"How much will a bullet bump up?"

[Red River Rick]

Out of curiosity, how much can a bullet "Bump Up", to achieve proper Obturation?

Normally, say, 0.006 - 0.008" thousands would seem logical, but what if the bore diameter is 0.430 and the groove diameteris 0.446. Will the bullet bump up enough to obturate properly or will there be blow by?


RRR

[Digital Dan]

Maybe, dunno for sure. A lot would depend on alloy and pressure in the load but I'd suspect there would be some blow by with GG bullets. If dealing with your example I'd opt for as much patch as the cartridge mouth and chamber will accept and see what happens. I have issues with a picket rifle with grooves of .018" depth. Haven't figured out the solution as of yet....not for conicals anyway.

[pdawg_shooter]

I dont believe smokeless will bump any bullet. Progressive burning keeps that from happening.

[Baron von Trollwhack]

Heavy for caliber boolits of near pure lead, with as large as possible diameter card wad, and heavy felt wad, patched with real rag bond and lubed traditionally to fit the bore, all over a heavy charge will slug up 12 thousandths. OK for BPCR , maybe a deep grooved picketeer, and certainly a shallower grooved Whitworth type. BvT

[shooter93]

With smokeless powders and alloys such as ww's and maybe softer...there is no bump up at all. Very soft alloys and Black powder they will bump some.

[Red River Rick]

Here's the senario:

A M71/84 (.43 Mauser) with a 0.446 groove and a 0.433 bore. Will a naked bullet of 0.423 diameter, patched to 0.432 and cast from say a 30:1 mix, bump up the 0.015" needed to fill the groove diameter using BP.

That 0.015" seems like a lot to bump up, will it work.

RRR

[calaloo]

I have a friend who shoots an original Whitworth rifle. for those who do not know, the Whitworth has a hexagonal bore that is .451 flat-to-flat, I don't recall the dimensions point-to-point. This rifle was engineered to shoot a mechanically fitted bullet that was paper patched. Whitworth supplied moulds to make both hex and cylendrical bullets. Hex bullets are hard to cast. My friend shoots this rifle competitively in long range muzzle loading matches and has tried many different schemes to produce winning bullets. Now he is shooting an exact copy of the Whitworth cylendrical bullet swaged in pure lead with a Richard Corbin die. He has recovered fired bullets and they are hexagonal. This has got to be the ultimate bump up.

[rhbrink]

Those rifle have always interested me, what kind of groups does he shoot at say 600 and 1000 yds?

[montana_charlie]

Here's the senario:

A M71/84 (.43 Mauser) with a 0.446 groove and a 0.433 bore. Will a naked bullet of 0.423 diameter, patched to 0.432 and cast from say a 30:1 mix, bump up the 0.015" needed to fill the groove diameter using BP.

That 0.015" seems like a lot to bump up, will it work.

RRR
Can't say how much bump you'll get. Simply don't know.
But, with paper .0055" thick (.011" / 2) and a groove .0075" deep (.015" / 2), I'm curious about how the paper gets cut without the steel going into the lead.

I guess you have to hope you don't get full expansion...
CM

[powderburnerr]

Rick,
I have shot .444 diamater after wrapped bullets in my 110 with favorable results and no problems using 100 gns of black and a cookie. a couple dug out showed good marks on the base section that wasnt damaged by impact, they will load and shoot all day with no help and will maintain hunting accuracy for at least 30 rounds , probably depending on the weather,,,,,,,,,,bore on rifle is 450 groove dia is 458 so that is pretty close to 15 tho. I also find that the softer lead works best for this load .. it isnt a screamer but is dependable....Dean

[montana_charlie]

Rick,
I have shot .444 diamater after wrapped bullets in my 110 with favorable results
Dean, are you saying those bullets measure .444" (6 thousandths under bore) after being wrapped?

I'm not trying to say that's good or bad, right or wrong...I'm just asking.
CM

[Don McDowell]

Don't know about whether or not smokeless will bump a paper patch bullet, but the pp mold I use for bp loads in the 45.. rifles, drops from the mold at .435 wrapped up to .448 they shoot well enough to acquire minute of deer out to 300 yds or so. They will hold about a 6 inch group at that distance but the vertical stringing is readily evident, and at 500 yds its all you can do to keep 10 of them on a F class target.

[Red River Rick]

But, with paper .0055" thick (.011" / 2) and a groove .0075" deep (.015" / 2), I'm curious about how the paper gets cut without the steel going into the lead.

I guess you have to hope you don't get full expansion...
CM



Exactly!

When the depth of the rifling exceeds the total thickness of the patch, what happens, or better yet what should happen?

If these parameters exist, would it not be better to do so as Kurachan has done in his thread: http://castboolits.gunloads.com/showthread.php?t=46205.

His great success lays on the fact that his bullet is a copy of the original, and therefore will fit the leade/throat area of his chamber after patching.

RRR

[powderburnerr]

Charlie , that is exactly what I am saying , and it worked fine. makes a very good hunting load as there is no wiping or blowing needed, and the load seems to be well balanced and leaves a very clean barrel.
Rick when you shoot a heavier patch than the depth of the rifling it either comes off in whole or it cuts the outer wrap and the inner wrap is still in one piece, and you get 1/2 confetti and half a patch , this was one of my better loads with an english bullet mould, it started out 438
and wrapped to 448 or so.

[montana_charlie]

would it not be better to do so as Kurachan has done in his thread:
Well, his wrapped diameter (.446) is one thousandth shy of the .447" groove...which shows he is using the patched-to-groove 'style' with black powder loads.

His rifling is .0075" deep ~ (.447 - .432) / 2 = .0075
His patching (counting both layers) is .008 thick ~ (.446 - .430) / 2 = .008
It looks like a perfect fit, to me.

The rifling will cut clear through the outer wrap, and most of the way through the inner wrap.

The tapered bullet makes it interesting to cut a curved patch that will roll on straight without being wrinkled at the ogive.

One thing about the whole deal...
His chamber at the neck diameter must be about .466" to allow room for the .446" bullet and the case wall x 2. And, he says there is no chamber step.

So (I assume), the .466" chamber must get down to the .447" groove diameter by using a tapered freebore. Since he is using BP and pure lead, I wonder how much 'bump' he is getting in that fairly roomy freebore section -- and what happens to the paper when the bullet suddenly gets 20 thousandths fatter as it comes out of the case.
'What happens' isn't really important as long as the target looks good, but I am curious...

CM

[calaloo]

rhbrink:

I don't really know what his group size is but he is usually listed in the top 10 shooters at Friendship and Oak Ridge. He also has a wall full of framed certificates. I don't even know how big the 1000 yd target is. Guess I need to ask him some questions.

Bill

[Lead pot]

Smokeless powder will obtrude a bullet, even a Jacketed bullet.
Lp

[Kenny Wasserburger]

In my experience, too thick a patch and undersize bullets you end up with dirt diggers at the long range matches. Been there done it. You get a big warp coming off it never does it consistantly and you will shoot 4-6 good shots then one in the dirt. Been there done it.

Go with a bullet in BPCR that with thin Paper gives you about bore or .001 over bore and you will have good accuracy. Thin as in .0015 or so thickness.

Kenny (the Lunger) Wasserburger

[Digital Dan]

Smokeless powder will obtrude a bullet, even a Jacketed bullet.
Lp


You bet it does, in spades.

BvT, thanks for the reminder, must try that soonish.

Picketeer Dan

[405]

Smokeless powder will obtrude a bullet, even a Jacketed bullet.
Lp

Most any expanding gas will obtrude most any kind of bullet down the bore and out the muzzle. As far as amount of obturation or "bump up" goes- the acceleration (and pressure to some extent) along with the length/mass ratio, bearing surface and hardness is directly proportional to the amount of obturation. Most cast/swaged bullets are shot at pressures and velocities far below high power smokeless/jacketed loads. I wouldn't think a BP or light smokeless charge used for cast bullet velocities of 1200-1500 fps and pressures under 20 thou psi under a regular Jbullet would cause much obturation.

And, just not interested in trying to obturate a Jbullet in a trapdoor :mrgreen:

[TAWILDCATT]

I just expanded a .402 bullet to .420 in a vise.now if it was lubed why cant it be put in a die and bumped up.:coffeecom [smilie=1:

[montana_charlie]

Excellent question. If somebody starts a thread about using oversize dies in heavy-duty lubrisizers, to swage bullets into a new design, you should ask it.

[wonderwolf]

I'm not having any trouble bumping up a .360 pure lead slug to .410 and .429 in my swage dies. granted its a short .60" long but I can try it with a much longer pure lead slug when some core molds arrive from RRR.

I've often wondered if even with some of the shorter 45 cal bullets (in the 400-450gr range) if they all bump uniformly throughout. Everything I read and look at gives me one answer or another.

One thing though I'm guessing is the amount of time that the pressure is applied to the bullet itself has something to say about it being bumped up in a bbl vs anything we do with a vise or swage dies. In bumping a bullet up in size in a swage die that takes a few seconds vs. a bullet traveling down a 30" bbl at 1400 FPS or whatnot.....

From a physics standpoint now that I think about it would the pressure from a swage die or a vise be from two directions, Bullet nose and tail? Where in a firearm the bullet is getting the pressure at the tail end and relatively little pressure at the nose end? Thus the "shock wave" of the exploding black powder charge would bump up the bullet at the base first and move up the body of the bullet?(think minie balls and how the skirts blew out and stayed flared out maybe?)....Would a dry (unlubed) patched bullet then bump up better since it offers more resistance to this tail end pressure (or is that just relative?)? :coffee:

[243winxb]

Lee wants the pressure below where Obturation would happen. http://www.realguns.com/archives/118.htmCompare the pressure listed here for Obturation to take place.http://en.wikipedia.org/wiki/ObturateIf a cast lead alloy bullet Obturates, it will deform and break down, leading the barrel. The structure of the bullet will be changed when jumping for the cylinder to the forcing come. Not so much change will take place in a auto fixed chamber firearm. Bullet's BHN x 1422 = Pounds per square inch.
According to the chart, a very popular #2 alloy carries a 16 BHN, has a strength indictor of 22,703 PSI and should be limited to 20,000 PSI as maximum pressure. Wheel weight alloy with a BHN of 9 carries a strength of 12,748 PSI and a MAX pressure rating of 11,473 PSI The paper patch fills the void/diameter between the alloy bullet and the bore.

[leftiye]

243, I really liked that approach several years ago. But as person after person here reported outstanding results with high pressures, and softer than expected boolits, it becomes obvious that softer boolits will shoot accurately regardless (not an absolute statement, it doesn't always shoot well. Bad news is - nothing does) of pressure level, and sometimes higher pressures shoot better. The trick lies in making your boolit fit the leade and throat in your chamber. If the boolit is supported when the pressure is applied, the boolit doesn't deform and can still shoot accurately. I have to agree with the obturation not being desired part though, as (especially in revolters) gas seal is critical to stopping leading, and this is accomplished by pushing a slightly (+.001") oversize boolit into the chamber mouth or leade.