how much varation in weight should I be getting when casting bullets

[rojo]

hi guys , how much varation in weight should I be getting when casting bullets ??
taking into account termal expansion of the mold ,, what should I expect ??
and how should it affect accrucacy ??

[onondaga]

My match bullets are plus or minus 1 grain. What is left from the batch that is either heavy or light is always less than 10% of the batch. Many things are much more important to accuracy than exact bullet weight match.

Plus or minus 2 grains error or more is usually related to casting skill, mold handling problems/maintenance , and alloy problems.

When I start with a new caliber or new mold working up loads for accuracy I don't even start to weight match bullets until the load groups less than 1 inch at 50 yards.

Gary

[MikeS]

Gary:

When you say mould handling problems, what do you mean? Generally when I cast these days I can get most of the boolits to stay within one grain from each other, but I do get an occasional light or heavy boolit. I've also noticed when I start getting frosted boolits they usually are light weight as well.

The last time I was casing 311041's I cast 150 of them, and had most of them at 172gr but had like 10 that were at 169gr, and a couple that were 176gr. The light ones I can understad, possibly a bubble in the boolit, or something else like that, but why would I get just a couple that were substantially heavier than the rest?

[cbrick]

Plus or minus 1 grain could be a pretty broad statement, it depends on the weight of the bullet your talking about.

Its a percentage of the whole. Are you talking about a 450 grain 45 caliber bullet or 45 grain 22 caliber bullet? 1 grain variation of a 450 grain bullet is a far smaller percentage of the total bullet weight than is 1 grain of a 45 grain bullet.

Effect accuracy? All depends on what your shooting, low velocity short range rounds shooting 3 inches at 25 yards won't be effected nearly as much or possibly not at all compared to a 2200 fps rifle that is used for shooting 200 yard groups from the bench with the same percentage of weight variation. You didn't give us any information so there is no way to know how much or even if your accuracy will be effected. We don't know what bullet your casting or how much variation in weight your getting, how fast your shooting this bullet or at what range.

If your concerned about casting more uniform weights during a casting session its the rythm of casting, a consistent and proper mold temp and reasonably consistent pot temp. Even if you pre-heat your mold on a hot plate your first few pours will probably be your lightest bullets. If you do not pre-heat the mold your first 12-15 pours should be the lightest.

Bottom line, if you work on acheiving a good casting rythm and a proper mold temp your weight variation should come down and the quality of your bullets should improve regardless of the bullet your casting.

Rick

[onondaga]

Mike, I can point out mold handling problems of my own that cause weight variation. During a casting session I noticed that I began to get very slight finning on bullets at the mold parting line. The mold wasn't closing completely because a guide pin had gotten some lead on it. This caused boolits to cast several grains heavy until the problem was fixed. On another occasion a splatter on the vented area of a block did the same thing and caused heavy boolits.

I have noted light boolits when using a particular old mold of mine that has no vents, My swirl casting method has to be perfect every time or I get hot spots that shrink or voids from poor venting when alloy gurgles entering the sprue gate dead center instead of an off center pour that leaves an easy air escape during the pour.

I have had carbonized chunks from stick-on wheel-weight adhesive get into cast round ball boolits when I get near the bottom of the pot and this causes bullets to be light.

A few years ago I taught a friend to cast and he repeatedly had his boolits get heavier toward the end of the pot because he ran his pot too hot and he was continually skimming skimming off and discarding his tin until I lowered his pot temperature and got him to increase his casting cadence by not inspecting every boolit when he dropped it from the mold. He was only dropping only once or twice a minute and running his pot very hot.....I'd call that a casting skill problem.

Boolits that are wrinkled or have poor fill-out due to an insufficiently warmed mold or slow cadence can be significantly light... again casting skill.

Some of my large caliber/heavy boolit molds require me to increase the flow rate adjustment on my Lee 4-20 bottom pour as the pot level goes down or I get poor fill-out and light boolits.

If I overheat a mold at the start of a session, my boolits will be severely frosted and light in weight.

Oil in a mold will cause cratering of the boolit surfaces and those boolits will be light in weight.

I tried a tip from a member here that didn't work for me. Tapping or jiggling the mold before the sprue puddle solidifies to get better fill-out; maybe that works for him, but for me---my boolit weight ran all over the place casting 12 ga slugs and trying that jiggle trick to get better fill-out on the big slugs. It didn't work for me. That problem was solved by cleaning out my pot spout and getting my flow back to maximum.

Gary

[MikeS]

Gary, thanks for the info. It more or less confirmed what I was already thinking. One thing I noticed when using the 4-20 with Lyman double cavity moulds that if I pour right between the sprue openings that I fill both cavities at the same time. This only works with moulds that have the newer thicker sprue plates, as the larger opening in them makes it easy to pour right in the middle, whereas the older thinner sprue plates have too much space between them to do this. I just ordered 2 new sprue plates from Midway for just this reason.

[fredj338]

Depends on the bullet size. Larger bullets can tolerate a larger % of variation. FOr my practice bullets, I don;t weigh them, only cull the bad bases. For match or hunting bullets, I weigh them & allow +/- 1/2% from average wt. A large swing in a bullet wt is likely an internal void. Not much else it could be if it varies by more than 1% w/ the same alloy & sim casting temps.

[pdawg_shooter]

I allow a total of 1%. A 400 grain bullet is acceptable form 398 to 402.

[hydraulic]

I cast up 103 bullets from the RCBS 45 - 530, today, and wound up with :

2 @ 526
8 @ 527
8 @ 528
12@ 529
27@ 530
28@ 531
14@ 532
4@ 533

This gives me 69 bullets from 530 to 532 which I set aside for BPCR matches, and 34 others I will use for my twice weekly practice sessions at 100 @ 300 yds. I shoot over cross sticks and, ususally, I can keep 20 bullets inside the 9 ring which is 4 inches wide with my Shiloh .45-70 at 100 yds. Over the bench it will shoot three in an inch and a quarter. At Alliance two weeks ago I shot 9th in my class of 19 seniors, and 35th out of 70 shooters overall. I'm 73. I go to the trouble (fun?) of weighing my bullets, but truthfully, I can't tell a bit of difference between my match bullets and my practive bullets, and if I had to I'd use my practice bullets in a match and never worry about it.