Do barrels "get faster"?

[NYDAN]

Last fall I very quickly worked up a deer hunting load for my new 300 WSM. I then loaded up about 20 cartridges. I used six cartridges to sight-in and used one to shoot a deer.

This winter I started a more thorough load development for elk hunting. After a bit, I wanted the brass from the cartridges I had loaded for last fall's deer hunting and shot them up. They were about 30 fps faster.

Last fall I had an average (extremely consistent) velocity of 3073 fps at 67 *F.

Late winter after shooting more load development rounds, the 13 left over cartridges from the same batch yielded an average velocity of 3105 fps at 35 *F.

Is this a "normal" occurrence?

Dan

 

[truck driver]

Normally I would suspect the velocity to be lower since the temps were lower but you may have experienced some bullet case weld from storage.
I try to load only what I would use say 5 rounds and if I need more I then load fresh ammo to use.
If perchance I'm loading for my 257 Rob I will load 20 since I will be hunting ground hogs and expect to shoot more.

 

[MAinAR]

Its been normal for a new barrel to make a velocity increase usually from 50 to have had as many as 150 shots on it when I see it occur. Have seen speed go up 100fps on occasion but about 50fps seems more the norm.

 

[DrMike]

Certainly no unheard of. One of my 280s had a great increase in velocity (almost 200 fps) after an extended break-in. I persisted in using the rifle, even when I had doubts about the rifle ever yielding expected velocity, simply because it was deadly accurate. It accounted for quite a number of whitetails and mulies. It is not not only deadly accurate, but has greater reach than ever with the velocity increase.

 

[NYDAN]

Thanks, guys. That is what I thought, but I wanted to make sure. That barrel is easier to clean now than when new. I get mostly black powder residue and very little copper. I think I get more copper from the bronze brush now than I do from the bullets. Once I stop using the bronze brush, the copper color goes away. When I use a nylon brush I don't seem to get any copper color.

Dan

 

[DrMike]

Good observation, Dan. New barrels (especially in mass production rifles) have tool marks on the throat. Firing multiple rounds tends to smooth these tool marks, allowing for greater velocities. I'm not nearly so convinced that the copper wash fills blemishes in the barrels, making for a "smoother" barrel. I haven't used copper brushes in years. I use nylon brushes exclusively. It allows for a far more reliable assessment of copper removal from the barrel.

 

[SJB358]

Its been normal for a new barrel to make a velocity increase usually from 50 to have had as many as 150 shots on it when I see it occur. Have seen speed go up 100fps on occasion but about 50fps seems more the norm.

Seen it quite a few times now. Most of the time I don’t like to get real busy with load work or anything serious until I get at least 100 rounds through the barrel and cleaning it as necessary. Dyna bore coat has helped a bunch for me but still requires smoothing out the barrel to get it really broken in.

 

[350JR]

The fact that barrels themselves do change combined with how different custom barrels are to factory in performance is a very intriguing to me.

While I doubt we can ever grasp how even minute changes in any of the factors could be controlled, the fact that there USUALLY is a difference and often a HUGE difference is one of the reasons, I myself, treat every rifle, every barrel like it's a "wildcat" cartridge when I first load for it..........and not often enough, do over again as time wears on.

Embarrassingly, I spend literally hundreds and hundreds of hours pouring over statistics on internal ballistics and the end results we get from even the tiniest of changes. I just never get all the answers I seek and it sometimes seems each answer I start to understand unleashes even more questions.

Related, IMHO, is why I IGNORE posts on "What velocity I can get" from a wildcat based ONLY on usable case capacity. The so-called "4-1 rule" is even more ludicrous when used to compare differing cartridges AND rifles, regardless of the above factors, all on CASE capacity, not even USABLE capacity, "if all else is equal". :?

All is NEVER equal and I'll admit I grind what's left of my teeth every time I see "if all else is equal" in a post on velocity. They wont be......ever. It makes the entire principal null and void.

The fact that the ORIGINAL 4-1 rule was not a certain gun writers who blathers such about, nor did it apply to different rifles......does as well. It may even "irritate" me even to a greater extent.

Sorry. Rant subject for me. But yes, I am in full agreement. Not only do barrels OFTEN produce greater velocities over time, barrels of different make can start out that way or CAN gain more velocity compared to a similar counterpart.

I think if this was all simple, cut and dried and "here follow this recipe" kind of hobby........I wouldn't be doing it.....at all. :wink:

God Bless
Steve

 

[Dwh7271]

I believe they should speed up.
Even if hand lapped there is still lots of bumps and such in there. As they wear down resistance and drag should lower at least to a point.
Whether or not you buy the fire lapping method, the smoothing of the various inconsistencies is the idea behind that.
Scotty is spot on, 100 or so down the bore smooths it and gets it more predictable

 

[Whitesheep]

OK, so I am the ignorant one. (not stupid, just ignorant) What is the "4 in 1 rule" your talking about Steve? No google search revealed anything for me.

Yes, increased speed and more consistency too in my experience.

Thanks for a "learning" in advance.

 

[SJB358]

White sheep the 4-1 rule is basically this, for every 4% in capacity you have you gain 1% in velocity. It’s fairly useful for comparing cartridges. The easiest to see the rule is the 308 Win vs a 300 RUM. I believe a typical 308 load for a 180 is about 50 grains plus or minus a couple grains for a speed of about 2600’ish while the 300 takes about 95-100’ish with the same 180 and attains about 3350’ish.

So you can see just because the 300 doubles charge weight doesn’t mean we double FPS. I’ll let someone else do the math. :lol:

 

[350JR]

However, in the real world.......comparing "load data" with the 4-1 "rule", until one can buy 10 rifles of the same caliber and they ALL get the same velocities (instead of 50-100fps difference).....is hardly accurate for real results.

The ORIGINAL "4-1" estimate was stated by Homer Powley in the early 60s concerning what estimated....repeat, estimated, difference in velocities one could expect by rechambering the SAME rifle (same throat, same barrel conditions, etc, etc) to a larger capacity.

Often you will see "if everything else is equal" attached to the "modern" version......when comparing DIFFERENT rifles in different chamberings, different brass (and the difference in case capacity between brass manufacturers, different throat lengths, different leade angles, different ...........everything. It is physically IMPOSSIBLE for "all else" to be equal.

I have read where it was "discovered" by a certain gun writer "studying load data charts"........which alone makes it VERY unreliable.

Case in point.

IF one were comparing the 243 Winchester round LOAD DATA to another cartridge using said rule, using MY rifle and MY brass cases would toss it all in the trash bin.

Hodgdon states that with a Speer HP 70 grain bullet loaded to 2.625" that 51 grains of Superformance powder is "compressed", 3661fps and 57,900 PSI.

With the same MFG case, the sames Speer bullet, load to the same COAL.......compressed, it is not.
With 52 grains its not either, nor 53 grains but at 54 grains...the powder is just touching the bottom of the bullet.

Needless to say but using that 243 data to compare to anything and using the 4-1 "rule"......it may show up as similar comparing LOAD DATA, but neither pressure NOR velocity is anything close to similar with the same load in my rifle and therefore useless to use as a "rule" of any kind comparing to another.

Not even close enough to compare.

Once I sent an email to Hodgdon and asked them what Case Capacity and what CHAMBER size they used, trying to get a real world feel for comparing loads to my rifle(s).

They stated they "mimic" SAAMI chamber stats. SAAMI clearly state their chambers are "of maximum material condition". In fact, viewing any stardard or "velocity and pressure" chamber drawings in the SAAMI product report shows "ALL CALCULTIONS APPLY AT MAXIMUM MATERIAL CONDITION (MMC)". The TOLERANCES for the V and P chamber.......differ.

MMC refers to the size of a testing feature that contains the greatest amount of material, yet remains within its tolerance zone. (AKA......smallest chamber within the tolerances stated for the cartridge)
For a comparison, production barrel tolerances shown in the chamber drawing for the 243 Winchester (shown in the lower right hand corner) are:
" UNLESS OTHERWISE NOTED,
ALL DIAMETERS + .002 (0.05)
LENGTH TOLERANCE + .015 (0.38)"

Yet the tolerances on the P & V chamber states:
" UNLESS OTHERWISE NOTED,
ALL DIAMETERS + .0005 (0.013)
LENGTH TOLERANCE + .005 (0.13)

While just my opinion, take it for what it's worth, this is completely understandable.

The SAAMI product tests (and that's all they are is standardized commercial product test results almost exactly like millions of other commercial products must go through to maintain "truth in advertising" so differing products, of the same type, are tested in the same way with the same tolerances for customers to get a decent comparison)..........and also the "load data"charts are doing what we as hand loaders have been taught and teach to NOT do.
Use loads for one rifle in a different rifle. All is not equal and pressure issues can rear their ugly head.

By default, commercial products MUST do so. They are offering testing and loads for cartridges for use in every rifle of that caliber, of every age, of all conditions, regardless of chamber sizes, case capacities, bore dimensions, barrel conditions.......and on and on and on.

Also by default they use the smallest of all POSSIBLE capacities within the cartridge's tolerances in insure that there is zero chance of commercial loads ending up in one smaller.......and higher in pressure.

The "case in point" I listed above with my 243 Win.....is not at all rare, but instead, almost always the case.
The "load data loads" take up much less of my case capacities and produce differing velocities and pressure due to the larger amount of area their powder charge recommendation is going into.

Useful? OH yes...but only a directional sign for me, that gives me perspective of where my real life loads will possibly end up.

Accurate maximum loads for ALL rifles?.............that's mathematically, physically, and statistically, IMPOSSIBLE........and so is the accuracy of the 4-1 rule when used between different rifles and different cartridges. While comparing LOAD data....it may come close. In the real world? Maybe if one got lucky but hardly a "rule".

YMMV
God Bless
Steve

MY APOLOGIES to the original poster for taking this in another direction. I'll not further respond on the subject within this thread without expressed permission from him.

 

[30-338]

White sheep the 4-1 rule is basically this, for every 4% in capacity you have you gain 1% in velocity. It’s fairly useful for comparing cartridges. The easiest to see the rule is the 308 Win vs a 300 RUM. I believe a typical 308 load for a 180 is about 50 grains plus or minus a couple grains for a speed of about 2600’ish while the 300 takes about 95-100’ish with the same 180 and attains about 3350’ish.

So you can see just because the 300 doubles charge weight doesn’t mean we double FPS. I’ll let someone else do the math. :lol:

This was done over 24 hr


Dunno either, and can only guess at what Steve's point is about Homer Powley and the 4-to-1 Rule.

For those who aren't familiar with it, the 4-to-1 Rule is that any increase or decrease in the powder capacity of rifle cartridges of the same caliber results in about 1/4 that amount of potential velocity, with the same bullet at the same basic pressure. One example I've used frequently is the .300 RUM and .308 Winchester: The .300 RUM has just about twice the powder capacity as the .308, but does NOT produce twice as much velocity--a 100% increase. Instead the velocity increase, with the same bullet at the same pressure, is about about 25%, which is 1/4 of 100%. This rule does not apply to the SAME powder, but the powders producing the highest velocities in each cartridge.

I am quite familiar with Homer Powley's slide-rule calculator, having purchased one around 40 years ago--and still have it in my bookshelves, packaged in a manila envelope with all the accompanying literature. Can't figure out what the 4-to-1 Rule has to do with any of Powley's basic rules, except that it's another phenomenon derived by crunching the numbers from LOTS of pressure-tested data.

The only similar rule I can remember from Powley is that pressure with single-based powders increases at twice the rate of velocity--which might be called the 2-to-1 Rule. But that was derived from copper-crusher pressure data, not the piezo-electronic data used by the best pressure-labs today, which shows the velocity-pressure relationship isn't quite that simple, even with single-based powders. It varies even more with double-based powders.

Steve also seems to be arguing that pressure-judging by primer appearance works very well. Would love to hear if he can supply some data. I seem to remember Denton mentioning that he'd tried it, and found no correlation.

John

"Gunwriters, as you know, aren't as informed as their readers are and if it wasn't for the readers, there would be no need for writers..."--Shrapnel, May 2015

 

[350JR]

as mentioned......"YMMV"
What MD doesnt understand about comparing the same rifle to multiple and with any kind of "rule".......scares me, and I'm fearless. LOL
and yes, the SOFTER , PRESSURE FIT primer is indeed the "weak link" pressure wise in properly sized to chamber brass. Ask any long range bench shooter.

Sorry to intrude.
Believe what you will.
I'll leave you to your own opinions.
God Bless

 

[SJB358]

White sheep the 4-1 rule is basically this, for every 4% in capacity you have you gain 1% in velocity. It’s fairly useful for comparing cartridges. The easiest to see the rule is the 308 Win vs a 300 RUM. I believe a typical 308 load for a 180 is about 50 grains plus or minus a couple grains for a speed of about 2600’ish while the 300 takes about 95-100’ish with the same 180 and attains about 3350’ish.

So you can see just because the 300 doubles charge weight doesn’t mean we double FPS. I’ll let someone else do the math. :lol:

This was done over 24 hr


Dunno either, and can only guess at what Steve's point is about Homer Powley and the 4-to-1 Rule.

For those who aren't familiar with it, the 4-to-1 Rule is that any increase or decrease in the powder capacity of rifle cartridges of the same caliber results in about 1/4 that amount of potential velocity, with the same bullet at the same basic pressure. One example I've used frequently is the .300 RUM and .308 Winchester: The .300 RUM has just about twice the powder capacity as the .308, but does NOT produce twice as much velocity--a 100% increase. Instead the velocity increase, with the same bullet at the same pressure, is about about 25%, which is 1/4 of 100%. This rule does not apply to the SAME powder, but the powders producing the highest velocities in each cartridge.

I am quite familiar with Homer Powley's slide-rule calculator, having purchased one around 40 years ago--and still have it in my bookshelves, packaged in a manila envelope with all the accompanying literature. Can't figure out what the 4-to-1 Rule has to do with any of Powley's basic rules, except that it's another phenomenon derived by crunching the numbers from LOTS of pressure-tested data.

The only similar rule I can remember from Powley is that pressure with single-based powders increases at twice the rate of velocity--which might be called the 2-to-1 Rule. But that was derived from copper-crusher pressure data, not the piezo-electronic data used by the best pressure-labs today, which shows the velocity-pressure relationship isn't quite that simple, even with single-based powders. It varies even more with double-based powders.

Steve also seems to be arguing that pressure-judging by primer appearance works very well. Would love to hear if he can supply some data. I seem to remember Denton mentioning that he'd tried it, and found no correlation.

John

"Gunwriters, as you know, aren't as informed as their readers are and if it wasn't for the readers, there would be no need for writers..."--Shrapnel, May 2015

The 300 RUM vs 308 seemed about the easiest to compare. Thanks for laying it out with the math.

 

[30-338]

SJB358, It was John Barnesss who post that.

 

[NYDAN]

MY APOLOGIES to the original poster for taking this in another direction. I'll not further respond on the subject within this thread without expressed permission from him.

350JR, As long as my orginal question was answered (which it was) I don't care what direction the discussion goes in. This is, after all, a forum, a place for discussing topics of interest to those participating. Discussions here are like conversations at the dinner table. You start out asking your spouse how his/her day went and end up talking about the squirrels in the bird feeder. Conversations evolve as new comments are made. All forum participants should feel free to express their views on my initial posts regardless of the topic I start with.

Dan

 

[SJB358]

SJB358, It was John Barnesss who post that.

Thanks buddy....

On that note it’s time to set some steel and air the 220 Lapuas from the 300 RUM out some.. :lol:

 

[350JR]

Perhaps........just perhaps, I am not understanding the calculation. I am not perfect but.....

Those standing behind the 4-1 "rule", show me the calculations.

240 Weatherby mag
6mm Remington

Regardless of what the maximum pressure "rating" is believed to be for maximum pressure, THIS maximum velocity for the 6mm Remington shows an ending pressure below either cartridge's MAP values.

Regardless of the lower pressure it IS the fastest 80 grain bullet load listed for the 6mm Remington (unless I missed a higher one.) in the Hodgdon load data site.

Since "all else is equal" the listed pressure for this load is the one to match. It is also below the accepted max pressure for the 240 Weatherby mag so such should not be an issue.

Hodgdon lists the 6mm Remington with an 80 grain Barnes TTSX bullet at 3581 FPS and 59,600 psi.

The info I find shows the 240 mag at 65 grains and the 6MM Rem at 55 (one other says 54.6) grains.
If you have other info, please list the source with a link. Lord knows they vary by website way too often for unknown reasons.

And then show me the math where the 240 loads with an ANY 80 grain bullet that equates to what your 4-1 calculation shows how it "works" with a link to any powder company's published load data.

As I understand the rule its "four percent more case capacity equals one percent more velocity" and in the pasted Barseness post about he clearly says its accurate REGARDLESS of what powder is used and is for "maximum velocities" with equal pressure..........correct?

MY math shows 65 grains-55 grains is 10 grains. Thats 10/55 for a 0.1818181818181818 increase in capacity over the 6mm Remington.

Divided by 4 equals 0.0454545454545455 percent to apply to find the increased velocity of the larger round over the smaller round.

0.0454545454545455 times 3581 equals, 162.7727272727273 fps

162.7727272727273 fps plus the smaller 6mm Rem's velocity of 3581 fps eguals....., rounded down, is
3742.7 fps as a calculated velocity for the 240 magnum.......at, let's not forget, 59,600 psi of pressure.

I must be missing a load data information page....or the above is not the formulation to use?

My thanks to the OP as well.
God Bless
Steve

 

[30-338]

Perhaps........just perhaps, I am not understanding the calculation. I am not perfect but.....

Those standing behind the 4-1 "rule", show me the calculations.

240 Weatherby mag
6mm Remington

Regardless of what the maximum pressure "rating" is believed to be for maximum pressure, THIS maximum velocity for the 6mm Remington shows an ending pressure below either cartridge's MAP values.

Regardless of the lower pressure it IS the fastest 80 grain bullet load listed for the 6mm Remington (unless I missed a higher one.) in the Hodgdon load data site.

Since "all else is equal" the listed pressure for this load is the one to match. It is also below the accepted max pressure for the 240 Weatherby mag so such should not be an issue.

Hodgdon lists the 6mm Remington with an 80 grain Barnes TTSX bullet at 3581 FPS and 59,600 psi.

The info I find shows the 240 mag at 65 grains and the 6MM Rem at 55 (one other says 54.6) grains.
If you have other info, please list the source with a link. Lord knows they vary by website way too often for unknown reasons.

And then show me the math where the 240 loads with an ANY 80 grain bullet that equates to what your 4-1 calculation shows how it "works" with a link to any powder company's published load data.

As I understand the rule its "four percent more case capacity equals one percent more velocity" and in the pasted Barseness post about he clearly says its accurate REGARDLESS of what powder is used and is for "maximum velocities" with equal pressure..........correct?

MY math shows 65 grains-55 grains is 10 grains. Thats 10/55 for a 0.1818181818181818 increase in capacity over the 6mm Remington.

Divided by 4 equals 0.0454545454545455 percent to apply to find the increased velocity of the larger round over the smaller round.

0.0454545454545455 times 3581 equals, 162.7727272727273 fps

162.7727272727273 fps plus the smaller 6mm Rem's velocity of 3581 fps eguals....., rounded down, is
3742.7 fps as a calculated velocity for the 240 magnum.......at, let's not forget, 59,600 psi of pressure.

I must be missing a load data information page....or the above is not the formulation to use?

My thanks to the OP as well.
God Bless
Steve

Read this again

One example I've used frequently is the .300 RUM and .308 Winchester: The .300 RUM has just about twice the powder capacity as the .308, but does NOT produce twice as much velocity--a 100% increase. Instead the velocity increase, with the same bullet at the same pressure, is about about 25%, which is 1/4 of 100%. This rule does not apply to the SAME powder, but the powders producing the highest velocities in each cartridge.