6.5 Creedmoor- Effect of Barrel Length on Velocity: Cutting up a Creedmoor!

Since its introduction by Hornady in 2007, the 6.5 Creedmoor (sometimes shortened to Creed) has established a strong foothold in the US rifle market.  The 6.5 Creedmoor balances the excellent external ballistics of .264″ diameter bullets with manageable recoil. (FOLLOW US ON FACEBOOK!)

Left to right, 6mm Norma BR, 6x47 Lapua, 243 Winchester, 6.5 Grendel, 6.5x47 Lapua, 6.5 Creedmoor 120 A-MAX, 6.5 Creedmoor 142 SMK, 260 Remington, and 308 Winchester
Left to right, 6mm Norma BR, 6×47 Lapua, 243 Winchester, 6.5 Grendel, 6.5×47 Lapua, 6.5 Creedmoor 120 A-MAX, 6.5 Creedmoor 142 SMK, 260 Remington, and 308 Winchester.

The 6.5 Creedmoor was originally designed as an across-the-course high power rifle cartridge.  While it excels at its intended role, the precision rifle crowd was quick to follow suit and adopt it.  Among the common 6.5mm cartridges, the 6.5×284 Norma has developed a reputation as a barrel burner, 260 Remington has greater case capacity and speed, and the 6.5×47 Lapua is arguably more accurate with a greater level of panache, but, unlike these others, the 6.5 Creedmoor has readily available factory match grade ammunition for a reasonable price.  This allows the new shooter access to a high performance cartridge, without the expense of reloading.

I built a custom 6.5 Creedmoor on a Surgeon action and was happy with the results.  To see how the rifle above was constructed, see Building a Custom 6.5 Creedmoor Precision Rifle.

6.5 creedmoor custom rifle on gravel 2

I ended up with a finished barrel length of 22″.  At the time that seemed like a good idea, but, I was unsure what I gave up from a longer barrel.  Given the success of Rifleshooter.com’s other barrel length experiments and the surging popularity of the 6.5 Creedmoor,  I decided it would be an excellent candidate for a barrel length and velocity test.

For this experiment, I built a test gun on a Remington Model Seven receiver with a Green Mountain Barrels .264″, 1:8 twist chrome moly barrel blank.

6.5 creed barrel length gun

The barrel is untapered, with cutting index grooves machined every inch.  Headspace was set to minimum.

I ordered the following parts from Brownells:

Before we get to the test, take time to carefully read the disclaimer below:

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.

I selected two different kinds of ammunition to test, a light 120 grain factory load, and a heavier 142 grain hand load.

6.5 creedmoor 142 AMAX ammo

The light load is represented by the Hornady Match 120 grain A-MAX.  This is a popular round with the factory ammunition crowd, often receiving accolades for performance.  All test ammunition was from the same lot number.

6.5 creedmoor 142 SMK

To represent heavier loads, I selected the Sierra 142 grain HPBT MatchKing (#1742).  I’ve had great results with this bullet in both the 6.5 Creedmoor and 6.5×47 Lapua.  Using new Hornady brass and CCI #200 large rifle primers, I loaded the 142 SMK over 41.8 grains of Hodgdon H4350.  This load exceeds the 41.5 grain published maximum listed by Hodgdon in their reloading manual, so it should only be considered safe in this gun (reread the disclaimer above).

Test protocol

The rifle is fired from a bench off a bipod.  Five rounds of each type of cartridge are fired at each barrel length and the velocity data is recorded with a MagnetoSpeed V3 barrel mounted ballistic chronograph.  The rifle is cleared and the barrel is cut back one inch at a time from 27″ to 16″.

cutting the 6.5 creed barrel

The cut is made with a cold saw.  Once the cut is completed, the experiment is repeated, until the rifle looks like it does in the picture below.

6.5 creed with 16%22 tube

A quick note on range conditions.  This test was conducted at 23F.  This is notable when comparing velocity figures.  While modern powder tends to be less temperature sensitive than older powders, the low temperature will undoubtedly yield slightly lower velocities than those expected at higher temperatures.

 

6.5 creed bbl length and velocity overview

Results by cartridge.

120 amax bbl length velocity creed

For the 120 grain A-MAX, a muzzle velocity of 2961 feet/second was recorded at the 27″ barrel length, and 2728 feet/second at 16″ barrel length, resulting in a total decrease of 233 feet/second.  The average loss of velocity was 21.8 feet/second per inch of barrel.  The largest decrease in velocity, 61 feet/second per inch of barrel was recorded when the barrel was cut from 19″ to 18″.   When the barrel was cut from 20″ to 19″ a 3 feet/second increase in muzzle velocity was recorded. Average standard deviation for was 21.3 feet/second.

142 bbl and velocity 6.5 creed

For the 142 grain Sierra HPBT MatchKing, a maximum velocity of 2683 feet/second was recorded at the 24″ barrel length.  A velocity of 2663 feet/second was recorded at the 27″ barrel length.  At the 16″ barrel length, a velocity of 2505 feet/second was recorded.  Velocity decreased 158 feet/second as the barrel was cut from 27″ to 16″, or 14.4 feet/second per inch of barrel length.  The velocity reduction from 24″ to 16″ was 178 feet/second, or 16.2 feet/second per inch of barrel length.  Average standard deviation was 15.7 feet/second.

How does barrel length effect bullet drop and wind drift?

To show how barrel length affects the bullet’s flight path, I modeled both cartridges using a ballistic calculator application.  I assumed a 100 yard zero, scope 1.75″ above the bore, and temperature of 59F.  The drop in mils is shown for 200, 400, 600, 800 and 1,000 yards.  The drift for a full value 10 mile/hour cross wind is shown in mils for 200, 400, 600, 800 and 1,000 yards.

For comparison purposes, I included data for a 308 Winchester (shown as 308/22″/175SMK in the tables below) and 300 Winchester Magnum (shown as 300/24″/190 SMK in the tables below).  The 308 Winchester data is taken from my 22″ 308 Winchester match rifle using 175 SMKs.  The load has a velocity of 2670 feet/second, hotter than the published velocities for M118LR in use by the US Military.  The 300 Winchester Magnum data was obtained using Federal 190 grain Gold Medal ammunition in a 24.25″ Shilen barrel with the observed muzzle velocity of 2892 feet/second.  Federal advertises the load at 2900 feet/second.  The comparison data is shown in the last two lines of the tables below.

120 amax bbl length drift and path v3

With the 120 A-MAX, there is little lost as the barrel length decreases from 27″ to 24″ inside of 800 yards.  At 1,000 yards, 0.3 mils of elevation  and 0.1 mils of drift are sacrificed.  Note the 6.5 Creedmoor 120 grain A-MAX with a 16″ barrel shoots inside of the 308 Winchester 175 grain SMK with a 22″ barrel at 1,000 yards!  Impressive!

142 bbl length path and dirft 6.5 creed v 3

As noted earlier, the 142 SMK hand load gained velocity as the barrel length decreased from 27″ to 24″.  For purposes of this table, assuming other barrels and loads would exhibit the same decrease, there was no benefit in either velocity, flight path, or drift from a 27″ over a 24″ barrel.  The 6.5 Creedmoor with 142 SMK and 17″ barrel shot inside the 308 Winchester 175 SMK 22″ barrel out to 1,000 yards.  The 308/175 SMK outperformed the 6.5 Creedmoor/142 SMK inside of 800 yards, however, at 1,000 yards the superior characteristics of the 142 SMK allows it to perform better.

Discussion:

What do you think the ideal barrel length is for a 6.5 Creedmoor?

That is a question you have to answer for yourself.  Selecting an appropriate barrel length depends on the rifle’s intended application.  The needs of a hunter and competitive shooter differ greatly.  While there are velocity, path, and drift benefits to the longer tubes with the lighter bullets at longer ranges,  as bullet weight increases these benefits become less apparent.  A 24″ tube seems to be a good compromise on the longer end, however, a 22″ gun doesn’t leave you wanting for much.  If the majority of your shooting is inside 600 yards and you like short barrels, serious consideration should be given to a 16-18″ barrel length (especially in suppressed applications).

For purposes of precision, shorter barrels vibrate (whip) less than longer ones.  Anecdotally, Rifleshooter.com has found shorter barrels easier to tune and more precise (they also look cooler).  We built quite a few 16″ 308 Winchesters with good results, for more on this take a look at Short and Loud: The 16 inch 308 Win Precision Rifle.

What are possible sources of error?

Sample size.  Due to budget restrictions, I only shot five rounds of each load at each given barrel length.  As sample size increases, so does the validity of the results. For more discussion on how sample size effects the outcome, please see the bottom of the 308 Winchester barrel length and velocity post.

This test controlled for the barrel, which, in my opinion, is better than comparing velocities between different rifles with different barrel lengths.

You didn’t use a premium barrel for this experiment.  Do you think this provided slower than expected velocities?

No, I don’t think it did.  For the 120 grain A-Max load, Hornady advertises a velocity of 2910 feet/second from a 24″ barrel.  I recorded 2918 feet/second at 24″.  The same 142 SMK load in my 22″ Bartlein was clocked at 2707 feet/second with a SD of 14.1.  In the test barrel the load was 2649 feet/second with a SD of 14.9.  While the 58 feet/second difference suggests this barrel is slower, the Bartlein data was recorded at 80F, while the test data was recorded at 23F.  Even though H4350 isn’t particularly sensitive to temperature, I would expect to see a similar decrease in velocity if I shot the Bartlein barrel in the same temperature.

What do you think of the velocity decrease observed for the 142 SMK in barrel lengths greater than 24″?

I think this part of the data raises more questions than it answers.  I would like to see this experiment repeated with a premium barrel and larger sample size.  I’ve conducted this experiment with a 223 Remington, 243 Winchester, 308 Winchester, 7mm Remington Magnum, 300 Winchester Magnum and 7.62x39mm Russian.  Only with the 7.62x39mm Russian, which has a much smaller case capacity, did I notice a decrease in velocity at the longer barrel lengths.  The decrease may be related to the barrel length, however, it may also be related to the fact the barrel was new and may have needed more fouling prior to the test.  The 142 SMK has a much longer bearing surface than the 120 A-MAX, which may help explain why this was observed in the 142 SMK but not the 120 A-MAX.

Do you see an advantage to a heavier bullet in the 6.5 Creedmoor?

Yes.  While a heavier bullet, like the 142 grain Sierra MatchKing drops faster than the 120 grain A-MAX at a given barrel length, the 142 SMK is less wind sensitive.  When comparing similar barrel lengths, the 142 SMK has .4-.5 mils less drift than the 120 A-MAX in 10 mph full value crosswind.

Do you think the 6.5 Grendel is similar to the 6.5 Creedmoor?

No, it isn’t even close.  I did quite a bit of work with the cartridge, see 6.5 Grendel Review: 18″ Special Purpose Rifle.  I tested 30 different hand loads in an 18″ barrel.  While it does fill a niche, it fills a small one.  I wasn’t impressed.

I was considering the 6.5×47 Lapua over the 6.5 Creedmoor, what do you think?

If you don’t hand load, or are new to precision rifle shooting, get a 6.5 Creedmoor.  If you shoot a lot, reload, have more disposable income, and like more esoteric cartridges, get a 6.5×47 Lapua.  I am a big fan of the 6.5×47 Lapua.  In my personal experience, the Lapua seems to be slightly more accurate than the Creedmoor.  I attribute this to the quality of Lapua brass.

Did you shoot any groups?

No, I did not.  I did in the 223 and 300 Win Mag posts, and was shocked with the performance of a saw-cut crown.  Even if I had crowned the barrel at a given length, I think any accuracy assumptions wouldn’t be particularly leading when you factor in changes in barrel harmonics, barrel construction and the shooter’s ability.

Why didn’t you crown the barrel each time you cut it?

Time.  My lathe is a two hour round trip to the range.  Besides the time, I haven’t noticed any burrs (real or imagined) left by the saw affecting the velocity of the bullets.  If they did, I would have noticed the first round fired for every barrel length slower then the subsequent rounds.  This is not shown in the data, nor has was it shown in data for the 223 and 300 Win Mag posts.

What do you think of the MDT HS3 chassis?

I love it.  It is a solid value for the money.  For more information about the MDT HS3, visit MDT’s website here.

What did you think of the MDT AICS style magazine?

It works great with the 6.5 Creedmoor.  I haven’t encountered any magazine related problems with it in various different firearms.  I’ve run 6.5 Creedmoor, 243 Winchester, 7.62x39mm Russian and 308 Winchester in it and have had great results.

How would you respond to this?

I found this on Facebook from Scott A.,I too love the 142 SMK. From a statistical standpoint, the article is bunk. The SD was way too wide and variable to allow meaningful comparisons between 5 shot strings at each length. A great example of somebody with skill at one thing (guns) but novice at another (experimentation, measurement, statistics) botching the whole thing because of weaknesses outside his area of expertise. He should have consulted somebody. And he would have had more measurement precision firing 10 shot strings and cutting off two inches at a time”

Scott, unsure where the novice comment comes from.  I would suggest rereading what I wrote as it was presented.  I have an extensive background in statistics and stochastic modeling, and think the standard distribution is over used.   Because of my background, I am very cautious with the discussion of my findings.  Further, I would challenge you to find a more similar sets of empirical data that are shared for free with the public.   As mentioned above, I agree with sample size.  However, take a look at this from my 308 Winchester post, and how the results change with sample size:

Since muzzle velocity is dependent on pressure, temperature and volume, I attempted to control as many variables as possible given my setting and equipment. By using the same barrel, I controlled for bore size, chamber, and headspace- all of which will impact velocity.  Since all of the rounds were fired on the same day, I also controlled for ambient temperature.  I did not control for barrel temperature.  The barrel did heat up during firing.  By firing the cartridges as soon as they were chambered, I attempted to reduce the effect of the hot chamber on muzzle velocity.

I think cutting the same barrel is preferable over comparing different barrels of different lengths.  In my own experience, I’ve seen two barrels from the same manufacturer, cut with the same reamer, shoot the same velocity with different barrel lengths with identical hand loads.  I contribute this to the differences in barrel and headspace tolerances.  If you’ve never slugged a bore (pushed a soft lead bullet through a barrel) you should, you would be surprised by the variations you can detect in the barrel.

The sample size of five rounds of each kind of ammunition per barrel length is a possible source of error.  However, testing indicates it may not be as much as initially thought.  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

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