Barrel Gaining Speed after Break in?

[idahohunter8]

Is it common for a barrel to gain velocity after proper breakin?

Last summer, I put a new Shilen Barrel on my .270. I finished it at 24.75". I put approx 100 rounds down it (Barnes, Accubonds, Partitions) to break it in and develop a load for 2016 fall hunting season.

I ended up settling on 55.0 grains of IMR 4831 W/ 129 Barnes LRX. The book showed this to be around 3150, but my chronograph was showing an average of 3075 - so I ran with that. The velocity was questionable as I had a tad longer barrel than the book, but it wasn't enough for me to care too much.

FAST FORWARD - This spring I have brought out the 270 for two separate range visits - one about a month ago in 50 degree weather and one today in 75 degree weather.
NOTHING HAS CHANGED on the rifle or the loads, in fact I was shooting the same loads I developed last fall that have been sitting in the safe all winter.

In my first range visit a month ago, the velocity average for the 15 rounds I shot was right at 3140 FPS. POI stayed exactly the same and group size was 3 shots in .5-.6 range which is what this load has always done. Overall an average velocity increase of approx 75 FPS over the last time I shot the rifle in the fall.

Today, I get out and I shoot 24 rounds - 6 4 shot groups. POI is same. Was shooting .5-.6 4 shot groups (Super Stoked about that) but Velocity average was 3217 FPS. Highest Velocity was 3240, lowest was 3180.

Will a barrel normally speed up like this? By now I consider the barrel broke in as I can shoot quite a few barnes loads with minimal fowling. Again, these are all the same loads from a batch of 60 I whipped up last fall. I know it was hotter today, but the speed increase has came every range session.

I am mainly curious because I shot today to get a final chrono speed to submit for my Leupold CDS Dial. I was going out to verify 3150 ish, and now I am averaging 3200. I wont be shooting far enough for it to really matter (5-600 max) but I still want to be as accurate as possible.

Thoughts? Do barrels speed up?

 

[DrMike]

Yes, barrels show increased velocity on occasion. Sometimes, the velocity gain is significant. One of my .280 Remingtons was more than 250 fps slower than projections with maximum loads. After ~250 rounds, velocity dramatically increased to where it should have been all along. I worked that barrel repeatedly, refusing to give up. It was always a shooter, giving excellent accuracy. Now, it yields excellent velocity as well.

 

[Anonymous]

Some barrels do increase velocity with break in...but it's generally incremental of time and rounds down range like Dr. Mike describes.

If I read the narrative right...you're under 60 rounds total from first to last reading. That seems suspiciously low to see huge leap in speed. Perhaps something in the crony setup? Sometimes they can be temperamental with regard to setup and ambient conditions.

Also as a general rule- you wouldn't see a 100fps increase in velocity without a corresponding POI shift. My vote is on the chrony data.

 

[idahohunter8]

Some barrels do increase velocity with break in...but it's generally incremental of time and rounds down range like Dr. Mike describes.

If I read the narrative right...you're under 60 rounds total from first to last reading. That seems suspiciously low to see huge leap in speed. Perhaps something in the crony setup? Sometimes they can be temperamental with regard to setup and ambient conditions.

Also as a general rule- you wouldn't see a 100fps increase in velocity without a corresponding POI shift. My vote is on the chrony data.

No this rifle had approx 100-120 nosler rounds through it first. At that point I switched to barnes searching for the load. In total it had approx 150-160 rounds down it when I shot today.

I thought it was the chronograph too, so I tested the two other rifles I had. The first was a 22...chronograph showed exact velocity within a few fps of what the box advertised.

The second rifle I had was my 375 H&H shooting a Load that in the past has been around 2750 FPS and the book says thats about what it should be. I shot 15 rounds out of that and all of them were right there within a few fps.

 

[MAinAR]

Yes new barrels will speed up but in this case powder choice may be attributing as well.

IMR4831 can show swings in speeds depending on load, cartridge bullet weight, primer etc. lots of variables but on average across different calibers I see IMR4831 change speed along the lines of 1.5 fps per degree of temperature change.

Plus chrony can act up in differing conditions as well.

 

[SJB358]

It does seem like it has gained alot more. I do believe barrels speed up as they smooth out and break in. I wouldn't actually believe they would gain with the same powder charge though since if they smooth out you get less pressure and less speed.

Don't know for sure, but that is how I think of it. I honestly don't like to do serious load work with less than 50 rounds through a barrel just because of this. I have chased my tail a few times with this sorta stuff.