Tech Tip: Same Load Varies in Velocity with 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:
- Life Lesson: Every Barrel is Unique. Same Load Registers 4 Different Velocities in 4 Different Barrels
- Same Ammo in Four Barrels — Surprising Velocity Test Results
- Same 6BR Lapua Ammo in 4 Barrels — Surprising Velocity Results
- Velocity Test with Four Different Barrels — Surprising Results
- Speed Variance in Barrels — You May Be Surprised
Share the post "Tech Tip: Same Load Varies in Velocity with Different Barrels"
Speculation only, “Brand S” was a button rifled barrel and “Brand K” was a cut rifled barrel and “Brand PN” was also a cut rifled barrel? Lapua test barrel?
I think it would be of interest to know the manufacturing method of the barrels tested.
Roy
I’m with Roy.
This is a great write up, and I appreciate the information. However, I wonder if there are factors involved that can have a deterministic effect on how fast a barrel will be.
Cut vs button
# of grooves
depth of grooves
bore/groove diameter
Of course, when you compare two identically spec’ed barrels, the variation in MV between them is indeterminate/unavoidable. I’m just curious what deterministic correlation the above barrel specs have on MV.
Thanks for another informative bulletin!
-Bryan
Brand PN was probably a 3-grove barrel and was also probably hand-lapped. not sure about the other barrels. but my speculation was that the lower amount of groves and hand lapping added to the speed a bit.
It’s as abstract as accuracy, and why not?
Specs mean nothing when barrels are not actually
made to any. I once sought a barrelmaker with the capability to MEASURE(not air guage), and lap to ‘spec’.
I concluded based on the responses that only Loather Walther possessed such capability. No coincidence then that they can also can make barrels any way they have ever been made.
Anyway, I believe barrels are a crap shoot, and this is why none(brand) can be proven better or worse than the market over-shared.
Sorry, but I find the comparisons irrelevant. In the first place lapua bullets are smaller in diameter than just about any other match grade bullet, so bore/groove measurements are important, furthermore, are these aggregate figures or based on single shot comparisons? Again, depending on the barrel, ES can be very high.
Lastly, with the exception of Krieger, I have never done a barrel swap (of identical specs) that did not require all new load development. I believe it is an “ism” that there are far too many variables between any two barrels to expect that any two will shoot the same.
I have two Savage 10BAS-K & 10BATS-K, hand loads of 5 rounds each one ave. 54fps faster
I did more test 4 Savage rifles 308 win, American Eagle 168 HP-M sorted 4 boxes to get 20 rounds same weight jump ave. 090 they have Speer bullets and loaded 20 rounds Benchmark 43gr CCI 250 Speer 168 HP-M .030 jump BHA-M cases.
#1, 10BAS-K AMER=ave2660 h2668 L2653 es15 sd6.8 BENCH=ave2721 h2737 L2712 es25 sd8.9 used has 600rds
#2,10BATS-K AMER=ave2705 h2714 L2701 es13 sd4.9
BENCH=ave2740 h2747 L2735 es12 sd4.2 used has 300rds
#3,10BATS-K AMER=ave2737 h2760 L2694 es66 sd24.8
BENCH=ave2779 h2791 L2769 es22 sd8.9 new 2rds sightin
#4,10BATS-K AMER=ave2697 h2721 L2665 es56 sd18.5
BENCH=ave2734 h2738 L2725 es13 sd4.8 new 2rds sightin
#3 shot the fastes both loads to fast!
#2 shot both loads good but not tight.
#4 shot the AMER .293 the BENCH 1.099
#1 slowes the AMER .801 THE BENCH .309 slow is best!
At least the Speer bullet likes 2700-2725!
Dose this help anyone? The one thing I can not control is the Primers you take them as they come!
One thing that groove diameter and bore dimensions will not tell you is net area of the bore, in other words, how much room the lands are removing from the area of a groove diameter circle. Still, all in all, the main point of the test is well demonstrated. If your numbers don’t match someone else’s, it may be as simple as the fact that you have a faster or slower barrel.
I had two Barnard actions fitted with Tru-flite 30″ barrels both fitted and chambered by Tru-Flite 3 years apart the
older barrel was faster by 50fps even after the second barrel had shot the same
number of rounds, you never know what you
have until you shoot it.
Robert.
As has been noted, bore and groove sizes, groove width, surface area of the bore will have an impact on velocities. Not to mention chamber specs./free bore length/jump etc….I tell customers that a difference of 100fps slower of faster etc….is in the normal range.
Also what is not mentioned unless I missed it is how many rounds where thru the barrels when the velocity was measured. Where the barrels brand new, did they have 100 rounds thrum or 1000 etc…I know of ammunition manufacturers that will not use a ammunition test barrel for any data until they have at least 100 rounds thru the barrel before testing. They want to know that the barrel has stable and being consistent etc…
Always go for accuracy first and the velocity second. Frank @ Bartlein Barrels
To many varriables not to have big differences.
Different barrel makers use different steel from different manufactures.
Bore, groove diameter, numbers of lands and grooves. Methods of manufacture, hammer forged, button, cut rifled, polygonal etc.
Differences in seatin dept., etc.
Nat Lambeth
Umm… the ‘fast’ barrel is also an inch longer than the others…
Editor: We have done a cut-down test on 6mmBR barrels (slicing it down at 1″ increments) and found the average difference in speed per inch (from 33″ to 27″) to be 8 fps. Hence the article states: “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.”
Can anyone tell me what is the overall length of the Lapua Factory loads please?
If you can’t say what barrel will do what even if they are from the same maker than this is all pretty pointless IMO. All you have said is that it is a crap shoot what you will end up with no matter what you use. Unrepeating numbers are meaningless when trying to measure things.
EDITOR: It’s not pointless to have this discussion, because people often post (in frustration) that they can’t reach velocities published in load manuals or on our Cartridge Guides. If they don’t understand that every barrel is different (even from the same maker), they may experiment with excessive loads in an effort to try to “hit the numbers”. Additionally, this shows the importance of developing loads specific to each barrel. When you change out a barrel, you can’t just lift a load from your reloading log and expect that it will be ideal for your new tube. Some folks, new to reloading, don’t realize this.
Make the barrels the same length and you dont have much more then the expected extreme spread in the load. Ive found a 1″ to more like 17 to 22 fps then 10. I dont think the example makes a case for the 100 fps change apples to apples.
EDITOR: This is NOT true for the 6mmBR: We did a 6mmBR cut-down test, starting with a 33″ barrel. We cut it in 1″ increments down to 28″. Total change in velocity was just 40 fps, very consistently about EIGHT (8) FPS PER INCH. Among the barrels referenced in this story, the length variation was only ONE INCH.
SEE Test HERE: http://bulletin.accurateshooter.com/2011/12/barrel-length-and-velocity-barrel-cut-down-tests/
To make the editors point Alliant will tell you their pressure test barrels will get 100 fps more then most barrels we are using. Adds to the confusion a bit.
One person mentioned this barrel maker being able to do anything etc…I disagree…
Get the above barrels listed in the bulletin measured for starters.
Different bore and groove size variation and groove width all effect the overall bore surface area and will impact on the velocities and pressures.
Send the barrels here. I will measure the bore and groove sizes and will post the data and send the barrels back.
That’s the only way you will learn anything to start with.
If brand PN has a groove size that is say .0004″ bigger than brand S than I’m going to say that is the difference but with out measuring we’re all guessing!
Later, Frank
Bartlein Barrels
i wish Lapua started up production again on 300 WM ammo or brass???
EDITOR: This is NOT true for the 6mmBR: We did a 6mmBR cut-down test, starting with a 33″ barrel. We cut it in 1″ increments down to 28″. Total change in velocity was just 40 fps, very consistently about EIGHT (8) FPS PER INCH. Among the barrels referenced in this story, the length variation was only ONE INCH
I believe when using a slower powder you will see a proportionately larger change in fps per barrel inch. For example the change would be larger if you used 2000MR instead of Varget or RL15. The test was done cutting from 33″ to 28″. If you cut from 26″ to 20″ I believe the spread would also be larger then 8 or 10 fps. Interesting discussion.
Useless unscientific comparison. Far FAR too many variables as has been stated.
EDITOR: You folks don’t seem to get it. We are not claiming that one brand of barrel is alway better than another. In fact we stated clearly that speed variances are “barrel specific, NOT brand specific.” What we have found, empirically, is that different same-length barrels chambered for the same cartridge will show a significant variance in measured velocity, with the SAME LOAD. That is a fact, and any one who has built many rifles will attest to that. It doesn’t matter if there are many underlying factors in the speed variances. We are only stating that the end result — different speeds with the same brass, bullets, and powder amount — is a “fact of life” that shooters should understand when they change barrels and when they work up loads.
We often get questions from readers asking “why can’t I get the velocity it shows in the load books?” or “why does my buddies’ Savage shoot faster than my [same-model] Savage?”, or “Why is my new barrel slower than my old barrel”. The point of this article is to provide the simple truth that some same-length barrels, with the same load, are faster than others. That may seem obvious to the critics, but there are many shooters who are not aware of this phenomenon, or who didn’t realize the variance in velocity can be 100 fps or more. Once they learn this fact, they will not be tempted to boost their powder charges to unsafe levels in order to read a velocity that can only be achieved in an inherently faster barrel.
Wouldn’t you need a strain gauge to validate that the increased FPS was not due to increased but acceptable pressure?
i.e. shouldn’t the statement of a fast vs a slow barrel should be correlated against pressure generated for the same fps?
Just using the same ammo seems to be too much of an assumption that pressure and therefore FPS should have been equal and it was just the barrel that was fast.
EDITOR: Your point is well-taken, but IF there is a pressure differential that further proves the point that each barrel is different. As long as each barrel is not exceeding max pressure (and none did here as we were using conservatively-loaded factory ammo), the fact remains that some barrels were faster than others — GIVEN the SAME LOAD. There can be a number of reasons — different land/groove configurations, different levels of internal smoothness, different bore diameter, different amount of chokes. But the fact remains that with the same ammo, different velocities were recorded.
You might say — oh well, all this proves is that I need to add more powder to “equalize” the slow barrel. In fact, in the real world, we have found this usually does NOT work out. Slow is slow. The slow barrels (chambered in 6mmBR) we tested could simply NEVER achieve the velocities of the “fast” barrels, when both were loaded to max acceptable pressures. Meaning, even when we adjusted the charge upwards for the slow barrels, they could NOT shoot as fast as the fast barrels. With our handloads, we tried to get all the barrels to deliver 2890 fps with 105-107gr bullets. We simply could NOT get there with the slow barrels — they would max out around 2850-60 fps before there were clear pressure signs. By contrast, the fast barrels could shoot 2900+ before we started to see ejector marks, cratering, or other signs of pressure. In specific examples, we have one 28″ barrel which can run 2910 with 30.3 grains of Varget, and another 28″ barrel that hits the wall at 2865 with 31.0 grains of Varget, and you can’t get any more speed from that slower barrel without ruining the brass.
We can get into an elaborate discussion, but the bottom line here is that some barrels just deliver fewer FPS (at max acceptable pressures) than other same-length barrels (at max acceptable pressures). If you have a slower barrel, you need to accept what your barrel can give, and don’t pursue dangerous pressure levels to try to make the slow barrel deliver the velocities of the faster barrels. That’s sort of the point of the story.