Bullet Diameters

[CJR]

In my readings, there appears to be three schools of thought for sizing PP bullet diameters. One school (BP users) advocates first sizing bullets to bore diameter, PP, and then shooting. This is because BP fouling prevents chambering follow-up bullets that are sized to groove diameter. The other school (most smokeless powder users) advocates sizing bullets to bore diameter, PP, then sizing to throat or groove diameter. The third school ( NRA PP articles) recommended just PP cast bullets, and sizing to throat or groove diameter. For smokeless powder users, has anyone noticed improved accuracy of one school over the others?

I would think that PP a cast bullet and sizing it to throat or groove diameter achieves the same thing as first sizing a cast bullet to bore diameter, PP, and then sizing to throat or groove diameter. The only reason to justify the extra sizing steps would be better accuracy.

Best regards,

CJR

[docone31]

My bore is .312.
When I sized to .3135, my groups were 20ft at 100yds.
When I sized to .314, my groups were 1-2" at 100yds.
when I sized to .315, my groups were unpredictable although still better than .3135.
This is a .303 British, with 40.4gns of 4895.
I size to .308, then wrap, getting .317-.318, then size to .314.

[montana_charlie]

In my readings, there appears to be three schools of thought for sizing PP bullet diameters. One school (BP users) advocates first sizing bullets to bore diameter, PP, and then shooting. This is because BP fouling prevents chambering follow-up bullets that are sized to groove diameter.
The school attended by the majority of BP users advocates something slightly different than what you gathered.
First, the bullet is normally 'cast' at the desired diameter. It's only 'sized' down to that on rare occasions...usually when experimenting.
Second, the bullet is cast at a diameter which is less than bore...then patched up to bore, or slightly more.
The reason for shooting bore diameter 'packages' is so the bullet can be seated out of the case far enough that almost all of it is in the bore (not in the case) when fired.

The black powder fouling is handled in a variety of ways. Wiping between shots is common among target shooters, but 'shooting dirty' is more common for hunters. They will use one of several methods to incorporate lube within the loaded round...which is meant to keep the fouling soft enough to allow reasonable accuracy on following shots.

Some BP shooters are successful with bore diameter bullets patched up to fit the groove diameter of the rifle. Even they can fire a few rounds while 'shooting dirty'.


The other school (most smokeless powder users) advocates sizing bullets to bore diameter, PP, then sizing to throat or groove diameter. The third school ( NRA PP articles) recommended just PP cast bullets, and sizing to throat or groove diameter. For smokeless powder users, has anyone noticed improved accuracy of one school over the others?
It is true that smokless paper patchers look for a 'package' that is groove diameter, or close to it.
Most of the sizing you read about, before and after patching, results from using bullets and paper which are not pre-matched for the desired diameter. Frequently, the bullet comes from a mould that produces grease grooved bullets of groove diameter. It must be sized down to make room for the paper.
The use of 'whatever's handy' paper may result in a package that is a bit too fat, and running the whole thing through a sizing die is one way to 'adjust' it.

But paper patching can be done successfully without sizing anything, if the original bullet is cast at an appropriate diameter and the paper is carefully chosen.

CM

[1874Sharps]

Charlie said it well. Paper patching is an art as well as a science. You will find some great innovation and depth of experience in this part of the forum on paper patching. It is interesting to me that there does not seem to be hard and fast rules, as many have had good results using a variety of papers and methods and procedures.

The way one goes about paper patching probably depends most on what type of shooting you will be doing. For myself, I am interested in performance in the field more so than on the bench (I do not shoot competitely). The long range target competitors who swab the bore between shots will be looking for something different than the hunters, in general.

BP shooters can get away with shooting bore size packages because the BP will "bump up" the boolets. Smokeless will do a little bumping on a soft lead boolit, but not nearly as much. Your choice of boolit will be determined by the type of shooting you wish to do.

[Lead pot]

Charlie, Son I'm proud of you, well said.

1874 Sharps.

You can load a PP bullet for use out in the field for hunting or just busting rocks using a BP load and a PP bullet patched about .002 under bore diameter or right at bore but seated a couple thousands off the lead.

I have a Pedersoli I use just for this purpose just using barrel sights out to 600 yards that I have shot this way and stayed on the iron at the Quigley range, just load and shoot for many rounds with out a blow tube or swabbing the bore and accuracy is decent enough for busting rocks or hunting distances.

[pdawg_shooter]

For smokeless I size to BORE diameter +.001/.0015, patch to GROOVE diameter +.002/.003. I then lube and size to as large as the throat will handle. Works for me.

[barrabruce]

Do you really need lube on a paper patch???

I seem to get better groups with out lube with my grasshopper attemps. Smokeless of course without any type of lube.

These I don't size after wrapping either.
I only size to get a diameter I need/ Think I need to wrap.
bore -001" on the driving bit of the bullet.
wrapped to groove + 0015" or so at the driving lands and bore + just enough to leave a mark when chambered on nose section.
They seem more fragile than the lubed boolits but shoot better for me.

Ammended for zeek and others if you feel the need to wade though it all.
This aint a full power load but more of a Shuzten experimental load for fun and plinking maybe game.
I wanted to see if I could bump up like black powder loads but with a slightly different approach. IE patched to groove.
I think it does for the results I have seen that a fast powder and a mid load with soft lead does somthing. Probably not as good as holy black thou.
Best efforts so far have been in my 30-30 H & R 4 groove barrell 180 rnd lee. Mangleated to a 185 flt point..now a 190 fp. My bore is 0.302-3" grove 0.308" .
Alloy used stick on wheel weights with a few old clip on wheel weight reject bullets added.
Quiet soft but not finger nail pure lead soft.
Sized to 0.302 2x wrapped with cig papers.
Cig papers are folded so the gummy bit sticks up when wet and doesn't stick to the boolit; and ...the fold extends to the normal lube groove base section. The single layed bit of the fold extends up till it is a bit past the contact area when seated in the chamber.
Bases are folded and sat up to dry on bases which I have found needs to be more in towards the centre than just a thin lip around the base. This helps prevent the pushing down of the bullet and the paper stretcing over the base of the bullet when seated some times.
I do not size as these come out at 308.5"-309" at the base and 304" athe the nose.
I do get some bump up at the nose but they seem to work just fine seated at normal seating depth and not touching the lands.
I was getting a bit of paper hang up in the case/thoat start but maybe a bit of a moving start has help from a standing inertia at this junction.

I have less vertical stringing with soft annealed cases and made a flaring tool to make sure they are pretty unifrom in diameter before seating.
I haven't bothered with indexing anything yet but may.
Load is worked up form hunting around and finding a 2400 load for shuzten shooters for 30-30.
I have tried 16 grns of 2400 bit it cratered the primer so I stopped. Groups started to blow out as well. Dropped it back to 14.5 and I.ll just leave it there for these.
Worked up to this from groups and primer detent in MY gun and MY boolits. As always change one variable and results will differ.
14.5 gns 2400 guestimate @ 14-1500 fps.
3/4" at 100 yrds. not tested to 200 or 300 yrds yet.
No lube on paper.
Have to test with some lube thou.
Flat out loads with 2208 (Vargent) showed a bit of slipping and I may have to harden up the alloy to 50/50 pure wheel weights.



Barra.
They's bean teachi'n me all they know'd and I still know'd nothi'n.

[pdawg_shooter]

I lube for 2 reasons, 1: to reduce bore friction and 2: I hunt with my paper patched bullets and the lube waterproofs the patch.

[barrabruce]

Thanks Pdawg

[Zeek]

My bore is .312. When I sized to .3135, my groups were 20ft at 100yds. When I sized to .314, my groups were 1-2" at 100yds. when I sized to .315, my groups were unpredictable although still better than .3135.
This is a .303 British, with 40.4gns of 4895. I size to .308, then wrap, getting .317-.318, then size to .314.

Nice, Docone31, but what design, weight, alloy, and hardness is that bullet?
Thanks, Zeek

[Zeek]

Smokeless of course without any type of lube. These I don't size after wrapping either. I only size to get a diameter I need/ Think I need to wrap. Bore -001" on the driving bit of the bullet. Wrapped to groove + 0015" or so at the driving lands and bore + just enough to leave a mark when chambered on nose section. They seem more fragile than the lubed boolits but shoot better for me.

Dear Barrabruce:
Please add in your alloy hardness and, if different from starting J-word loads, your pressure range. That makes it easier for others to repeat your approach successfully.
Thanks, Pesteriferous Zeek

[montana_charlie]

Nice, Docone31, but what design, weight, alloy, and hardness is that bullet?
CJR began this thread looking for confirmation of his understanding of some paper patching fundamentals.

Docone has posted his load and alloy specifics in a number of threads where that kind of information was traded.
If you really think you want to duplicate his bullet hardness, be ready to add some zinc to your pot...as you use the search feature to find his detailed posts.

CJR, are you still here...?

CM

[303Guy]

Alloy composition could be more important than one thinks.

I have just cast a few boolits and am astounded at the difference in as cast size. Same alloy, same mold, same pot temperature (more or less).

Base shank with warm mold - 6.45mm/.2539"
Base shank with very hot mold - 6.02mm/.2370"

Nose shank actually tighter on hot mold sample!

Nose shank with warm mold - 6.03mm/.2374"
Nose shank with very hot mold - 6.04mm/.2378"

Base shank with very hot mold - 6.02mm/.2370" (Mold size .258)
Nose shank with very hot mold - 6.04mm/.2378" (Mold size .2375?)

Go figure!:shock:

So how much does alloy and contaminants influence the boolit size we choose or find to work best for us?

[CJR]

CM,

I'm still here. All the responses have helped me. The one thing that keeps me interested in PPCB is the NRA's work that produced loads used in regularly scheduled 1000 yd. competition. My groups at 100 yds. are now about 1.5 to 2" , with no keyholing, and I'm happy with that. My 311291 CB are water dropped WW and are weighed and separated into lots that vary by one(1) grain. However, I'm still playing with H4895 powder/charge selection, but my tightest groups so far occurred at an estimated 2600 to 2700 fps (based on manual info). These loads are approaching 100% loading density and are really moving out of a 308Win. If a deer were standng at 100 yds, he'd have a hole in him. Once I finish my load development, I will chrono my final loads. I've also followed the NRA's advice and I'm using a teflon/wax spray. This seems to work better than lithium grease which I tried.

I think, based on the responses given here, I'll pick up a Corbin 0.301" sizing die and first size my 311291 CB to this diameter, then PP, then final size to 0.3095". Then I'll compare their groups with an as-cast 311291 PPCB just sized once to 0.3095". All this effort has also caused me to re-evaluate all my handloading equipment and upgrade were necessary. This has been a very satisfying effort and my goal is to see if I can get some 0.5" groups at high velocity. I plan to do a lot of load shooting/note-taking next Spring. Life is good!

Best regards,

CJR

[barrabruce]

Is that better Zeek???

[303Guy]

Something that I have found. Seating the boolit does a measure of sizing or compressing the paper.

Something else - and this has no field trials to say it's good or bad - is that if the lead core is reasonably soft, it bumps up so that a bore-ride nose section that leaves no rifling contact marks on the paper on chambering will have rifling impressions on the core after firing at low enough velocity to recover boolit intact.

This could also mean that higher velocities with the soft core might not work. I don't know. There is a simple test I could do. I know that a certain alloy with a cirtain powder charge shoots well in plain cast. I could size and patch those same boolits and test them with the same powder charge. Mmmm ..... :idea:

[Zeek]

Is that better Zeek???

Well, yes, even though it had lots more detail than I would ask you to provide. Thanks plenty! WHY do I ask for the alloy hardness guestimate to be included? Here is what your new input tells me that I could not get without it.

Bringing up your bullet weight and charges on QuickLOAD, I find that the 20gr charge yields ~59 Kpsi (way plenty!), and the 14.5 grain charge yields ~28 Kpsi and just under 1700 fps MV. Most rifle-cartridge BP loads max out at ~25 Kpsi. So, now you know that you are "in the ballpark" for your desired goal of duplicating BP pressure to see if a groove-diameter softish-CBoo-PPCBoo would work. Excellent work & a damn good experiment!

Now, given your additional input, let's take it a bit further, to the real succulent core, even. Your mostly-PB-&-some-WW-no-thumbnail-mark comment makes be guess that the Bh of your alloy is ~8. If so, then the Kpsi/Bh ratio is 28/8 = 3.5. By contrast, the standard Kpsi/Bh ratio for GC/lube-in-grooves CBoos (= 1.5) would have made a good-for-accuracy pressure of ~12 Kpsi which, with that powder, would have been 9.5 grains for an MV of ~1200+ fps. Hitting the optimal Kpsi/Bh ratio for any PPCBoo test load is really important, but FIRST, we need to FIND what that ratio is (impossible with just the powder, charge, and wrap info usually provided here).

In my opinion, this is exactly the sort of thing we need to do, here at this site, is to work out the WHY and HOW of all parts of the PPCBoo trick, not just the how-to-wrap-it-and-what-with part. I have DOZENS of 3"+ 50 yard PPCBoo targets (using loads provided here) to prove how useless it is to work in the absence of the full range of essential basic load information. Not good!

One of the few other folks (on this site) who provided the powder, charge, bullet weight, and bullet hardness info for a well-functioning PPCBoo load yielded a Kpsi/Bh ratio of 3.1. Instead, most folks say the CBoo weight, powder, and charge ~~~> with which one can learn NAAAAH-thing and it prevents one from being able to repeat their experiment. So, thanks way-plenty for providing your additional input. It really helps.

Please, folks, include your best guess as to the Bh or your alloy. If not heat treated, then just the alloy description is enough. Thanks a bunch,
Zeek

[303Guy]

...is to work out the WHY and HOW of all parts of the PPCBoo trick ...I like your thinking Zeek.

I want to devise a way of 'measuring' boolit alloy along the lines of;
min hardness (annealed) - ductility, hardness, bend strength, impact hardness;
max hardness (oven heat treated) - ductility, hardness, bend strength, impact hardness.

The idea is to compare the properties of alloy batches rather than composition and somehow relate those properties to boolit performance, in the gun, in flight and on impact. (Something like comparing soft apples to hard oranges [smilie=1: )

I'm not seeing anything simple here but it needs to be simple enough to be do-able at home.

[Zeek]

Well, 303Guy, I may not SOUND like it, but I'm a KISS kind of guy, at least where the ladies are concerned. From my view, all that really matters, here, is malleability versus max-chamber-pressure. Foddermore, malleability follows close on the heels of Bh of the alloy, whether inherent in the annealed alloy or put there by heat treating. I promise you there there IS a REAL and RELIABLE relationship between the Kpsi/Bh ratio and the optimal pressure range.

My theory is that this IS a matter of matching the CBoo-core's malleability to its obturation-and-therefore-sealing performance in the bore. The CBoo core MUST obturate to clamp the PPatch the against the bore, if sealing is to occur. That also crushes the PPatch to the point where it is dead-hard and can transfer the large torque (of the rifling spin-up) to the CBoo core.

Why relate Bh to that fact? Ha! ALL Bh measurement tools work on the fact that their point PENETRATES (i.e., pushes-aside) the alloy . . . the softer the alloy, the more malleable, so the further the point can penetrate. That's a very direct relationship, so fits my KISS (keep it simple, stupid!) proclivity to a tee.

I can PROVE it to you, too, I believe. Look at all the successful (accurate) combos that patch-up a too-small CBoo core to just over the rifle's groove diameter, yet they shoot like a house-afire. In order to work, the CBoo core must expand to the point where it has crushed the everlovin' sheets out of that patch, at which point it KEEPS ON trying to expand, thereby providing a seal, AND, at the same time, keeping the PPatch so damn hard that it can transfer the torque.

If you shoot that PPCBoo at lower and lower max pressures, at some point, it will STOP expanding enough and you will loose accuracy until you use a softer core, at which point you can move on down the max-pressure scale further. Likewise, you come to a limit (reflected by the Kpsi/Bh ratio) where the core is too soft for the pressure you are running. There IS a range of what works, and we really need to find out what it is and then make that clear to folks trying to find workable loads.

So, the key is to KNOW what the "sweet spot" is for the Kpsi/Bh ratio. Can I get that yet on this website? Can I even figure it out? Heck no! Folks keep talkin' lovely loads for succulent chamberings, but almost never mention their core-CBoo's Bh. "Thank you very little!" is all that I can say to that. How many first-timers are we loosing who try it, but fail to hit minute-of-hippo-ass at 50 yards because their loads have the wrong Kpsi/Bh ratio for the pressures they are running? We'll never know, but we need to STOP that and provide VIALBE WORKABLE load-development formulas. That way, when the newbie tries it, it just flat works, right from the get-go. I hope this lets you see why I get a bit "exercised" when I keep finding half-measure information on post after post.

If you know the range of Kpsi/Bh ratios that WILL JUST FLAT WORK for a PPCBoo, and if you know your CBoo core's Bh, and if you have QuickLOAD installed on your PC, you WILL be able to come up with low-to-high loads for ANY powder, ANY chambering, ANY (viable) PPCBoo, and then go to the range and have one thing after another just flat WORK for a change. Perhaps it is just me, but I find that preferable.

Next time, I'll tell you how I REALLY feel. Thanks for your and Barrabruce's good input! It is a start.
Regards, Zeek

[303Guy]

OK. So the Brinnell hardness tells us all we need to know. Great! It makes it that much simpler.

I figured there was a hardness chamber pressure ratio and possibly muzzle pressure too. You put my magnets together so to speak when you mentioned the ratio. It was one of those aha! moments. There are so many variables but there must also be set of rules or imperical formulae that covers them all and as you put it, will get the beginner going right from the get go.

By the way, I have just discovered another variable. Not only does paper have a grain direction, an inside and an outside but a top and a bottom side too! In trying to econimize on scissor strokes, I fitted my printed patch upside down and back to front with each other. Some will roll to make the ends meet and some will leave a gap! Doh!:veryconfu This is still cutting accross the grain. I'm trying to figure it out right now.

Different papers also stretch and take a shpe in different ways. Two papers same pattern patch and the one overlaps at the bottom edge only. Result - slightly different pattern for that paper.

I do think that the first time patcher is going to need a little practice to get the patches on right. That's just a practice thing.

[docone31]

I do not know my Brinnel number on my patched loads, but I do know, I cannot scratch it with a fingernail.
I water drop wheel weights with 2% zinc or so.
I mix in zinc untill it gets thick, then remove a bit, and add an ingot.
Those I then size, and wrap, and then finish size.
Works for me.

[Nrut]

docone31,
Perhaps you can mail a few of your unpatched boolits to someone (Zeek?) who has a hardness tester.. It would be interesting to see what your alloy with zinc test out at on the bhn scale..
Zeek,
What type or brand of hardness tester do you use?

[Digital Dan]

No intention of raining on the parade but it seems to me y'all are backing into the issue at hand.

http://en.wikipedia.org/wiki/Obturate

Lead BHN is well understood so far as alloy mix goes so it's mostly a matter of mixing what you want or need. Even standard use alloys such as wheel weight lead are fairly predictable and minor variations of alloy content are not going to skew the BHN greatly.

Looking at the practical aspects of alloy vs. pressure gives the perspective that there are two thresholds of significance so far as accuracy is concerned. First is having enough pressure to obturate the bullet, second is having enough hardness that the bullet does not strip the rifling. So far as I've experienced BHN 5 is adequate for up to about 1800 fps (18-20" twist) from large bore rifles and that's a lot of leeway in my opinion. Bullets only obturate to the degree the bore allows.

The only other consideration of merit has to do with nose design re: slumping, otherwise the mechanics of PP loading are the same as GG bullets. Both methods require proper bore/bullet dimensional compatibility.

My way of saying that perhaps this subject is being over thought a bit.

On the previous comment about lubing or not lubing patched bullets, one may do or not do that as they see fit. Make no assumption that unlubed patched bullets do not carry penalty, for they will accelerate wear on the bore via abrasion. Have used that characteristic a couple of times to polish gray bores in old rifles, works like a charm...quickly.

[barrabruce]

Digital Dan...Thanks for that comment on the dry PP bullets. Didn't know that.
Zeek interseting theory.
I have no Loader program to play with.

But I was thinking that...with a fast burning powder it would whack more the base of the motionless bullet and deform it more than a slower burning powder with more of a push.
And build up its pressure real early in the peace instead of mostly along the full lenght of the barrell.

Any who I find reading of others theorms interesting.
I didn't fare to well today at the range...but lernt something new anyway. :)

Barra

[Digital Dan]

BB, on your comment about fast and slow powders re: obturation, it all boils down to how much pressure is exerted on the bullet base. Sounds simpler than it is actually. Exactly how much pressure and when it occurs is a matter of comparing pressure curve and acceleration of the bullet. A crude comparison might be found in the initial pressure rise from primer detonation, which is small, but it does begin to move the bullet. It certainly does not contribute to obturation however.

More flies in the ointment: a slow powder may generate greatly increased pressure as compared to fast, but that does not preclude an ability to obturate lead. What a lot of folks do when discussing this subject is forget about quickness as defined by internal ballistic speak. Burn rates are one thing, quickness is another and it is variable as a function of pressure. In other words, maybe a slow burn rate, but under confinement the rate quickens substantially as pressure increases. It's a phenomenon BP doesn't really experience as it's burn rate is largely stable, regardless of pressure.

The calculation gets a fair bit beyond anyone's ability without serious lab test equipment in any case, therefore I don't see a lot of point in speculating on any level other than broad conceptual standards.

In the end, what is considered here boils down to a question of whether a given load will function well within certain parameters of alloy, weight and charge. The variables are so many that for the lay person the path of least resistance is to simply go shoot and see what comes of it.

Questions posed with conditions:

Given:

-Expansion ratio (ER) during the firing/ignition sequence of 1.5:1, meaning the bullet has moved sufficiently from the case such that the then existing volume between bullet base and interior case base has increased 50%.

-The bullets are lead, of the same alloy and sectional density

-variables such as bore friction, engraving forces, neck tension etc. are equal

-one cartridge is loaded with a "fast" powder and generates peak pressure before the bullet base exits the case mouth, and that pressure is 28KPSI.

-second cartridge has a "slow" powder and generates peak pressure at the previously mentioned ER of 1.5:1 location in the bore, and that pressure is 48KPSI.

-From the link above there is the formula that provides a threshold value for obturation as a function of pressure and alloy hardness.

Questions:

1) Can you define and support the amount of obturation that has occurred with each bullet by calculation?
2) Can you illustrate the different ratios of pressure vs. acceleration affecting obturation in each circumstance?
3) Would you prefer to follow a more pragmatic research program dominated by a lot of shooting?

[303Guy]

Digital Dan

It's true what you say. I can't speek for others but I cannot resist the opportunity of using any scap lead I can get hold of cheaply or better yet, free. Therein lies the need to find out what I've got and what to mix it with to get what I need.

Just to complicate things a tad, I not only want accuracy and range, I expect hunting performance from those boolits which means a balancing act between too hard and brittle and too soft for both terminal performance and bore performance.

Then, when the boolits are better described as torpedo's, well ...

Not to overlook the fun factor either!:mrgreen:

You mention the boolit stripping the rifling if too soft or driven too hard. I've not found evidence of that occuring. I would have thought it more a problem of exessive pressure against the bore resulting in 'seizing' and surface melting of the lead which would destroy the integrity of the boolit, not to mention leading of the bore. That I have seen and surprizingly, not a lot of leading with it. Just a grey 'dusting' in the bore.

[longbow]

303Guy:

Bullet hardness is a balancing act amongst several issues, largely alloy strength versus chamber pressure and rotational acceleration.

Chamber pressue is what exerts the force on the base of the boolit to cause acceleration. Inertia of the boolit wants it to stay where it is. When the applied force produces stresses exceeding the yield strength of the lead, it yields.

In the case of obturation, the base of the boolit yields first and depending on the chamber pressure and stress the boolit may yield along more of its length. I have had boolits almost completely slug up and lube grooves disappear when alloy was too soft (low yield strength).

For rotational forces, the boolit is forced into the rifling which digs in and trys to spin the boolit and again inertia does not want it to rotate. If the alloy yields to the rifling the lands will cut larger/wider grooves in the boolit and if stresses are high enough the lead will smear out of the way. Also contributing at that point is gas cutting as a gap is produced at the trailing edge of the groove in the boolit so there is a passage for gas to get by unless the base of the boolit keeps obturating enough to seal.

I have found recovered boolits from my .303 that show wide grooves in the boolits and gas cutting. This is for plain base boolits or gas check boolits without gas checks. I wound up oven heat treating to solve the problem. The harder boolits seem to do much better.

However, if boolits get too hard to obturate then you may get gas cutting if the fit is not good.

There is a common misconception that the yield strength of the lead has to equal the chamber pressure but that is not true. The strongest heat treated lead antimony alloy runs about 12,500 Psi yield strength and not many of our cast boolit loads (in rifles at least) run pressures that low.

The rule of thumb is that the chamber pressure should exceed the yield strength of the lead by 3 to 4 times. The yield strength is related to Brinell hardness and that is what is usually used to work out the correct alloy strength for a given chamber pressure or vice versa.

I have a very good article by Ed Harris describing this but do not find it on the internet anymore.

Much of the same or similar content is here:

http://www.lasc.us/Brennan_3-3_CastBulletHardnessRequirements.htm

Here is another good read by Glen Fyxell:

http://www.lasc.us/CastBulletNotes.htm

Personally I think it is a very complicated issue that can be over thought and take up much time unnecessarily.

In my case, I found I was getting poor accuracy with ACWW and noticed gas cutting and potential stripping of boolits so decided to oven heat treat. It worked. I'm happy.

I think boolit fit and barrel condition are about the most important aspects shooting cast boolits. If the boolit is undersize it will lead and generally not be accurate. If the barrel is rough and uneven so allows gas cutting then the boolit will lead and generally not be accurate.

Gas checks help keep the gas where is supposed to be so make it easier to avoid leading and achieve decent accuracy with a less than perfect fit of boolit/barrel.

Paper patching allows a caster to easily tailor the boolit diameter to the barrel. It also provides a material that seals well and won't gas cut to produce leading ~ or not unless fit is really bad and the paper burns off.

Paper patching also allows softer alloys to be driven at higher velocities than bare lead as well. I do not recall having read about stripping issues with PP boolits of proper fit.

Digital Dan summed it up nicely:

"In the end, what is considered here boils down to a question of whether a given load will function well within certain parameters of alloy, weight and charge. The variables are so many that for the lay person the path of least resistance is to simply go shoot and see what comes of it."

Those are my thoughts anyway.

Longbow

[1874Sharps]

Obturation is indeed a function of alloy strength and acceleration from chamber pressure. In my custom made mold for 30 caliber that casts a boolit at 0.301 inches and is then patched up with vellum paper to either 0.310 or 0.309 inches I hit a speed barrier at 2,500 fps with alloy that could be scratched by the fingernail test before accuracy degraded. When the cast boolit was of harder alloy accuracy was restored at higher velocity. The photo shows this boolit recovered from a mule deer about two weeks ago. It expanded to over twice its diameter and retained 120 of the original 165 grain weight. It was shot from a K31 Swiss at about 2,500 fps and anchored the deer as well as any bullet I have seen.

[Digital Dan]

Longbow, very good post there.

1874 Sharps, those PP loads are killers, no? I've generally had higher retained weights than you report, but the velocity is much lower, running about 1,600 fps at the spout.

303Guy, The stripping thing is something I've experienced but I have no solid basis to describe when or if it will happen. The load I developed is a MOA shooter at MV of around 1600 fps or a bit higher, and minute of barn at about 1750. Grooves are shallow (.004") and twist is 1:20", caliber .430" with a FNFB bullet. Cupped base bullets go haywire above 1,400 fps and I presume it due to blown skirts. Pressure at the top end is running around 36-38 KPSI per the load manuals, but I think that a crude reference. Have no photos of the bullets that stripped, but there was no doubt that's what occurred after inspection.

I've experience with a Marlin 1985 CB in .45-70 that will do the same alloy to 1,800 fps and still run sub MOA at 100 yards for 5 shots. One is flat base, the other cupped base, 9# onion skin and dress pattern paper respectively. Dunno how much higher it could go and never will. 510 grain bullets at that velocity leave a lasting impression at both ends.

[303Guy]

This thread is jam packed with information. Good solid information. Great thread!


510 grain bullets at that velocity leave a lasting impression at both endsI'll bet! :mrgreen:

Thanks for the great posts all.

It's great having some theories or suppositions confirmed (or close anyway) by those with real life experience.:grin:


I hit a speed barrier at 2,500 fps with alloy that could be scratched by the fingernail test before accuracy degradedThat's valuable info! Surprizingly high for such a soft alloy (not that soft mind you but still malleable) - that's the hardness (or softness of my latest alloy which I am hoping will perform in my 25/303). 1874Sharps, would that K31 have a 1 in 10 twist?

My 25 has a 1 in 10 twist and I am hoping the alloy will be soft enough the cut the patch up to the ogive band. At low velocity it doesn't but the rifling engraves on the boolit just fine.

http://i388.photobucket.com/albums/oo327/303Guy/MVC-409F.jpgTop boolit softer than bottom one.

Those patch pieces show hardly any rifling marks from the bore yet you can see the rifling engraving on the bore-ride section of the boolit. The patch pieces were nicely curled up in the wet rag were the boolit entered - so the patch did not come off the nose!

This is relevent to this thread I think because the patched size of the bore-ride section is just on a tight fit in the bore meaning it shows what happens when the core is under bore size with low pressure. (P.S. Penetration was amazing!)


I have had boolits almost completely slug up and lube grooves disappear when alloy was too soft ... That's actually quite amazing. More so to me now that I am beginning (I hope) to grasp the meaning of the fundamentals. It's not simple by any means but hell it's interesting!


The load I developed is a MOA shooter at MV of around 1600 fps or a bit higher, and minute of barn at about 1750.That's quite a significant piece of information!

Oh, I've taken to dry patching with printer paper for the 25. Works great!

Yup. This is indeed a great thread!:drinks:

[1874Sharps]

303Guy,

The K31 Swiss has a 1:10.6 twist, so it is very comparable to your 25/303 rifle for which you are working up loads. I have not done a quantitative study (with hard numbers and measurements) on the effects of expansion of cast PP boolits verses velocity, but qualitatively it seems to be an exponential function. In other words, if a given boolit of a given hardness expands to X at a given velocity, it will expand mucho more at a little more velocity. I suspect, but have not proven, it is according to the square, but seems to be at least exponential. Recall from physics that force (F) equals one half times the mass times the velocity squared, or F=1/2mV2. I suspect that the alloy strength of the boolit to resist deformation under barrel acceleration (recall that also F=ma where a is acceleration) is likewise inversely proportional to the square of the velocity at which the boolit comes out of the barrel. In other words, a mucho stronger alloy is needed to increase the velocity by a relatively small amount. Again, these are my subjective, or qualitative opinions on this matter and not supported with hard research numbers.

[CJR]

This thread has turned into a very informative one. Thanks to all. Since we started talking about proper bullet size, I have another observation about that. I noticed in the NRA's Cast Bullet Manual, that when they started their PP work, i.e bullet sizing regular CB designs to groove diameter, this gave them essentially hunting load accuracy. It wasn't until they started reducing bullet diameters of regular CB designs, in a lathe, in steps of 0.001 " that they found 0.301" best for 308 & 30/06. They then had Lyman make a special mould to cast 0.301" size bullets. Their procedure then became; size the special CB design to 0.301", PP and lube it and then size it to 0.309 or 0.310". At that point, their loads were at match accuracy. I note that Ed Harris, on the CBA website, stated these PPCB were equal to government match ammo and he then used them in regularly scheduled 1000yd competition. Also, the NRA found teflon spray to be best.

Best regards,

CJR

[303Guy]

... if a given boolit of a given hardness expands to X at a given velocity, it will expand mucho more at a little more velocity ...That makes sense.
Recall from physics that force (F) equals one half times the mass times the velocity squared, or F=1/2mV2Ah! That would be E=½mv². Boils down to the same thing. That means simply that a small increase in velocity is a large increase in energy which requires a large increase in force.

It's interesting that the ratio of alloy strength to chamber pressure is about 3 ~ 4. I suppose that would depend somewhat on the relative length of the boolit.


The K31 Swiss has a 1:10.6 twist, so it is very comparable to your 25/303 rifle ...That makes it quite comparable to the 303 Brit. That would be a bit quicker at .312 groove and 1 in 10 twist, so I might expect 2300 ~ 2400 fps which with the smaller Brit case sounds about right. Mmm....

The 25/303 should have a healthy velocity threshold. I'm hoping for 2800fps. Mmmm...

Thanks for that very interesting info CJR.

An observation of my own regarding boolit size is that too large a base diameter results in a deformed base! I wonder whether that factor is what makes a group seem to open up exponencially with distance?

I wonder too whether boolit length and alloy hardness has a relationship? Too long a boolit with insufficient strength for the spin and perhaps the boolit bends in flight?

[Digital Dan]

I wonder too whether boolit length and alloy hardness has a relationship? Too long a boolit with insufficient strength for the spin and perhaps the boolit bends in flight?

Thinking that slumping might possibly contribute to that with spitzer nose forms but it is speculation on my part. Perhaps an interior flaw that leaves the bullet severely out of balance might do this? In his book "Modern Exterior Ballistics", Bob McCoy describes as many as 4 possible precession modes, two of which are induced by specific imbalance at the nose or base of bullets. My mind is not that agile....

Anyway, long bullets for caliber imply high sectional density. Such circumstances favor obturation and if some other nose form is used than basic RN or RFN such as a semi round nose or spitzer shape, the resultant deformation in the obturation sequence may contribute greatly to slumping. I've not ventured down this path so what I say is conjecture, but the tribulation involved is getting such forms to shoot well as GG bullets is legend so far as attempted high velocity relates to the endeavors.

[felix]

That is not conjecture; it's factual. Non-uniformity can be generated anytime a boolit is created and used, before being shot, during the shot, and after. It's a treat to see a totally non-jacketed boolit play the BR game and do as well as they do. ... felix

[barrabruce]

Its gotten all technical again.
And to think that I had just figured out that PP anything over a 150 grn'er in 30 cal would most likely end up seated past the neck of the case.
And with out any great loss of accuracy or ill effects.

Bugga...now you hit me up with stuff that just whizzes over me head.
I think if the soft lead runs out of accuaracy then I.ll bump up the hardness a notch and see if it helps.

Barra
I'm becomming amazed that it is possible to actually hit anything.
With all these things one needs to get right 'n stuff.

[Digital Dan]

I think if the soft lead runs out of accuaracy then I.ll bump up the hardness a notch and see if it helps.

Thinking that's a righteous path.


I'm becomming amazed that it is possible to actually hit anything.
With all these things one needs to get right 'n stuff.

Hitting things intentionally is a surprise to me too. [smilie=l:

The pursuit of accuracy is interesting because of the challenge and rewards...to me. Too, it is a world of diminishing returns. I do not spend much time shooting paper, other than to work up loads and investigate certain issues, but there comes a point where good enough is good enough. My way of saying if I need 1 MOA accuracy at 200 yards, the need for reducing dispersion to 1/2 MOA is lost on me. The effort expended in doing so is great, the reward very small (pun intended)...if I need it I will do it, but otherwise, no. A way of saying, some guns get enough effort, others might suffer the full Monty. Long range precision is one such task master, but I am not a slave to that discipline...yet...preferring beasts up close.

Felix, I agree it is factual, but having no hands on experience with such things I'm not the party to argue the point with great energy. OTOH, I take great pleasure in using lead bullets to embarrass gas gun shooters at the local range, and do so frequently. They take particular umbrage when I do it with a flintlock.:bigsmyl2:

[Baron von Trollwhack]

Perhaps the hardness of the boolit was related to velocity (44-77 SBN/44&90SBN) which is why Sharps sold patched boolits of the exact same diameter and shape for specific calibers in different alloys, !/10, 1/20, don'tcha think? Bore diameter=soft lead type patched boolit:Groove diameter=hardlead type thinner patched boolit.

Lowes has your PTFE(teflon) in a nice spray can too. BvT

[303Guy]

OTOH, I take great pleasure in using lead bullets to embarrass gas gun shooters at the local range, and do so frequently. They take particular umbrage when I do it with a flintlock.:bigsmyl2:I love it!:twisted:

I have a suspicion that with all the variables involved, the accuracy potencial for an 'ordinary' gun with patched or cast boolits is actually greater than with J-words. But at a price! (Which mostly involves having fun).:roll::mrgreen:

[yondering]

So, to make things even simpler, why not just patch a boolit that is already groove diameter, then size down? This completely eliminates the need for obturation. That paper needs compression to be able to grip the rifling; sizing down compresses it and makes a tougher and more durable boolit for handling purposes, and doesn't rely on obturation to compress the paper during firing.

I use this method in my Whelen; accuracy is equal or better than jacketed bullets at all velocity levels I've tried, from 1,000 fps to 2,650 fps. I do size to .360", because that is what fits the throat.

One other item of note, in my experience, you need a slightly smaller sizing die for paper. My Whelen PP boolits are sized at .360" in a Lee push-through, but that die will size lead boolits to .359".

[303Guy]

yondering
Might I ask on boolit hardness, bore and groove diameters, paper thickness and all that? You obviously have the 'formula' right (by no accident, I'm sure!) Interesting that you size to throat fit. I do too but am having a problem (I think) with boolit base feathering. When I try rounding the base edge, I can't get my patches to fold down securely. With a sharp edged boolit i get a beautifull flat and sharp base fold (more of a crimp, actually).