Why Do We Put Tin In Our BPCR Bullets?

[Guy La Pourqe]

I am curious because I am new to BPCR. I know for my muzzle loaders they are running on near straight lead. Why can't our black powder powered cartridge guns do the same?

And another question for the gurus, if you don't mind: how many shots do you guys go with BPCR before mopping the bore?

[17nut]

Tin lowers the alloys surface tension, thus helping with fill out in all the nooks and crannies in a grease groove bullet.
Rould balls dont need no stinkig tin, they are round

It depends!
Thats the best ansver you'll get with no data.

[upnorthwis]

Some shooters wet mop after every shot followed by a dry patch. Some use a blow tube after every shot. Was reading some Quigley results from a couple of years ago and some of the top shooters weren't doing anything for fouling control and didn't even clean between targets. You will have to try them all to find out what works for your rifle. While I have cast with pure lead just to experiment, it takes a lot of heat to get good fill. And then they didn't shoot that well either.

[Gunlaker]

In addition to making the bullets fill out better, the tin does harden the bullet to some degree. Not at all like antimony does, but enough for our purposes. Kurt has posted a bunch of pictures of bullets cast in various alloys and how they bump up when fired.

A decent rule of thumb for black powder rifles is to use 25:1 or 20:1 for blunt designs and 16:1 for the more pointy ones.

Chris.

[vagrantviking]

As mentioned, the tin gives you much better fill out with minimal hardening of the alloy so that you will still get some bump-up.

I never mop my bore except maybe after an extended break on a really hot dry day. It then needs a fouling shot or two. I do use a blow tube every shot though. My feeling is that wiping might be more beneficial in the small bores but haven't tested it yet.

[Toymaker]

"Depends". I love to hate that answer, but it's true. Part of the game is to find out what works for you. Tin will reduce the surface tension of lead and it will harden the lead slightly - those are facts. In theory this prevents bullet slump (when the nose of a long pointy bullet distorts), reduces/eliminates leading, reduces/eliminates blow-by and a couple of other things.
I have a 405 grain Lyman and a 500 grain Hoch mold that throw beautiful bullets in pure lead. I smoke the molds and dip cast at 800°F using a PID and keep my molds hot with a hot plate. And I have a 45-70 rolling block that loves both bullets. Strange thing - this is true for black powder AND smokeless loads. The rifle also loves the 405 grain LaserCast bullet which is super hard (BHN 22).
On the other hand I have a Lyman and BACO mold that throw beautiful bullets in pure lead, but my 38-55 high wall hates them. Black powder loads need 20:1 and smokeless loads need Lyman #2.
For both rifles, when using BP loads, I wipe after each shot keeping the bore in the same condition each time.
At a BPCR shoot one time I saw a shooter who kept his rounds in a rack, nose down, in an ice chest with two ice packs. He never wiped his bore but his rifle was literally dripping water out the muzzle after each shot. His rounds had a 1/4 "cookie" of gelatin instead of lube.
What ever works.

[1Hawkeye]

Like the rest have said tin makes the bullet harder. As for the swabbing between shots that's personal choice. I shoot with they same group Toymaker does and iv'e seen three types of shooters using black powder.
Shooter 1 swabs every shot.
Shooter 2 uses a blow tube every shot then patches every tenth.
Shooter 3 patches after every tenth round and sometimes scrubs like hell.
It is truly what ever works best for you, but some other things to consider are how smooth is the rifle's bore?, what lube are you using?, is it very humid out?, are you hampered (cursed) with a finicky bore? example it only shoots good when spotless or dirty. BPCR is an experimenters paradise.

[Drm50]

I shoot 20:1 in all my S&Ws, being mostly WCs, except for one 25-5 that is tuned for 250 RnFp
at 850fps, but still with same alloy.

[Tom Herman]

All good advice... I tried casting without Tin, and I get butt ugly bullets that don't want to fill out, all other things being the same.
With my handgun operations, I find about 2% Tin in with half scrap "soft" lead and half wheel weight alloy fills out really well.
I've added 2% Tin to relatively pure lead, and I'm still struggling. I may up this to 4-5% (20 or 25:1) and see how that does.
I'll figure out the secret eventually. All of this is what is so frustrating and rewarding at the same time: Mastering an art like casting (with all of the different alloys and bullet types) is where Art meets Science...

[BAGTIC]

The reason some bullets need bumping up is that they were too small to begin. Lead bullets should not be bumped up they should be swaged down by the barrel.

[Don McDowell]

Tin helps the alloy fill the mould better, and also helps support the nose to keep from having accuracy problems from set back and or nose slumping.

[Boz330]

The reason some bullets need bumping up is that they were too small to begin. Lead bullets should not be bumped up they should be swaged down by the barrel.

Not necessarily, long range MLs shoot both grease groove and PP bullets that are bore diameter and they depend on slug up to groove diameter for them to shoot accurately out to and beyond 1000yd. Some BPCR shooters do the same with PP bullets in their cartridge rifles. I shoot PP bore diameter in my 45-70 and they shoot as good as or better than GG bullets that are .001 over groove.

Bob