a hot 6.5mm roudn with tungsten core would match the penetration of these CBJ rounds.

i had a questions, if you necked up a 7.62 sabot so the sabot diameter is about 10.5mm, would it achieve much higher energies? like 2800ft lbs instead of 2100 ft lbs

why do tanks use APFSDS tracers? whats the point of the tracer if the round is moving so fast?

smg762 said:

why do tanks use APFSDS tracers? whats the point of the tracer if the round is moving so fast?

To observe the trajectory of the shot.

Like with all tracers.

smg762 said:

why do tanks use APFSDS tracers? whats the point of the tracer if the round is moving so fast?

Even though the projectile is traveling at a high velocity, it is flying almost directly away in nearly a straight line from the viewers in the tank.  This makes relatively easy to track by the tank crew.   There has been a little discussion of tracers being used as a pointer to guide others to a particular target, but that it not what is going on in this case.

smg762 said:

i had a questions, if you necked up a 7.62 sabot so the sabot diameter is about 10.5mm, would it achieve much higher energies? like 2800ft lbs instead of 2100 ft lbs

Yes, but not by as much as you might expect, because the sabot will be bigger and heavier so some of the extra energy will be lost in accelerating that extra weight which is then thrown away.

yes, i imagine a CBJ style sabot which enveloped the bullet, would weight maybe 25 grains in 10mm caliber

you would be better with a tiny sabot which pulls the bullet by the nose

I've seen small children lead a bull around using a nose ring but never a "tiny sabot which pulls the bullet by the nose."  Of course bulls have a rear exhaust that may function as a base-bleed to reduce drag. How does the tiny sabot grip the nose?

Very interesting read, thanks for sharing. I binged on 1980's parents regarding 7.62mm SLAP sabots. 

https://patents.google.com/patent/US4841863A/en

In this 1989 patent I think it says (2nd page of the file, under 'detailed deacription') they developed a gunpowder that if they slightly compress it into the case they get both acceptable pressures and the desired 4200 fps muzzle velocity. Acceptable pressures are important because the sabots come apart at 50 kpsi (when using commercially available gunpowder - it specifically says so and I don't understand how this works. If someone has any insights, please do share). 

But then there is this, from 1986:

https://patents.google.com/patent/US4574703A/en

The sabot design described here is made out of polyetherimide or glass-reinforced polycarbonate with a rounded square washer (material isn't specified beyond "metallic") touching the base of the projectile. Instead of the separate fingers of Remington's accelerator sabots, these are whole around the outside but have sharp notches on the inside. These notches and the recess the washer sits in cause the petals to break off once no longer kept in place by the bore. This sabot should be able to take up to 70000 CUP (88 kpsi?) nonetheless, a fair bit more than the 50 kpsi wall from 1989. So, who knows ¯\_(?)_/¯

Either way, I'll be spending my idle hours next week coming up with some cartridge that makes use of this. Or more likely, decide that something I did years ago turns out to be less fantastical than I thought.

Another thing i'm curious about is why the M60 has less trouble with SLAP than the M14. Something to do with feed ramp geometry, and where and in what orientation the to-be-fed round is located? It seems like SLAP is prone to similar feeding issues as hollow points are.

Spotted this in the wild, couldn't resist

Nice discussion of what lead to Swedens adoption of the 7.62 + 5.56 mix. Interestingly he believe Sweden will stick to 5.56 for mechanized infantry, and also believes that Finland will focus more on 5.56 then 7.62.

Lots of other stuff in there.

https://corporalfrisk.com/2023/04/08/the-future-arrives/