What change in velocity can be expected from a brand new barrel and a "broken in" barrel, if any?

More drag in a new barrel? Higher pressure? Less drag in a broken in barrel?

Ok, my Google foo is saying 75 to 150 fps increade in a custom barrel. That can explain my constant velocity with a lesser charge in my. 257 WM and change (increase) in 6.5 CM factory ammo in my other thread. It's great talking to myself! <grin>

George Gardner (Georgia Arms Precision) has said this.

You're not talking to yourself, that's interesting...and if you had bet me...I would have lost money on that, never dreaming it was that much.

The only new barrel I've ever shot enough factory ammo from the same lot to notice was a factory Ruger. It seemed to increase around 35-50fps after about 100 to 150 rounds. The temp also rose a little during that time period so unsure about making an absolute statement.

Both of the above barrels (Bartlein and factory Browning) were brand new out of the box when I initially checked velocity.

This is making sense now.

Depends on what you mean by "broken in." The guy who ran the pressure department at a major rifle manufacturing company told me that once the throat starts to erode a little, pressure actually goes up, due to more friction, and an accompanying tendency to copper-foul. This is very similar to what was reported in research done by the Australian military, which I've reported on here and there. He said that contrary to popular belief, a throat has to REALLY become worn before pressures start to drop.

Georgia Arms Precision? Gnat’s Ass Precision

The topic is of interest to me. What’s the sense set of how many rounds is required to break in? I ask because I’ve noticed 3 new Tikkas (270, 270wsm and 30-06) all are shooting slower with both factory and hand loads. Bases loading for other rifles, I’d expect to see 50fps+ velocity with my loads. That I’m seeing this in all 3 suggests it’s not an anomaly. For the record, they shoot accurately.

I often see about a 50-100 fps gain after putting about 100-200 rounds down a new match-grade barrel. I haven’t noticed this as prominently with factory barrels.

Tikkas are notoriously slower than most other rifles. That’s my only knock against them. Think its due to the longer than average throats.

Yah same as Wesley2 mentioned, all my Tikkas have had very long throats, sort of like most Remingtons, and all shoot slower than they should. Presuming this is the factory legal department's doing.

At work, Barnes Bullets ballistic lab, we break in a new barrel so both velocity and pressures will stabilize. These are custom barrel, not factory, We typically see a velocity increase but as the throat wears a decrease in velocity if the same COAL is maintained.

Alan

Good handloads are a simple solution to Tikka's "slow" barrels. I've been loading and shooting Tikkas for over 20 years now. They've all been stupid accurate and not the least bit finicky.

If throats are to SAAMI specs, why so much variance?

With a custom barrel I've seen very little change. On a lapped barrel, what are you breaking in to make an increase in velocity? I always prep the throat on a fresh chambered barrel to allow me to start shooting right now, not after a so called break in.

I'd never heard of this increase in velocity during "break-in," which I quit doing formally years ago, finding it didn't work any better than just shooting new barrels, and cleaning them after every range session.

Just checked my range records with and three rifles fitted with top-grade custom barrels. Analyzed the results from the range sessions when new or nearly-new, and after 100-150 rounds, using the same loads. Couldn't find any significant difference in velocity.

Must be your Banana Belt air....

Dunno....

Do know that the most recent rifle was a 6.5 PRC, a custom rifle that Charlie Sisk rebarreled a couple years ago with a 1-8 twist Lilja that I purchased directly from Lilja. It was built to do an article for the Hodgdon Annual Manual.

I also purchased dies and several boxes of 147 ELD-M Hornady Match factory ammo from GA Precision. Used the factory ammo during the rifle's very first range session, to sight-in and get a general feel for the rifle. It averaged 2769 fps.

About 2-3 weeks later, after I'd tested more than 100 handloads, I shot some more of the same Hornady load, which chronographed 2752 fps.

The other two rifles were a 6XC with another Lilja, and a 7x57 with a Shilen. In the 6XC the same handload worked up early on (which ended up being my main load for the rifle) chronographed 23 fps faster after 156 rounds down the barrel.

I found a good load with the 7x57 during the very first range session. Chronographed it three days short of a year later, again after more than 150 rounds had gone down the bore, and the average velocity was ONE fps slower.

Edited to add that both handloads used the same manufacturing lots of components--bullets, cases, primers and powder--and the powders with H4350 and IMR4451. Both are very temperature resistant, and the temperature didn't vary more than 20 degrees Fahrenheit during the chronographing. The temperature varied 10 degrees between the two sessions with the Hornady factory ammo. All three were also chronographed on the same chronograph during the two sessions.

Am NOT saying an increase in velocity can't happen. But am saying it didn't happen according to my records with the first three rifles I checked, and by that time I growing weary of paging through my records to find examples of the same ammo tested in he same rifle, both when the barrel was new, and later--but not so much later the barrel might be worn.

Jordan Smith has witnessed the phenomenon in match grade barrels and not in ordinary factory barrels, while burchlambert1 has seen very little effect in custom barrels, and Mule Deer has seen no effect.

I join the crew that has never ever seen any effect in any kind of barrel.

For me, it is hard to believe that some microscopic changes in the barrel dimensions can have such an effect in the powder pressure burning curve that could translate into 100 or 150 fps difference.

Which is quite a lot. To put it in perspective, Winchester factory 130gr loads for the 270WSM are fps faster than the WSM.

I am now in the process of shooting with a new barrel which following's Mule Deer breaking in process of a thorough cleaning every range session and not every one, or, three and then five, shots, has already gone through 53 shots and two cleanings.

My favourite load so far, has lost .according to my Lab Radar, 10 fps from the first session to the third. I am right thinking it will now have to regain 110-160 instead of the original 100-150 that seems to be the norm?

Ain,t that funny?

Alvaro

I have a 6.5 Creedmoor with a 24” Benchmark barrel that in a little over 3 years has had almost 1600 rounds through it. I recently shot some of the same lot Hornady factory ammo through it as I used when it was new and there was less than 30 fps difference. That is just about what the ES of this ammo is.

Alvaro,

To be clear, I'm not making a definitive statement about the issue, one way or the other. For me to have a high enough level of confidence to make a statement on the matter, I'd have to witness the phenomenon in a statistically significant sample size of barrels where the pertinent variables were controlled, such as barrels that were as identical as possible, loads that were as stable as possible, etc. So I'm just reporting my observations, not stating that they are more or less valid than anybody else's observations.

Jordan,

As noted earlier, I'm interested in this partly because I'd never heard of it before--and partly because I dunno why it wouldn't happen with factory barrels, some of which are of VERY high quality these days.

Am going to look at more of my loading notes and see what's there, with both good factory and custom barrels.

John

I appreciate your effort John B.

Because I experienced this in 2 different rifles, both new and both shot at least 150 rounds, I thought my chronograph got out of whack as stated in a different thread.

I started to Google search the velocity increase and came across many instances where a velocity increase was "claimed". I am anxious to see what your written records show.

Here is an example of my Google search. There are others but it is easy to cherry pick.

http://bulletin.accurateshooter.com/2018/06/tech-tip-velocity-increase-in-new-gun-barrels/

Sakoluvr,

Thanks for the info, especially the link.

Don't understand why the "smoothing" of the throat would result in higher velocity, because in general less resistance to the bullet's passage (especiallyl in the throat area) results in LESS pressure, and hence velocity. They are pretty much tied together, due to basic physics.

But have done considerable research in various writings on benchrest accuracy. One guess is that the increase might occur due to bullet seating-depth changes as the barrel's broken in--which affects pressure/velocity considerably. This isn't mentioned in Speedy's article, but it's apparently pretty common. All my tests used exactly the same load, including seating depth.

The other factor that might apply is how much many powders vary in velocity with temperature. This isn't as much a factor in benchrest shooting as it used to be, due to far more temp-resistant powders.

I’ll offer this - how a bullet is imprinted by the rifling actually occurs in the throat area and different bullets imprint differently based on hardness and other factors, so a new barrel with a rough throat ?

Well, yeah--but why would a "rough" throat result in lower pressure/velocoty? Why would a smoother throat result in more velocity, which according to the laws of internal ballistics means higher pressure?

And again, am baffled about why this would only apply to "custom" barrels and not factory barrels.

I’m not saying this is it BUT in a freshly cut throat the edges of the lands would be nice and sharp and imprint the bullet easier (cut vs. press) than a broken in throat where the lands were more rounded. Somewhat like a serrated knife blade cuts a softer surface (like tomato) vs. a non started blade which pushes on the surface but doesn’t cut and displace as well as the surated.

So the pressure to imprint could be lower with a sharper / ruff land than with a rounded off one...

Again - just postulating

Me neither, and I really value your systematic approach.

I just wanted to point out how different people would share so different opinions or observations on the same subject. I say opinions or observations, not scientifically driven conclusions after examining a statistically relevant sample size and I apologize if my post read different.

Alvaro

Please keep us updated, John.

Just a quick thought, similar to what Spotshooter mentioned, if the freshly cut throat has edges/tooling marks that minimize surface contact with the bullet, I would expect to see lower pressure caused by bullet engraving. As the marks in the throat wear and become more smooth, surface contact would increase, thereby increasing pressure and velocity. As the throat wears toward the end of the barrel’s life, the bullet is jumping so far to the lands that pressure from bullet engraving drops, and velocity starts to decline with it.

I don't see where it is stated that it only happens in custom barrels. The link I posted happens to be with custom barrels. My Google searches indicate it happens to both factory and customs.

I am convinced it happened to both my Bartlein and my factory Hells Canyon.

Edit: I see where Jordan said it was more pervasive with customs. Maybe folks with customs tend to be more apt to check velocities, hand load and keep up with such things.

I said I haven’t noticed the effect as much with factory barrels, but that could partly be because I haven’t tracked them with good record-keeping as closely as I have my custom barrels. That’s not to say that I haven’t noticed it at all in factory barrels, but not as often nor as much of a velocity increase as I have seen in my customs.

But again, these aren’t hard facts, just my casual observations.

I was thinking my barrels got a little faster. After looking at some examples I could find of shooting the same loads when it was new vs. 100s of shots later, it seems if anything it is a little slower. I can't be sure it's apples to apples data with the same chrono, same temp, same powder scale, etc. Very low confidence data. I have a new barrel I'll be working with before long and I'll try to keep good track. Might even load up ~15 rounds as a baseline test where I shoot some when brand new, then repeat shooting a few at some interval, say every hundred rounds or two and measure with the magnetospeed.

That would be a good idea. If you end up doing that, it would make sense to load the bullets a little long, and seat to the given depth just before you're going to fire them, just to avoid any "cold welding" and associated difference in pressure.

Good point. I will plan to do that. Easy enough to do and obtain a few data points. I'm still waiting on the reamer before I send the barrel off for a rebore. Possibly be shooting in the next month and half.

here is my question : what brand chronograph are you using ? new batteries ? warm weather or cold weather ?

I use both the Magnetospeed and Lab Radar. For the purposes of conducting a specific comparison I'll use Magnetospeed with everything at room temperature.

Well, I decided to look at my records for another rifle, this time a factory barrel. It's a Tikka T3 Superlite with a 1-twist stainless barrel, one of aspecial run from Whittaker Guns in Kentucky, acquired in 2016.

I tried a bunch of different handloads, and didn't settle on one until 87 rounds had gone down the barrel: It consisted of the 140-grain Nosler AccuBond and 45.0 grains of Reloder 23, in Lapua cases with CCI 200 primers.

Here's how it chronographed on various dates, all with a ProChrono that I had checked against my Oehler 35P (and eventually against a LabRadar). It matched right up with both. The velocities are all averages with the chronograph 15 feet from the muzzle:

4/17/16, after 87 rounds through the barrel: 2581 fps. (The conditions were 70 degrees and sunny.)
8/20/16, after 103 rounds: 2660 fps (70 and sunny.)
12/8/16, after 137 rounds: 2694 fps. (This was during one of my periodic cold-temperature tests, at 0 Fahrenheit, on a sunny day).

On 2/3/17 I took the magazine apart and lengthened it slightly, because the 140 AB couldn't be seated close to the lands with the original magazine configuration. The load wasn't shooting as well as I thought it should, so tried some loads with the bullets seated out to the lands, single-loading them into the chamber. They did shoot more accurately--which is when I decided to lengthen the magazine.

My last chronographing of the load took place on 10/2/19, with the bullets seated further out, and 150 rounds down he barrel:
On a 40-degree, sunny day, they averaged 2711 fps. Since the load shot a little faster at 0 than at 70 (not uncommon with "temperature resistant" powders), this could have been due to the 40-degree temperature. But seating bullets closer to the lands also tends to raise pressures, and hence velocity.

This seemed to be an instance of a barrel getting "faster" after being broken-in, but during my very first range session with the rifle, on 3/7/16, I shot some Remington 140-grain Core-Lokt factory loads, to sight-in the scope. They averaged 2533 fps on a sunny 50-degree day, so I decided to use some more of the same box to begin testing a Magnetospeed, mounted on a Caldwell rest in front of the muzzle. The temperature was 75 degrees, and they averaged 2545 fps, Due to the warmer temperature of this test, some increase could be expected--but the factory ammo obviously didn't gain as much velocity after barrel break-in. (This test was after 156 rounds down the barrel.)

During the same 75-degree session I also chronographed some new SIG Elite Hunter factory ammo, loaded with a 130-grain plastic-tipped bullet. Over the Magnetospeed they averaged 2758 fps. Later I also tested them over the ProChrono on a 40-degree day, and they averaged 2711 fps, again about what I'd expect, due to the cooler temperature and the velocity being 15 feet from the muzzle, rather than the muzzle velocity recorded by the Magnetospeed.

Dunno why the handload gained so much velocity during barrel break-in, yet the Remington factory load didn't--but it might mean such velocity gains can be bullet-specific.

Could be John. I don't think the barrel i.e. factory or custom has a real bearing on this. It would take a lot of data points to narrow down bullets, but I am now convinced that there is a very real possibility of a velocity increase after a barrel has been shot for a while.

I looked at my meager records and have found my son's Rem 700 CDL SF in .257 WM has also exhibited (indirectly) a velocity increase via a lesser charge giving the same velocity. That make 3 rifles for me that showed the increase. I rarely buy brand new rifles, so I have limited data.

The bullets that were used are the following: Nos Accubond, Hornady ELD X and Barnes TTSX.


Thank you for contributing to this.





I can only wonder if the velocity increase would have been even higher if you checked the velocity starting with the first few shots.

Magnetospeed

Tikkas are notoriously slower than most other rifles. That’s my only knock against them. Think its due to the longer than average throats.[/quote]

In some cases such as the 257 Weatherby, Military cartridges and I suspect some others too, the CIP specification calls for a longer throat, leed, or free bore than SAAMI specs. In many cases the two or the same, where they differ significantly the reamer makers will usually list both as an option.

In some of the loadings with the longer throat the European loadings can be slightly hotter than US although for the most part they are the same. Some Euro factory loads were too hot to shoot in my short throat-ed 6.5x55.

This makes sense..

Which is also why Butch Lambert isn't seeing the velocity increase. He smooths the throats in the rifles he puts together with fine steel wood BEFORE he shoots them the first time. I also know another custom gunsmith who uses a similar method, and is well-known for the accuracy of his rifles.

Will keep looking at my range notes. Something tells me there just might be an article in this!

Thanks,
John

I was hoping you would say that.

I don't think it is widely known or talked about. How many folks take a rifle out of the box and check velocity immediately? Then, after load development go back after 100 rounds being fired, check velocity again? Another 75-100 fps might not be noted on the same original drop chart if shooting out to 4 -5 hundred yards.

If velocity is checked for a different bullet, well data is lost. Same with a different lot of powder.

Checking for velocity increase has to be purpose driven from the first shot, after X amount of shots, with the same bullet, same lot of powder under the same weather conditions and same brass, loading procedure etc.

Hell, only some loony would do that. LOL

Puzzling, to say the least.

That sometimes-yes / sometimes-no behaviour does not stand well against the law of physics and look more like a thing of medieval alchemy. I would tend to take your chronograph readings with the handload with a grain of salt, and I really hope you can shed some more light on the subjetc as I am very curious about it at this point.

Thank you!

Alvaro

Alvaro,

I've done some more investigating in my range-notes. It gets even more interesting--and confusing!

But hope to make some sense of it all with more research.

Good hunting,
John

I linked an article a while back, DoD research, I think.(might have it saved) where at a certain temperature (the higher of two flame fronts) copper oxide, and lead oxide deposition on barrel (rifleling/lands) was promoted.

My thought was that this deposition works like leaded gasoline providing a bit of lubrication.. it would likely fill in, preferentially, small pits and divots associated with throat erosion.
Perhaps corners as well..

I will look around for the article.

2002, NATO/OTAN " Combustion of Solid Propellants", France, presented at RTO/VKI special course on "Internal Aerodynamics in Solid Rocket Propulsion" held in Rhode-Saint-Genise, Belgium 27-32 May 2002.

It's a bit technical, rocket science after all, but if you spend some time starring at and thinking about the phase diagrams it starts to make sense...
But you might pick it up quicker than I did...

Is it possible that a well broken in barrel looses velocity not because of wear induced increased tolerances but the barrel is too smooth? I have experimented with barrels that were either fire lapped or had lots of JB used on them and to recreate the original longitudinal scratches taking a couple of passes with a stainless steel bore brush. This only on barrels that were close to heading to the tomato patch anyway. So far I can't document any changes.

In my experience (and that of some barrel makers) a "too smooth" barrel often results in more velocity (and copper fouling) because there's more contact between the bullet and bore, that in a bore lapped with not-too-fine grit--resulting in higher pressure and velocity/

Can immediately think of at least two examples.

Thanks MD. Seems like the counterintuitive is the rule and the exception is the norm when it comes to this ballistic gak stuff. I am still learning how much I don't know about these things, it keeps it interesting though.

In medium size cases ( 260, creedmoor, 6.t-284...) i have found that i get 30-40 fps INCREASE in velocity once the velocity stabilizes. This usually takes 70 rounds or so.

This correlates with what a lot of match shooters see- guys that blow through a couple barrels a year. IF you clean a lot, this can be different
Once i get 75 rounds down a barrel i only clean every 100-200 rounds.

I shot another 20 shots this past weekend and the average speed of the last 5 is now 8 fps higher than the first batch I shot, and 18 higher than the previous range session.

All seem well within SD and chronograph tolerances.

For reference, barrel is a custom 1:8" 22-250 and load is 36.5grs of H414 with a magnum primer (RWS 5333) pushing 77gr TMKs and 75gr ELDMs.

To avoid fuzzy math and to get solid data:

1) Chronograph the first 5 or 10 shots on day 1 of the brand new rifle/barrel.

2) Shoot at least 100 rounds of the same load or play around finding a load.

3) Go back to the exact same load that was used for the first 5 or 10 shots and chronograph them from a squeaky clean barrel.

4) compare velocity from day 1 with the brand new rifle/barrel and the same load after at least 100 rounds were fired.

The problem that I see is not chronographing the very first shots on day 1 from a virgin barrel. + or - 20 fps is insignificant.

While not a new barrel (#6 Benchmark 7.7 twist, 26.0625" long) it is a rechambered one. 6 Dasher to 243 Win, barrel has about 1500 rounds on it before rechamber and 0.0625" taken of the crown for a clean up.

To fire form the new brass (Lapua) I jam it 0.010" with a 105gn Hornaday BTHP. This brass is out of the box no prep at all.

Using QL the velocity should be 3074 ft/s, so after operating the soft ware I arrived at 43.06gns of RL 22. This gives me an average of what was predicted, 3074 ft/s. ES is high (22 ft/s) due to the brass not being prepped at all.

This fire form load goes right ~0.750", 5 shot at 109 yards for the last 45 rounds.

There has been no detectable change in velocity as the round count goes up and averaged from the start. However, there is 55 rounds to go.

Some thoughts and questions: Is there enough gas leakage to 'wash' the barrel ahead of the bullet ? Is there enough change in the throat profile to alter the resistance of the passing bullet? Does the thin layer of copper/carbon deposited on the bore make more or less resistance as the bullet passes? Or a combination of all?

I have only had one barrel ( an 8 twist, #3 Benchmark in 280ai) exhibit increasing velocities as round count went up, so just kept reducing charge weight to stay on a barrel time.

To add another data point, I just received one of my match rifles back from the 'smith with a new JC Custom 7" twist 4G MTU contour barrel chambered in 6mm Creedmoor with 0.100" throat. Loaded up twenty 105AM with 42gr of StaBALL. Fired fifteen of them between curing the DBC with 10 shots and fouling the bore, post-clean. Average velocity was 3010 fps with an SD of 15. Saved the other five to chrono after shooting 100+ rounds down the barrel. Between testing the 115 DTAC, 112 MB, and 108 ELD, round count is 45 right now, with another 20 loaded for testing. I'll likely have 100 rounds down the barrel in the next week or so, and then I have a local PRS-style match on the 24th, with another ~100 rounds. I'll try and chrono those original five 105 AM loads either before the match or after. I'll update once I've done that.

Jordan, you fired 15 rounds BEFORE curing the DBC? You said between curing.

Assumption being that DBC has no affect.

Looking forward to your result

Applied DBC before firing the rifle. Fired 10 rounds to cure (naked 105 AM). Average velocity 3012 fps. Cleaned the bore. Fired 5 more rounds (moly coated 105 AM). Average velocity 3007 fps. I have another 5 rounds loaded with moly coated 105 AM that I’ll chrono after 100-200 rounds down the bore.

All velocity measurements taken with LR.

i wonder if harry pope had these same problems?

The commonly used Chromium Molybdenum (chrome moly) barrels are so individual I don't know that any facts can be determined. I certainly would not expect it.
I have a bunch of barrels from brand new to severe alligator cracking in the throat and that barrel is still one of the more accurate barrels I have as is the newest one with less than 200 rounds down the tube.

Many people have noted an improvement in accuracy after a barrel has a few hundred rounds through it but because I am perpetually testing loads, bullets and powders all of different batches over time, it makes it more difficult to be definitive.

You would need to make some rounds and document a barrel accurately for round count and then on similar days in terms of temperature and humidity, take sample groups with the original ammo etc. All variables apply from shooters consistency to target range to test ammo management and housing between usage. Alternatively you could put the same handloading items aside and reload the same combinations fresh before use.

What ever you do, it wont mater to the target, whatever it is. Most people will just develop a load and stay with it until the barrel noticeable goes off in accuracy then visit the 'smith.

Any updates Jordan?

The match got cancelled so I went to see if any bears were out and about instead. I hope to put another hundred rounds through that rifle in the next week or so.

As another data point, a friend has the exact same barrel that I just had installed on my match rifle. After approximately 300 rounds we checked velocity on his initial load, and it had increased by about 65 fps.

Very interesting. I don't think my chrono lied anymore.

Finally got those initial loads chrono’d on the 6 Creed barrel. After 115 rounds down the barrel the load had actually lost 41 fps.

Just checked some more records, and velocities after a couple hundred rounds down the bore increased by 40-70 fps on 3 other custom barrels I currently own.

Thanks Jordan.

Yep, thanks, Jordan.

Am still wondering if this supposed phenomenon is worth more investigation--especially enough for an article. So far it doesn't look like it....

Haven't read the entire thread, because I am too lazy, but some semi-prominent shooters such as Jake Vibbert, John Pynch, and Scott Satterlee have mentioned barrels "speeding up" during break in. IIRC, they seem to agree that the barrels settle at 200 rounds or less. That's what I recall them saying but I could be wrong.

Maybe confirmation bias, but in my own personal experience, most of my factory rifles "settled" after 80 - 100 rounds with my handloads. That includes several Tikkas. My current 700 seemed to be similar, but with factory ammo from the same lot. That said, I have never taken detailed notes, but I have seen higher velocities as round count increases for several rifles.

In the end, it probably doesn't matter for most hunters. That is my guess.