What makes it happen??

[Edd]

Just recently, when testing some patch and lubes, I discovered once again that changing to a different patch or lube can change the point of impact dramatically. Please read the following and give me your opinion regarding why this happens.

The rifle in use was a Vincent percussion, blessed with a 36" GM barrel in .40 caliber.  Forty-five grains of 3f Goex was the powder charge. A .400 ball was employed in the mix. I began by loading an Eastern Maine .015 patch and using my Beeswax/Crisco for the lube. Shooting offhand at 25 yards, every shot went 2" low and 2" left.  And I mean that it shot like that consistently.

Next, I went to my favorite load for this Vincent and used once again, forty-five grains of 3f Goex. The patch was Eastern Maine's .018 patch, lubed with whatever they lube it with. I just know it shoots like a house afire in this little .40 caliber. You guessed it...the rifle was now shooting dead center at the same twenty-five yard mark.

I've seen this stuff happen with my other, fixed sights, rifles. Once while using .025 denim patch, one of my rifles started to shoot 3" high and to the left at the 40 yard range. I switched back to that particular rifle's favorite .015 patch and lube and went back to shooting center again.

What the heck makes this happen?? It certainly lends credit to finding the exact patch and lube that a particular gun prefers, before filing on those fixed sights.

Edd

[roundball]

I've experienced exactly the same thing and wondered myself...its not a question that a change in patch or lube changes POI, but like you said, why...

I've wondered iF a tighter fitting PRB gets a better gas seal and velocity picks up some but that wouldn't make a 2" difference at only 25yds.

Another thing might be that the thicker patch grabs the ball better and is influenced more heavily by the rifling at muzzle exit.

Maybe somebody knows for sure...

[BrownBear]

Interesting question.  I've seen the same thing with component changes in metalic cartridge loading over the years, but it was highly variable from gun to gun, and to a lesser degree from cartridge to cartridge.  In my experience the 375 H&H is almost immune to changes in POI with all but the largest changes, while smaller calibers are more susceptible.  The old 17 Remington was one of the worst.  OTOH, I've got a 257 Roberts that RCBS built for me back in the early 70's that will put all bullet weights into the same group, even with changes in charge within a bullet weight. 

All that's a lead-up to wonder if there's a difference in this with different calibers of muzzleloaders and even from one gun to the next.  I've got a shooting bud who reports it with his full-stocks, but not with his half-stocks.  Too small a sample size for generalizing, but it helps pose the question.

[Dphariss]

Changing loads can change EVERYTHING.
You could try having the barrel cryoed or perhaps annealled in a furnace with a controlled atmosphere to see if this would "fix" it.
There are many factors involved. Different lubes change the friction characteristics, this effects velocity and prerssure. This can effect harmonics. This may make the bore point to some other point down range as the ball clears the muzzle.
Most firearms react to load changes. Should not be too surprising.
The question is not why it changes but "why would it NOT change".
Dan

[Candle Snuffer]

Agreed.  Change anything in an established load and things will change.

I'm sure all of us here know this when we're trying to find that perfect load of powder/lube/patch/ball combination.   It's not so important where the shots are grouping on the target as is the importance of the shots grouping consistantly.

I do think it is in our human nature to experiment with things such as loads
for our smoke poles, even if we're shooting one hole groups at 25 and 50
yards, we still have that tendancy of, "I think I can do better."

Heck, this is one of the things that help keep this sport/hobby interesting.

[Daryl]

In testing the larger bores, years ago, I found going from a spit patch to a lubed patch always resulted in a lower point of impact. The oiled patch always gave higher velocities than spit lubed.  Due to recoil of the larger bores, higher speeds means faster barrel times and the ball is out before the muzzle climbs enough to influence it as much. My .40 does exactly the same, but the .45 barrel, same size, same stock, shoots higher with higher speeds - go figure. Sometimes, there is no guessing- it just does!  Reminds me of a PMS joke I once heard.

[Dan]

I would favor barrel harmonics as a primary explanation.  Barrel time usually indicates vertically but harmonics can do a number  of tricky things.

My abject apologies for posting cartoons of-cough-modern guns in the simulation of 9 harmonic modes but it seems appropriate to the discussion. Scroll down to :

Barrel Harmonics Mode Shape Movies at this web site.  http://www.varmintal.com/amode.htm

The modes are not related to full stock flinters of course but they illustrate some of the more common modes.  In BP arms the impulse may be weaker but barrel time is longer...so's the barrel. The influences of the fore stock and slow lock time on the barrel and resulting vibrations are probably too complex to imagine.  For me anyway.

[roundball]

I understand the potential of harmonics on a long slender .30-06 barrel with a 50,000 PSI happening inside the barrel...however, seems hard to believe a mere 7,000 PSI inside a big heavy 1" octagon barrel would suffer the same fate...and show up at 25 yards 

[Daryl]

Consider even a normal '06 barrel is considerably stiffer and stronger than most muzzleloading barrels, not considering length, which is also a detriment in this regard, to the ML.  I can see barrel harmonics effecting the muzzleloading ball for sure.  I've also seen it on target as when zeroed with a 55gr. 2F load in the 7/8" X 42" .40 barrel, prints 1" to the left and 1 1/2" low at 50 yards with 65gr. 3F.  On the other hand, a 75gr. 2F charge, developing the same velocity as the 3F load, prints an additional 1/2" lower than the 3F load, but 2" to the right of it.  Different harmonics of the 2F charge can only be the answer to the windage changes - in my opinion, of course.

 The .375's are unto themselves for some reason. Every one I've had, puts 235gr. through 300gr. into the same basic group at 100 meters and case size doesn't seem to matter - full length magnum, standard length magnum, short magnum and standard '06 case Improved all show this characteristic. A 2" to 2 1/4" circle usually covers groups of 5 different bullet weigths inbetween the weights listed - that's 25 shots., with 5 from each. No other modern gun I've used, will do this and all muzzleloaders I've used also show differences with different charges, rarely in line vertically, but sometimes, do.  The .69 shoots inline and fairly close to the same elevation at 50 yards - maybe 1 1/8" difference between 3 drams and 6 drams. Perhaps the .69 is the 'first' .375 magnum, however it certainly hits harder than the modern one.

[Dan]

Roundball,  column stiffness is relative to length and diameter. A 1" barrel 42" long is not as stiff as one of 3/4" x 20" if all else is equal.

[Dphariss]

I understand the potential of harmonics on a long slender .30-06 barrel with a 50,000 PSI happening inside the barrel...however, seems hard to believe a mere 7,000 PSI inside a big heavy 1" octagon barrel would suffer the same fate...and show up at 25 yards 

We are talking apples and oranges here.
Stiffness is not the only criteria.
Its harmonics.
How rough is the bore?
Barrel time. Compare a 30-06 with a 22" barrel launching a bullet at 2800 fps or more to a 42" ML barrel with the bullet going out at 1800.
Recoil characteristics.
Bedding in the stock.
Some rifles/calibers are nearly immune. Typically 375 H&H rifles throw 235-270-300 gr bullets to virtually the same place at 100 yards.
Old time ML slug gun makers used to determine where to install the front rest on the barrel by clamping the breech of the barrel in a vise, putting powdered sure or similar on the top flat and then striking the barrel with a hammer or mallet and watching how the powder on the top flat reacted. Where this part is placed if CRITICAL and off a few inches can make the rifle useless.
When the load is changed the way the barrel reacts to firing changes. This has unpredictable effects.
Cast a lead lap in an "imperfect" barrel and push it back and forth and sometimes the barrel will actually "sing" as the lap runs over the reamer marks and other imperfections.
Dan

[Bill of the 45th]

If point of impact is point of aim with that combo, why are you doing anything.  Buy a lifetime supply of that lubed patch.  Some people spend countless hours, weeks months, or longer finding that magical JuJu.  Just take it out and kill squirrels.

Bill

[Edd]

If point of impact is point of aim with that combo, why are you doing anything.  Buy a lifetime supply of that lubed patch.  Some people spend countless hours, weeks months, or longer finding that magical JuJu.  Just take it out and kill squirrels.

Bill

Bill, I'm not sure who you directed this question to. I do know that if I bought a lifetime supply of the Eastern Maine lubed patch, alluded to in my original post, then my Vincent would go up for sale, just to pay for the lubed patch these folks offer for sale...

Much of my experimenting is promted by economics. Much of the same is done out of curiosity and jess plain ole shooting fun.

Edd