Why bore for BP, groove for smokless?

[JeffinNZ]

Team.

Probably been asked before but why patch bullets to bore (or slightly over) for blackpowder and to groove for smokeless?

[docone31]

Hey Jeff,
I donno, I patch my .303 by sizing it to .308, then wrapping to .314. If I followed the standard sizing formula, I should size it to .304, then wrap to .314.
I get great groups my way.
I get with .3135, 3" at 100yds with starting jacketed loading.

[EDK]

Black powder is an explosive and the boolit gets hit so hard it slugs up to fit. I'll also offer that it is a carry over from the 1870s when barrel tolerances were pretty loose....all over the place!

Smokeless doesn't cause the boolit to slug up that much.

Go over to shilohrifle.com or one of the other Black Powder web sites and do some searches....there's some guys with good credentials and results to support their views....a lot of which are not even close to the other guy's position. I've had suggestions of pre-patch diameter for my 50 SHILOH of anwhere from .490 to .500 or larger. I've got a box of .497s to patch and try out...mould runs .494 from dead soft lead, according to the guy I got it from....I got .497 from mystery alloy of about 20-to-1.

Get a copy of Randolph Wright's LOADING AND SHOOTING PAPER PATCHED BULLETS, A BEGINNER'S GUIDE. Orville Loomer's booklet on paper patch bullets from SHILOH SHARPS is another excellent book.

:Fire::cbpour::redneck:

[Idaho Sharpshooter]

EdK,

I got the tracing paper (finally!) this afternoon. It may be what you need. 4-thickness measures .0052"

Rich

[longbow]

My understanding is that the bore size for BP allows for some clearance for fouling in the throat. I don't know from personal experience as I haven't paper patched for BP, just smokeless.

Also, what EDK says ~ the BP thumps the boolit hard in the butt so it slugs up and fills the barrel. I would guess that the fouling and the tolerance issues would both be addressed by using the "undersized" PP boolit.

So far my paper patching has been limited to .44, .308 & .303 with smokeless loads and they all like patching to groove diameter with boolit at or near bore diameter.

Longbow

[Digital Dan]

Fouling.

Anybody that thinks obturation is less profound with smokeless propellants than with BP needs to rethink the process a bit. The process is a function of pressure vs. alloy hardness, not propellant. Even lead core jacketed bullets obturate.

[montana_charlie]

Some weeks ago I was asking the same question.
As I understand the answers...

With smokeless, you must patch to groove because the bullet won't bump up.
With BP, you have a choice. Which you choose depends on the type of chamber you have.

* Note: These dimension comparisons relate to .45 caliber rifles.
If you have the standard GG chamber (grease groove) which is .480" or larger in the neck area, your best bet is probably 'patch to groove'.
If you have a PP chamber (only around .470" or less in the neck), then patching to bore is best.

For calibers other than .45, the PP chamber would have a neck area diameter equal to case wall x 2 + bore.

Patched to bore bullets can be used in a GG chamber if your brass has a thickened neck wall...or if you will tolerate a case neck which fits loosely in the chamber.

These (above) are my understandings from the answers I received. If I misinterpreted those answers, I'm in trouble...
and so are you if you follow my advice.
CM

[Idaho Sharpshooter]

Digital,

it ain't the amount of pressure, it's the type and the way the pressure builds. Having owned an Oehler M43 for several years, I get to see printouts showing how the pressure builds and the BP vs Smokeless curves are different all the way thru the barrel.

Rich

[leftiye]

+1 on what Idaho said. Black is not only an explisive, but it produces a shock wave when it explodes. This shock wave is what causes the the lead to obturate. If black powder paper patched loads were built to groove diameter, pressures would be way up, as the boolit would obturate to fill the chamber neck area, and the freebore area, then be forced into the rifling. Another issue is that many BPCR loads are paper patched in such a manner that they are INSIDE the rifling when chambered, just like a muzzle loaded PP boolit would be. Almost the same effect can be had with a long freebore (maybe .001" over groove diameter) and PP boolits to fit this with either smokeless, or black poudre.

[Digital Dan]

Digital,

it ain't the amount of pressure, it's the type and the way the pressure builds. Having owned an Oehler M43 for several years, I get to see printouts showing how the pressure builds and the BP vs Smokeless curves are different all the way thru the barrel.

Rich

Pressure curves are a variable and can be modified greatly by the nature of the load. In any case, I can show you curves where BP and smokeless are virtually indistinguishable as quickly as you can present different versions. Obturation is a function of pressure and alloy.

I would appreciate it you would read the short article in the link below. Note the reference to "1440 X BHN".

http://www.sixguns.com/crew/obturation.htm

[longbow]

Digital Dan:

You are absolutely right about pressure and alloy ~ when pressure exceeds the yield strength of the alloy, the boolit will obturate regardless of how or when the pressure is applied.

I made a couple of assumptions in my post:

- most BP shooters use soft alloys (like 20:1 lead to tin)
- smokeless shooters use harder alloys like ACWW (I do anyway)

So the softer alloy will yield (obturate) at lower pressure than the harder one.

The only reason I can see for using the bore size PP boolit though is to allow for fouling. I can't see any other good reason to allow a boolit to obturate up to about 0.010" in diameter if you don't have to.

Whether there are any accuracy differences between bore and groove sizing or not is another discussion.

The barrel tolerance issue that EDK brings up may well be true as well but the tolerances wouldn't likely vary by more than a few thou so is more a reason to use a soft enough alloy to obturate rather than intentionally sizing to bore diameter.

[Idaho Sharpshooter]

Longbow,

I have measured Trapdoor barrels as small as .457" to as large as .468"
I have also measured Krag barrels as small as .3085" to as large as .314"
The list goes on and on...

Rich

[Idaho Sharpshooter]

Dan,

I have seen pressure curves with BP that are sharp and peak within the first 5-6" of barrel.
I have not seen any with Smokeless that peak that quickly. The two curves differ with propellant, and are a Law of Physics. To contradict that you would have to believe that there is zero burn rate difference between the two types of propellants. If you question that, I can arrange to load you Black and Smokeless to the same velocity levels and stand about 100 feet away and photograph you shooting and show the chronograph pressure curves. Absolute Pressure is not nearly as important as the shape of the curve.

Rich

[compass will]

EdK,

I got the tracing paper (finally!) this afternoon. It may be what you need. 4-thickness measures .0052"

Rich

I guess I got the wrong stuff. Mine measures .004 thickness for one piece!

Tonight I will get out the micrometer and throw away my calipers (I dropped the calipers 2 nights ago and now they read different every time I close them).

So much for $15.00 harbor freight calipers, but they did work great for a year until I dropped them.

Edit: I must have been having a "brain freeze". My paper is .002 dry. so if you wrap it 2X you will have 4 layers of paper for +.008". I need to see if it scratches some when wet to make the final dry boolit wrapping thinner

So If I can find some of that paper your using, I would have .308 + .005 = .313, so I will still need to size after patching. I guess I could try a .313, but I think the cases are .312 after fire forming.

[Digital Dan]

Dan,

I have seen pressure curves with BP that are sharp and peak within the first 5-6" of barrel.
I have not seen any with Smokeless that peak that quickly. The two curves differ with propellant, and are a Law of Physics. To contradict that you would have to believe that there is zero burn rate difference between the two types of propellants. If you question that, I can arrange to load you Black and Smokeless to the same velocity levels and stand about 100 feet away and photograph you shooting and show the chronograph pressure curves. Absolute Pressure is not nearly as important as the shape of the curve.

Rich

We'll, I expect we'll have to respect each others' different perspectives on this and call it good enough. [smilie=s:

To the point of the post, my opinion is "Fouling". On the ancillary issue of obturation, it happens with both BP and smokeless....not my opinion, simple fact.

[EDK]

The ONLY absolute here is that there aren't any! Black powder shooting, and especially paper patch!, can be an exercise in frustration. You have to use the books and other people's experiences as a starting point....not the finish line!

Other people have gotten good results with the diameter boolit I got out of the KALYNUIK mould and my alloy. If it doesn't work with what I have, next step will be softer alloy to reduce the size and maybe have BUCKSHOT make me a reducing die(or two) to what I originally had in mind...and then if it works, probably send some yankee dollars to Red River Rick for another mould. Whatever I do, I'll be kept out of mischief while I'm experimenting.

Refer to Randolph Wright's LOADING & SHOOTING PAPER PATCH BULLLETS, A BEGINNER'S GUIDE for some more detailed information and/or explanations.

:Fire::cbpour::redneck:

[EDK]

Rick Kalynuik, aka Red River Rick, PM'd me with an offer to replace the paper patch mould that is throwing .497 out of a wheel weight(?) blend with a smaller one. As most of us know, you can change diameters with casting temperature, alloy, etc (AND THEN you get into paper thickness!) I told him I wanted to keep it and would do some experimenting AND he replied (in a second PM) that he would still replace it if my ideas didn't work out. This kind of customer service/desire for a satisfied customer, besides the high quality of the mould itself, is why you buy one of his moulds.

Thank you again

:Fire::cbpour::redneck:

[uscra112]

OK, my nickel's worth.

J-word boolits obturate very very little or not at all, the jackets being rather stiff.

Soft lead boolits can and will. And you can drive a dead-soft patched boolit at pressures and speeds that would normally eject a semi-molten mass from the muzzle if it were not patched.

The standard boolit diameters in the paper-patch / blackpowder era took full advantage of this. The patched boolits were very small, compared to the groove diameters. Some were LESS THAN bore diameter. This also led to the chamber NECKS being small. The 71/84 Mauser being a prime example, but also many American 40 and 45 caliber rifles were the same. It worked. It allowed a cartridge to be chambered into a fouled rifle, but it also worked in a clean rifle. MY take being that the front edge of the patch slips into the rifling before the boolit is fully expanded, thereby to some extent preventing the patch leading edge from being cut as it passes thru the leade area.

Now, if you're patching wheelweight metal boolits, you're making your life difficult.
You will need a boolit diameter closer to groove diameter, because the harder metal won't obturate much, or not at all, and you'll get blowby and gas cutting. Only way to stop that is to use faster powders, to get higher peak pressures, or enlarge the boolit, or use a softer metal so that the boolit will enlarge itself. I vote for softer metal.

Finally - black powders necessarily have a fairly limited range of burn rate. You can vary it by the granulation size, but not much else. And it's fairly quick, by modern standards. Smokeless ranges from slow cannon propellants to EXTREMELY fast - for example blank-cartridge powders, which are much faster than even the fastest pistol powders. So any comparison between the two has to take this into account. Arguing about it is futile until you've specified what smokeless powders you're comparing to your black.

Sorry to be so long-winded. I'm just unwinding from this last debate . . . .

Maybe I'll go fix an adult beverage.

[Digital Dan]

Well, if something is to obturate there is only a need for sufficient pressure, BHN sufficiently low to allow the process to occur and room for it to occur. If a bullet is groove diameter to start out with it will difficult to quantify magnitude but it does not preclude obturation. The previously referenced "1440 X BHN" is a valid reference and makes no distinction regarding powder type, because to do so is irrelevant. It says simply that for a given pressure and hardness you will cross the threshold.

Copper properties:

Tensile Strength 32,000 psi min.
Yield Strength (0.5% Extension) 20,000 psi min.
Elongation in 2" - approx. 30%
Shear Strength 25,000 psi
Compression Strength 20,000 psi min.

BHN scale hardness for copper ranges from 40 up, depending on alloying additives. At about 45 KPSI it will yield to some extent. Pure lead (BHN ~5) will do so around 7.2 KPSI.

For the record, I'm not arguing this, but am presenting the information for the interpretation and/or benefit of the members here. What anyone does with info is up to them.

[leftiye]

DD, You're right, given sufficient pressure lead (or steel for that matter) will obturate.

As stated, Black powder is an explosive, not merely a propellant, it does produce a shock wave. Where the boolit is when the pressure is applied makes a huge difference in how the pressure applied affects it. Though some smokeless powders do reach their max pressures fairly quickly, pistols are rarely treated to paper patched boolits, and it is safe to say that the fastest smokeless powders (the only ones to produce anything remotely like the pressure rise of black powder) are generally not used in rifles and paper patched situations (where obturation is desired) mostly because slower powders are more correct and safe, and make better loads in those loadings.

In the case of smokeless powders, in almost all cases the boolit has started moving before (maybe long before) the pressure peak is applied to it. It is not only how much pressure is applied, but how it affects the acceleration of the rear of the boolit against the inertia of the nose of the boolit, ie if the boolit has engraved and is moving, the inertia of the boolit is proportionately less, and does not act like (in fact is not a stationary object) a stationary object would. All of this is very different from a stationary boolit, maybe wedged against the rifling being hit by a pressure wave.

NOBODY that I have ever heard of has advocated trying to "bump up" any alloy of lead boolit with smokeless powder. This is a practice brought forward from the era of black powder when boolits were seated atop the rifling in muzzle loaders, and expanded into the rifling as a matter of standard practice (paper patched boolits too). This fact alone should say something about the desirability, or practicality of doing so with smokeless powder. The fact that today we size boolits to bore diameter or larger before patching for use with smokeless powder probly isn't just someone's whim, it don't work to set undersized paper patched boolits inside the bore and touch off a charge of smokeless powder. The slower the powder, the worse it gets. The gasses push past the un obturated boolit - burning off the paper, and melting lhe lead and deforming the boolit while at the same time depositing the lead on the barrel surface. Given the constraint of better accuracy coming about at moderate pressures, with smokeless powder it is not about obturation, but rather about minimum deformation of the boolit.