Downside To SG = 1.5 - Exploding Bullets?

[JarheadAZ]

Could atmospheric friction also be a factor?

Seems to me that if all the heating was taking place inside the bore, those bullets would self destruct as soon as they emerge. Also allowing that the stresses between being driven and emerging from a highly stressed state should emphasize the immediacy of the self destruction.

But this would appear not to be the case. Coupling recent discussion about melting plastic tips, and the appreciably longer disruption distance downrange; my estimation suggests that atmospheric heating becomes the final insult to bullet integrity.

I've been reading the 'net continuously for several decades, and the emphasis has always appeared to be on pushing the limits of velocity, BC, and stability. There had to be a limit sometime, and I simply believe we may be getting up against the material limits of bullet integrity at extended distance.

The next logical question may be which materials can better withstand these challenges? Bismuth has a similar density and higher melting point than lead for bullet cores. It also has some nasty attributes, like expanding as it solidifies. Plus, it's not what I would call a cheap material, at least in smaller quantities.

TANSTAFL (There Ain't No Such Thing As A Free Lunch) - Larry Niven.

Greg

 

[ThunderDownUnder]

An update on whats going on with testing an alternate barrel.

After taking notice of some of the well informed posts on this thread a new barrel has been tried. As mentioned earlier a 32" identically chambered new 9T barrel was available. This brand new identical barrel, (except for slower twist rate) has been has been shortened to 30" and run in, and a load developed to drive the Berger 195s at 2900 fps.
From initial testing yesterday with a 17 shot rapid fire string, simulating 2 x sighters and 15 shots to count. The news is good with no bullets exploding and all bullets arriving with good accuracy on the target at 800 metres. Obviously the magic SG = 1.5 cant be reached with this barrel and load combo, but the accuracy even with a brand new barrel looks to be very good!

The plan is to keep his 32", 8.5 and 8.0T new barrels for use with the heavier jacketed 195gr target bullets when Berger finally release them. He now feels he has a barrel and a load that will launch his 2000 x 195gr hunting/match bullets in FC competitions. This is very good news as these bullets dont come cheap and can now be used competitively.

He also tested a some heavy 30 cals with 230gr projectiles. It would appear he is going to enter our state's LRFC comp (2 weeks away) using the 7mm, Berger 195s at the shorter of the long ranges and the big 30 cal, 230gr bullets at the 1200 yard targets.

Ian

 

[bruce moulds]

ian,
lucky he's not shooting a long range black powder gun.
they go better at s.g. = 1.8 to 2.0.
that would make excellent puffs of dust on the way to the target from a 9tw or faster.
keep safe,
bruce.

 

[spclark]

Another consideration.
Some types of rifling are harder on jackets than others.

Sometimes these big bullets have a lot of inertia and really refuse the initiation of spin.

I think lead angle, rifling pattern, copper fouling, and even bullet jump which may cause the bullet to resist the initial spin can cause significant smearing or tearing of the jacket as it engraves the rifling.

I suspect you're correct in that.

A friend of mine shoots Palma with 155's in 1:14 & 15 twist barrels at speeds none of the rest of us would even consider (let alone attempt in our 1:13 & faster) but he's using custom-made barrels with very shallow grooves and larger root diameter bores. Our conjecture is that the shallower deformations affect bullet jackets less so markedly reduce stresses imposed when bullets are "swaged" into the lands and grooves upon firing.

The bullet jump aspect I'm not sure about; gain-twist rifles I know are popular among smallbore shooters, not so much for high power / center-fire. Maybe the non-jacketed bullets benefit from being introduced to the lands with reduced stress before being rotated?