Bench Rest quality swaged core design questions

[martinwf9c]

Hi gang,

I am new to this forum but have some experience in swaging copper jacketed 22 and 6 mm bullets in both dies that I have purchased and dies that I machined myself.

Recently, I have been dissecting commercially available 22 bullets (cutting them from tip to base) and noticed somthing interesting in a Sierria Match King hollow point boat tail bullet.  The core was made and/or swaged into the jacket in a method where the core had a formed tip which minimized the contact with the ogive.  Where the core entered the ogive, there was about a .050 gap that extended about .100 inches up into the ogive.  The core on the base and on the bearing surface of the bullet made complete contact but not so in the ogive.

This got me to thinking.... Did they do this to maintain a precisly centered core?  Is it possible that flat lead cores forced into the ogive become inconsistantly centered when doing point forming?  Then I thought, what effect would an off center core have on accuracy (my thought is that it would affect group size)?

To do an empirical test, it would seem that one should have access to some sort of high speed wind tunnel with the ability to spin the bullet during testing.  Is there another method?

Your thoughts?





 

[talon]

While I can't comment as to how or why Sierria did what it did with those bullets you sectioned, I do know through experience as a hobby swager using Corbin dies that if the jacket isn't fully supported by a lead core there's a good chance that the upper end of the jacket, along the ogive,can get wrinkled ( parallel with the length) when pointing up.  When you make open-tip bullets and the core is set down deep into the jacket you have to be careful about this effect.  Too, it is a possibility that Sierria forms their bullets with accuracy only being one criteria. The method /design they use also takes in the capabilities/limitations of their presses and tooling. As far as use of a wind tunnel to observe flight characteristics of ANY bullet or shell is concerned, I've never heard of such a thing. Where the holes show up on the paper at 100, 500, and 1000 yards is a true indication of accuracy, given all else remains constant. If they aren't accurate, finding out 'why' usually is a very difficult problem as there's more to it than the bullet itself. I can see when wind tunnel observations would be really beneficial, but the technology isn't there yet ( I think).

[84Jim]

That's an interesting concept!  However I don't figure many bullet companies are that hi tech.  3000 fps translates to over 2000 mph.  A quick check on Wilkipedia confirms that they can create Mach 1 speeds (1125 fps).  Plus you'd have to instrument the bullet somehow to measure very minute differences in force.

I think that the trial and error that we all do on the benchrest range is the simplist way to test bullet design.  Talon, do you have any pictures of your sectioned bullets?

Jim

[martinwf9c]

Hi again,

My initial post and thoughts about wind tunnel testing was to eliminate the many hundreds of variables that exist when actually putting bullets down range and just concentrate on the bullet itself.  I was not really thinking about trying to achieve high velocities of air speed (although that would be very interesting), I was contemplating enough air speed to keep a bullet suspended like an air hockey game.  This would then allow the bullet to rotate to show if the bullet was heaver on one side than the other where the heaver side would be drawn by gravity to the bottom similar to a bicycle wheel. 

As a secondary experiment, if the bullet could be made to spin, it would then show a wobble or yawing effect where the actual center of gravity would be different than the physical center of the bullet.

Given that this testing could be done, I am sure that it would show some interesting results for both commercial and hand made bullets.  My original premise was that lead, when forced into the ogive, may affect the actual center of gravity as it may be displaced along the folds of the jacket when the ogive is formed.

I will try and post some sectioned bullets if I can get some close up pictures with my digital camera.  I have cross sectioned 3 of my own bullets and about 10 other commercial bullets.  I cut them with a jewelers saw and then flat file them to get samples similar to what they do for metallurgy.

Another interesting thing is that the amount of the core extending into the ogive varies depending on manufacturer.  Some just start to enter the ogive while others will go ¾ up the ogive.  The most common hollow point is about ¼ up the ogive.

Martin   

[Steve P]

.22 jackets are relatively thin.  It doesn't take much pressure to cause the jacket to wrinkle when point forming.  It sounds like Sierra may have used a core seating die with top punch that causes expanding lead to form into the point shape.  Less chance of jacket deformation if lead is already partially formed. 

I think you may have unveiled one of Sierra's proprietary processes that leads to less rejects and possibly more accurate bullets. 

hmmmmmmmmmmmm  how can I use this info............. 

Steve

[talon]

A Hollow point(HP) bullet is one that has an indent or cavity in the forward portion of the core. An open tip(OT) bullet is one where the jacket's walls have been closed at the point, leaving a small opening, with the core material not seen at the tip. Sometimes an OT bullet's core is real close to the tip, sometimes it's even below most of the ogive. For us hobby swagers, sometimes the amount of core in the jacket has more to do with us not having the proper length jackets for the weight desired. How deep the core is set does effect the C of G and therefore the stability, greatly after a certain point. An OT bullet's effect on the target is  irrelevant for bench rest shooting, but significant on game. An OT with a deeply set core doesn't hold together in a deer ( for instance) and you get immediate separation of the jacket and core. Then, the core starts separating making a mess with what would otherwise be nice steaks or roasts. The closer the core is to the tip the 'slower' this separation happens. Core bonding almost totally prevents seperation, but that is an extra step and a few more pennies per bullet in costs. A HP bullet used on game is not wise at all. On coyotes, raccoons, woodchucks they are OK I suppose. I digress. Sorry. This has nothing to do with ballistic science except for the definitions. As far as wind tunnel technique, the test subject is mounted in a fixed position. I suppose a jig could be made to rotate the subject at whatever RPM is needed. A more practical method to study a projectile's free flight is to use a series of high speed cameras along the flight path... perhaps every 10' or so. I wonder how much 100 high speed cameras and their miles of film ( or digital recording chips) cost?

[martinwf9c]

Talon et. al.,

Sorry about the misuse of terminology between open tip and hollow point.  Guess it’s a throwback from the commercial manufacturers and the terminology that they have been using for years.  In my case, I have been making open tip bullets and not hollow points.

What initially started me down the path of cross sectioning 22 bullets was that I had been making them on a .704 J4 jacket at 50 grains with good results.  I then made a batch (500) at 55 grains with the same jacket where the lead came all the way to the meplate (opening).  I tested these 55 grain bullets in my bench gun and they opened up my 5 shot groups from .15 to about .375 at a hundred yards with all else being relatively equal.

Disappointed with the results, I started thinking about some of the military bullets that are lathe turned out of bronze.  If the military shooters can get good results out of a homogeneous bronze bullet, why could I not get satisfactory results out of bullets that the core extends up to the meplate.  The only thing that I could come up with was that the core when swaged into the ogive was somehow not uniform or the center of gravity moving forward had a big effect on bullet stability.  After that, I began to think how would one test bullets without all the other influencing variables of shooting them.

I understand your point about the bullet holding together for hunting but since I am a paper puncher and not using these for hunting, I don’t necessarily think that core bonding would increase accuracy (but I could be wrong).  The dissecting of bullets that I have done indicates that the core bonding between the core and the jacket is pretty darn good – 15,000 psi pressure forms the core tightly to the jacket.  I have to exert a lot of force to dislodge the core from the jacket and close examination indicates that the core exhibits slight imperfections that exist in the copper jacket.

Where I am going next is that I have some .740 J4 jackets on order (should get them sometime after the first of the year) and I intend on making some 55 grain bullets with the ogive partially filled.  My guess is that they will group better than the fully filled ogive .705 open tipped bullets.

In terms of high speed cameras, it would work but it is not in my budget range.  Is this what they do for military projectile ballistic testing?

By the way Talon, it sounds like you have a lot of experience in this… What’s your background?

Martin

[ANeat]

In my limited benchrest experience I didnt see a lot of folks shooting Sierra bullets.  Going from a 50gr to 55gr bullet and seeing the groups open up a little can be any number of factors including the ones you mentioned.
  
 
   If you wanted to make a bullet like you described in your first post I would think that instead of a flat core seating die you could substitute die with a point up feature.  (basicly a point up die with a smaller diameter)
 
  Point up/core seat and then point up the jacket.
 
   I would be curious to see what something like a 68gr berger 6mm would look like sectioned and how much space is in the tip
  

[talon]

The more I think about space between a core having the same shape as the jacket, in say, a 6S ogive bullet, the more I think springback is the cause due to, perhaps, improper annealing at the factory. If this space was created on purpose, I have a problem understanding the benefit.  Sierria does not make any  mention of the unique core-space-jacket construction you've pointed out.  Another possible reason there is that space is that the jacket material was heated up from your sawing and may have simply expanded. As the ogive area was under the most stress, it could have expanded more than at the waist. True, this separation isn't seen in other sectioned bullets one sees in publications: did you use a powered tool to do the sawing?  As far as having a core seating punch designed to place an ogive on the core while seating it there are at least 2 issues: a. a punch having a feathered edge doesn't last long and, b. If the punch has a squared edge, there will be, at the minimum, too much space between the core and jacket ogives. This will probably result in a deformation at the beginning of the ogive as the jacket is being pointed. These are just thoughts as I've never seen such a bullet and have never tried to make one. I've been fooling around making jacketed bullets for only 13 years, but make lots of different calibers using commercial as well as tube jackets from .012 to .065" walls, with manual as well as powered presses.  Believe me when I say I still am in the learning phase in this hobby.

[MIBullets]

I have seen pictures of Sierra's process for their long range 30 caliber bullets. They preform the boat-tail on the the core and on the jacket, possibly the nose as well. I don't believe they use dies and punches designed like the ones we use or use the same exact steps. My guess is the core seating and point forming are done together. Maybe the bullet is then very slightly sized to the correct diameter with a parallel shank. This is just my guess from what I saw and by no means how they may actually do it.

I agree with Talon. If the jacket is really separated from the core and the core was preformed, jacket spring back could be the cause. Also they can't use a punch like we would to make boat-tails since theirs are not rebated. That's why Corbin and others use a rebated boat-tail, so we don't break the fine edges on a punch that makes a normal boat-tail. I know no one asked about boat-tails, the reason I brought it up is that it is a design that points to the fact that they don't make bullets exactly like we do for the most part.

I would think that a flat ended core would be best, unless you preform for a boat-tail, but you still need to core seat before point forming to get the jacket spring back to grab the core.

The 50 versus the 55 gr bullet could possibly be just the guns preference or the fact that the twist rate for the barrel may shoot the 50's better. I am assuming that you have a 1 in 14" twist. 55's and even 60's will shoot in a 1 in 14" twist but they are getting close to the high side. Average shooters would be jumping up and down with those groups but slight differences are more easily noticed in a gun/barrel that can shoot like a bench gun. I will be interested if the longer jackets make a difference for you.

Again, just my thoughts.

[martinwf9c]

Dear bullet swaging gang,

Sorry I have not kept up with the posts, it’s a busy time of year. 

In regards to ANeat’s post, yes that is true that Sierra bullets are not used much for bench rest.  Most of what I see are Hottenstein, Euber, Bart, and Ulrich which are to my knowledge all custom made bullets to very exacting standards and somewhat limited in availability.

I have machined a point up die for core seating and made a few hundred bullets to try but the weather has not been cooperating.  I live in Illinois and only get the chance to shoot during the weekends (somehow work always seems to get in the way of fun things I want to do).

In regards to talon’s post, I seriously doubt that springback is the cause because it would have to be .1 overall to produce .050 on each side.  It would also seem unlikely that at the beginning of the ogive it is against the wall of the jacket and the gap is only at the tip. I also did not see this on any other bullets I crossectioned.   I did not use a power tool to cross section the bullet.  My method is rather crude in that I lightly clamp/hold the bullet in a small vice and use a jewelers saw to cut it as far as I can.  The bullet will free itself from the vice when I get a little more than half way through as it wants to close the gap created by the blade.  At that point, I will take the bullet in my hand and manually move it back in forth on the blade while holding the blade stationary in a vice.  When the bullet is in two pieces, I will select the largest piece and flat file the bullet half until I get a clean cross section.  Even though I have been swaging for a few years, it is a never ending learning process for me.  I started out with a reloading press and have moved to horizontal press that I built a couple of years ago.  No powered press for me as I want to “feel” everything that is happening during each step of the process (I am probably old fashioned in this regard).

In regards to MIBullets post, I have not seen much published in the way that commercial operations make their bullets.  It would be educational to see pictures and get an understanding of how different their process may be.  If you have some information, I would be very interested.  In terms of barrels, I have both 1 in 12 and 1 in 14 twist rates.  Most of my testing has been in the 1 in 12.  The testing that I was doing involved taking a .704 J4 jacket and making (in the same dies) 50, 52 and 55 grain flat based bullets.  Each bullet was identical with the exception of the size of the lead core and how much it filled the ogive.  I have to admit one other variable which involved a half grain difference in powder charge between the 50/52 and 55 but I would not expect this to have a large impact on group size.

You all have a good Christmas and thank you for your input.  I will keep you posted on additional results.

Martin

[Cat Whisperer]

....
I can see when wind tunnel observations would be really beneficial, but the technology isn't there yet ( I think).

Back, almost a hundred years ago,  Dr. Franklin Mann wrote much about perfection of cast bullets.  One of the devices shown in his text was a bow used to spin the bullet (on it's nose) at high speed to determine it's stability whilst rotating.  Hmmm.  Low-tech, but quite functional in producing an observable spinning bullet.