Do barrels pick up speed? It’s a concern to many in the precision shooting sports though it isn’t talked about as widely as I’d have thought. This topic should be of particular interest to hand loaders since it could affect their load development and result in wasted powder, bullets, primers, etc. The idea here is that a brand new barrel, if chronographed with it’s first rounds out of the tube, will see a speed increase as the barrel “breaks in.” I’ve got some data to support this, both anecdotal and hard numbers. However, I did make an error when I set out to really try and confirm this in the manner I planned. Do barrels pick up speed? Read on to find out!
Do Barrels Pick Up Speed?
I’m going to say yes from the start of this article. If you’ve ever wondered, “Do barrels pick up speed?,” the answer is yes. When they pick up some extra muzzle velocity and how much are where it get’s interesting because it’s different for every barrel. In my early days of precision rifle shooting I didn’t have a clue what I was doing. Any difference in muzzle velocity on the first two barrels on my 308 Winchester would have easily gone unnoticed as they were absorbed among other errors I was making. Fast forward a few years to when I was putting a 6.5 Creedmoor together in an AR10 barrel and I was a little wiser. I was chronographing ammunition from Copper Creek Cartridge Company.
I detailed some of this testing in a review of the ammunition that I had purchased with a certificate I had picked up at the Sniper’s Hide Cup. The load I had purchased was advertised as having a muzzle velocity of around 2910fps. When I fired the first rounds through the barrel I was disappointed to see only 2750fps as the result displayed on the chronograph. Shortly thereafter while shooting at a local monthly field match I noted during the match that my rounds were hitting way high at around 715 yards. When I chronographed the ammunition again it was around 2875fps. More than 125fps faster than the initial results and more than enough to throw things off at distance. I ran out of ammunition so I couldn’t continue firing the same load to see exactly when the velocity settled, but it was still notable.
The Failed Plan
I have since rebarreled that AR10 with a match grade 24″ barrel from Criterion Barrels Inc. I had planned to conduct a test of the barrel and see what the initial speed was with some factory ammo and what it increased to as time went on. Do barrels pick up speed? Absolutely. Did I have my act together to conduct a well planned test to prove it? Not so much! I completely spaced chronographing the initial rounds through the barrel. As a result, I have data for rounds 40-50 and then I have data for rounds 113-125. While the test is flawed in that I failed to accurately document the initial speed of the Hornady 120 AMAX through the new barrel, I feel confident in assuming it would have been similar to the Copper Creek. Likely in the range of about 2750fps.
So what does this chronograph data show us? It tells me that the barrel likely already sped up in the first 40 rounds. Different barrels may take more or less time to have their muzzle velocities settle in. In my previous story with the Copper Creek rounds I suspect it happened somewhere between 75-150 rounds through the barrel. In this case it appears to have happened much earlier. How do I know it’s already happened? Well, I don’t know for sure but I can make an educated guess. If you look at the boxes ammunition comes in the manufacturer will typically print your expected muzzle velocity from the ammunition. In this case Hornady says to expect 2910fps from their 120 AMAX load. This barrel appears to be shooting a bit faster than that, but with a fairly stable muzzle velocity in the area of 2950fps between rounds 41 and 125. If there were still more room for it to speed up, I’d expect less consistency in muzzle velocity over those 84 rounds.
I’ve said it before, have some goals or some kind of plan when you head to the range. If you wing it this is what happens. You leave equipment at home or forget part of why you were heading out in the first place. So I can’t really show you guys the before and after in this article on barrels picking up speed. I stand by my statement. If the question is, “Do barrels pick up speed?” The answer is yes. I’ll hit you with one last photograph of some chronograph results here. This is what I got running 5 rounds of my pet load for the old barrel that I removed. It’s a 123gr Lapua Scenar and the muzzle velocity on the new 24″ barrel (Old barrel was 22″) is 3005fps with an SD of 7fps! That’s awesome! It also tells me that the barrel has likely settled in because my muzzle velocity on the old barrel with the same load was 2925fps. The old barrel was 2″ shorter and this one seems to be running a tick faster which all tells me it’s already broken in!
I’ll try to duplicate this experiment the next time I put a new barrel on a rifle with better before and after data. I realize my evidence of the barrel picking up speed is rather anecdotal but it’s all truthful information. I’m not embellishing and I don’t have anything to gain by showing one thing is true over another. My hope is that this sheds some light on the concept of “breaking in” a barrel. The muzzle velocity settling in is likely why the old porch stories from Grandpa include “breaking in” a barrel. It’s just giving the barrel time to settle in a bit. If you were to do load development right away, you would likely have to adjust the load or start over completely after the velocity change. I believe this is also why many rifle builders want the new owners to put 100-200 rounds through it before calling up with accuracy concerns or any other gripe. It’s like a new car, you need to drive it around a bit and let all the parts settle in before you start whomping it on a highway onramp.
It also shows you that you don’t have to necessarily clean after every round and fire another unless you want to. Just get out there and shoot the new rifle and by the time you hit 100-150 rounds you can expect that it has settled in and the performance you are observing is likely what you’ll have to look forward to with that rifle! If you have anything to add to the discussion, please do so below in the comments! Next up is some accuracy testing with the new Criterion barrel!