We have discussed this a bit before, but from slightly different perspectives.

Some believe if more Pressure is generated, the Bullet will always go Faster. Some believe the actual Bore(condition, cleanliness, dimensions, twist rate, etc.) can cause higher Velocity. Some believe in Fast Barrels and Slow Barrels, while some do not believe they exist. Some believe all those conditions exist. And some do not believe any of it.

Question:
If a Barrel is made "Slicker" (less Bullet Friction and Drag), will the Velocity be Higher or Lower using the same exact Load.

Choices:
1. It will be a Higher Velocity.
2. It will be a Lower Velocity.
3. It may go in either direction.
4. Other??? Please explain.

 

quote:

Question:
If a Barrel is made "Slicker" (less Bullet Friction and Drag), will the Velocity be Higher or Lower using the same exact Load.

My gunsmith just rebarreled a .264 WM for me. He checked the bore dimensions and reported it was a "tight" barrel. Lands and grooves were 1/2 to 3/4 of a thousandth tighter. He warned me that I would probably not reach the velocity I would like before pressure signs were reached.

There are "slow barrels" and "fast barrels"
He has a .264 as well. With his load his velocity was dismal (Slow barrel). He rebarreled his rifle recently and with the same load gets 300 fps greater velocity.

I see it like this:

If one does something to retard the passage of the bullet through the barrel then there will be a resultant increase in pressure as the powder will continue to burn regardless.

This higher pressure doesn't necessarily mean higher velocity as it may require a lessening of the amount of powder in order to keep the chamber pressure in safe limits.....and this then retards the acceleration in the balance of the barrel.

If, however, the barrel somehow allows passage of the bullet with greater than normal ease there will be resulting lower pressure and this allows one to add a bit more powder to enhanse velocity during the balance of travel.

Velocity is the result of how long we can keep the pressure on the bullet more so than the actual chamber pressure that is typically measured.....(in all types of ways)

quote:

Originally posted by vapodog:
I see it like this:

If one does something to retard the passage of the bullet through the barrel then there will be a resultant increase in pressure as the powder will continue to burn regardless.

This higher pressure doesn't necessarily mean higher velocity as it may require a lessening of the amount of powder in order to keep the chamber pressure in safe limits.....and this then retards the acceleration in the balance of the barrel.

If, however, the barrel somehow allows passage of the bullet with greater than normal ease there will be resulting lower pressure and this allows one to add a bit more powder to enhanse velocity during the balance of travel.

Velocity is the result of how long we can keep the pressure on the bullet more so than the actual chamber pressure that is typically measured.....(in all types of ways)

I have to agree, it's a balancing act. Look at data w/ moly bullets, less friction less vel w/ identical loads. I'm sure there isa point where too much friction only increases resitance & pressures, too little friction & there is a loss of pressure & vel.

It can go up or down. Pressure curves change and that puts you back at square one in most cases as it relates to accuracy and velocity.

There are possibilities, I suspect, that either could occur.

Why? Seldom is ANY powder exactly the right burning rate for the effective bore capacity, bore surface and exact bullet being used. Bore capacity, of course, depends not only on both internal land and groove diameters, but also on barrel length and cartridge case length. And of course burn rate is not a static, unchanging thing. It changes as the pressures within the barrel change. Burn rate also changes as the powder itself changes during the burn. Burn surface areas change, retardants are consumed, etc.

With a powder that is even a little hair too slow to start with, some minor retardation of the bullet may both increase the pressure, but in turn also cause the powder to burn more completely, thus releasing all of its energy to push the bullet for a longer time. That retardation could be occasioned by any one or more of barrel surface smoothness, internal diameters, having to shove a heavier bullet (or one with a harder jacket), or many other things.

To the contrary, sometimes the "perfect propellant burn" may be the result of slicker barrel surfaces, different barrel dimensions, lighter bullets, whatever.

At any rate, the max velocity likely needs the very BEST match of powder burn rate and powder amount with all the other conditions and components at the time of firing. That may be one reason some lots of the same nominal powder can sometimes produce dramatically different velocities.

The only way to know for sure what will produce max velocities at aceptable pressures with all the variables at hand, is probably to chronograph individual load combos in individual barrels.

Some combinations WILL doubtless produce higher (and lower) velocities than others.

I know we have been over this from many different perspectives in the past. And I realize some believe one thing and not the other.

What brought this to mind was an ad in a magazine that a buddy of mine sent to me. I did a "Find" on the product on this Reloading Board and only saw one mention of the product at all by Grumulkin.

The product is made by Microlon Products and has a very interesting Test that one of the Gun Rags did. You can find the report in a Link at the site.

They coated a 22LR Bore with the product and the Bullet kept going higher at the specific distance they were Testing and the Velocity kept increasing - with the same 22LR load. It eventually stabilized and he shot a group.

I'm not normally drawn toward Snake Oil, but this product looked kind of interesting. They did not go into a lot of detail about "how often" to re-apply the stuff, but I could have missed it.

Once I got through reading about the stuff, I got to thinking about the old Slow Barrel and Fast Barrel discussions. Wasn't trying to trick anyone, cause I do believe valid arguments can be made for different answers.

If anyone has tried this stuff enough to have an opinion on it, let us know how well it worked for you.
-----

For those of you who "changed the Load", What if the Load remains the same in the original Poll question?

I agree with Vapodog and Fred. AIU

pressure, as an absolute, has NOTHING to do with velocity ... nothing ..
(its okay, you don't believe me .. if you have 200K, the gun blows up .. if you have 50K for .0005seconds, you probably wind up with a stuck bullet in the barrel, and if you go 20K for 1 seconds, it goes amazing speeds)

120K will blow up a gun ... and the bullet may not exit the barrel...
area under the pressure curve is one of the factors associated with velocity ...

and to answer the question, if you have a load of X, and you slick up the barrel or moly coat it, it will go slower, MOST of the time, no other changes ..

just exactly as more twist INCREASES presure, if you could have two indentical barrels ..

why most of the time? if you have a pocked and cratered barrel, you could have a period where the slicked up barrel makes it go faster, to a point ...

a decent lapped barrel will probably go slower (and therefore hit higer).

Plane and simple! If all the powder burns and less energy is used to overcome friction than that energy is put into heating the barrel and making the bullet go faster. The barrel will heat less so what do you think? Now this is a real brain teaser. roger

My crony readings are always slower with the first shot from a clean barrel and then they speed up after that.

rodger,
"overcoming friction" happens at 1 fps mv ... backpressure also matters

quote:

Originally posted by jeffeosso:
rodger,
"overcoming friction" happens at 1 fps mv ... backpressure also matters

even if that were true ,and it ain't,with perfect powder burning the energy in equals the energy out. I did leave off one energy Out and that is that contained in the exhaust gas temperature and velocity. Do you have any KNOWLEDGE weither that is significantly greater or less? Feelings and opinions are invalid.If someone can show legitimate test results proving me WRONG I'll feel that we are that much ahead. I've been wrong more than once.Whim and wisdom are only the same as they each start with W. roger

yeah, actually .. and without a straingauge, about the best you can get

2 douglas airgauged .358 barrels.. differnce was twist .. faster twist showed pressure faster, every time ... barrels cut and chambered litterally 1 then the other ... as close to the same as possible...

proof? there you go ... every time, each time, no exceptions to the trend ....

how much? now THATS asking for thousands of my dollars to satisfy your curiosity

quote:

backpressure also matters

This is a new one on me.....can we explain "backpressure" as it relates to rifles please?

quote:

Originally posted by jeffeosso:
yeah, actually .. and without a straingauge, about the best you can get

2 douglas airgauged .358 barrels.. differnce was twist .. faster twist showed pressure faster, every time ... barrels cut and chambered litterally 1 then the other ... as close to the same as possible...

You do know that no two barrels are alike & even if chanbered on the same equip, one after the other will not be identical. So minor changes in pressures form one bbl to the other could be slightly diff steel, slightly smaller/larger chamber or rifling.

In theory if the bullet passage down the barrel was frictionless with obturation still maintained then a powder that brought chamber pressure quickly up to the maximum level and burnt at a rate to hold that pressure constant during the passage of the bullet to the muzzle, then the maximum velocity that could be attained from that rifle would be achieved. The limiting factor would be the safe pressure limit of the chamber and barrel, assuming of course the bullet holds up and doesn’t rivet or distort in the barrel.

From this it is reasonable to expect that by reducing friction of the bullet in the barrel, while still achieving proper obturation, through having a smooth well gauged bore and lubed bullet, then a faster powder than usually used in the cartridge could be used to achieve and maintain maximum chamber and barrel pressure to give maximum acceleration to the bullet.

When a cartridge is fired, powder burns, deflagrating rather than detonating, and rapidly produces gas. The expanding gas generates pressure in all directions. When pressure is high enough to overcome the friction holding the bullet in the case and to overcome the inertia of the bullet at rest then the bullet begins to move toward the muzzle. Pressure continues to act upon the bullet as it accelerates down the bore until it clears the muzzle and the pressure is relieved.

If all the powder was consumed before the bullet left the case it would still continue to accelerate all the way to the muzzle. But we know that the powder continues to burn after the bullet leaves the case and some powder is burned in the bore. The degree to which that happens depends on many factors, perhaps greatest of which is the powder capacity of the case relative to the caliber of the particular cartridge.

So now we have a bullet speeding down a bore. The main things limiting the acceleration of the bullet are the inertia of the bullet, the amount of force exerted by the gas on the base of the bullet, and the amount of resistance the bullet encounters going down the bore. Air resistance the bullet encounters ahead of it in the bore is real but negligible in relation to the other forces acting upon the bullet. Assuming the bullet still acts as a gas seal, if all we do is reduce the amount of resistance the bullet encounters going down the bore, then the bullet will accelerate at a greater rate and reach a higher velocity before exiting the barrel.

However, various treatments that we apply and things we do that we think "slick" up the bore may actually be imparting additional resistance. For example, you might expect a good coating of oil to reduce friction and allow the bullet to achieve higher velocity. But in reality, as the bullet is being squeezed down the barrel, it may end up pushing sufficient oil ahead of it to cause additional resistance, enough to have a net negative effect on velocity. Another case might be one in which the bore is treated with a coating of some substance with a low coefficient of friction. The substance coating the bore, slick as it might be, may add enough material to cause a very slight reduction in the bore size. Because the bullet must be squeezed through the bore, even a slight decrease in internal diameter may result in higher resistance and a reduction in bullet velocity.

I am not saying that you should never treat or oil your bores. Rather, conservative use of carefully selected oils and treatments must surely be the best way to go. You can try to predict what will happen when you apply something to the bore but only the chronograph will tell you for sure.

The factors in velocity are:-

Owner
Chronograph
Bravery (or poor eyesight?)
Internet usage

Occasionaly the barrel hits a sweetspot in these factors at which point serious velocities are generated.

I said a slick barrel would be faster but then one poster said that his velocity went up as he fouled his barrel. I remember a study that addressed that very factor. Starting with a clean barrel, for the first half dozen shots, the velocity went up incrementally and then stabilized. This was repeated several times with different rifles. Now what does this mean?

Pressure= resistance to flow.
IN my "opinion" a clean barrel or a moly'd bullet or a smooth barrel has less resistance, and has less pressure and usually less speed.

HOWEVER, at the risk of contradicting myself I would say you will be able to add more powder and get a more even transfer pressure/flow to the smooth barrel situation thus attaining more velocity than the rough barrel.

In short I would believe with like charges the smooth barrel will be slower...but at like pressure it will be faster.

My experience has been that "slicker" bores/bullets lead to slower velocities.
That is as described in Hot Core's question. Only variable is friction in the bore.
I had a hard time wrapping my mind around this one. But after shooting many many "naked" and "mollied" bullets thru several rifles. Using an Ohler chronograph to track velocities. Only variable was the molly or lack of molly. Carefully cleaning between groups. The data tapes always said the mollied bullets were slower than the bare bullets. cartriges shot were 223 308 and 30-06.

muck

quote:

Originally posted by wasbeeman:
I said a slick barrel would be faster but then one poster said that his velocity went up as he fouled his barrel. I remember a study that addressed that very factor. Starting with a clean barrel, for the first half dozen shots, the velocity went up incrementally and then stabilized. This was repeated several times with different rifles. Now what does this mean?

The velocity will rise as the bore becomes fouled but if you were measuring pressure you would also record the pressure rising as well hence the bullet in each successive shot will gain more velocity.
This will continue with each shot until equilibrium is reached where the fouling reaches its maximum for the given barrel and the friction produced inhibits the bullet gaining any more velocity.

So while it is true to say in some circumstances a dirty barrel gives more velocity, some posters here are correct in their observations that a good slick barrel and bullets will keep fouling to a minimum and allow maximum pressure build up and retention to accelerate the bullet to it's maximum velocity. The trick is to use the powder with the correct burning rate to achieve this.

quote:

Originally posted by vapodog:

quote:

backpressure also matters

This is a new one on me.....can we explain "backpressure" as it relates to rifles please?

nah, its not new to you .. nitro powder burnt loose just fizzles, right? underloaded cases can explode.. and when you are reloading, there is THAT load the you get 2-3X the increase per grain in velocity... and h335, which is by FAR the most commonly burnt powder from my house, is grossly ineffcient with loads under and estmated 45Kpsi ... lots of powder boom/burn outside the barrel, THEN its better and better burns .. if you don't contain nitro powder, its kinda boring to watch burn

quote:

Originally posted by fredj338:

quote:

Originally posted by jeffeosso:
yeah, actually .. and without a straingauge, about the best you can get

2 douglas airgauged .358 barrels.. differnce was twist .. faster twist showed pressure faster, every time ... barrels cut and chambered litterally 1 then the other ... as close to the same as possible...

You do know that no two barrels are alike & even if chanbered on the same equip, one after the other will not be identical. So minor changes in pressures form one bbl to the other could be slightly diff steel, slightly smaller/larger chamber or rifling.

yep .. except EVERY barrel is different .. though we freely compare hammer forged vs button vs cut rifle barrels against "book" and then decry fast and slow barrels ... these two barrels were as close to equal as i was willing to pay for ... so accept that i put MY money into that, and that i also have a larger sample set of barrels that came on the gun... includes steel blr in 358, savage 99 in 358, mexican mauser with douglas barrel and springfield 1903 with same, though this is the 10 twist, special ordered tooling, vs the 12 on the mexican, and 14 for the blr and savage

After I brought my first crony I gave up guessing what a certain barrel or caliber will do. Now I load them shoot them across the crony and know rt to the fps what it does.

I'm sure glad I asked this since it will totally clear up the issue for the Beginners and Rookies.

quote:

Originally posted by Hot Core:
I'm sure glad I asked this since it will totally clear up the issue for the Beginners and Rookies.

Me too! roger

quote:

Originally posted by p dog shooter:
After I brought my first crony I gave up guessing what a certain barrel or caliber will do. Now I load them shoot them across the crony and know rt to the fps what it does.

Add to this, that if you consistently get plenty of bang/flops on the game you hunt, then p dog shooter, that all we need to know.

quote:

Originally posted by eagle27:

quote:

Originally posted by p dog shooter:
After I brought my first crony I gave up guessing what a certain barrel or caliber will do. Now I load them shoot them across the crony and know rt to the fps what it does.

Add to this, that if you consistently get plenty of bang/flops on the game you hunt, then p dog shooter, that all we need to know.

Here's a couple of guys that are not afflicted with analysis paralysis!

if you use a good quality barrel grease on a rifle that has had its weight reduced you might just end up with - greased lightening

quote:

Originally posted by eagle27:

quote:

Originally posted by wasbeeman:
I said a slick barrel would be faster but then one poster said that his velocity went up as he fouled his barrel. I remember a study that addressed that very factor. Starting with a clean barrel, for the first half dozen shots, the velocity went up incrementally and then stabilized. This was repeated several times with different rifles. Now what does this mean?

The velocity will rise as the bore becomes fouled but if you were measuring pressure you would also record the pressure rising as well hence the bullet in each successive shot will gain more velocity.
This will continue with each shot until equilibrium is reached where the fouling reaches its maximum for the given barrel and the friction produced inhibits the bullet gaining any more velocity.

So while it is true to say in some circumstances a dirty barrel gives more velocity, some posters here are correct in their observations that a good slick barrel and bullets will keep fouling to a minimum and allow maximum pressure build up and retention to accelerate the bullet to it's maximum velocity. The trick is to use the powder with the correct burning rate to achieve this.

Could possibly the fouling be "slickening the barrel" by filling in the imperfections in the bore?

I think I read on the Lilja website a while back that if a barrel is too slick it actually has more friction. They said they polish their bores to a certain point and quit.

quote:

Originally posted by Silverado:
I think I read on the Lilja website a while back that if a barrel is too slick it actually has more friction. They said they polish their bores to a certain point and quit.

Could be something in that. If you rub two highly polished pieces of steel together they can almost bind. Then again reloading dies and bearings etc are normally polished to a high degree?