Patch thickness &RB Dia VS Cal. & Rifling depth

[Vaino]

Have read many posts that include PRB loads and the patch thicknesses are plainly too thin, so thought a good discussion would enlighten things.

Some pics showing the PRB leaving the muzzle also show flames ahead of the PRB showing that the patch and RB combo didn't obturate the grooves. Have posted info of my calculations to try and achieve a combo that attempts to obturate the grooves....which are the problem. But, some said the calculations weremn't necessary. Well, I beg to differ because you have to start somewhere.

The present day bbl makers for some reason make the rifling grooves too deep and therefore hard to seal off.... why so deep? Don't have a clue. An improvement in sealing off the grooves is the radius groove rifling.....no corners to seal.

Below are my calculations to determine minimum patch thickness for a .54 cal. bbl w/ .016 deep rifling. Both .530 and .535 RBs are used.

.540 + .032 {double rifling depth} = .572 bore dia. .572 -.530 RB dia. =.042 divided by 2= .021 minimum patch thickness.

.540 + .032 {double rifling depth}= .572 bore dia. .572 -.535 RB dia.= .037 divided by 2=.0185 mimimum patch thickness.

Seeing both calculations are for minimum patch thicknesses, thicker patch mat'l must be used to seal off the grooves because I don't think the minimum will do it. Also...it's evident that the deeper grooves are hard to seal off.

Using a ,535 RB might be harder to load, but does enable a better groove seal w/ a patch that's thicker than minimum.


Don't really know if the bore can be obturated w/ a suitable PRB combo, but at least w/ the above calculations, an attempt to do so can be made....Fred

 

[Loyalist Dave]

I am wondering if so many of us are using patches which are too thin, how come so many of us aren't experiencing poor groups? Also would a round-bottom rifled barrel where the depth of the rifling is deepest at the bottom of the á´— will make a difference compared to squared rifling?

LD

 

[zimmerstutzen]

Or round bottom rifling where the edges of the groove are deepest. Or where the grooves are five times wider than the lands. Or....

Groove Depth, is only a small part of it.


Years ago, I got a barrel in trade that had rifling that was about 20 thousandths of an inch deep and grooves were very narrow. IMO, it was impossible to combine a round ball and patch that would seal the bore without using a heavy mallet to swage the round ball into the grooves.

My best barrel had very narrow lands and wide round bottom grooves, that were deeper along the edges. It shot best with a thin patch. I used natural muslin which is only about 5 thousandths

 

[Boomerang]

My guess is if the patch doesn't burn through and the gas has to go around the patch to escape, then I would think the gas would be escaping equally around the patch and not causing the ball to go off course as much. If the patch burns through, then there is no telling where the gas is going to escape around the ball causing un equal pressure around the ball and therefore causing the ball to get thrown off course. Still the best case would be to seal all the gas off behind the patch. :hmm:

 

[Vaino]

A thin patch if it imprints the rifling onto the RB could be accurate but very inefficient because of the excessive gas blowby through the grooves.

Because of the greater depth of the grooves in modern day bbls, I think the radius groove rifling enables a better seal in the grooves....and therefore increased efficiency.

Sometimes I wonder if the patch thickness is related to efficiency of the load w/ many shooters.....Fred

 

[ohio ramrod]

Since a tighter than needed patch/ball/bore fit is hard to load I discovered years ago that an over powder wad will seal the gasses. I started with just my cleaning patch folded over after swabbing. Now I use a leather over powder wad for the seal and have good groups and can actually reuse most of the patches, if I can find them. Since I make my own punches and get leather scraps free it doesn't cost me anything but my time. :idunno: :idunno:

 

[Vaino]

An OP wad is just another item to load. Don't think they were used by shooters of yore. Load what you will, but I like to keep things simple.....Fred

 

[azmntman]

I too like to keep things simple BUT as we have a single shot I also like to keep things as accurate as possible, at least with that first shot, so I use what works best for the BEST groups, if it be a over powder wad then I use em (just getting into it really).

Been like 140 years since I had to load quick in an ***** attack, then I made sure I made a great 1st shot and then I started dumping powder n ball and just shootin and running too). Had me a notion to create and patent a "scoop" to fit like a bayonet so I could just dump powder, scoop some projectiles on the run and keep firing. But that was a long time ago and the facts seem blurry these days :idunno:

 

[Shifty]

Common sense tells me that Radius bottom rifeling would seal better, isn't it easier to compress something into a round bottom groove than into a groove with a flat bottom and square corners,but i don't think that the rounded groove rifling should really be any deeper that square bottomed ones because they still have and almost square corner at the edge of the lands to grip the patch,just my thinking.

 

[piper987]

:grin:

 

[hanshi]

For all my rifles, round groove and square, I load a .024" patch. So a .50 + 032 (.016" radius grooves) = .532" groove dia. So .532 + .490 ball + .048 = .538. This gives me reasonable compression in a radius groove bore. For the square groove bores there is .50" + 2x.012 or .024 = .524" groove dia. With .524 + .490 ball & .048 patch = .538 and good compression. Nevertheless, I often use an op wad. These loads are tight but load safely using the wood underbarrel rod which is an absolute IMO.

 

[Boomerang]

With .524 + .490 ball & .048 patch = .538 and good compression.

What kind of material are you using for a .048" patch? Is that a compressed measurement?

 

[nkbj]

With all the gazillions of variations it makes me wonder if anyone has ever been able to prove that any given pattern is the easiest to make accurate.
My first rifle was a .45 Kentucky with lands so narrow that it looked like a Remington .22 bolt action. With tight patches it was a head shooter until I wore it out.

 

[Vaino]

In this age of "unnecessary complications", it's nice to hunt w/ a rifle that's not complicated at all...except when the "modern mindset" wants to "re-invent the wheel". The many years that I've shot MLers, have never needed an OP wad....and the accuracy and efficiency of my loads continually astounds me.

Previous to MLers, I was into handloading extremely accurate CFs w/ all it's complications and was and still am astounded that w/ so little effort my MLers begot accuracy that could take the heads off of squirrels at fairly long distances.

The "plain old" PRB has been around for 100s of years and hasn't needed any help...until the "modern mindset" deemed it did.

Shoot what you will and if it does the job. so be it.....Fred

 

[rushlake1]

Ok I'll Bite!
Really Fred?????Cabin fever ????
Is adding an op wad that much effort for you?
Would adding a folded patch pass muster then?
If my patches were not getting it done my vote would be go for it.
Isn't the point of shooting a rifled barrel to keep them touching???
Don't we owe it to the game hunted?
We all come to different conclusions based on what we experience..
lots of different experience levels here on the forum.
Glad others are willing to share.
Ok fire away!!!

 

[Vaino]

You sound incredulous. Why would I use an OP wad if I don't need one?

I start w/ an excellent bbl and develop a PRB load that's suited to the intended game.

My squirrel PRB load has taken the heads off of 100s of squirrels....Fred

 

[Khufu]

I agree with you, adding another useless component to a prb load is simply adding another variable to the mix and offers no return an op wad or cussion under shot, sure, helps with shot deformation, but under a prb? what benefit is there? the "KISS" principle is always the best way to go.

 

[rushlake1]

Fred.... my point is sometimes a simple patched ball is not enough for the most accurate load in each particular rifle.
Not all shooters here have the perfect bore-rifling ect.
I get it on keeping it simple..but there are times when its just not good enough.
when an op card is added and your group shrinks its a win-win.
Do you understand this point yet?

 

[M. De Land]

Have you ever tested a OP wads Fred to see if it might not improve your rifles accuracy on paper.
Who knows it just might make an improvement so you can head shoot squirrels to greater distance.

 

[Vaino]

Shooters can shoot what they will....what ever floats your raft. Have never needed an OP wad w/ a PRB because the accuracy of my loads enables the "head shooting" of squirrels. That requires very accurate loads.

22fowl....Why should "I get the point" of something that's not needed....anyways for me. Have spent a bit of range time developing my highly accurate loads...possibly the OP is an excuse to "short cut" the req'd time?

Really am not concerned as to what people shoot in their MLers....just so my loads get the job done w/o adding complications. Simplicity, simplicity.....Fred