everything consistent and ready to go. Then the group opens for no reason. The Silver Stream has a mind of its own :)

[Digital Dan]

Would suggest that exercising OCD is best rationed in accordance with objective. Don't scrap bullets with minor deviation, segregate into separate lots. IMO .3 grains is OK for shorter ranges or arms that are not terribly precise such as military style autos. If one is shooting very long range go for zero spread on the weight within each segregated lot.

[Duckdog]

I usually do not weigh them unless something gives me cause to do so. I get good groups, so I just shoot away! With that being said, every now and them I will spot check them to make sure my alloys are not throwing light bullets.

[6622729]

I usually do not weigh them unless something gives me cause to do so. I get good groups, so I just shoot away! With that being said, every now and them I will spot check them to make sure my alloys are not throwing light bullets.

I get good groups with my 16" Hbar 300AAC too and thought I was at the limit of "me" until last weekend when I shot my new build 20" barrel .223 Wylde. Using commercial reloads in random brass I shot even better groups. I cast for 300AAC supers (1850fps ish) so now that I know I can shoot better than I was giving myself credit, I want to try to tighten it up a little. I cast another 110 bullets using the same single cavity last night and didn't have to discard a bullet after the first 5 to get things flowing.

In regards to the person who said I should group the bullets allowing for NO weight variance, is this textbook or are you a long range shooter and have experience doing this?

[Texantothecore]

I just started weighing my bullets and my casting has improved dramatically. Now down to +- .3 grn on an 82 grn roundball and my shooting has improved. Somewhat smaller groups.

[Shiloh]

Less that 3 grains on a 200 gr boolit.

Shiloh

[quilbilly]

I have been shooting the Lee 160 gr RNGC for years and do random samples of four or five groups of 3 at a time. As long as the groups are within 2% of each other and the mold fillout is OK, my accuracy in my 308 has remained below MOA. Most of the time the weights are under 1% variability in a single run. I do my own alloys so this group weighing is also how I check my alloy. My "160's" usually come out to about 165-166 on average.

[Digital Dan]

I get good groups with my 16" Hbar 300AAC too and thought I was at the limit of "me" until last weekend when I shot my new build 20" barrel .223 Wylde. Using commercial reloads in random brass I shot even better groups. I cast for 300AAC supers (1850fps ish) so now that I know I can shoot better than I was giving myself credit, I want to try to tighten it up a little. I cast another 110 bullets using the same single cavity last night and didn't have to discard a bullet after the first 5 to get things flowing.

In regards to the person who said I should group the bullets allowing for NO weight variance, is this textbook or are you a long range shooter and have experience doing this?

Segregating bullets into zero variance lots is not magic. One will have something akin to a bell curve weight distribution in any lot of cast bullets. If you have 32 out of a 100 with the same weight, make a lot out of them. Don't mingle the lots when shooting LR. In answer to your question, yes, I have experience with LR shooting. I've never read of this in a book, but I'm not the only 8-ball that does it.

Do you have to do it the way I suggest? Nope.
Do I do it for all my guns? Nope.
Do I do it for handguns? Nope
.30-30s? Nope
.44 Mag paper patch? Nope
.30 Sneezer? Nope
BPCR and slug guns? You betcha.

[karlrudin]

No I'm not shooting long range but I'm shooting for score and group. in C.B.A. shoots