design and alloy

[M3845708Bama]

Ian, this is the best explanation I have seen anywhere in the past! It does point out the vast amount of known unknowns, that this group is working to define and resolve. I hope as we progress that we can maintain an area we’re best practices will be maintained in a clear concise manner so that those who will follow will have a good starting place to build upon.

both can cause it.
if you have the nose pressed against the rifling and whack it with pressure the bullet pushes forward while being held in place at the same time.

don't be confused by thinking you don't want engraving on the nose you absolutely want the nose to be engraved.
evenly and firmly by all the rifling.

Other ways of looking at it is the forceson the alloy at the moment of firing is given in its simplistic form is given by. F= (M x A) / gc Where F is the force acting on alloy at point of interest, M = mass of bullet- in this case,the mass of bullet forward toward to tip from point of interest. A is acceleration resulting from powder burn and finally gc is a gravitational constant. There can be a number of other factors this is a very simplistic method of looking at what happens. It explains why the very tip of bullet is not usually engraved. There is less pressure because not much mass past tip

 

[M3845708Bama]

Go back and read what Ian said about the 190X.
With the perfect fit the nose is held tight. Sounds great, in theory.
In actual use what you discover is that a certain amount of force must be applied to the bullet to engrave the rifling. With that much land contact the force required is much higher than in a bullet like the 165A with far smaller land engagement on seating.
Because the nose can't move until a certain force level is applied the bullet doesn't move initially on firing. Sounds good except for the reality of igniting all that powder behind it. If the pressure curve gets ahead of you the bullet base moves too much before the nose engraves and the bullet rivets. Think about it, that soft lead bullet fills in any space it can, like the space at the end of the neck of the chamber. The base is moving forward, the nose is held firm, and the lead has to go somewhere. This all happens very fast.
Like Ian said, with lower pressure loads and the right alloy it works great. Where is fails is where we exceed the strength of the alloy with the pressure curve.
That nose shape also really needs a berry straight feed into the throat. It doesn't self center if it jumps to the rifling from any real angle. If we have a .007 difference between loaded round and chamber neck dimensions the bullet is not fed straight into the throat. That "Morse taper fit" doesn't self align so well and all in for naught.
I really like how the 30 Sil self centers and handles the pressure. Before I got rid of my XCB rifle I was firing a 3% Sb, 1% Sn heat treated bullet at 2700 fps with RE15 into 1.5-2" groups at 100 with a varsity ofmcharge weights. Pressure was approaching 50K PSI and the bullet never failed. No leading, no blown up groups, no issues at all due to design failures. What I did learn was that it wanted a running start. It liked 15-25 thou jump.

Brad, you refererenced that the nose is held firm, on a bore rider, what is holding it firm other than the mass of the borerider section being acellerated from zero to final velocity in a short instant of time at least until the walls of the borerider is impressed into the rifling. Or am I missing something.

 

[Ian]

The tops of the lands, or "bore".

 

[Brad]

Brad, you refererenced that the nose is held firm, on a bore rider, what is holding it firm other than the mass of the borerider section being acellerated from zero to final velocity in a short instant of time at least until the walls of the borerider is impressed into the rifling. Or am I missing something.

Look at my photos of the 30 Sil. See the nose engagement withnthe tops of the lands. Seat that bullet into the lands a little or just touching and the nose isn't going forward until a certain force level is reached. How much did the bullet base move in the same time?
I don't use bore riders for HV shooting as they aren't up to the task. I own the 30 Sil and it does well for me. The XCB has a good reputation too but isn't what I would call a bore rider either.

 

[fiver]

it isn't but it does engrave way up the nose.
you want it to 'run up' into the throat.

now the 165 starts out as a bore rider but when it gets jacked the nose will stay put for a bit and the back will come forward.
I explained how the rest of it works.
the 180 works in a similar fashion only on a different scale and needs a different powder rise to make speed.

 

[Rally Hess]

Great thread folks. Gave me an idea to try on that 188 hunter I had so much trouble with.

 

[Ian]

The 188 hunter has a parallel, bore riding nose, and a taper behind that. It misses the whole point of the two-taper nose and should be treated as essentially a bore-rider needing nose support and no jump. Lack of jump may cause the same issues my 190X had.

I'm gonna stick this here so it doesn't fall off the page, Fiver put some gems in there about whys and wherefores of alloy...especially post #21, worth a read for anyone reading this thread: https://www.artfulbullet.com/index.php?threads/alloy-question.2810/

 

[M3845708Bama]

Bore riders that the front portion just fit Inside the bore also expand to completely fill bore and show full rifling without having any mechanical interference before firing other than engagement of the drive band portion of the bullet. Seems only explanation is the drive band portion is moving before the nose portion can start to move. If close fit, it helps the bullet maintain center of mass on barrel axis. OR am I overlooking something?

 

[Ian]

Bore riders that the front portion just fit Inside the bore also expand to completely fill bore and show full rifling without having any mechanical interference before firing other than engagement of the drive band portion of the bullet. Seems only explanation is the drive band portion is moving before the nose portion can start to move. If close fit, it helps the bullet maintain center of mass on barrel axis. OR am I overlooking something?

I'd say you pretty much hit the nail on the had there.

To tie it into the thread and get a more complete picture, "if", when, and how much that "bump" occurs depends greatly on bullet shape/throat shape relationship (where the gaps are), amount of jump, bullet lube groove design, and most importantly the relationship between alloy characteristics and powder pressure rise/peak pressure level.

 

[fiver]

no that sounds right.

one other thing they do is the nose also starts the bullet turning.
poor engraving doesn't allow that and the little bit at the back has to do all of the work of being jammed ahead, taking the rifling, blocking the gas, and supporting the nose squarely.
it's super easy to over run the whole system on a long nose bore ride bullet even one with an alloy capable of doing the job if the fitment and the base of the nose isn't capable of doing it properly.

 

[fiver]

me and Ian need to coordinate our timing better.

 

[Ian]

hey, I pecked it out one-handed...whaddaya want?

 

[bns454]

I got some more pics taken today.The two on the right are before and after sizing off the front of the band so I can seat deeper.I still am not sure what type nose design I need,maybe tapered.I dont think a square front band is the answer.Input is appreciated.

 

[Ian]

That's the soup can in the tranny funnel thing I was alluding to earlier, not enough contact/support soon enough in the bullet's movement. I'd think a Loverin with small bands clear to the nose that exactly matched the throat taper would be the way to go with that throat.

 

[Ian]

Like this: http://accuratemolds.com/bullet_detail.php?bullet=32-180D-D.png

 

[bns454]

That's the soup can in the tranny funnel thing I was alluding to earlier, not enough contact/support soon enough in the bullet's movement. I'd think a Loverin with small bands clear to the nose that exactly matched the throat taper would be the way to go with that throat.

It likes the 323471,but I havent worked with it much.

 

[bns454]

Will the Loverins take much velocity,say 2300 ?

 

[Ian]

I'd like to see a lot less unsupported nose than the 471 myself.

 

[Ian]

Will the Loverins take much velocity,say 2300 ?

Maybe. Depends a lot on the alloy you use (weak bands), barrel length, and powder selection. A slow powder and compacting buffer, very carefully worked up, can do wonders for Loverins. I managed to get 2200 fps/1MOA from a Swedish Mauser using a lapped-out 266469 that everyone said wouldn't do high-velocity.

 

[bns454]

So on that 32-180D I would design the mold so the nose engraves too ?,or just the bands.