design and alloy

fiver

Well-Known Member
Bama had asked me a question in the sidebar discussion area, and it was starting to get too big for a discussion there so I decided we should get one going in the open forum where everyone can see it.

as many of you know I use a couple of different alloys for higher velocity's in different rifles.
why would I use an alloy of 4% tin and about 6% antimony in one case.
not really 'case' I guess, instance or design would be a better word to use, but we will start with a single case as an example.
lets go with the 308 since it is popular right now, several people have one, and are using it for target and higher velocity shooting.
so why would I then turn around and use an alloy closer to .75-1% tin and 2-2.5% antimony in the same case to achieve the same velocity and accuracy.
[velocity is 2300+ fps and accuracy is under an inch]

I'm gonna let this sit as a question for a while [Ian/Brad no cheating let's see what the others have]
 

fiver

Well-Known Member
as an addendum I also use those same alloys at the proverbial 18-1900 fps, so don't feel left out if your not trying for warp speed loads, this discussion is relevant to both.
 

bns454

Active Member
Are you using the harder alloy with a powder thats faster and spikes pressure higher/sooner and using a slower more gentle powder with the softer alloy.<------I am guessing.
 

fiver

Well-Known Member
the second one is a yes for sure.
there is a definite advantage to using a longer gentler push to accelerate the softer alloy.
but the powder speed is more chosen to allow the bullet to move into the barrel before that happens.
too slow and your just gonna glide the bullet down the barrel without really gaining any speed the engraving bump is also too soft to help spike the pressure enough to get a decent burn.
 

bns454

Active Member
My second guess would be a stiffer alloy in a faster twist barrel not to strip the bullet in the rifling while using the faster powder.
 

Ian

Well-Known Member
Stripping only happens when abrasion happens on the leading edge of the land engrave, and ironically the abrasion happens with "hard" brittle alloys like Linotype, due to high antimony content.
 

Brad

Administrator
Staff member
How fast and hard can a simple heat treated 3/1 alloy be pushed? I know what I did with it.
Might shock some of you.
 

VZerone

Active Member
I hate the word stripping for bullet use. Makes me think the bullet has stopped turning and just going down the bore. I've never seen anyone do that with a rifle bullet. I'd rather it be called something on the order of what Ian was describing of the walls of the lands if we can pin a name on that.

I've seen people use both fast and slow powders (depending on what you would call fast for cast) do well at HV with cast. Would you consider 4064 fast pushing a 50/50 alloy to HV fast?
 

waco

Springfield, Oregon
I think bullet design plays a part. Design A might get away with a softer alloy while design B needs a stronger alloy to preform well. The overall shape of the bullet and how the alloy moves when it's fired.
 

RBHarter

West Central AR
Well I would speculate that you might be looking for a particular terminal result .
A harder alloy for target use where you might use a higher velocity and higher pressure load and the terminal idea is to poke a hole in a piece of paper . A softer alloy where expansion is desired .

As an alternate possibly to reach an A/C vs W/C , but the one soft alloy is to lean to harden well with the quench . The harder alloy might be used to get a same result as the softer alloy paper patched .
 

fiver

Well-Known Member
I think bullet design plays a part. Design A might get away with a softer alloy while design B needs a stronger alloy to preform well. The overall shape of the bullet and how the alloy moves when it's fired.
keep going down these lines..
 

popper

Well-Known Member
Alloy toughness to take the base pressure until it gets in the bore, dynamic fit. Mould design to give static and dynamic fit. Fit the bore for bore rider, slumps into the groove.
 

Brad

Administrator
Staff member
It also isn't just about hardness but how you get the hardness.

I don't like the term stripping either. Gas cutting to an extreme I can buy but I don't think we ever have a bullet truly "strip the rifling".
 

Brad

Administrator
Staff member
I hope this is what fiver was looking for.
Here are the XCB, 165A, and 30 sil.

Sized .308
IMG_3001.JPG
Sized .310
IMG_3002.JPG
Sized as I had them.
.3107, .3105, .3115
IMG_3003.JPG

A 30 Sil unsized, as cast. Measured. 314
IMG_3004.JPG
 

Brad

Administrator
Staff member
Rifle is my fathers post 64 Model 70 in 30-06. I know the rifle well and have shot cast in the past thru it.
These were all dropped into the throats and a rod was used to gently hammer them into the rifling.
I then used a cleaning rod to tap them back out.

Notice how the unsized 30 Sil shows lead shaving on the rear band. Too big for the throats and it shows. The .3101 shows a little scuff on that read band too. Tells me it is too big for the throat. This rifle will probably prefer them .309.

These photos also clearly show how each bullet takes the rifling in a different manner.

The 165A has the most nose with no engraving.
 

oscarflytyer

Well-Known Member
Following, but funny in that I am going in the totally opposite direction. Been casting all COWW+2% tin (~12bhn?!?) for all my bullets. Recently really getting into traditional pressure loads for 45 Colt and 44-40, and slower loads for a 38 snub. Plus 45-70 loads with a heavy HB bullet. As such, I plan on casting softer with 20-1 and maybe 30-1 alloy. Can start a sep convo if you prefer. Probably keep things much less convoluted!!!

Other BIG reason I am following this is because I am getting ready to cast a lot for a lot of rifles that will go a lot faster than my pistol stuff and potentially faster than I have pushed the 30-30/35 Rem and def the 45-70 (currently 1325 fps!)
 
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Brad

Administrator
Staff member
COWW plus tin is never a bad choice. It heat treats well, casts well, and just about does it all. Pretty sure it is almost all Rick uses.
 

oscarflytyer

Well-Known Member
COWW plus tin is never a bad choice. It heat treats well, casts well, and just about does it all. Pretty sure it is almost all Rick uses.
Brad - truly all I have used to date. I DID alloy some 15 bhn with Lino. But the COWW+Sn has worked so well in everything that I haven't monkeyed with it, AND I am LA-Zee! Done nothing with the 15/HB alloy, cause 1911 loves the std stuff. But I really want to try the 20/30-1 for the fat slow stuff, just to see. My 45-70 load is with 405 HB/IMR 3031 @ 1325 fps!