RCBS Sprue Plate Retaining Bolt Annoyance

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RCBS Sprue Plate Retaining Bolt Annoyance

Post by jmoore »

First time using a RCBS mould, specifically the 140gr 7mm assembly. Did a test run using linotype and had a couple of dramas.

First, my usual generous sprue puddle would regularly get up against the hex nut that retains the sprue plate and commence to unscrewing said nut a bit when the plate was opened! Very annoying, and afraid to tighten the wee set screw that supposed to keep this bother from happening any more. Hasn't been a problem with my Lyman or Lachmiller moulds. Or even the Saeco 32-20 mould which has a hex nut, too, but it's weirdly placed.

The other drama was the reluctance of the solidified sprue puddles to disengage with the sprue plate! Even when the puddle was well away from the retaining bolt. Bullets fell out quite easily. But almost had to pry the excess off the top.


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Re: RCBS Sprue Plate Retaining Bolt Annoyance

Post by 260 Striker »

With a cold, empty mold, tighten the sprue plate bolt until tension is what you like. Remember, sprue plates will loosen a little when the molds get hot. Take a felt pen and make a mark on the top of the bolt inline with the set screw. Remove the bolt and eyeball where the set screw meets the side of the bolt. Take a small file and file a flat spot where the set screw will contact the bolt. Just enough so the set screw has a flat spot to seat against. Install the washer, bolt and snug the set screw against the flat spot you just made. This should keep the bolt from backing out. I also have difficulty dropping the cut sprues some times when using linotype. I coat all surfaces of my blocks and sprue plates with NEI Mold Prep and this helps a little with releasing the cut sprues. Linotype seems to be the worst since it shrinks the least. I have also slowed my casting down to let the sprue set a little longer and that also helps release it (sometimes). I have even filed the sides down on the sprue plates if they have jagged edges since the sprue overflow seems to bite into those edges and don't want to release the sprue. Some days everything works great and other days I have fits. Just part of casting I guess.
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Re: RCBS Sprue Plate Retaining Bolt Annoyance

Post by jmoore »

Thanks for the input! Whilst cutting the flat, the hex may get some attention as well. As in turning it round! A small slot on top ought to do for re-install.

The sprue's reluctance to release may prove to be the more vexing problem.

Since the mould casts fairly large, wondering if throwing in some reclaimed range lead would reduce the size significantly without going too soft.

First time casting bullets this small in diameter and intended for higher chamber pressures and velocities.

Wondering if it's time to finally get "store bought" lead of known alloys! The 20 or so pounds of linotype was salvaged from an old print shop years ago, and most of my other lead is old bullets.
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Re: RCBS Sprue Plate Retaining Bolt Annoyance

Post by high standard 40 »

Linotype may be a little much for your 7mm. I have had great success with Hardball alloy (92-6-2). I'm pushing that over 2000 fps with no problems. I have made the jump to foundry alloy for all my silhouette usage, that being the Hardball alloy I mentioned. If you have any wheel weight alloy you could try mixing that with the Linotype for a good useful alloy. When you say that your mold drops a "large" bullet, what exactly is the diameter? My RCBS mold always dropped a bullet too small. Have you slugged your chamber? Fit is king with cast bullets. I have several 7mm guns and none of them need a bullet smaller than .286" Your goal should be to size the bullet drive bands to be a snug fit in your chamber throat.
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Re: RCBS Sprue Plate Retaining Bolt Annoyance

Post by 260 Striker »

You might try using wheel weights and dropping the bullets out of the mold directly into a bucket of cold water. I have used this in my TCs and didn't cause any leading. I don't drive my cast bullets very fast, probably 1700 fps at the most, with no problems. Another trick with the RCBS 145 (and 168) mold is to push bullets nose first into a .277 H&I die till they touch the driving band. This usually will just smooth out the parting line and allow you to seat the bullets further out in the cases. If you feel you need a heavier bullet for rams then the RCBS 168 is the way to go. It has the same exact nose profile as the 145 so you don't need to adjust your seater die if you use the 168s. These two RCBS molds are very accurate in any of the 7mm cartridges I have tried them in (7BR, 7IHMSA, 7-08, 7-30W and 7TCU). I think you will find your sprue problem goes away or at least won't be as bad when you switch to another alloy.
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Re: RCBS Sprue Plate Retaining Bolt Annoyance

Post by jmoore »

Tried the 0.277" die and got the bullet so stuck it required removing the assembly from the Lyman 450, then pressing it out in a vise! Even with bullet lube applied beforehand! Will try again later....

I did note that there's an unsized area extending about 0.100" forward of the driving band which tapers off for about another 0.100". However, the sized portion will now squeeze into the bore at the muzzle end of the TC.
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Re: RCBS Sprue Plate Retaining Bolt Annoyance

Post by jmoore »

So, mods:

Image

Image

Did an undercut to the hex, and a quick polish to the sprue funnels.
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Re: RCBS Sprue Plate Retaining Bolt Annoyance

Post by high standard 40 »

I have two Lyman 450s mounted side by side. Since 95% of all my cast bullet shooting is 7mm one of them stays equipped with the .277" die. My process is to size the drive bands and lube first, either .286" or .287" depending on the gun, then I size the nose in the .277" die. I did add some taper to my .277" to prevent shaving any lead and I apply a small amount of Lee case sizing lube to the bullet nose of about every 5th bullet that I size. If your nose die was dry, I can understand a bullet getting stuck. I have seen that problem before with a new unlubed die.
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Re: RCBS Sprue Plate Retaining Bolt Annoyance

Post by jmoore »

First real run of the RCBS 7mm-145s:

Image

While weights were pretty consistent, only one that was well under the pack by about 2 grains, the base fill was variable. Random as to cavity which would have rounded edges. Even when "force fed" molten lead to the point that vent line whiskers were everywhere, the bottom of the bullets just didn't want to fill out. But the next cast might be fine! Venting problem?

Image
Just had to weigh 'em! Very close to nominal weight using linotype.

Sprues still sticky. Thinking now that the very rough texture of the sprue plate top is the drama.

What do y'all use for alloy when running 7mm bullets? If relatively hard, I reckon it may be time to get "store bought" lead from somewhere.
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Re: RCBS Sprue Plate Retaining Bolt Annoyance

Post by 260 Striker »

Nice looking bullets. I think you will find a 2 grain variance to be nothing as far as accuracy. That is only 1.3 percent difference. I never weighed my cast bullets but inspect for fill out and accuracy seems to be the same. I have used WW in 7TCU and 7INT with no leading but I don't go for max velocity just accuracy. If you worry about using WW then water drop them and you won't have any leading problems. You might try loosening up your sprue plate a little. I have some molds that I can swing the sprue plates on an empty mold back and forth and that seemed to help with base fill out. Other molds I tighten down the sprue bolt more and they work OK. If a little loose it seems to help venting at the bases. As long as you don't force pour with a loose sprue plate you shouldn't get any finning on the bases. Just have to experiment a little. I also run my pots on the hot side and get frosted bullets but that just means they are filled out more than using a colder mold. Frosted bullets are just as accurate but maybe not as pretty as yours. Sounds like you will get it solved soon since you are getting some nice looking bullets now.
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