Flat bottoms. How Flat?

[shooting on a shoestring]

Working with 225438 in my .22 Hornet, #3 Ruger. Using Lil'Gun or H110 to drive them about 2500 fps. I've seen groups about 3" at 100 yds with occassional 1.25" groups followed by more 3" groups, then some 4" or worse, then some 1.25" etc...

I'm thinking it may be how flat the boolit bases are or are not. The fill hole in the sprue plate is almost the same size as my boolit base. If I cut it early, the base tends to smear, if I cut it a little later, the base tends to pull before the sprue pops. Either way the base gets slightly deformed. I get maybe 10% that look to have perfect bases. I see about 10% of the groups in the 1.25" range. I'm currently high grading a batch of boolits to get the 10% that appear to have perfect bases and I'll see if they group more consistently.

The little #3Ruger is the only cast boolit rifle I am currently using with a scope. My other cast boolit rifle is an open sigthed Model 94 in 30/30. I Shoot only 4 to 6 inch groups in the Model 94 and thats as close as I can see with iron sights. So I don't know how flat boolit bases have to be to shoot about an inch at 100 yds. I suppose perfectly flat bases are what Hoch moulds are about. But in terms of base pour moulds, can someone give me an idea of how flat rifle boolit bases should be?

[Ben]

Have you tried closing the sprue plate so that only 1/2 of the hole is allowing molten metal to flow into the mold. In essence the sprue hole is sitting on the edge of the mold cav. edge, not the center of the mold.

You can get a super smooth bases with this method.

Ben

[Bullshop]

The flatter the better. How do you cut sprues? Do you tap the plate over with something? If the plate is loose enough to swing freely and it should be and you tap the plate with a stick or mallet the plate can angle upward during the cut leaving an uneven base. The best way to cut sprues with a base pour mold to get consistantly flat bases is to cut the sprue hot using heavy leather gloves and holding downward pressure on the plate while turning it. I would suggest using bull plate sprue plate lube for this. Mainly because it will allow you to cut the sprue while it is soft. Holding downward pressure on the plate will leave a perfectly flat base.
Another step I have found equally important especially with 22's to insure a flat base after the check is installed is to use a gas check seater to install the check.
Little things go a long way in making the little boolits shoot good.
Blessings!
BIC/BS

[shooting on a shoestring]

Gentlemen, Thanks for the thoughts. I do like the idea of experimenting with sprue plate askew.

Bullshop, Yep I have the sprue plate fairly tight and tap it open with a mallet. I'll take a run at running it looser and try your downward pressure while opening it early.

Ah the joy of casting. I can hardly wait to get to cast in a few evenings and try these ideas.

[Phil]

Shoestring,

You really need some of the Bullshop Sprue Plate Lube. I discovered it not long ago and its really fantastic stuff on molds (moulds). It will solve your 22 caliber problem by letting you cut the sprue very quickly so they come out nice and flat with no distortion of the boolit base. Plus, it makes a superior boolit lube. Get some! You won't ever want to be without it.

One more thing you can do is to make an aluminum sprue plate with a much smaller sprue hole. I've made several this way and it really makes a difference.

Cheers,

Phil

[beagle]

Another area to take a look at on .22 cast accuracy is the gas check fit. Are they staying on or coming off.

I've also found that small pistol primers enhanced accuracy./beagle

[HORNET]

Shoestring,
I gotta agree on the Aluminum sprue plate. I use 1/8" plate with about a 0.094 through hole to start with, chamfered to a good sharp edge at the hole. Leave it slightly loose and dipper cast using the dipper to hold the plate flat on the mold. Probably a good idea to coat it with Bullshops Plate Lube or graphite or molyD spray for clean release. Run the pot temp up to about 750, pour 'em, cut the sprues when they turn color, and keep up a fairly quick tempo. If you really want fun, push them ahead of about 11.5 gr of IMR4227 with a warm primer (I use R-P 7-1/2). You might have to open the hole(s) up a little if you can't get them to fill.
As a bit of pure heresy :holysheep, I've been casting those .22's with a small radius on the corner of the base that goes inside the gascheck , about .015" or so. Doesn't seem to hurt grouping a bit but still experimenting to confirm. I'm using the size of the radius to indicate when I need to speed up or slow down:twisted:.

[shooting on a shoestring]

Another busy evening w/o casting. But, another couple of good thoughts, yep I'll bet I try the aluminum plate with a smaller hole. As for plate lube, I use an old stock of Dri Slide leftover from our machine shop. It works wonders on sprue plates and mould tops.

I've also decided to shoot some of my culls backward, let the slightly deformed base become the nose, and the beautifully rounded nose become the perfect boat tail. I'll be anxious to see the results. They might make great skunk thunkers with maximum meplat for .22. I do end up shooting a couple of skunks per year out of my yard (I try hard to get them before my pair of Jack Russell's do).

[shooting on a shoestring]

P.S. Beagle, Yep GCs are a very tight snap fit going on, and after the lubrisizer, solid. But thanks for thinking.