SluggerDoug
02-09-2008, 12:23 PM
Old story but some of you guys might be interested in it.
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 (availble 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. Some SB guns shot it better. Here is the short story,
I believe the secret to an accurate Foster style slug (esp. in a Smooth Bore) 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 I think I 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.
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. (37 grains of IMR 7625 with the 1 oz slug in the 2 ¾ load was very nice, Lyman gave 1575 fps for its velocity, probably out of a 28" barrel)
5. I gained some accuracy by filling the slugs cavity with dense granulated plastic. This helped to assure the Hard Card under the slug did not blow into cavity of slug and it made the fired slugs cavity a bit bigger, making for slightly longer side walls touching barrel.
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 used a drill press to roll crimp my slugs and felt it helped accuracy by making the crimps more uniform. I would hold the shell loosely on DP’s table and drop the spinning crimper slowly on to shell mouth till shell spun slightly in my fingers and found its center. Then griping shell tighter I would lower crimper slightly and hold for a couple seconds while it heated shell mouth slightly, and then I ran the crimper home. That said, a friend who also loaded these slugs got reasonably good results with a hand drill.
9. 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.
Doug
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 (availble 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. Some SB guns shot it better. Here is the short story,
I believe the secret to an accurate Foster style slug (esp. in a Smooth Bore) 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 I think I 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.
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. (37 grains of IMR 7625 with the 1 oz slug in the 2 ¾ load was very nice, Lyman gave 1575 fps for its velocity, probably out of a 28" barrel)
5. I gained some accuracy by filling the slugs cavity with dense granulated plastic. This helped to assure the Hard Card under the slug did not blow into cavity of slug and it made the fired slugs cavity a bit bigger, making for slightly longer side walls touching barrel.
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 used a drill press to roll crimp my slugs and felt it helped accuracy by making the crimps more uniform. I would hold the shell loosely on DP’s table and drop the spinning crimper slowly on to shell mouth till shell spun slightly in my fingers and found its center. Then griping shell tighter I would lower crimper slightly and hold for a couple seconds while it heated shell mouth slightly, and then I ran the crimper home. That said, a friend who also loaded these slugs got reasonably good results with a hand drill.
9. 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.
Doug