Life Lesson: Every Barrel is Unique. Same Load Registers 4 Different Velocities in 4 Different Barrels
Put the same load in a variety of barrels (with the same length and chamberings) and you’ll see a wide variance in muzzle velocity. In fact, it’s not unusual to see up to 100 fps difference from one barrel to the next. We demonstrated this with a comparison test of Lapua factory ammo.
Chron Testing Lapua Factory Ammo
At our Southern California test range, we chronographed Lapua 105gr 6mmBR factory ammo in three different 8-twist barrels of similar length. The results were fascinating. Lapua specs this ammo at 2790 fps, based on Lapua’s testing with its own 26″ test barrel. We observed a speed variance of 67 fps based on tests with three aftermarket barrels.
Brand ‘S’ and Brand ‘PN’ were pre-fit barrels shot on Savage actions. Brand ‘K’ was fitted to a custom action. All test barrels were throated for the 100-108 grain bullets, though there may have been some slight variances in barrel freebore. With a COAL of 2.330″, the rounds were “jumping” to the rifling in all barrels. Among the four barrels, Brand ‘PN’ was the fastest at 2824 fps average — 67 fps faster than the slowest barrel. Roughly 10 fps can be attributed to the slightly longer length (27″ vs. 26″), but otherwise this particular barrel was simply faster than the rest. (Click Here for results of 6mmBR Barrel Length Velocity Test).
Results Are Barrel-Specific, Not Brand-Specific
These tests demonstrate that the exact same load can perform very differently in different barrels. We aren’t publishing the barrel-makers’ names, because it would be wrong to assume that ‘Brand X’ is always going to be faster than ‘Brand Y’ based on test results from a single barrel. In fact, velocities can vary up to 100 fps with two identical-spec barrels from the SAME manufacturer. That’s right, you can have two 8-twist, 26″ barrels, with the same land-groove configuration and contour, from the same manufacturer, and one can be much faster than another.
Don’t Demand More Than Your Barrel Can Deliver
We often hear guys lament, “I don’t get it… how can you guys get 2900 fps with your 6BRs and I can only get 2840?” The answer may simply be that the barrel is slower than average. If you have a slow barrel, you can try using more powder, but there is a good chance it may never run as fast as an inherently fast barrel. You shouldn’t knock yourself out (and over-stress your brass) trying to duplicate the velocities someone else may be getting. You need to work within the limits of your barrel.
Factory Ammo Provides a Benchmark
If you have a .223 Rem, 6BR, .243 Win, 6.5×47 Lapua, 6.5×55, .308 Win, 30-06, or 300 WM Rifle, we recommend you buy a box of Lapua factory-loaded ammo. This stuff will shoot great (typically around half-MOA), and it can give you a baseline to determine how your barrel stacks up speedwise. When you complete a new 6BR rifle, it’s wise to get a box of the factory ammo and chronograph it. That will immediately give you a good idea whether you have a slow, average, or fast barrel. Then you can set your velocity goals accordingly. For example, if the factory 6BR ammo runs about 2780-2790 fps in your gun, it has an average barrel. If it runs 2820+ in a 26″ barrel (or 2835 fps in a 28″), you’ve got a fast tube.
Similar Posts:
- Tech Tip: Same Load Varies in Velocity with Different Barrels
- 6BR Lapua Ammo Yields Different Velocities in Four Barrel Brands
- Speed Variance in Barrels — You May Be Surprised
- Same Ammo in Four Barrels — Surprising Velocity Test Results
- Velocity Test with Four Different Barrels — Surprising Results
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Tags: 6mmbr, Barrel, Chronograph, Pac-Nor, Savage
This is a phenom that should be expected.
#4 in my opinion should have been excluded due to the extra inch.
Anyway the general info is OK. Too many potential variables make specifics moot.
The main variables are barrel length, bore diameter & twist rate. My observation is that hammer forged barrels tend to shoot faster because the bore is slightly tapered.
I suppose this offers another advantage to “switch barrel” platforms. Get a pile of the same barrels and test them to find the good one. NASGUN
You need to narrow down your variables a considerable amount to make this test have a more quantifiable result. Like using the same reamer, same batch of powder, brass, and bullets, same bump on the brass as per the chamber, neck tension, action, and so on and so forth.
The results are not surprisingly.
What I’d like to see is this test done on 3-4 of ostensibly the same barrel (same manufacturer, bore dimensions, twist rate, length, and contour, etc.), maybe if possible from the same run/lot of steel, chambered with the same reamer, on the same action.
An AR would seem to be an ideal rifle for a test like this. Order a few identical barrels (same part#, etc.), load up some precision ammo, and get testing. Perhaps buy or fabricate “false” gas blocks without ports to simplify barrel swaps.
quote: Mike says:
September 21, 2014 at 1:22 pm
The results are not surprisingly.
What I’d like to see is this test done on 3-4 of ostensibly the same barrel (same manufacturer, bore dimensions, twist rate, length, and contour, etc.), maybe if possible from the same run/lot of steel, chambered with the same reamer, on the same action.
Mike statement is on the money. There are to many variables to say this or that barrel makers barrel is faster/slower etc…if your going to compare barrels and velocities weather from the same maker or not the barrels should be measured to the 4th decimal place, same bore and groove size, number of grooves, twist etc.. they should be made from the same lot of steel, the same chamber reamer is to be used, and the same loads/ammo run thru them and shot in the same conditions. Changing any of these things can change how the barrels shoot etc…
Later, Frank
Bartlein Barrels
If you can only try more powder to make a barrel pick up speed this is all really pointless. The barrel is what it is when it’s finished IMO. The chambering etc will certainly change things as well. Way to many variables and not all the much deviation to worry about it.