Twist,plasticity, and proof.

[Harter66]

Sometimes I wake up with my mind going 10,000 miles a min,today is 1 of those times.
No I'm not about the rev theory ........exactly,so put away pole axes, for a few posts anyway.

Goodsteel makes a good "nuts and bolts" explanation of boolit dynamics, while Larry tends toward physics for proof and it always leaves me going so why doesn't the boolit just poof at the end of the bbl.

It seem to me that a high level machinist should be able to make a threaded together 3 piece bullet for a 7mm or 30 cal projectile of about 1.5 inches in length. Stick it in a BO or a Russian or a 7x57 and shoot it for recovery. Made from aluminum my money says that the plastic theory of twisted projectile in the bore or at release proves out .

We make a wad cutter shaped bullet in half inch sections load it against the lands ,the nose has to turn but the base and center section are still in friction lock with the case . In the more or less 1-8 twist with the base now in the mostly released neck the nose will be .5 in into the bbl and be turned about 1/16th of a turn from where it started and the base may still be in a fit lock in the case .
1 inch into the bbl the base is still in the case mouth and may or may not have rotated the nose has and is now (in a perfect vacuum) 1/8 of a turn ahead of the base and at least a 16th ahead of the center section which is now locked in the grooves . Some twist may have been imparted to the base but if the neck doesn't expand as the motion started the mouth may still be holding enough friction that the base hasn't turned . The result is when the boolit is fully engaged in the rifling the nose is 3/16 of a turn ahead of the base .
With the modeled bullet in 3 sections threaded together this would prove out . The faster the model is pushed the more likely it is to get full values while at lower acceleration rates the values would be less due in part to time but also loading.
I suggest that the same thing happens to a 275 gr 30 cal wad cutter and is why shorter bullets and proper bore rides with short drive sections shoot so well and are so easy to get shooting well.

We know from sizing that lead has some memory and some spring back . To prove it out size a pure lead ball then a lino type ball in the same sizer , even WW will be bigger than pure . So it stands to reason that our bullet with 3/16 of a turn in its length will want to restore part of that as it is released from the rifling . This won't happen to the multiple part bullet but will in a solid 1 piece bullet .
Even in a 1-12 bore the potential exists for a wad cutter to be stable in flight while inside the bbl it was twisted (on paper nose to tail) potentially 30 degrees (at 1.1 inches long as a maximum bullet length for a 1-12 30 cal) . I don't know how much release there is but it can likely be extrapolated from sizer dia vs start/finish dia of the bullets and work back . This also requires acknowledging that a more rigid alloy will take less twist than a softer alloy while the softer alloy keeping more twist will be dependent on its own properties.

This makes sense to me in explaining why I've shot Red Dot to a point then picked up with Unique and gone faster and the same with jumping from fast to medium and slow rifle powders . The more gently the bullet slams into the rifling and the longer it takes to clear the case the less twist load is imparted to the boolit. Reduce the twist rate and you get a little bonus of having less twist to introduce.

I think I have it now .
Now I just have to figure out how this fits in with bbl dynamics and why a portion of the twist spring back can't be off set with a long forcing cone straight choke at the muzzle .

[44man]

Twist is important and grip to rifling with the boolit. I have no idea for limits so I leave it up to Larry.
We face under spin and over spin with every gun. Distance shot comes in too. Slower for closer and more spin for distance.

[Wayne Smith]

Soo.., a bore riding boolit vs a louverian (sp)? One with very little actual twist (base contact) and one with contact most of the length, but both accurate?

[vzerone]

Harter66....then according to what you are saying a Linotype bullet, which we know to be hard and brittle, would snap from this twist especially near the rear area portion that hasn't entered the bore/rifling yet. This doesn't happen.

[Yodogsandman]

If you had a "long forcing cone straight choke at the muzzle" hot gasses would be blown past the boolit, causing gas cutting to the boolit sides.

[runfiverun]

Harter has it correct.
you need to really read the context of exactly what he wrote.
and then put what is here with what others are saying about H/V rifle stuff elsewhere on the board.
adding in mechanical fitment and static fitment and fitment under pressure is what it's all about when getting going over 2400 or so fps in the faster twist rate rifles.

this isn't so much about shooting a rcbs 30-165 silhouette boolit at 1900 fps.
but even there a harder alloy will usually shoot smaller groups than the softer alloy because that long mostly unsupported nose is doing so much of the work and needs to resist the stress of spinning everything long before the full diameter part even gets close to the rifling.

using a softer alloy [I use my rcbs's 165gr silh boolit alloy cut in half with pure lead] I rely more on full groove diameter support and boolit design to get spun up into the 2400+ fps area in the same rifle with the same accuracy.
now I can't so much just do this with fast or even normal jacketed type powder speeds in this cartridge, so I have to go past that and slow the kick in the butt further down the barrel with a non standard powder.

[vzerone]

There is no doubt a twist applied to a bullet, but it's not as great as one would suspect. As I said Linotype and other brittle alloys would be fracturing at both the breach end and at exit from the muzzle. Throw a paper patch on and throw the theory out the window huh?

[Harter66]

1 that takes well to speed and 1 with a long but only moderate amounts bearing surface. I think that a lovern would tend to skid on the front half but remain a self centering boolit the low contact ratio allows it to be unloaded .......or something like that. This was 1 of the flaws as I thought through as I was writing this. I can't account for the long bearing/low contact boolits other than most of those designs have stepped rings in a 7mm they start about 280 then up to 284 then the base 3 step up to around 287. They also tend to be light for length and are more often from harder alloy ......based on recall of reading here .

I've spent a lot of time of late focused on what makes some designs Uhaul trucks and some Corvettes ,I really just want Hemi Ram . It seems that when the 3 meet it is often in a way that shouldn't work but proves out over and over . The bullet with 80%exposed contact that starts in full contact shoots best . The tapered design that fits the bbl and starts 2/3 of the bullet all at once.

[Harter66]

Harter66....then according to what you are saying a Linotype bullet, which we know to be hard and brittle, would snap from this twist especially near the rear area portion that hasn't entered the bore/rifling yet. This doesn't happen.

The more rigid bullet will turn into the rifling more as a monolithic block.

Yodogs
I was actually envisioning ,using the 308 dia, a half inch or so that tapers from .308 to .3075 and exit at .3075 in another half inch . Presuming a 308 groove dia.

[vzerone]

It would probably be more easy to visualize at exit from the muzzle when almost all the bullet has exited, but the muzzle has a hold on the rear end of the bullet while that front portion is free to snap it.

You still offered no explanation for a very soft core paper patched bullet.

[Hick]

OK-- being new at this I'll try not to let too much ignorance show (besides,I'm a chemical engineer-- what do we know about physics??) Slightly slower burning powder, less twist (like my 32 WS?), maybe better accuracy? Is this what we're talking about?

[centershot]

Hmmmm......pressure is building inside the case as the boolit starts to move aaaannnndddd, the case is expanding, loosening it's grip on the boolit, yes??

[vzerone]

Hmmmm......pressure is building inside the case as the boolit starts to move aaaannnndddd, the case is expanding, loosening it's grip on the boolit, yes??

Well there are a couple schools of thought on that, one is such as you say the case is expanding so the neck loosens it's grip. Another is the bullet starts to move before the neck has lost it's grip. A third is both are happening at the same time. Now here is something to think about. This is with a crimped load. How many of you have observed your fired case and the mouth is tighter then the rest of the neck? Put it another way the mouth still shows a little bit of a crimp. Wouldn't you think that the crimp would get ironed out? Something else...you don't see the same thing on a j-word fired case that was crimped. Why not? Don't answer because j-word loads are usually higher velocity and more pressure. Done this with high velocity high pressure cast and the mouth still looks slightly crimped.

[popper]

so why doesn't the boolit just poof at the end of the bbl. Unless it's already broken, it won't. Grab some long rifle boolits and vice grips and try to break one by twist. Not as easy as you think and you will tear the base and nose long before the lube groove breaks. Twist force on the boolit isn't really that much when fired. Slow down, you are thinking too hard.

[runfiverun]

vzerone look at what happens to the paper patch at the muzzle.
it shreds. [it better or you done it wrong]
the patch is what takes [almost] all of the forces generated inside the barrel and at the muzzle, your lead to steel contact is .001 at most.

[vzerone]

vzerone look at what happens to the paper patch at the muzzle.
it shreds. [it better or you done it wrong]
the patch is what takes [almost] all of the forces generated inside the barrel and at the muzzle, your lead to steel contact is .001 at most.

Yes what you said is true except their are rifling marks on the alloy core so that core is getting torqued too. I wouldn't exactly say it's taking all the forces and the core is not, I would say it keeps the alloy from getting the friction from going down the bore and also insulates it some from the propellant gas heat and friction heat.

On popper's idea putting a bullet in the vise and twisting it I say try that with a Linotype bullet and watch it break in a lube groove. Has anyone dropped a Linotype bullet on a concrete floor and it hits on it's side and break at a lube groove? I have and I'm not talking about one fresh out of the mold either.

[vzerone]

I think this will fit in here and not be off topic. This is from Lilja:

As mentioned above, a uniform twist rate is also crucial, so is matching the proper twist rate for the bullets to be used. Ideally a barrel would have a twist with no variation. If the twist rate decreases, accuracy will suffer, but a slight increase in twist is not detrimental. The explanation for this is fairly simple. If we look at a recovered bullet we’ll notice that the rifling cuts a partial helix in the bearing surface of the bullet for each land. The helix is on an angle matched by the twist in the barrel. If the twist rate decreased, the angle of this helix would decrease also, and would effectively cut a wider groove into the bullet. This condition is undesirable because the bullet could then yaw while still inside the barrel. It would lack the full support of the barrel, especially on the driving side of the land. The yaw would be demonstrated by poor grouping on a target once it was released from the barrel.

[centershot]

WHow many of you have observed your fired case and the mouth is tighter then the rest of the neck? Put it another way the mouth still shows a little bit of a crimp. Wouldn't you think that the crimp would get ironed out? Something else...you don't see the same thing on a j-word fired case that was crimped. Why not? Don't answer because j-word loads are usually higher velocity and more pressure. Done this with high velocity high pressure cast and the mouth still looks slightly crimped.


Very interesting point! I've observed this myself but never gave it any consideration relative to the question "What's happening to the boolit?". Crimped J-words iron out the crimp, cast don't, my only consideration was the accuracy if the load.

So, if the crimp partially remains, is their enough plasticity that the boolit squeezes through unscathed? Is the boolit deformed and then "jugged" back up to bore diameter by pressure? Does chamber pressure expand the case enough to clear the boolit's OD? A combination of factors? Hmmmm......

[Forrest r]

I was actually envisioning ,using the 308 dia, a half inch or so that tapers from .308 to .3075 and exit at .3075 in another half inch . Presuming a 308 groove dia.

Actually I've been wondering the same thing, got started on some initial tooling/testing. Just too many irons in the fire.

I have made a swaging or bump die, whatever you want to call it. I need to make a couple of different nose profiles but the bodies done.

A picture of a lyman (squib bullet) 311414 that was loaded and chambered in a 308. Both bullets have rifling marks from being chambered but the swaged/bumped bullet are longer and deeper. Keep in mind that a standard 308 has a 1 1/2* tapered throat. The rifling is even the length of the taper, hence the bump die is a different angle.

http://i162.photobucket.com/albums/t242/forrestr-photo/riflingleademarks_zps5d0d19fd.jpg (http://s162.photobucket.com/user/forrestr-photo/media/riflingleademarks_zps5d0d19fd.jpg.html)

Sorry for the crude drawing but it actually shows the demensions of the swaging/bump die. These are lllllooooooonnnngggggg 230gr bo lee bullets.

http://i162.photobucket.com/albums/t242/forrestr-photo/swaged30cals_zps90d0ed5c.jpg (http://s162.photobucket.com/user/forrestr-photo/media/swaged30cals_zps90d0ed5c.jpg.html)

A close-up of the reformed bullet, the arrow points to step in the bullet where the bullet will seat in the throat of the chamber. That line/area of the bullet sits where the freebore ends and the actual tapered throat begins.

http://i162.photobucket.com/albums/t242/forrestr-photo/stepdowninbullet_zpsc30ae8bc.jpg (http://s162.photobucket.com/user/forrestr-photo/media/stepdowninbullet_zpsc30ae8bc.jpg.html)

What bumping the bullets should do is allow me to take a bullet and test it for accuracy with different alloys and then swage/bump that same bullet and retest the different alloys again. There should be a pressure point where 1 fails and the other doesn't.

The other test I wanted to try this year was to do the same thing with a lee 312-155 tl bullet.

http://i162.photobucket.com/albums/t242/forrestr-photo/312tl_zpshnfnqijf.jpg (http://s162.photobucket.com/user/forrestr-photo/media/312tl_zpshnfnqijf.jpg.html)

And lastly, cut my own mold with a 6r .312 reamer making a pc bullet. Then test that bullet plain and bumped.

Anyway, allot more questions than answers. Just need to start doing the legwork/testing.

[gtgeorge]

I think a better way than separating bullet pieces might be simple straight lines installed on the bullet to examine after a recovery. This might aid in the twisted theory to either prove or disprove with physical evidence?

[44man]

All my most accurate boolits show a skid at the start but skid stops before the base.
I don't feel you need a bore ride to slump into the rifling.
A boolit too hard is not good either. It never is the same as a jacketed.
I like hard boolits in my revolvers but never straight lino either.
There are times softer is better. Could it be boolit design? Testing is in order in any case.

[vzerone]

Very interesting point! I've observed this myself but never gave it any consideration relative to the question "What's happening to the boolit?". Crimped J-words iron out the crimp, cast don't, my only consideration was the accuracy if the load.

So, if the crimp partially remains, is their enough plasticity that the boolit squeezes through unscathed? Is the boolit deformed and then "jugged" back up to bore diameter by pressure? Does chamber pressure expand the case enough to clear the boolit's OD? A combination of factors? Hmmmm......

Yes, I wonder all that too. It's very difficult to find out because once the bullet is squeezed into the bore all evidence is obliterated.

[BAGTIC]

Beware of 'over thinking' a problem as it can give one a headache.

[44man]

Beware of 'over thinking' a problem as it can give one a headache.
All I have made work is from imagination, sitting here to imagine what goes on.
Most problems are "over reading experts" with opinions. Not like actual testing and measurements.
I will give our military top dog here. never a gunzine. Think and test but to imagine a smooth bore tank gun able to hit anything on a fast run blows me away. To drop a bomb into a window! Smart bullets and grenades. Darn I need a Ransom Rest! I need to point a laser at a deer and drop a boolit right there! Thinking works but why do I need to hold that revolver out in my hands?

[Harter66]

The tank question I can answer . The 120 mm uses a sabot'd (pesky french words spell check doesn't like em') lawn dart something over 3000 fps . They range from a solid rod of DU to something similar to an HE 40mm AA shell.

A friend called and we talked at some length about how to mark a boolit to see the effect ,the challenge being catch the bullet w/o mangling it . Gallery loads no problem, but higher speed becomes a problem.

I could try a couple of things in 22 and 30 having a 1-10 and 1-8 in both . Any suggestions on how to stop 1200 ftlb w/o turning it into a cherio ? I have a 310-230 NOE I guess I'd need a few ACWW 223-80 ish as I have only a Bator and 22-55 NOE .

[runfiverun]

you don't need anything that heavy in the 223 the 55 gr rcbs boolit will work just fine.
I use a harder but not eutectic alloy in mine 4/6ish/90 it's to help get everything aligned across the 5.56 gap.
imr 4895 works just fine too. 18 grs will operate the action on an ar rifle, more will shoot faster.

[Harter66]

I have a 222 1-10 and a 223 1-8 . The 222 in the Savage 340 is a really amazing rifle (to me I've had so many that were so touchy) . Ive shot a 12 shot 4" group from 4 boxes of different makes of ammo. The 223 shoots like a GI 556 best group 3"@100 . I admit I'm still learning the platform and only ran a couple of flavors . That's about as well as I shoot anyway.

[vzerone]

Harter,

You could try oiled sawdust like Mann did to capture the bullet. Another way is couple high speed camera's. What would be really nice is a very large pool of shallow water and stand in the middle of it shooting straight up.

I was talking to fellow into military armament and he had saw a demonstration of a Germany tank cannon, smooth bore, having an unbelievable velocity of 10,000 some fps.

Let us know if you find a good easy method of recovering bullets undamaged.