Barrel Speed: 6.5 Creedmoor Bartlein vs. Factory barrel muzzle velocities
In addition to gunsmithing and reloading content, rifleshooter.com is well known for the barrel length vs muzzle velocity experiments. Over the years I’ve tested all kinds of cartridges and provided empirical data sets for them. I was recently testing factory 6.5 Creedmoor ammunition and ended with muzzle velocity data in the same atmospheric conditions for 7 different types of factory ammunition in two different rifles (I’ll be posting other findings related to these data soon).
I tested a custom and factory rifle. The custom rifle, was a Surgeon action with a 1:8.5″ 22″ premium cut-rifled Bartlein stainless-steel barrel. The factory rifle was a Ruger Precision rifle with a 1:8″ 5-groove 26″ hammer forged carbon steel barrel. When I started looking at the data set I was shocked to see that the Bartlein barrel, despite being 4″ shorter, was always producing a higher muzzle velocity than the factory barrel.
In 6.5 Creedmoor- Effects of Barrel Length on Velocity 2019, test results indicated that (in our test barrel) for most loads an inch of barrel loss would reduce muzzle velocity an average of 14.8 ft/second. If barrel performance was equal, the 22″ Bartlein barrel should be approximately 59 ft/sec slower than the 26″ RPR barrel for a given load.
I tested seven different factory loads (from left to right), Federal American Eagle 120 gr OTM, Hornady 129 gr InterLock American Whitetail, Norma 130 gr OTM, Federal Gold Medal 130 gr OTM, Sellier and Bellot 140 gr FMJ, Winchester 140 gr OTM, Hornady 140 gr ELD Match and Hornady 147 gr ELD Match. While this isn’t an exhaustive list of factory 6.5 Creedmoor ammunition, it is representative of what is available to most shooters.
This is the custom rifle. It has a custom action with a barrel I threaded and chambered at my shop, 782 Custom Gunworks. I seated it in an MDT ACC chassis. The barreled action assembly includes these parts from Brownells:
- Surgeon 591 short action
- Bartlein heavy varmint barrel
- Timney 510 trigger
- Nightforce BEAST 5-25×56 F1 scope
To record muzzle velocities I used a MagnetoSpeed barrel mounted ballistic chronograph. Most of the data represents ten-shot strings for the match loads and five-shot strings for the rest of the ammunition (with the exception of the 147 ELD, which was a 5 round string).
The 22″ Bartlein barrel produced faster muzzle velocities than the 26″ factory RPR barrel with all 7 loads. Despite being 4″ shorter, the Bartlein speeds averaged 8 to 88 ft/sec faster with an average muzzle velocity 39.8 ft/sec faster than the Ruger.
This data set shows that you can’t always predict with certainty how a load will behave in a particular barrel. Both barrels had been used quite a bit. Was the Bartlein faster because it is cut rifled, hand lapped or had a tighter bore? Was the Ruger Precision Barrel slower because it was hammer forged, carbon steel or possibly had a larger diameter bore? I’m not sure we’ll ever know, but speculating is fun!
Frank Green of Bartlein Barrels emailed me this:
|Hello Bill, |
With out even looking at the guns/barrels that where tested I can pretty much tell you what is going on.
It’s in the bore dimensions of the barrels and the chamber spec. most likely.
We make all of our barrels to min spec. on bore and groove size. Doesn’t matter if it’s a ammunition pressure/accuracy spec. barrel or a guy buying a barrel for a F Class gun, PRS gun or a hunting rifle etc….
Factory barrel tend to run bigger/looser on bore/groove size. Also chambers can be looser as well. It could have a min. spec. chamber or what is called a production chamber which again is looser. The Ruger RPR being either a button or hammer forged barrel is most likely looser/bigger on size and this can be from the actual rifling operation and or the bore size could have gone sour when they contoured/threaded the barrel etc..due to residual stress in the blank where as we don’t induce any stress into the barrel during rifling so we don’t have a problem with our bore sizes going sour.
Out of 24” test barrels Hornady rates they’re ammo at…. 147Eldm @ 2695fps140Eldm @ 2710fps
Our barrel on the custom rifle at 22” and the velocities listed where… 147 @ 2628fps.140 @ 2659fps.
For a good rough number figure 25fps of velocity gain/loss per inch of barrel length. So cut the barrel down to 22” and the velocity makes total sense on our barrel on that rifle.
If the bore/grooves of the Ruger RPR barrel is looser/bigger your going to lose velocity. A tighter bore usually will drive up pressure and usually will drive up velocities and looser means the pressure is going to drop faster and usually you lose velocity in that case.
Also other variables are how many rounds are on the barrels and how they have been cleaned can effect velocities as well but my guess is the difference is because of the chamber spec and or the bore sizes between the barrels. Only way to know is to measure the barrels to the 4th decimal place.
That’s why I tell guys over and over again…..you are not comparing apples to apples when you say brand B is slower than brand X and vice versa. Unless you know the exact dimensions and what chamber reamer was used you are not comparing apples and apples.