Didja ever notice that aluminum rod stock comes in the same diameter as drill bits?

[Bigfoot]

Respectfully:

Remember the Barnes lathed turned MRX? It was market failure only because the lower cost TTSX beat it out. They increased the SD by using heavy Tungsten..

That didn't affect the terminal performance, just the muzzle velocity.

Assuming that the drilling and the AL rod replacement is concentric it should't affect terminal ballistics at all if the core is monolithic or bonded. Like a LRAB, AB, InterBond or mono.

Mea Culpa. I know none of this is is new to anybody. This is just what my brain does instead of shutting down. You should see my shop toys...

[stanc]

[customcutter]

I use #9 tungsten shot for my turkey loads. The last I bought 2 years ago, was $60/# and that was purchasing 5 pounds. It's twice the density of lead, so yes it will have a great BC if added to a bullet.

I didn't have any aluminum rod, so I used a large rivet. It was .114", so I used a .106 drill and tapped it in.

[Bigfoot]

Ah you guys missed it. The goal is lighter weigh bullets without affecting the overall shape, BC and mushrooming.

You could chuck them in your lathe and drill out about thirty grains of core and replace it with eight grains of AL rod. AL generally has a quarter of the density of lead.

This isn't something that interests me as much these days but I figured I'd pass on the idea. It would best be done in a factory. 130 gr is the sweet spot as lightening the bullet mass requires a tighter twist. A lightened LRAB would be something else.

[ricsmall]

Very interesting point BF. I just saw this. Something I may try. Shop time is wrapped right now tho, will pursue asap

Richard

[stanc]

Ah you guys missed it. The goal is lighter weigh bullets without affecting the overall shape, BC and mushrooming.

You could chuck them in your lathe and drill out about thirty grains of core and replace it with eight grains of AL rod.

If I'm not mistaken, reducing the weight while retaining the overall shape, will reduce the BC.

I have no idea if mushrooming would be affected.

[Drift]

It sounds like a project worth trying. I'll speak to a friend who has the machinery about trying it.. (And while I am no physicist, I suspect the main determining factor for BC is shape (friction through the air) not mass). My worry is more to the issue that high BC bullets are long and take up a lot of room in the Grendel case that could be otherwise used for powder-which has a lot more to do with velocity....Then there is the issue of the center of gravity changing and causing keyholing.... And I might be worth it as well to look around for magnesium rod in place of aluminium, its even lighter... It sounds worth trying

[stanc]

(And while I am no physicist, I suspect the main determining factor for BC is shape (friction through the air) not mass).

That may be true, but the BC will still take a significant hit from reducing mass.

IIRC, there are two, 6.5mm Lapua Scenars (or is it Sierra MatchKings?) which have identical shape and size, but differ in weight by ~15 grains, and the BC of the lighter projectile is ~10% lower than that of the heavier bullet.

[JASmith]

The BC is proportional to the product of the sectional density and the shape factor.

The sectional density is the weight of the bullet divided by the square of the diameter, so is proportional to the weight if the she remains fixed.

So, when the shape is fixed, and one changes only the weight, then the BC is proportional to the weight.

The advantage to lightening a sleek bullet is increased MV while retaining a presumably good shape factor, so there may be a gain in performance depending on what one is trying to accomplish.

[Drift]

So lets see: pros (1) reduce recoil by 15-20 % (2) increase velocity by 200 fps (3)give you something to do on a rainy day. Cons (1) decrease BC by 10 % (2)strike sparks some if you use magnesium instead of aluminium.
If I understand what is said above, we could start out with a 130gr super high BC bullet and end up with a 108gr bullet (and 108gr velocity and 108gr recoil) still with the BC of a 117 gr factory bullet.

[stanc]

So lets see: pros (1) reduce recoil by 15-20 % (2) increase velocity by 200 fps (3)give you something to do on a rainy day. Cons (1) decrease BC by 10 % (2)strike sparks some if you use magnesium instead of aluminium.
If I understand what is said above, we could start out with a 130gr super high BC bullet and end up with a 108gr bullet (and 108gr velocity and 108gr recoil) still with the BC of a 117 gr factory bullet.

Could be. I'm not saying it isn't a worthwhile experiment. Only that Bigfoot's goal of lightening bullets without affecting the BC is simply not possible.

Oh, regarding con #2: I would expect aluminum to also do this. The 1st generation Winchester Silvertip ammo in lower-velocity handgun calibers (.45 ACP, .44 Spl, .380 ACP, .38 Spl, etc) had bullets with aluminum jackets, and produced a bright white flash upon impact with steel plates. Not sure why you rate this a "con" since I consider it a plus that adds to fun of shooting steel targets.

[customcutter]

Ah you guys missed it. The goal is lighter weigh bullets without affecting the overall shape, BC and mushrooming.

You could chuck them in your lathe and drill out about thirty grains of core and replace it with eight grains of AL rod. AL generally has a quarter of the density of lead.

This isn't something that interests me as much these days but I figured I'd pass on the idea. It would best be done in a factory. 130 gr is the sweet spot as lightening the bullet mass requires a tighter twist. A lightened LRAB would be something else.

That's what I did with the 77.5 gr aluminum tipped bulled. It has 1/2 inch of aluminum inside the bullet, not shown with the tip.

[Drift]

So if I remember (and I really dont ) the the applicable physical laws that (may) apply here are.(1) as you cut a bullets weight by 2% you increase its velocity by 1% (2) If you double the velocity of a bullet , you square it's energy. (3) With each 1% decrease in bullet weight you get a decrease of 1% in recoil.
So ballpark..If this works out these bullet should get somethin like a 30% increase in velocity, 60% increase energy and @ least 30 decrease in recoil. At the expense of some loss in BC but maintaining the same SD.

[Bigfoot]

The primary advantage is the cost, ease of modification, minimal changes to the BC and no change to the nose.

With the reduced mass you lose some BC, stability, SD and momentum. I doubt you would notice much of it in the real world. The increased velocity will help trajectory and impact but it would penetrate less than a slower, heavier, unmodified bullet.

If you wanted to make a 108 from a higher BC 140 length bullet you would run into stability problems in an 8 twist barrel. All the 130s are short enough however.

Since drilling through the base will most likely weaken the jacket and increase the chance of separation bonded jackets are your best bet. A 130 bonded reduced by 20+ gr should still have plenty of penetration for deer and hogs. My choice would be the Noslers with their thick copper base. Of the 130 bondeds the ABLR should give the least penetration and the Interbond the most. The 129 SST might work too if the impact velocity isn't too high, it has a tapered jacket and a better interlock than the 123 SST.

You don't want the AL core slipping out during loading or inside the loaded case. Running them through a .264 die afterwards should grip the core enough but if not I'm thinking knurl the core slightly with a file before insertion. I'd worry about adhesives affecting balance.

You're going to want a very good holding drill bit depth guide, maybe epoxy them to the drill bits. It's probably best to make a custom depth guide for each bullet.

My 260 doesn't have recoil or case volume issues. In my 06 BAR and 300 WSM however I'd like to take 40-50 grains off of some high BC 180s and 190s for deer.

Good luck.

[stanc]

So if I remember (and I really dont ) the the applicable physical laws that (may) apply here are.(1) as you cut a bullets weight by 2% you increase its velocity by 1% (2) If you double the velocity of a bullet , you square it's energy. (3) With each 1% decrease in bullet weight you get a decrease of 1% in recoil.
So ballpark..If this works out these bullet should get somethin like a 30% increase in velocity, 60% increase energy and @ least 30 decrease in recoil. At the expense of some loss in BC but maintaining the same SD.

Cutting the weight of a 130gr bullet to 108gr is a 17% reduction, so according to Rule (1), the velocity increase would be only 8.5%, not 30%. Which gives an energy increase of 18%, not 60%.

And SD will not remain the same after reducing the bullet weight. SD (as well as BC) will be significantly lower.

[customcutter]

BF, why wouldn't you just load and shoot 150 gr bullets or lighter, if you want a lighter bullet in .30 cal? I'm afraid if you try to drill out the base of cup and core type bullets, that you will simply blow the cores out of them, if they are just epoxied in. Then again, maybe not. Maybe you're looking at a specific VLD or something?

[Rootshot]

Another consideration is that if you compare two bullets with the same weight, the one with a lower density will have a larger volume and (if seated to the same OAL) will consume more case capacity. This means that the less dense bullet is at a disadvantage.