6 Creedmoor barrel length versus muzzle velocity (31 to 17 inches)

6 Creedmoor barrel length and velocity

6 Creedmoor is rapidly rising in popularity among long range shooters. Combining an efficient case design with the wide range of excellent 6mm bullets, the 6 Creedmoor becomes an intriguing choice. While it isn’t standardized by SAAMI as of this writing (January 2017), my understanding is it will be soon.

The 6 Creedmoor’s design and name come from it’s parent case, 6.5 Creedmoor. Simply neck a 6.5 Creedmoor down to 6mm and you have a 6 Creedmoor. Commercially produced cases and ammunition are available for 6 Creedmoor, however, forming brass from a more commonly available case is always an attractive option.

In this post we will look at how barrel length affects muzzle velocity for a 6 Creedmoor with four different loads, 110 Sierra MatchKing (SMK), 107 SMK, Copper Creek Cartridge Company (C4) 105, and 95 gr. Sierra Tipped MatchKing (TMK) shot through the same barrel at different lengths from 31″ down to 17″.

Commonly encountered match cartridges, left to right: 6mm BR, 243 Winchester, 6×47 Lapua, 6 Creedmoor, 6.5×47 Lapua, 6.5 Creedmoor, 260 Remington, and 308 Winchester

Selecting test loads

Selecting the proper loads is an important part of an experiment like this. In our 300 Win Mag barrel length and velocity testing we only shot one 190 gr. factory load. While this did succeed in providing a limited data set for that particular ammunition, it did not address heavier loads (you only get one shot per barrel, once you chop it up you can’t do it again). Since that time I have made an effort to be more inclusive of the bullet ranges available to provide a data set that is applicable to a wider range of end user applications.

Since the 6 Creedmoor is primarily used as a match cartridge, I’ve selected what I feel is an appropriate range of bullet weights to represent what might be encountered by a shooter considering this cartridge (above, left to right); 110 gr. SMK, 107 gr. SMK, C4 105 gr. and 95 gr TMK. Until recently, the 6 Creedmoor was viewed as a hand loaded or custom ammunition (C4) only option; however, companies (including Hornady) have started offering factory ammunition for it.

Three of the test loads, the 110 gr., 107 gr. and 95 gr. are hand loads that I have developed in other rifles. The fourth, the 105 gr. is loaded byCopper Creek Cartridge Company (C4)) as part of its custom made ammunition line. C4 was early to the 6 Creedmoor party and has an excellent reputation for quality ammunition, particularly in the 6 Creedmoor.

Load data for the 6 Creedmoor is pretty scarce, most shooters report excellent results with Hodgdon H4350 powder. I have tried H4350 as well as a few others and have found that H4350 works well. For this reason, I used H4350 in the hand loaded ammunition.

Before we get to the loads and the test, take a few minutes to read the following disclaimer:

The contents of Rifleshooter.com are produced for informational purposes only and should be performed by competent gunsmiths only. Rifleshooter.com and its authors, do not assume any responsibility, directly or indirectly for the safety of the readers attempting to follow any instructions or perform any of the tasks shown, or the use or misuse of any information contained herein, on this website.

Any modifications made to a firearm should be made by a licensed gunsmith. Failure to do so may void warranties and result in an unsafe firearm and may cause injury or death.

Modifications to a firearm may result in personal injury or death, cause the firearm to not function properly, or malfunction, and cause the firearm to become unsafe.

For reloading information: WARNING: The loads shown are for informational purposes only. They are only safe in the rifle shown and may not be safe in yours. Consult appropriate load manuals prior to developing your own handloads. Rifleshooter.com and its authors, do not assume any responsibility, directly or indirectly for the safety of the readers attempting to follow any instructions or perform any of the tasks shown, or the use or misuse of any information contained herein, on this website.

Test rifle

I assembled a rifle specifically for this post.

The test rifle was built with the following parts from Brownells:

Test Protocol

The test barrel is a 31″ Bartlein HV barrel with a 1:8″ twist that was chambered with a Manson 6 Creedmoor reamer and installed on a Stryker Ridge Action made by Defiance Machine. Headspace was set at minimum.

Since the barrel is new, I fired 5 rounds of C4 ammunition to verify the rifle functioned and the chronograph, a MagnetoSpeed V3, was properly adjusted. After this initial test, 4 rounds of each type of cartridge were fired with the average velocity information recorded for each. The barrel of the empty rifle was then cut back, one inch at a time, with the test repeated, down to 17″.

This experiment controls for barrel (the same barrel is cut), chamber (same chamber), ammunition (same hand loads and C4 ammunition) and temperature (the range was 24F). The range’s elevation is 30 feet above sea level. Information about precision (group size) was not recorded since it was outside the scope of this test.

Further discussion on the rationale of the methods used and sample size can be found at the bottom of this page.

Results

The average velocity for each barrel length and cartridge combination is summarized in the table below.

The data was dis-aggregated by cartridge into the following tables showing the barrel length (inches), muzzle velocity (ft/sec), change in velocity from previous barrel length (CHG), change in velocity from 31″ barrel length (CHG 31″) and the average rate of change (ROC). Rate of change was calculated by dividing the change from 31″ by the number of inches removed from the barrel, thus indicating the rate of change per inch of barrel length.

Effect of barrel length on drop and drift

I modeled the drop and drift in MRAD for each cartridge and barrel length combination shown. These values assume the shooter is at sea level, with a temperature of 59F and a scope height of 1.75″. The 110 SMK, C4 105 and 95 TMK are modeled using banded G1 ballistic coefficients (BC). The 107 SMK is modeled using a G7 BC (these were the values I had available).

Note in both the case of drop and drift, the majority of movement occurs when the barrel length decrease below 25″.

Effect of barrel length on standard deviation of loads

I’m often asked if I notice any trends in standard deviation (SD) relating to barrel length for a given cartridge. See the line graph, see below:

I don’t see any trends in SD that apply across the different loads, do you? It did give me a good chuckle though (note the sample sizes are fairly low and the loads are not tuned to the barrel).

Effect of barrel length on rate of change in muzzle velocity

I plotted the ROC for each cartridge and barrel length combination in the line graph below.

Note the downward trend of the graph above. If the ROC was fairly consistent, the line would be relatively flat, the change is slope indicates the change in velocity increases as the barrel length decreases.

Thoughts on 6 Creedmoor barrel length

Prior to building this rifle, I had been shooting two other 6 Creedmoors, one with a 27″ tube and the other with a 25″. I like them both, and while the 27″ seems a little long at times, the gun shoots very well. Looking at the data above, I would think guns from the 24-27″ range are ideal for the cartridge. The data shows there seems to be a diminishing return with longer barrels, but if your sport or shooting style supports it, go for it. If you made me pick an all around barrel length for a precision rifle, I would choose 25″.

I think the 6 Creedmoor has great potential as a hunting cartridge for lighter game, with external ballistics similar to, or slightly better than the 243 Winchester’s I have tested. When I conducted a similar test on the 243 Winchester with factory ammunition (link), a 100 grain bullet had a velocity of 2488 in a 16″ barrel. The 6 Creed loads above are all at least 347 feet/second faster with a 17″ barrel (this was with the same methods and chronograph in nearly identical weather conditions). That is impressive (ironically, those tests were conducted a year ago). This disparity was unanticipated since the 243 has a much larger case. I would think a 16 or 17″ 6 Creedmoor would make a great choice for a compact deer rifle. I would also note that hand loaded 243 Winchester ammunition would likely perform better than the factory loads I tested.

Discussion

How should I apply this data? That is up to you. This post shows the data set I gathered and the methods used to obtain it, consider this when you reference it. Often, someone will comment something to the effect of this shows longer barrels are slower. While it may show a few instances of this, I think that the data set applying to longer barrels raises more questions than it answers.

What do you think of the inconsistent data at the longer barrel lengths? I’ve recorded this in a few different cartridges (notably 6.5 Creedmoor and 7.62×39 Russian) and it has sparked some debate. What it doesn’t tell you is the longer barrel is necessarily slower or the data set is flawed. I think it is safe to say that longer barrels will always go faster than shorter ones, even when anomalies like this are recorded. I believe part of the reason this occurs is the relatively small sample size encountered (4 rounds) and proximity of the average velocities for adjacent lengths. I believe if a larger sample size was recorded at these longer lengths, the data would show a more consistent decline. Data is data, you talk to people that conduct objective research and they will tell you they record the data they get, not the data they want. When my toes were frozen in the snow, I wanted nothing more than a pretty chart that showed a continual downward decline for all four loads, but this is the data I recorded.

Don’t new barrels speed up? Did this affect the results? They do. The entire test, including the 5 test rounds fired at the beginning consisted of 245 rounds. I would guess that the barrel did “speed up” during that time. How much, I am not sure. Anecdotally, you’ll often hear 50-100 feet/second around the 250-300 round mark. For comparison sake, my 27″ 6 Creedmoor (which I has been shot quite a bit) was only 10 feet/second faster with the same load tested here. That data was recorded at 45F. Is this a great comparison? No, but it is another data point to consider. In the future I plan on testing how barrel speed increases.

Why did you you cut the barrel in 1″ increments instead of 2″? I’ve considered increasing the interval and sample size at each distance, however decided against it, preferring the larger number of data points to sample size. The 243 Winchester barrel length post was conducted in 2″ increments, click here for more information.

Why did you use a 31″ blank? Didn’t you waste a good barrel? I spoke with a few different shooters about using either a new 31″ blank, or a used barrel on my 25″ or 27″ gun. They all agreed that the longer barrel would provide data they were interested in seeing. I plan on finishing the barrel and making it into a 16.5″ 6 Creedmoor- not that I am recommending it; but, it won’t be wasted.

Why don’t you test for accuracy at each barrel length? I’ve addressed this in the past, but I’ll take another shot at it. Time is a factor, first, you’d be comparing a given load without tuning at various lengths. While this would be of value if you were using only one kind of ammunition, for hand loaders, it doesn’t really apply. I think you would be hard pressed to determine which barrel length is more precise than another. Further, removing the rifle from the range, crowning it and bringing it back would introduce more variables, such as a change in temperature. There are a handful of places in the US that would be able to effectively conduct a test like this, and even then, if they were only working with a sample of one rifle, the lessons would be less than 100% conclusive. If you would like to conduct a test like that, I would be happy to publish it for you.

Why didn’t you crown the barrel? We haven’t noticed the need for the crown across the rifles and pistols we have conducted testing on. In all of our data sets, we haven’t noticed a detectable decrease in velocity with the first shot hitting a burr.

Is there anything you wished you had done differently? Yes, I wish I tested a different, faster powder. While H4350 is a staple in the Creedmoor, in retrospect, I would have liked to see at least one more powder represented.

Why did you select a sample size of four cartridges for each bullet at each range? Limited resources. I had a lot of the same Hornady brass I purchased from GAP a few years ago, I had 245 cases left. That left me roughly 60 pieces of brass for each hand load to be tested. I could have used newer brass, however, since this was all drawn from the same lot, I decided to limit the sample size as well.

To examine how sample size affects a test like this, I had conducted the following test a few years ago with a 308 Winchester. I fired 30 rounds of IMI Samson 150 grain FMJ at 28″ and 16.5″ and recorded the results. Comparing the data from the 30 shot strings (28″ 2824 and 16.5″ 2555) to the 5 shot strings (28″ 2823 and 16.5″ 2561) I found a loss of 269 ft/sec (23.4 ft/sec per inch) as the barrel was cut. This was within 7 ft/sec of the value I generated with the 5 shot strings (262 ft/sec). Velocity loss per inch of barrel was .6 ft/sec away (22.8 ft/sec) from the value calculated with 5 shot strings.

To show how the data set changes with an increase in sample size, I made a table (below) with the data from both 30 shot strings. The “shot” column represents the shot number in the respective string. “28” barrel ft/sec” and “16.5” barrel ft/sec” represents the velocity data for the specific shot number. “AVG 28″ ft/sec” and “AVG 16.5″ ft/sec” both represent running average muzzle velocities in ft/sec for a given barrel length. “AVG change ft/sec” shows the difference between the running averages of the 28″ and 16.5″ barrels. “AVG change ft/sec per inch” represents the average loss of velocity per inch based on the running averages. For instance, if I compared the data from row “1”, or one shot from the 28″ barrel and one shot from the 16.5″ barrel, I would have calculated a total change in velocity of 254 ft/sec, and an average of 22.1 ft/sec per inch. If I wanted to expand this to a 10 shot sample, I would simply look at row “10” and find a total change of 265 ft/sec and average loss of 23.0 ft/sec per inch of barrel. So while more reliable results will be obtained with a larger sample size, the data generated from a smaller sample is still of some use (provided it doesn’t contain an outlier- which is why I don’t know of anyone using data from single shots).

308 Winchester/ 7.62x51mm NATO Comparison of velocity data Rifleshooter.com
Shot	28″ barrel ft/sec	AVG 28″ barrel ft/sec	16.5″ barrel ft/sec	AVG 16.5″ barrel ft/sec	AVG change ft/sec	AVG change ft/sec per inch
1	2835	2835	2581	2581	254	22.1
2	2814	2825	2533	2557	268	23.3
3	2821	2823	2541	2552	272	23.6
4	2823	2823	2551	2552	272	23.6
5	2824	2823	2601	2561	262	22.8
6	2834	2825	2572	2563	262	22.8
7	2811	2823	2587	2570	252	21.9
8	2816	2822	2546	2564	258	22.5
9	2821	2822	2545	2562	260	22.6
10	2827	2823	2520	2558	265	23.0
11	2835	2824	2584	2560	264	22.9
12	2820	2823	2592	2563	261	22.7
13	2825	2824	2554	2562	261	22.7
14	2820	2823	2551	2561	262	22.8
15	2842	2825	2585	2563	262	22.8
16	2833	2825	2573	2564	262	22.7
17	2825	2825	2540	2562	263	22.9
18	2813	2824	2492	2558	266	23.1
19	2791	2823	2550	2558	265	23.0
20	2797	2821	2546	2557	264	23.0
21	2836	2822	2567	2558	264	23.0
22	2850	2823	2541	2557	266	23.2
23	2826	2823	2559	2557	266	23.2
24	2842	2824	2478	2554	271	23.5
25	2838	2825	2537	2553	272	23.6
26	2831	2825	2569	2554	271	23.6
27	2842	2826	2601	2555	270	23.5
28	2833	2826	2534	2555	271	23.6
29	2796	2825	2578	2555	269	23.4
30	2810	2824	2536	2555	270	23.4

Closing:

I would like to thank the following for their help with this post:

Copper Creek Cartridge Company (C4)- Copper Creek has a great reputation among shooters I respect. I had never been in contact with the company prior to this test and they couldn’t have been more helpful or professional. Cooper Creek offers custom ammunition made to specification, either yours or theirs. I was extremely impressed with their product.
Brownells- Brownells has been a long supporter of this site and my work. This blog wouldn’t be what it is without their help and it is truly appreciated.
Sierra Bullets- Sierra has been extremely supportive of rifleshooter.com on the social media and bullet front. They make an excellent product that shoots well. I firmly believe the 110 SMK is a game changer in 6mm.
Manson Reamers- Dave Manson and Manson reamers are always quick to respond when we need technical and tooling assistance. The test rifle was chambered with one of his excellent reamers.
The readers- I have some of the best readers in the world. I appreciate your feedback and reflect on it. I think it has helped me improve the quality of content on this site.

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