How to make Lyam Foster slugs accurate
Found this off another site posted by a gentleman called "SluggerDoug". I always suspected that if you could expand the skirt of this slug, that accuracy may improve. Great read:
I am not sure many guys are interested in this slug anymore, but it may be a fun read for some who are working hard on their own slug projects.
I thought I would go crazy trying to get these slugs to work, but it was 2 years of frustration and then big celebration. This was about 25 years ago and I loaded 100's of these for myself and friends, till I started to use BRI's
I started to load my own Foster style 12 ga slugs in the late 70’s , using a Lyman mold and roll crimp in 2 ¾ slug casings. It was a long hard learning experience just to get to factory like accuracy. But eventually, I got better then the best factory accuracy (at the time) and better field performance on deer. Out of a good smooth bore with a scope, 5 shots would group into 3 inches at 75 yds.
I believe the secret to an accurate Foster style slug (esp. in a SB) is that it must expand rapidly and evenly in the CARTRIDGE as it is fired. The slug expands its outside diameter by collapsing in length by the force of the powder behind it and weight of slug front section and the resistance of crimp ahead of it. It then has to enter the forcing cone concentric to the bore. If it has expanded properly in the case/chamber, it will swage down to a perfect bore size and be quite accurate. If the nose is not concentric or the base is at an angle to bore the slug will not be accurate. This became apparent when I retrieved fired slugs from a snow bank behind my back stop one year. They were about half their unfired length and were a perfect fit in the bore of my gun. These were factory slugs and I could tell the accurate Winchesters from the poor performing Federals just by looking at them, the Winchesters at that time had a star on the nose. The Win. Nose and base were square to sides but the Feds were at and angle. I felt the Wins used a faster burning powder as the recoil was a quicker jab and less flame came out of the barrel, but that was just my guess at the time. Dissecting loaded rounds showed the Winchester slug to have a larger base diameter and a thick hard card under the slug, Federal lacked any HC, the slug was on top of a fiber like wad. So I tried to duplicate the Winchesters as best I could.
WHAT I DID WAS,
1. Slugs must be cast very soft, use pure lead. (Or as close to it as possible, cable sheathing, lead pipe)
2. Slug must be loaded concentric in cartridge case with roll crimp centering nose and holding slug firmly in place. The best way to do this is make slugs fit snugly in the cartridge case, their diameter should be .725 -.740 diameter. The undersized .690 cast slug will certainly expand to fill the inside diameter of the shell case when fired, but the trick is to do this while staying concentric (in line) with the bore.
( I did this by roll knurling the Lyman slug up to about .735 diameter. As cast it was about .690. I fit the slug on a pin shaped like the molds plug, the pin was pressed into a ball bearing mounted on a plate. A pivoting lever had a hand crank with a helical gear mounted inline with side of slug (when on the pin). By pivoting the lever to engage gear into side of slug and rotating crank once or twice it engraved “rifling” on side of slug, expanding the slugs out side diameter. This was controlled by an adjustable stop for the lever. For lack of a better term I called it a “slug rifler”. I never tried other methods but would see if just expanding the base diameter to about .735 with something might work, it would be slightly bell shaped, but much simpler then what I did
I do not believe this “Rifling” caused the slug to rotate, but besides making the undersize slug larger in diameter to fit the case, it made its side walls weaker and easier to collapse and expand quickly when fired. Plus it looks cool ;o) 3. Use a substantial Hard Card column under slug, ¼ to ½ inch tall. Then a fiber wad column that compresses easily under the HC. I used a BPGS or cut a AA wads gas seal section off, for over the powder wad. I used Circle Fly wads for the HC and Fiber. I ended up using 4 .125 thick HC and 1 fiber wad, 1/2 thick and a gas seal.
4. Use a near max. charge of fast burning powder to help expand the slug in cartridge quickly. I had good results with IMR 7625 and WW 571.
5. I gained some accuracy by filling the slugs cavity with dense granulated plastic.
6. I was able to cast heavier slugs by placing a small washer under the moulds shoulder screw that he cavity plug locks into, I found 1 1/8 (495 grain) shot good out of a SB, and plowed through brush better then the 1 oz. Long range penetration on large deer was also improved. Anything heavier then that seemed to only shoot good out of a rifled barrel.
7. A good tight roll crimp is important, but I found I did not need once fired cases. I would put Crossman Co2 cartridges in the empty case mouths for a few days prior to loading and got good crimps even after 3-5 firings.
*. If you don’t get good accuracy you must try to recover some slugs to see what is going on, soft back stop at the farthest distance you can should work.
8. I pan lubed my slugs when I switched to rifled barrels to keep leading down, but never tried lubed slugs in a smooth bore. The lube filled the grooves of the “rifling” and I used an empty case with primer out and a plunger inserted thru hole to cut slugs from lube pan and just push plunger to get slug out of case. Using a rifeled barrel and hitting deer with the same load as I had in a smooth bore showed improved shocking power, the rotating slug must transmit hydralic shock when it hits!
Doug
