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August 27th, 2019

Cutting .338 LM Barrel from 30″ to 17″ — Velocity Loss Revealed!

.338 Lapua Magnum LM barrel length vs velocity cut down test chrono rifleshooter.com

With Randy Wise’s recent record-setting ELR performance with a .338 Lapua Magnum Savage rifle, we thought our readers might be interested in a .338 LM velocity test conducted by our friend Bill Marr, Editor of Rifleshooter.com.

READ FULL .338 Lapua Magnum Barrel Cut-down Velocity TEST »

782 custom gunworks ltdA couple seasons back, Bill did a fascinating barrel cut-down test on a .338 Lapua Magnum rifle. Bill, a skilled gunsmith who runs 782 Custom Gunworks, cut down the barrel from 30″ to 17″ in one-inch increments. During the cut-down process, Marr measured velocities at each barrel length, shooting four rounds after each cut. As you’d expect, there was a huge change in velocity from long to short. Speeds were measured at the muzzle with a Magnetospeed barrel-mounted chronograph.

If you’re looking for max velocity with the .338 LM, go long. With 250-grain Sierra MK bullets, the peak velocity Bill measured was 2942 FPS at the full, 30-inch length. This decreased pretty steadily down to 2547 GPS at the shortest 17″ length. That’s an average decrease of 30.4 FPS per inch from 30″ to 17″.

.338 Lapua Magnum LM barrel length vs velocity cut down test chrono rifleshooter.com

Bill also tested 300-grain Sierra MatchKings. This is interesting because Randy Wise ran 300-grain bullets (Berger Hybrids) in a 26″ factory barrel for his ELR record. Peak velocity was 2833 FPS at 30″, 2799 FPS at 26″, and 2492 FPS at the shortest 17″ length. Interestingly, velocity at 29″ was higher than at 30″ for the 300-grainers. Bill notes: “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.”

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″.

.338 LM Barrel Cut-Down Test Results Summary

.338 Lapua Magnum LM barrel length vs velocity cut down test chrono rifleshooter.com

.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

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Permalink Bullets, Brass, Ammo, Gunsmithing, Tech Tip 3 Comments »
August 12th, 2018

6.5 Creedmoor Barrel Length Test — Velocity Per Inch Revealed

Rifleshooter.com 6.5 Creedmoor cut-down test

Rifleshooter.com does some great original research — providing “hard data” you can’t find anywhere else. Here are the eye-opening results of Rifleshooter.com’s 6.5 Creedmoor barrel cut-down test. You may be surprised at the results. Read on…

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.

» CLICK HERE to SEE All Velocity Values at All Barrel Lengths

To perform this velocity test, our friend Bill, Rifleshooter.com’s editor, built up a 6.5 Creedmoor rifle using a Remington Model 7 action, 1:8″ twist Green Mountain CM barrel, and MDT LSS Chassis, all obtained from Brownells.com.

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.

» Read Full Story with All Test Results at Rifleshooter.com

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.

Rifleshooter.com 6.5 Creedmoor cut-down test

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 good 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 6.5mm 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.

6.5 Creedmoor Rifleshooter.com velocity barrel cut cut-down test saw blade

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.” Now that Lapua offers 6.5 Creedmoor brass with small primer pockets, the 6.5 Creedmoor is even more attractive.

The creator of Rifleshooter.com also operates a Custom Rifle Building enterprise and gun shop in Long Island, New York: 782 Custom Guns Ltd.. He tells us: “We offer an unparalleled level of gunsmith machine shop services in the Long Island region. From precision rifles (USMC M40A3/A5/A6 XM3 clones) to customized Remington 870 and Mossberg 590 shotguns, and customized 1911s, chances are if you can dream it, we can build it!”

Permalink Gunsmithing, Tactical, Tech Tip 14 Comments »