April 16th, 2021

How Bullet Bearing Surface Length Can Affect Load Pressure

USAMU Bullet Ogive Comparison Safety Reloading
Three near-equal-weight 7mm bullets with different shapes and bearing surface.

This article, from the USAMU Facebook Page, concerns reloading safety. In the relentless quest for more speed and flatter ballistics, some hand-loaders load way too hot, running charges that exceed safe pressure levels. Hint: If you need a mallet to open your bolt, chances are your load is too hot. Stay within safe margins — your equipment will last longer, and you won’t risk an injury caused by over-pressure. In this article, the USAMU explains that you need to account for bullet shape, diameter, and bearing surface when working up a load. Don’t assume that a load which is safe for one bullet will be safe for another even if both bullets are exactly the same weight.

USAMU Reloading tips Army Marksmanship

Today, we continue our handloading safety theme, focusing on not inadvertently exceeding the boundaries of known, safe data. Bullet manufacturers’ loading manuals often display three, four, or more similar-weight bullets grouped together with one set of load recipes. The manufacturer has tested these bullets and developed safe data for that group. However, seeing data in this format can tempt loaders — especially new ones — to think that ALL bullets of a given weight and caliber can interchangeably use the same load data. Actually, not so much.

USAMU Bullet Ogive Comparison Safety Reloading

The researchers ensure their data is safe with the bullet yielding the highest pressure. Thus, all others in that group should produce equal or less pressure, and they are safe using this data.

However, bullet designs include many variables such as different bearing surface lengths, hardness, and even slight variations in diameter. In fact, diameters can occasionally range up to 0.001″ by design. Thus, choosing untested bullets of the same weight and caliber, and using them with data not developed for them can yield excess pressures.

This is only one of the countless reasons not to begin at or very near the highest pressure loads during load development. Always begin at the starting load and look for pressure signs as one increases powder charges.

Bullet Bearing Surface and Pressure
Bullet bearing surface length (BSL) is often overlooked when considering maximum safe powder charges and pressures. In Photo 1, note the differences in the bullets’ appearance. All three are 7 mm, and their maximum weight difference is just five grains. Yet, the traditional round nose, flat base design on the left appears to have much more BSL than the sleeker match bullets. All things being equal, based on appearance, the RN/FB bullet seems likely to reach maximum pressure with significantly less powder than the other two designs.

TECH TIP: Bullets of the same weight (and caliber) can generate very different pressure levels due to variances in Bearing Surface Length (BSL).

USAMU Bullet Ogive Comparison Safety ReloadingBullet 1 (L-R), the RN/FB, has a very slight taper and only reaches its full diameter (0.284 inch) very near the cannelure. This taper is often seen on similar bullets; it helps reduce pressures with good accuracy. The calculated BSL of Bullet 1 was ~0.324″. The BSL of Bullet 2, in the center, was ~0.430″, and Bullet 3’s was ~ 0.463″. Obviously, bullets can be visually deceiving as to BSL!

Some might be tempted to use a bullet ogive comparator (or two) to measure bullets’ true BSL for comparison’s sake. Unfortunately, comparators don’t typically measure maximum bullet diameter and this approach can be deluding.

Note: Due to time constraints, the writer used an approximate, direct measurement approach to assess the bullets’ different BSLs. While fairly repeatable, the results were far from ballistics engineer-grade. Still, they are adequate for this example.

Photo 2: The Perils of Measuring Bearing Surface Length with Comparators
USAMU Bullet Ogive Comparision Safety Reloading

In Photo 2, two 7mm comparators have been installed on a dial caliper in an attempt to measure BSL. Using this approach, the BSLs differed sharply from the original [measurements]. The comparator-measured Bullet 1 BSL was 0.694” vs. 0.324” (original), Bullet 2 was 0.601” (comparator) vs. 0.430” (original), and Bullet 3 (shown in Photo 2) was 0.602” (comparator) vs. 0.463” (original). [Editor’s comment — Note the very large difference for Bullet 1, masking the fact that the true full diameter on this bullet starts very far back. You can use comparators on calipers, but be aware that this method may give you deceptive reading — we’ve seen variances just by reversing the comparators on the calipers, because the comparators, typically, are not perfectly round, nor are they machined to precision tolerances.]

Thanks to the U.S. Army Marksmanship Unit for allowing the reprint of this article.

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April 16th, 2021

First Trip to the Shooting Range — Good Nosler Video

Nosler first day range safety video

To support the growing community of new shooters and hunters, Nosler has released a useful, informative video that can help prepare beginners for their first experience at a shooting range. This video was filmed at the Redmond Rod & Gun Club in Central Oregon.

Editor: Regular readers — if you have a friend or family member who is new to shooting, have them watch this video. It does a good job outlining important range etiquette along with safe practices.

Training at a gun range is critical to building foundational firearms skills. Unfortunately, this process can be intimidating for new shooters who are unsure of what a trip to the range fully entails. In this video Randy Newberg (Nosler Pro-Staffer) illustrates key points to help shooters feel safe and confident at any range.

Nosler first day range safety video

The 7-minute First Trip to the Shooting Range video covers key considerations that apply to all ranges: necessary equipment, firearm safety, range commands, and range etiquette. Differences between indoor and outdoor ranges, as well as range restrictions to consider before your visit are also covered. Newberg also notes: “Before you leave your house, double-check to make sure your firearm is empty”. (Editor: Yes we’ve seen people open their gun cases only to discover their rifle, pistol, or shotgun WAS loaded!)

Nosler first day range safety video

Important Firearms Safety Rules at the Range
Treat every firearm as if it were loaded.
Always keep your gun pointed in a safe direction.
Never point your firearm at anything you do not intend to shoot.
Always keep your finger off the trigger until your sights are on the target and you are ready to fire.
Always be sure of your target and what is beyond it. (Do NOT shoot unless you know exactly what your shot is going to strike.)

Always comply with ALL Range Commands (and make sure you can hear commands).
Nosler first day range safety video

Experienced Shooters Should Help Newcomers Learn Safe Procedures
Nosler’s video includes a call-to-action for experienced hunters and shooters to help mentor those new to the sport. As a seasoned shooter you can accompany a new shooter to the range, showing him or her the right procedures. This includes placing rifles on the bench, setting up targets during cease-fires, and properly unloading and clearing weapons. As a mentor, you can also share educational resources that benefit newcomers, and share your effective/safe reloading methods.

Nosler first day range safety video

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April 16th, 2021

Muzzle Brake Noise Levels Revealed by PRB Field Tests

PrecisionRifleBlog.com Cal Zant Muzzle Brake Test Noise Level Decibels Suppressor

A while back, Cal Zant at PrecisionRifleBlog.com did a big muzzle brake comparison test. Along with measuring recoil reduction, Cal’s team recorded sound levels in PRB’s exhaustive muzzle brake field test. In the PRB archives you’ll find comprehensive muzzle brake sound test results, with hard data on 20 different muzzle brakes.

Sound can be a tricky subject, but Cal Zant, the editor of PrecisionRifleBlog.com, presents everything an informed shooter should know about muzzle brake noise in a straightforward and practical way. Most sound tests are measured from the side of the muzzle, in accordance with mil-spec standards, and Cal did that. But he also measured the sound level of each brake from behind the rifle, closer to the shooter’s position. This provides a more accurate indicator of the actual sound levels firearms operators will encounter while shooting.

Muzzle brakes ARE really loud — that’s something most active shooters have observed. But this study finally gives us some hard data and makes objective comparisons. The difference between brakes was quite significant. Some brakes were ear-splitting — more than twice as loud as other brakes tested.

As a bonus, Cal also provides data on how the new Ultra series suppressors from Thunder Beast Arms Corp (TBAC) compare in terms of sound level behind the rifle.

Check out the Test Results: http://precisionrifleblog.com/2015/08/07/muzzle-brakes-sound-test.

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