it is common knowledge among loaders...

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cleardatum

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... that reducing bullet "jump" (the distance from bullet to lands) usually improves accuracy- i've corroborated this phenomenon first hand. the question is, why? i have my theories. what are yours? or are there hard, proven answers?
 

Jimbo357mag

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In rifle rounds yes. In pistol/revolver rounds, not so much.

I think keeping the bullet close to the lands makes sure it is started down the barrel straight.

I have a 357mag rifle that has about a 1/2 inch of freebore before a 158gr bullet hits the lands. Still shoots pretty well though. :D
 

Rick Courtright

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cleardatum said:
... that reducing bullet "jump" (the distance from bullet to lands) usually improves accuracy- i've corroborated this phenomenon first hand. the question is, why? i have my theories. what are yours? or are there hard, proven answers?

Hi,

One thing you're going to learn about "common knowledge" in this hobby is there is a LOT of supposition and very little actual hard facts/data/science behind much of it.

First off, one must test, test, and then test, before making definitive statements. The guys in the white lab coats with the millions of dollars worth of equipment behind them do just that, 40 hours a week, for entire working careers, and are generally less likely to make a definitive statement about a lot of this stuff than the guy on that barstool down at the end who "knows" the answer, even if his only testing was to check if that last beer was cold when the barkeep handed it to him!

The most common "explanation" for this phenomenon I've heard is the bullet enters the barrel straighter. (Jimbo's heard the same story!) Ok, maybe it does. But even with my impaired olfactory system, it's hard to get that to pass the sniff test:

First off, how much "wiggle room" IS there in the chamber, forcing cone/leade and initial rifling of the gun? While the bullet's nose may not be stabilized for a few thousandths of an inch until the ogive engages the rifling, at the same time its body and tail ARE being held "in line" by the mouth of the case. Frankly, there's just not that much wiggle room best I can tell!

From there, the bullet is accelerated to a rotational velocity somewhere over 150,000 rpm, mach schnell! It exits the barrel a traveling gyroscope, and spinning at that speed, it's pretty darn stable. Doesn't really make much difference where it was when it got started. Yet the phenomenon is still observed! Why?

My own theory, which can't be proven with the test equipment available to me (which is good only to determine if that last beer was cold!) has to do with the harmonics of the barrel/bullet combo. If you've ever seen high speed photography of a barrel being fired, and the lens is powerful enough to see it happen, there's a "wave" that travels down the barrel with the bullet. There's pressure in front of the bullet as it compresses the previously still air in the barrel to get it out of the way. There's pressure behind the bullet from the burning propellant. And all the various factors involved joined together serve to make the barrel move kinda like watching a garden hose jumping about as you put water pressure to it.

So the "secret" to accuracy is to get the bullet to exit the barrel as exactly the right moment (or millisecond?) the barrel is pointed exactly where it needs to be to place the bullet on target as desired. Not the biggest problem on paper, that task is a touch more of a challenge in the field. This is one of the reasons for heavy bull barrel designs--to minimize that "whip" effect. It's also one of the reasons for barrels being bedded in some cases, free floated in others. Various barrel tapers are also used for the same reason. It goes on and on, but the fewer variables one has, the easier it is to control the rest. So... seating the bullet out close to the rifling is simply a way of minimizing one variable. And with the proper charge of the right powder for his chosen bullet, MAY enable the shooter to sorta control that barrel whip in his favor. If he hits on the "magic" combo, he sees positive results! Goal achieved, even if he might be off a bit in attributing the observed result to the proper cause.

That's my story, and I'm stickin' to until someone can show me some hard data to the contrary! I'll have another beer now, thank you. ;)

Rick C
 
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Rick Courtright said:
One thing you're going to learn about "common knowledge" in this hobby is there is a LOT of supposition and very little actual hard facts/data/science behind much of it.

Rick C


Amen and amen!

:mrgreen: :mrgreen: :mrgreen:
 

Bucks Owin

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Keep in mind that pressures are also affected by bullet seating depth. Some target/varmit rifle shooters seat bullets to actually touch the rifling. This can improve accuracy in some rifles but bear in mind it can also raise pressure dramatically when the bullet has no "jump"...

Just sayin'... :shock:
 

mikld

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Thanks Rick. I seldom see such wisdom. Most of the time I read answers/replies that come off as the only true, logical answer and the poster know it, by God! I've read reasons for bullet to land distance that are "facts" and no other reply can possibly be correct...

I believe there aren't a many "absolutes" as some think...
 

Cheesewhiz

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I'm one of those guys that read the front portions of their reloading manuals before worrying about recipes. Lyman's and Hornady's manuals seem to come to this (these) points from different directions but arrive, sort of, to the same point. Hornady's latest book actually comes at it from two different positions, kind of interesting.

I only load rifle rounds like a trained monkey, my friend sets up his presses and I pull handles. I do get input on some runs and he may test those for effect later on.

So my input will be based on a couple of things from a couple of guys.

When it comes to loading 9mm and 45 ACP, the student is the master now, it's been that way for some years now. 45 ACP is more limited mechanically on overall length so much that your actual load length is fairly fixed but I load it to keep the ogive close to the rifling, around .010" clearance, and be within a length that is max or less and feeds with no issue.
9mm is a different animal, there are many FMJ RN bullets in 9mm that the ogive isn't close to the rifling at the max length of 1.169", that happens quite often. MY second most accurate RN 9mm round uses a bullet with a set OAL of 1.165" has .025" of free bore, were my most accurate 9mm RN that free bore is about .010" at 1.160" OAL.

I'm not sure how much it comes into play for rifle or pistol for that matter.

.....but my old teacher, the guy who taught me more about guns, bullets and shooting them, SGT. Pinky always stressed headspace as being the biggest factor when it comes to accuracy with anything. The less gas allowed in front of that projectile before it obturates, the more likely it will travel true.

So seating a bullet fairly close to the rifling I guess could be an extension on Pinky's truth, Pinky only had a theory long enough to prove it right or wrong. I should have taken more notes, there are things 35 years later that he told me that I find out as gospel to this day.
 

cleardatum

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hence the italicized usually- like usually typically. i understand that everything needs to be qualified. maybemaybe. sometimes. anyway, i appreciate the enlightened replies. i've only been loading for my savage .308 so far, and getting the bullets closer to the rifling has made a world of difference. of course, i'm using different bullets. and cases. and powder. and primers. i didn't bother trying it .1 off the lands as a control. i may try that. the freebore should be the same diameter as the grooves, right? which should obturate the bullet, maybe? i've read that the bullet stops and starts several times at the beginning of its journey. freebore would definitely have a profound effect on that sequence of events. there are a lot of very interesting (and some of it contradictory) data out there. some sources say NEVER let the bullet touch the lands, but some of the uber accuracy guys routinely "jam" the bullet looking for that perfect load. if i were retired, and had my own range, i could probably get a handle on this within a few decades...
 

DGW1949

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cleardatum said:
... that reducing bullet "jump" (the distance from bullet to lands) usually improves accuracy- i've corroborated this phenomenon first hand. the question is, why? i have my theories. what are yours? or are there hard, proven answers?

My "theory" is that sometimes it matters, sometimes it don't....and ditto on much of what we all have come to think of as "conventional wisdom" when it comes to what "should" constitute a realy-accurate rifle.
Just by going from "conventional wisdom", there shouldn't be any M1 Garands which can shoot 1-MOA using store-bought ammo....but there are.

DGW
 

5of7

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Shooting benchrest target rifles is a different game than shooting handguns.

In the bench rest game, clearance between the ogive of the bullet and the beginning of the rifling is important to accuracy......but bear in mind that 100 yd. 5 shot groups of .187" is the norm and a group that is .020" larger than the smallest group puts one out of the running.....depending on the particular event of course.

When I develop a load for the 6MM BR, I always start out with the bullets touching the lands and work back from there in .010" increments. I have found that the best bet for seating depth would be somewhere on the order of .020" short of the lands, but the barrel, the bullet, powder charge and primer used all have an effect on accuracy.
 

toysoldier

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I have read that, back in the days of early single-shot breechloaders and paper-patched bullets, target shooters would load the bullet up against the lands, then load the shell behind it. So the practice of limiting freebore has been around long enough to acquire considerable respectability. As others have noted, "your results may vary."

I find it interesting to note that virtually all modern .22 revolvers, and most older target guns, are based on .38 frames and cylinder length, which makes for a lot of freebore. Some of them shoot very well. The same holds true for .357/9mm and .45 Colt/.45ACP convertable revolvers.
 

Dan in MI

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5of7 said:
When I develop a load for the 6MM BR, I always start out with the bullets touching the lands and work back from there in .010" increments. I have found that the best bet for seating depth would be somewhere on the order of .020" short of the lands, but the barrel, the bullet, powder charge and primer used all have an effect on accuracy.

That is how we always tested our loads on single shot handguns to find the sweet spot.
 

Flash

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In addition to the harmonics, which plays a big part, the throat plays a major part in accuracy. Not so much because the bullet can become canted upon entering the rifling but because the throat becomes a chamber that the violent gasses create turbulent forces along the sides and the front of the bullet, before the bullet is firmly on it's way down the rifling. This is especially obvious with cast bullets.
 

Flash

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toysoldier said:
I have read that, back in the days of early single-shot breechloaders and paper-patched bullets, target shooters would load the bullet up against the lands, then load the shell behind it. So the practice of limiting freebore has been around long enough to acquire considerable respectability. As others have noted, "your results may vary."

I find it interesting to note that virtually all modern .22 revolvers, and most older target guns, are based on .38 frames and cylinder length, which makes for a lot of freebore. Some of them shoot very well. The same holds true for .357/9mm and .45 Colt/.45ACP convertable revolvers.

Cylinder length and throat length are two separate things. The 22lr cylinder can be an equal length of a 357 cylinder but the throat of the 22lr can be three or four times as long as the 357 throat.
The 357/9mm convertible is shooting a .356 bullet and a .357 bullet down the same barrel. I can say from experience that the 357/9mm convertibles aren't very accurate with 9mm loads for that very reason.
 

OldePhart

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It is common knowledge that knowledge is not common...

Sorry, OP, wasn't meant as a dig at you I just love the play on words and couldn't resist any longer when this thread popped up to the top again. :)

John
 

triggerpull

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For the handloads that I do--the answer is generally fairly close--but I'm not a shove-it-in-the-lands kind of guy. Call the bullet manufacturers and talk to a ballistician/designer--they are almost always eager to talk in depth on the subject in my experience. The answers you get from Barnes and/or Berger might just surprise you. : )
 

Pocketfisherman

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With soft swaged 200gr LSWC in 45 ACP, it does make a difference in accuracy. Seating the bullet out where the round will just sit flush in the chamber and the slide will still lockup is how you get the best accuracy. I think the reason though is that it forces the round to headspace snugly versus hanging off the extractor hook and running the risk of the round being displaced slightly in the chamber when the firing pin hits it. 45 ACP cases tend to be a bit short and when their rim contacts the chamber shoulder, there is typically a bit of space behind the bottom of the round and the slide's breechface. Seating the bullet out this way with soft swaged lead runs little risk of overpressure with typical low velocity wad loads.
 

sliclee

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Jimbo you are 100 % correct.
The closer to touching, the shorter the jump, all other things as perfect will enhance accuracy.

The person who wrote, distance can be set is not correct. The distance will change depending on the ogive of the bullet used. Lee
 
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