Home Forums Hunting & Shooting Ask The Gunwriters New barrel vs a broken in barrel and changes in velocity

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.