For most larger centerfire cartridges, increased barrel length augments muzzle velocity. That’s why you see F-Open rifles with 30″ and even 32″ barrels. But there is a limit — at some point, increased barrel length may not yield any additional velocity. And in the case of rimfire, too much barrel length can reduce MV. Today’s showcase explores how barrel length affects muzzle velocity, both in centerfire and rimfire rifles.
In the photo above you can see a test rifle fitted with what may currently be the longest barrel fitted to a conventional rifle. This was created by the team at MDT (Modular Driven Technologies) to test how velocity varies with barrel length.
You can see the results of testing with this one-of-a-kind rifle in the MDT video below, the first in our Saturday video showcase. This is followed with an MDT rimfire barrel length/velocity test, and additional tests for the .308 Winchester, 6.5 Creedmoor, and .223 Rem cartridge types.
World’s Longest Rifle Barrel Cut to Determine Velocity Change
This may be the most interesting velocity by barrel length test ever put on video. The MDT (Modular Driven Technologies) team started with a 69″-long barrel, chambered for .308 Winchester. The ammo was Federal Gold Medal match with 175gr Sierra HPBT Bullets (Video 3:30). This barrel had actually been fabricated from multiple sections, a challenge in itself.
Velocity was measured in one-inch increments starting at 69″ and going down to 19″. The speed at 69″ was 2778 FPS while the final speed, at 19″ barrel length, was 2567 FPS. “That is a difference of 211 FPS from the longest point to the shortest point”, observed MDT’s tester. Note that, the velocity did show fairly constant change per inch from 19″ to 45″. So going beyond 36″ inches can actually increase velocity. However, from 45″ to 61″ inches the velocity actually declined a bit. SEE VIDEO at 6:55 time-mark, and check out the chart below.
Ultra-Long .22 LR Rimfire Barrel Cut-Down Velocity Test
This video features Part 2 of MDT’s “Cutting the World’s Longest Rifle” test. This time the team shoots the diminutive .22 LR cartridge from an ultra-long barrel. The results may surprise you: “Get ready to have your assumptions shattered as the MDT team chopped a .22 LR rimfire barrel away inch by inch, recording velocities at each barrel length. In this test, the MDT team looked to determine the optimal length for a .22 LR barrel, from the standpoint of velocity. How long is too long? How short is too short? Does shorter always mean faster? Does longer always mean slower?”
In fact, MDT’s testers determined that, with standard rimfire ammunition, the velocity started to decline after 16″ length. That surprised some of the testers. So with the small .22 LR cartridge, more barrel length can actually reduce muzzle velocity from increased in-barrel friction.
6.5 Creedmoor Barrel Length Test (24″ to 16″)
For this video, testers for Western Powders took a standard test barrel chambered for 6.5 Creedmoor and cut it down one inch at a time. The velocity for five rounds at each length was then measured with a chronograph to determine velocity loss per inch of barrel reduction. Overall the recorded velocity loss from 24″ to 16″ was 197 FPS, almost exactly 25 FPS per inch of length. The velocity loss rate was fairly constant inch by inch, as you can see from the graph displayed at the 4:00-minute mark in the video.
.223 Rem (5.56×45) Velocity Tests (9 Guns, 7.5″ to 20″ Barrels)
In this video, the team from Classic Firearms tests a variety of firearms chambered for .223 Rem (5.56×45). This starts with an Springfield Saint Victor AR-type pistol with a very short 7.5″ barrel. This yielded a 2183 FPS average. Then the team tested eight more guns with increasingly long barrel lengths, adding barrel length with each gun in sequence. The test concluded with a Colt XM16E1 rig with 20″ barrel. That Colt AR averaged 3052 FPS. The guns used (and barrel lengths) are listed below.
The overall results are discussed at the 13:45 Time-Mark.
Test Lengths at Video Time — 7.5″ to 20″
2:11 — 7.5″ Springfield St.V. AR Pistol, 2183 FPS
3:23 — 10.3″ DD MK18 SBR, 2513 FPS
4:34 — 11.8″ PWS MK111 AR Pistol, 2644 FPS
5:35 — 12.5″ IWI Zion AR Pistol, 2789 FPS
.308 Winchester — 16″ Barrel vs. 24″ Barrel Velocity
With the .308 Win cartridge, many hunters prefer a shorter barrel for lighter carry weight. In this video, Gavin Gear of UltimateReloader.com compares .308 Win velocities with a 16″ barrel and a 24″ barrel, shooting the same ammo. Gavin notes: “We asked for input on our .308 build. Overwhelmingly, you all wanted a 16″ barrel, so ‘Shorty’ was born! Looking to compare velocities, I brought out my match .308 Win with a 24″ barrel to compare the results with some Hodgdon data.” CLICK HERE to read full report on UltimateReloader.com.
RifleShooter.com Barrel Cut-Down Testing
Along with these videos, our friends at RifleShooter.com have conducted a number of barrel cut-down tests, starting with fairly long barrels. Velocities were measured with each inch reduction
Most of us own a .223 Rem rifle. Now, thanks to our friends at Rifleshooter.com we can assess exactly how velocity changes with barrel length for this popular cartridge.
Rifleshooter.com performed an interesting test, cutting the barrel of a .223 Rem rifle from 26″ all the way down to 16.5″. The cuts were made in one-inch intervals with a rotary saw. At each cut length, velocity was measured with a Magnetospeed chronograph. To make the test even more interesting, four different types of .223 Rem/5.56 ammo were chron’d at each barrel length. The Rifleshooter.com team that conducts these tests has a full-service gun shop, 782 Custom Gunworks — visit 782guns.com.
Test Barrel Lost 25.34 FPS Per Inch (.223 Rem Chambering)
How much velocity do you think was lost, on average, for each 1″ reduction in barrel length? The answer may surprise you. The average speed loss of the four types of .223/5.56 ammo, with a 9.5″ shortening of barrel length, was 240.75 fps total (from start to finish). That works out to an average loss of 25.34 fps per inch.
5.56/.223 Barrel Cut-Down Speed Test 26″ to 16.5″
Start FPS at 26″
End FPS at 16.5″
Total Loss
Average Loss Per Inch
UMC .223 55gr
3182*
2968
214
22.5 FPS
Federal M193 55gr
3431
3187
244
25.7 FPS
Win m855 62gr
3280
2992
288
30.3 FPS
Blk Hills .223 68gr
2849
2632
217
22.8 FPS
*There may have been an error. The 25″ velocity was higher at 3221 fps.
Rifleshooter.com observed: “Cutting the barrel from 26″ to 16.5″ resulted in a velocity reduction of 214 ft/sec with the UMC 223 55-grain cartridge, 244 ft/sec with the Federal M-193 cartridge, 288 ft/sec with the Winchester M855 cartridge and 217 ft/sec with the Back Hills 223 68-grain match cartridge.”
How the Test Was Done
The testers described their procedure as follows: “Ballistic data was gathered using a Magnetospeed barrel-mounted ballistic chronograph. At each barrel length, the rifle was fired from a front rest with rear bags, with five rounds of each type of ammunition. Average velocity and standard deviation were logged for each round. Once data was gathered for each cartridge at a given barrel length, the rifle was cleared and the bolt was removed. The barrel was cut off using a cold saw. The test protocol was repeated for the next length. Temperature was 45.7° F.”
See More Barrel Cut-Down Tests on Rifleshooter.com
Rifleshooter.com has performed barrel cut-down tests for many other calibers/chamberings including 6mm Creedmoor, .308 Winchester, and .338 Lapua Magnum. See these test results at Rifleshooter.com.
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The Legal Brief is a feature of TheGuncollective.com that focuses on firearms rules and regulations. In this Legal Brief video, Attorney Adam Kraut explains key State and Federal regulations governing firearms, and explains how to ensure compliance with all applicable laws.
This five-minute video explains barrel length rules for rifles and shotguns, and also explains the best (and most fool-proof) methods to measure your barrel. In addition, the video explains how to measure firearm overall length. A rifle or shotgun which is less than 26 inches overall can also be classified as a “Short-barreled” rifle/shotgun subject to the NFA. NOTE: Under federal law “If the rifle or shotgun has a collapsible stock, the overall length is measured with the stock EXTENDED”.
Highlights of LEGAL BRIEF Discussion of Barrel Length and Firearm Overall Length
The ATF procedure to measure the length of a barrel is to measure from the closed bolt or breech face to the furthest end of the barrel or permanently attached muzzle device. ATF considers a muzzle device that has been permanently attached to be part of the barrel and therefore counts towards the length.
How to Measure Barrel Length: Drop [a] dowel or rod into the barrel until it touches the bolt or breech face, which has to be closed. Mark the outside of the rod at the end of the muzzle crown (if you don’t have a permanently attached muzzle device) or at the end of the muzzle device if it is permanently attached. Remove the rod and measure from the mark to the end of the rod. That is your barrel length[.]
Remember, if the barrel length is less than 16 inches, it is possible that the firearm could be a short barrel rifle (if you are building a rifle or it is already on a rifle) and if the barrel length is less than 18 inches, it is possible the firearm could be a short barrel shotgun (again if you are building a shotgun or it is already a shotgun). Both of these firearms would be subject to the purview of the National Firearms Act and would require the firearm to be registered accordingly.
How to Measure Overall Length:The overall length of your rifle or shotgun may also classify it as a Short Barrel Rifle or Short Barrel Shotgun. The overall length of a firearm is the distance between the muzzle of the barrel and the rearmost portion of the weapon measured on a line parallel to the axis of the bore. … If the rifle has a permanently attached muzzle device, that is part of the overall length. … If the rifle or shotgun has a collapsible stock, the overall length is measured with the stock extended.
The Legal Brief is a feature of TheGuncollective.com that focuses on firearms rules and regulations. In this Legal Brief video, Attorney Adam Kraut explains key State and Federal regulations governing firearms, and explains how to ensure compliance with all applicable laws.
This five-minute video explains barrel length rules for rifles and shotguns, and also explains the best (and most fool-proof) methods to measure your barrel. In addition, the video explains how to measure firearm overall length. A rifle or shotgun which is less than 26 inches overall can also be classified as a “Short-barreled” rifle/shotgun subject to the NFA. NOTE: Under federal law “If the rifle or shotgun has a collapsible stock, the overall length is measured with the stock EXTENDED”.
Highlights of LEGAL BRIEF Discussion of Barrel Length and Firearm Overall Length
The ATF procedure to measure the length of a barrel is to measure from the closed bolt or breech face to the furthest end of the barrel or permanently attached muzzle device. ATF considers a muzzle device that has been permanently attached to be part of the barrel and therefore counts towards the length.
How to Measure Barrel Length: Drop [a] dowel or rod into the barrel until it touches the bolt or breech face, which has to be closed. Mark the outside of the rod at the end of the muzzle crown (if you don’t have a permanently attached muzzle device) or at the end of the muzzle device if it is permanently attached. Remove the rod and measure from the mark to the end of the rod. That is your barrel length[.]
Remember, if the barrel length is less than 16 inches, it is possible that the firearm could be a short barrel rifle (if you are building a rifle or it is already on a rifle) and if the barrel length is less than 18 inches, it is possible the firearm could be a short barrel shotgun (again if you are building a shotgun or it is already a shotgun). Both of these firearms would be subject to the purview of the National Firearms Act and would require the firearm to be registered accordingly.
How to Measure Overall Length:The overall length of your rifle or shotgun may also classify it as a Short Barrel Rifle or Short Barrel Shotgun. The overall length of a firearm is the distance between the muzzle of the barrel and the rearmost portion of the weapon measured on a line parallel to the axis of the bore. … If the rifle has a permanently attached muzzle device, that is part of the overall length. … If the rifle or shotgun has a collapsible stock, the overall length is measured with the stock extended.
Here’s an extreme range of .224-Caliber bullets: 35gr varmint bullet and 90gr match bullet. Of course, along with bullet length/design, you need to consider MV when choosing twist rate.
Even with the same caliber (and same bullet weight), different bullet types may require different rates of spin to stabilize properly. The bullet’s initial spin rate (RPM) is a function of the bullet’s muzzle velocity and the spin imparted by the rifling in the barrel. You want to ensure your bullet is stable throughout flight. It is better to have too much spin than too little, according to many ballistics experts, including Bryan Litz of Applied Ballistics. The late Glen Zediker provided some basic tips concerning barrel twist rates and bullet stability. These come from his popular book, Top Grade Ammo.
Choosing the Right Twist Rate
I’d always rather have a twist too fast than not fast enough. Generally… I recommend erring toward the faster side of a barrel twist decision. 1:8″ twist is becoming a “new standard” for .224 caliber, replacing 1:9″ in the process. The reason is that new bullets tend to be bigger rather than smaller. Don’t let a too-slow twist limit your capacity to [achieve] better long-range performance.
Base your next barrel twist rate decision on the longest, heaviest bullets you choose to use, and at the same time realize that the rate you choose will in turn limit your bullet choices. If the longest, heaviest bullet you’ll shoot (ever) is a 55-grain .224, then there’s honestly no reason not to use a 1:12″. Likewise true for .308-caliber: unless you’re going over 200-grain bullet weight, a 1:10″ will perform perfectly well.
Bullet Length is More Critical than Weight
Bullet length, not weight, [primarily] determines how much rotation is necessary for stability. Twist rate suggestions, though, are most usually given with respect to bullet weight, but that’s more of a generality for convenience’s sake, I think. The reason is that with the introduction of higher-ballistic-coefficient bullet designs, which are longer than conventional forms, it is easily possible to have two same-weight bullets that won’t both stabilize from the same twist rate.
Evidence of Instability
The tell-tale for an unstable (wobbling or tumbling) bullet is an oblong hole in the target paper, a “keyhole,” and that means the bullet contacted the target at some attitude other than nose-first.
Increasing Barrel Length Can Deliver More Velocity, But That May Still Not Provide Enough Stability if the Twist Rate Is Too Slow
Bullet speed AND barrel length have an influence on bullet stability, and a higher muzzle velocity through a longer tube will bring on more effect from the twist, but it’s a little too edgy if a particular bullet stabilizes only when running maximum velocity.
My failed 90-grain .224 experiment is a good example of that: I could get them asleep in a 1:7″ twist, 25-inch barrel, which was chambered in .22 PPC, but could not get them stabilized in a 20-inch 1:7″ .223 Rem. The answer always is to get a twist that’s correct.
These tips were adapted from Glen’s newest book, Top-Grade Ammo, available at Midsouth. To learn more about this book and other Zediker titles, and read a host of downloadable articles, visit ZedikerPublishing.com.
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Shooters contemplating purchase of a .338 LM rifle often ask: “What length barrel should I get?” Rifleshooter.com recently performed a test that provides interesting answers…
Our friends at RifleShooter.com like to slice and dice — barrels that is. They have done barrel length cut-down tests for popular calibers like the .223 Rem, 6.5 Creedmoor, and .308 Winchester. But now they’ve tackled something way bigger — the .338 Lapua Magnum, a true “Big Boomer”. Starting with a beefy 30″-long Pac-Nor Barrel, RifleShooter.com chopped the tube down in one-inch increments all the way down to 17 inches (that’s 14 different lengths). At each new (shorter) barrel length, velocity was measured with a MagnetoSpeed chronograph using two different loads, 250gr SMKs with H4831sc and 300gr SMKs with Retumbo. Four shots were fired at each length with each load, a total of 112 rounds.
Load #1: 250gr Sierra MK, Lapua brass, CCI #250 primer, H4831SC, OAL 3.720″.
Load #2: 300gr Sierra MK, Lapua brass, Win WLRM primer, Retumbo, OAL 3.720″.
The .338 Lapua Magnum is a jumbo-sized cartridge, that’s for sure…
Donor Barrel Sacrificed for Science
Rifleshooter.com’s Editor explains: “Brandon from Precision Addiction offered to send us his .338 barrel for our .338 Lapua Mag test. I took him up on his offer and he sent me his used Pac-Nor chrome-moly barrel with about 600 rounds though it. This thing was a beast! A heavy 1.350″ shank that ran straight for 6″, until tapering to 1″ at 30″ in length.”
Results Summary
.338 Lapua Magnum with 250gr Sierra MatchKings
After shortening the barrel from 30″ to 17″, total velocity reduction for the 250-grainers was 395 FPS, an average loss of 30.4 FPS per 1″ cut. The amount of velocity loss per inch rose as the barrel got shorter, with the biggest speed reduction, a loss of 55 FPS, coming with the cut from 18″ to 17″.
Start Velocity: 2942 FPS | End Velocity: 2547 FPS | Average Loss Per Inch: 30.4 FPS
.338 Lapua Magnum with 300gr Sierra MatchKings
Shooting the 300-grainers, total velocity reduction was 341 fps, an average of 26.2 FPS loss per 1″ cut (30″ down to 17″). However, the speed actually increased with the first cut from 30 inches to 29 inches. The tester noted: “The 300 SMK load showed a slight increase from 30″ to 29″. I’ve recorded this in other tests and it seems to be more common with a heavier load. I suspect it is primarily due to the small sample sizes being used along with the relative proximity of muzzle velocities in adjacent lengths.”
Start Velocity: 2833 FPS | End Velocity: 2492 FPS | Average Loss Per Inch: 26.2 FPS*
*Velocity rose with first cut. Velocities ranged from 2,871 FPS (29″) to 2,492 FPS (17″) for a total velocity loss of 341 FPS.
RifleShooter.com crunched the velocity numbers in some interesting ways. For example they analyzed rate of velocity loss, concluding that: “after the initial rate change, the rate of the change in velocity is fairly consistent.” (View Rate of Change Graph)
How Velocity Loss Alters Long-Range Ballistics
The testers wanted to determine how the velocity reductions “affect our ability to hit targets downrange”. So, Rifleshooter.com plotted changes in elevation and wind drift at all barrel lengths. This revealed something interesting — drift increased significantly below 26″ barrel length: “Above 26″ things look pretty good, below 22″ they change quickly.”
We highly recommend you read the whole story. Rifleshooter.com put in serious time and effort, resulting in solid, thought-provoking results. The data is presented in multiple tables and graphs, revealing inch-by-inch velocities, change “deltas”, and SDs at each length.
What do you get when you cut a 6.5 Creedmoor-chambered barrel down to just over 16 inches? A lot more velocity than you might think. Our friends at Rifleshooter.com recently did a barrel cut-down test with 6.5 Creedmoor test rifle, shortening the barrel from 27 to 16.1 inches in one-inch increments. Surprisingly, with a 142gr Sierra MK, the total velocity loss (as measured with a Magnetospeed) was just 158 FPS, an average of 14.4 FPS per inch of barrel length. With the lighter 120gr A-Max bullet, the total velocity loss was 233 FPS, or 21.8 FPS average loss per inch of barrel.
Test Procedure
Five (5) rounds of each type of cartridge were fired at each barrel length and the velocity data was recorded with a MagnetoSpeed V3 barrel-mounted chronograph. The rifle was then cleared and the barrel was cut back one inch at a time from 27″ to just over 16″. NOTE: During this winter test, the air temperature was a very chilly 23° F. One would expect higher velocities across the board had the outside temperature been higher.
The photo below shows how the barrel was cut down, inch-by-inch, using a rotary saw. The barrel was pre-scored at inch intervals. As the main purpose of the test was to measure velocity (not accuracy) the testers did not attempt to create perfect crowns.
6.5 Creedmoor vs. Other Mid-Sized 6.5mm Cartridges
The 6.5 Creedmoor is a very popular cartridge with the tactical and PRS crowd. This mid-size cartridge offers good ballistics, with less recoil than a .308 Winchester. There’s an excellent selection of 6.5mm bullets, and many powder choices for this cartridge. When compared to the very accurate 6.5×47 Lapua cartridge, the 6.5 Creedmoor offers similar performance with less expensive brass. For a tactical shooter who must sometimes leave brass on the ground, brass cost is a factor to consider. Here’s a selection of various 6.5 mm mid-sized cartridges. Left to right are: 6.5 Grendel, 6.5×47 Lapua, 6.5 Creedmoor with 120gr A-Max, 6.5 Creedmoor with 142gr Sierra MK, and .260 Remington.
When asked to compare the 6.5 Creedmoor to the 6.5×47 Lapua, Rifleshooter.com’s editor stated: “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 6.5×47 Lapua seems to be slightly more accurate than the 6.5 Creedmoor. I attribute this to the quality of Lapua brass.”
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The Legal Brief is a feature of TheGuncollective.com that focuses on firearms rules and regulations. In this Legal Brief video, Attorney Adam Kraut explains key State and Federal regulations governing firearms, and explains how to ensure compliance with all applicable laws.
This five-minute video explains barrel length rules for rifles and shotguns, and also explains the best (and most fool-proof) methods to measure your barrel. In addition, the video explains how to measure firearm overall length. A rifle or shotgun which is less than 26 inches overall can also be classified as a “Short-barreled” rifle/shotgun subject to the NFA. NOTE: Under federal law “If the rifle or shotgun has a collapsible stock, the overall length is measured with the stock EXTENDED”.
Highlights of LEGAL BRIEF Discussion of Barrel Length and Firearm Overall Length
The ATF procedure to measure the length of a barrel is to measure from the closed bolt or breech face to the furthest end of the barrel or permanently attached muzzle device. ATF considers a muzzle device that has been permanently attached to be part of the barrel and therefore counts towards the length.
How to Measure Barrel Length: Drop [a] dowel or rod into the barrel until it touches the bolt or breech face, which has to be closed. Mark the outside of the rod at the end of the muzzle crown (if you don’t have a permanently attached muzzle device) or at the end of the muzzle device if it is permanently attached. Remove the rod and measure from the mark to the end of the rod. That is your barrel length[.]
Remember, if the barrel length is less than 16 inches, it is possible that the firearm could be a short barrel rifle (if you are building a rifle or it is already on a rifle) and if the barrel length is less than 18 inches, it is possible the firearm could be a short barrel shotgun (again if you are building a shotgun or it is already a shotgun). Both of these firearms would be subject to the purview of the National Firearms Act and would require the firearm to be registered accordingly.
How to Measure Overall Length:The overall length of your rifle or shotgun may also classify it as a Short Barrel Rifle or Short Barrel Shotgun. The overall length of a firearm is the distance between the muzzle of the barrel and the rearmost portion of the weapon measured on a line parallel to the axis of the bore. … If the rifle has a permanently attached muzzle device, that is part of the overall length. … If the rifle or shotgun has a collapsible stock, the overall length is measured with the stock extended.
Increasing Barrel Length Can Deliver More Velocity, But That May Still Not Provide Enough Stability if the Twist Rate Is Too Slow
