Having shot many a cast thru rifle barrels for measurements it becomes very obvious that what it takes to get a slug thru varies-- considerably.

I finally got around to casting some 175 Rapine spitzers which come out 311 for the bearing surface. Not having a dummy for seating I guessed at the length-- was too long and the bullet stayed put in the leade. No matter, I weighed up 3 grs of Blue Dot and fired at the bang box. Just the faint pop of the primer was heard meaning the bullet didn't complete the trip. 3 grs of BD shoulda shot thru easily enough, but that 311 into that 309 bore and the bullet freshly heat treated... made for some strong resistance. Tapping it out revealed it made only and inch or so.

Now this spitzer has a nice, wide forward driver.Really holds the burn back for those few precious milliseconds [a small fraction of that actually] for a good burn to develope. Means low ES's and accuracy with cast IMO. And I think that's why so much variation in cast performance is seen in many instances. So many of those designs have weak bearing surface ratio's and being sized to groove dia only promotes the problem.

Engraving resistance. Anyone heard the term before or did I coin one?

Yup, heard the word before. I always use a grain or two of bullseye, never stuck one.

Joe

Yep, again. 3 grains of BE is plenty potent! Use toilet paper over powder too. 2 grains of BE is very feable, but should push it through unless, like you say, the lead is really tough. ... felix

Felix,

That's what I use, between 1.5 to 2.0 grs depending on the case. Real small case gets less.

Joe

Aladin's point about a very sturdy heavy first band giving a lot of start resistance (it being a good thing for low SD and improved vertical stringing accuracy) is a good one.

It is good for another thing -- it gives you a fighting chance to get the slower mil-surp powders lit well because you can get up to the higher pressures and temperatures right at the critical primer flash ignition point. For example, you have got to have a heavy bullet and have a lot of starting resistance to get IMR 5010 to light well.

Aladin, you are going to need a very sturdy wide strong first band to support the nose on your HBC bullet. You have to have it for good pre-firing alignment or you will likely get slightly off line at firing and do the HBC "wobble through the air" thing.

Give us a sturdy wide band to jam deeply into the rifling (using neck sized cases) and this problem goes away.

We also REALLY need the high starting pressures for lighting the IMR 5010 types of slow powders. So make your first band as sturdy as you wish.

Just remember the long generous gas check shank so as to scrape up the heavy IMR 5010 fouling from shot to shot to shot. That stuff fouls a good bit in 8mm bores and fouls terribly in the smaller 6.5mm bores.

A longer shank allows the sharp edge of the gas check to scrape more fouling up, pack it in the increased check shank relief area and carry it on out the muzzle. This action also forces lube on to the bore wall to keep the fouling softer for the next shot to scrape away. I wish I had put a longer gas check shank on the ones I did (hindsight being 20-20 and all).

Oldfeller

Speaking of stuck bullets part way down the bore, did you know the US Gov did tests on that situation and the answer was to point it up vertically and put no bullet case with a full charge load of powder into the chamber (with the bullet an inch or two up the bore) and just fire it out ???

You might think this could cause barrel ringing, but it is really just a larger case volume "normal firing" situation with the pressure rising on a lower slower curve (because of the larger case volume) The pressure just increases until the bullet begins to move normally and then it just accelerates normally on out the bore.

I will never beat a "squib" bullet out with a steel rod again. It is hard work and you run the slight chance of damaging the bore at the muzzle with the steel rod (assuming autoloaders and you have to beat it out from the muzzle end).

Oldfeller

Tim's about got the HBC-A drawn. Methinks the driver sizes will adequately suffice.

Scraper action I doubt to the extent credit is given to it. A bullet makes that trip in some 2-5 thou of second.. I believe the speed and quantity of the gas volume itself does more to pull residue from the bore.

Bullet in the bore reminds me of the old Wither-bee catalog... jamming a 220 gr into the rifling and then firing another to clear the bore. Trick was having already engraved that first bullet, though I don't think I'd wanna be standing near said Kalifornia style shooten iron when it spoke.

Tapping a heat treated bullet otta the rifling isn't difficult because it doesn't compress into a wad and form around the rod edge. Wrapping that rod'd end with tape to center it is always been part of my explainer for making an impact slug too.

I'm with you on the wide front driving band and long shank thing. I want the rifling to have plenty of lead to grab on that first critical fraction of an inch of travel and a long shank amounts to an extra lube groove.

[Frick'n dam server... I answered this and it got dumped... sheeeeeiiii****ttt]

HBC-A design will be posted soon. Methinks no other design puts that much metal on the bore for a 30 cal. Plenty of lube'n too.

Scraper action is so over-rated. Yes some occurs but at 2-5 thousandths of a second for transit time of the slug in the bore the speed and volume of the gases do more for clearance. You can't design a bullet to shooten powders so far otta application as to negate the factors that are desired in the first place... being high BC and flat trajectory-- which IS the reason for this design.