4140, 4150, 316, 17-4, 6061, 7075-T6 — What is the significance of these numbers? No, they’re not winning lottery numbers. These are all designations for metals commonly used in firearm and barrel construction. 4140 and 4150 are carbon steels, with 4150 often used in mil-spec AR15 barrels. 316 and 17-4 are grades of stainless steel. 316 is “marine grade” stainless, while 17-4 has 17% chromium and 4% nickel. 17-4 is a harder steel used in barrels and receivers. 6061 and 7075-T6 are aluminum alloys. 6061 is “aircraft grade” aluminum, often used for rings and trigger guards, while 7075-T6 is a much stronger, heat-treated aluminum commonly used in AR15 uppers.
You can learn about all these metals (and more) in the online archives of RifleShooter magazine.
Written by Patrick Sweeney, RifleShooter’s Guide to Gun Metal summarizes the primary types of steel and aluminum used in gun and barrel construction. Sweeney explains the nomenclature used to define metal types, and he outlines the salient properties of various steel and aluminum alloys. This is a useful resource for anyone selecting components or building rifles. We recommend you print out the page, or at least bookmark it.
Metals by the Number
The number system for steel classification came from the auto industry. Sweeney explains: “The Society of Automotive Engineers uses a simple designating system, the four numbers you see bandied about in gun articles. Numbers such as 1060, 4140 or 5150 all designate how much of what [elements are] in them. The first number is what class—carbon, nickel, chromium, and so forth. The next three numbers [list other elements in the alloy]. 4140, also known as ordnance steel, was one of the early high-alloy steels. It has about 1 percent chromium, 0.25 percent molybdenum, 0.4 percent carbon, 1 percent manganese, around 0.2 percent silicon and no more than 0.035 percent phosphorus and no more than 0.04 percent sulphur. That leaves most of it, 94.25 percent, iron.”
Aluminum Alloys
Numbers are also used to differentiate different types of aluminum alloys. Sweeny writes: “Aluminum is used in firearms in two alloys: 7075 and 6061. 6061 is commonly referred to as ‘aircraft aluminum’ and has trace amounts of silicon, copper, manganese, molybdenum and zinc. 7075 is a much stronger alloy and has markedly larger amounts of copper, manganese, chromium and zinc.” 7075 Aluminum has significantly better corrosion resistance, and that’s why it is used for AR receivers. The “T6″ you often see appended to 7075 refers to a heat-treating process.
Aluminum (or “Aluminium” in the UK) is a chemical element in the boron group with symbol Al and atomic number 13. It is a silvery-white, soft, nonmagnetic, ductile metal. Aluminum is the third most abundant element, and the most abundant metal, in the Earth’s crust. (Wikipedia)
To learn more about the metals used in your firearms’ barrels, rings, receivers, and internal parts, read Sweeney’s article in RifleShooterMag.com. Taking the time to read the article from start to finish will expand your knowledge of metal properties and how metals are chosen by manufacturers and gunsmiths. CLICK to Read Guide to Gun Metal.
Story Tip by EdLongrange. We welcome reader submissions. Aluminum Alloy chart courtesy AluminiumDesign.net.
Share the post "Guide to Gun Metals — What You Need to Know"
Enjoy the Shooting Sports USA Archives
With winter coming, many Americans will soon be spending more time indoors at home. For some folks that means long sessions in front of the boob tube. Here’s a better idea — there’s a vast resource of great gun-related content available online for FREE. Check out the Shooting Sports USA Articles Archive. SSUSA maintains a vast digital library with hundreds of articles going back to June 2009.
It’s easy to find back issues of Shooting Sports USA magazine. Here’s how: First, navigate to the SSUSA Online Issue. Then click on the “ARCHIVES” icon in the upper right area (indicated with red arrow). When you click on “ARCHIVES”, a window will open with a selection of Shooting Sports USA magazine covers/dates in a vertical column. The most recent issue (November 2021) will appear at the top. You can then scroll down — use the vertical scroll bar to go from November 2021 (the latest issue) all the way back to June 2009. Click any issue cover to read.
How to Find and Save Articles
To search back issues, select “MORE OPTIONS” from the toolbar (top left). Then click the “SEARCH” button. When that opens, select either “Search Archives” for ALL back issues or “Search Only this Issue”. When you’ve made your choice, enter your search term(s). For example, you can search for “Camp Perry” or “Palma” or “F-Class Championship”. You can also save any archived issue as a PDF for viewing offline. Just click “SAVE” to download the article you’re currently viewing/reading.
Read Sample Articles
Here are a couple of our favorite SSUSA feature stories from recent years. There are hundreds of other informative articles worth reading.
Yes, the type of targets you use can make a difference during load development and training — helping you align your crosshairs, estimate group size visually, and also record load data/gun type. Here we provide selection of FREE printable precision and training targets. This selection includes popular load development targets AccurateShooter created as well as other useful grid targets. You can download ALL these targets as PDF files and then print them out on 8.5×11″ heavy paper.
AccurateShooter.com offers a cool page with over 50 FREE downloadable targets. You’ll find all types or FREE targets — sight-in targets, varmint targets, rimfire targets, bullseye targets, tactical targets, load development targets and more. CLICK HERE for all our free targets, including our LOAD DEV target.
We created the above target a decade ago. Since then it has been used by tens of thousands of shooters. It has proven very popular as a load development target, since all your load data fits neatly in the boxes under each target. In fact this target is being employed by both rifle-makers and barrel-makers (including Criterion) to test their products. The target was designed for aiming efficiency. The diamonds have 1/2″ sides and you can align your cross-hairs on the horizontal and vertical lines. It is a clean design that is easy to see even at 200 yards with a 20X scope. When we test, we usually crank in a little elevation, setting the point-of-impact higher, so that our shots fall in the gray circles. That way you leave the squares intact for precise aiming.
Versatile Targets with Multiple Aiming Points
We use the two targets below for load development and precision practice. For the left target, use the corners of the diamonds to align your cross-hairs precisely. The circle dot target (on the right) can also be used for informal rimfire competition at 50 yards. Right-Click Each Target to Download Printable PDFs.
Know-Your-Limits Target for Rimfire Training & Fun Matches
Here’s a rimfire training target with “big to small” target circles. Start with the largest circles, then move to the smaller ones in sequence. This systematic drill provides increasing challenge shot-by-shot. Novices often are quite surprised to see their accuracy improve as they move from bigger to smaller aiming points. That provides positive feedback — always a good thing.
Right Click and “Save as” to download printable PDF versions of target.
RED Center Pistol Target
Here’s a NRA-type target for pistol shooting. The bright red center helps when shooting indoors because well-placed bullet holes are much more visible. This target includes data entry boxes to record gun type, score, and load data. This is one of many good free targets available at Targets4free.com.
Share the post "FREE Printable Targets for Load Development and Training"
Sightron is now offering “instant holiday savings” on two premium riflescope lines, the SIII Precision Long Range (PLR) models as well as SVIII FFP tactical scopes. These are high-end optics, ready for competition. Save $250 on the SIII PLR optics and a whopping $800 on the SVIII. It is rare to see these kind of instant discounts on high-end optics.
Sightron’s 2021 holiday sales event kicked off on November 1st and runs through December 31, 2021. Visit an authorized Sightron retailer or online vendor to take advantage of these big discounts. For more information on the holiday sale visit: Sightron.com/collections/holiday-instant-savings.
Sightron SVIII ED $800 Instant Savings
Now get an instant savings of $800 off the very impressive new SVIII 5-40x56mm ED optic with low-dispersion ED lenses. This illuminated First Focal Plane (FFP) riflescope was designed for long range target shooting, tactical competitions, and hunting. The scope provides 20 MILS of windage and 40 MILS of elevation with 0.1 Mil tactical knobs.
Sightron SIII $250 Instant Savings
SIGHTRON is now offering a $250 instant rebate off all SIII Precision Long-Range (PLR) Series scopes. These SFP riflescopes are optimized for long-range benchrest, silhouette, and F-Class competition and general precision target shooting. Models include the 6-24x50mm, 8-32x56mm, and 10-50x60mm. The 10-50X optic (shown below) is a top choice among long-range benchrest shooters and F-Class competitors.
Let’s face it, AR-platform rifles run dirty, at least compared to typical bolt-action rifles. The AR-15 works by piping gas from the barrel back into the bolt carrier, causing the bolt to unlock and the carrier to move the bolt backward. The “exhaust gas” from the barrel contains soot and carbon. The carbon will form hard deposits on the bolt. In addition, the carbon can combine with lube on the bolt carrier to make a nasty, paste-like sludge. This can be particularly problematic when the black paste pollutes the ejector and extractor recess.
This Editor has inspected dozens of ARs over the years. Other than mag-related malfunctions, the most common cause of AR cycling problems I found was oily gunk in the extractor and ejector areas. Many AR owners overlook these critical areas. Look at an AR that hasn’t been cleaned properly and you’ll probably find black gunk (and small brass shavings) in the ejector and extractor recesses.
If you want to keep your black rifle running smoothly and reliably, you must clean it regularly and follow the correct maintenance procedures. Here are three videos that explain how to properly disassemble and clean AR-platform rifles. And then they cover the essential lubrication ARs need to run reliably.
Take-Down and Full Cleaning of AR15 by Jerry Miculek
Here ace shooter Jerry Miculek takes down and cleans an AR-platform rifle belonging to his daughter Lena. This is a good video because Lena’s rifle was “run hard and packed up dirty” so you can see where carbon and grease build up. This 35-minute video is very thorough. Jerry is one of the nation’s top action carbine shooters, so listen carefully to his advice on cleaning and lubrication.
General AR-15 Maintenance and Lubrication
There are various schools of thought on AR lubrication. Some guys like to run “wet” with lots of CLP, while others choose to focus lubrication on the key spots that receive the most friction and wear, such as the contact point for the bolt carrier. We do advice check the ejector recess and extractor spring recess frequently as gunk can get in there, causing malfunctions. Here is a good video from Pew Pew Tactical — a 7-minute guide to cleaning and lubricating AR-platform rifles. This shows important details for both the upper and the lower.
How to Clean Your AR-15 Bolt Carrier Assembly
This video offers very specific advice on the bolt carrier group, which receives the dirty gas directly from the barrel. Be sure to check the extractor and ejector recesses. That’s where old lube, brass shavings, and carbon accumulate. Follow the directions in this video for lubrication, and don’t over-lubricate the bolt carrier — that will only capture more carbon.
Share the post "AR-15 Rifle Maintenance — How to Keep Your AR Running Right"
Every firearms owner should have some basic first-aid/trauma training. And now during hunting season, hunters should be prepared to deal with injuries in the field. And bad things can also happen at the range, even if that’s just a blown primer, or a richochet off a metal target. That’s why all shooters should always wear ear and ear protection, and be PREPARED for situations requiring emergency first aid.
Thankfully, there is a way shooters can get emergency trauma training for FREE. The folks at Mountain Man Medical offer a FREE Emergency Trauma Course. This 100% FREE online course, entitled “Emergency Trauma Response” (ETR), consists of a 13-module training program conducted via a series of web-hosted videos. It can benefit anyone who wishes to be better prepared for traumatic medical emergencies.
Online Course Description — Module Subjects
“Emergency Trauma Response” (ETR) is a comprehensive training program for to help person become better prepared to deal with massive trauma. Building off the popular “Stop The Bleed” program, the online ETR course goes above and beyond to ensure the student has the practical knowledge to use emergency products and gear when dealing with a wide variety trauma emergencies. Of course, in any serious emergency, professional medical assistance (EMTs and First Responders) should be summoned immediately whenever that is feasible.
The Mountain Man Medical ETR Course Features 13 Modules:
1. Trauma Medicine and Combat Mindset
2. The Gear Of A Medic
3. Vital Signs and Anatomy
4. Intro to MARCH
5. Massive Hemorrhage
6. Airway
7. Respirations
8. Circulation
9. Hypothermia and Head Trauma
10. Reassessment
11. Other Injury Types
12. Practical Tourniquet Exercises/Solutions
13. Your Role As A Medic
Army Medic Commentary: This Editor’s brother was a U.S. Army combat medic in Viet Nam. He received months of special training before being deployed. He told me this online ETR course provides valuable information, but one should always summon qualified medical professionals when presented with serious trauma. But when that is not possible, immediate on-the-spot correct assistance can save lives or prevent further injury.
Share the post "FREE Online Emergency Medical Training Course"
With over 240 shooting-related videos, the Alabama Arsenal YouTube Channel is a remarkable resource. This video channel provides detailed field tests of tactical-type rifles, ARs, and pistols. The testers have access to some very impressive ranges, and many of the tests are far more thorough than you’ll typically find with most gun magazines and gun-centric YouTube channels. For example, Alabama Arsenal has a series of 1000+ round pistol test videos. These are well worth watching if you are considering purchase of a defensive handgun.
Today we showcase three rifle videos, two centerfires, and the CZ 457 .22 LR in two styles. After these rifle videos, you’ll find two very interesting technical videos regarding suppressors. The first tech video shows how to install suppressors, while the second video explores how suppressors can affect muzzle velocity.
Barrett MRAD .300 PRC at 2200 Yards — Extreme Long Range
Here’s a rugged tactical rifle put to the test at Extreme Long Range. This video, featuring a Barrett MRAD chambered for the .300 PRC cartridges, features accuracy testing out to 2200 yards (1.25 miles). There is some good drone footage covering the long path to the target. The shooter noted that the bullets fired from his .300 PRC “go sub-sonic somewhere between 1800 and 1900 yards”, creating additional ballistics challenges at this yardage.
Savage 110 Elite Precision for PRS Production Class
In this video AA’s team reviews the Savage Elite Precision Rifle with MDT ACC Chassis. Retailing for about $1750.00, this is one of the better production class options for PRS and NRL competition. Guns America Digest did a full review of this rifle, and was quite impressed.
CZ 457 Varmint Precision Trainer and Chassis
In this video, Alabama Arsenal compares two versions of the popular CZ 457 rimfire rifle, a great choice for the NRL22 tactical game. The test compares the CZ 457 in a Manners composite stock with a CZ 457 version in a Varmint Precision aluminum chassis. Right now basic CZ 457 rifles start at about $400.00, with the Varmint Precision Chassis models running $845-$900.
Informational Videos about Rifle and Pistol Suppressors
Alabama Arsenal regularly tests its firearms with suppressors. Over the course of time, the testing team has leaned much about modern sound moderators, comparing features and learning how to install and maintain quality suppressors. These two videos offer valuable information on suppressors.
Silencer School Pt. 3 — Mounting Basics
Field Testing — Do Suppressors Change Bullet Velocity
Want to see more content like this? Here are LINKS…
Alabama Arsenal has 240+ videos on its YouTube channel. In addition, you’ll find dozens of firearms photos and other shooting-related content on Alabama Arsenal’s social media pages: Facebook; Instagram; and Twitter. You can support the Arsenal’s gun testing by subscribing to the Alabama Arsenal’s PATREON Page.
Share the post "Video Showcase: Alabama Arsenal Rifle Tests & Suppressor Info"
Are you planning to purchase or sell a gun? Or perhaps you want to give one to a family member. Maybe you want to transfer a gun to a friend out of state. These are all situations that demand you understand the law before you buy, sell, or transfer a gun. Thankfully the NRA Blog has a series of helpful articles that can guide you through firearms transfers and transactions.
Do note that laws on private transfers vary from state to state. Also, some of these articles are a few years old. Laws do change, typically becoming more restrictive. You should carefully review current laws in your state before buying/selling any firearm. For a summary of state gun laws, we recommend Attorney Bryan Ciyou’s Gun Laws by State 2021 reference book.
Here are five articles providing key facts you need to know.
Click each title to read the specific article.
IMPORTANT: All five of these articles reference general rules that apply nationally and in MOST states. However, some states, such as California, New Jersey, and New York (and others) have very special rules and regulations on gun transfers. If you have ANY questions about gun transfers in your state/region, you should consult an attorney familiar the laws of YOUR state and municipality.
Share the post "Firearms Transfers — Gifts and Sales — What You Need to Know"
At the request of our readers, we provide select “Deals of the Week”. Every Sunday afternoon or Monday morning we offer our Best Bargain selections. Here are some of the best deals on firearms, hardware, reloading components, optics, and shooting accessories. Be aware that sale prices are subject to change, and once clearance inventory is sold, it’s gone for good. You snooze you lose.
1. KYGUNCO — Savage Axis II Precision Rifle, $699.99
⏺ Good entry-level PRS rifle that also works for hunting
The Savage Axis II, on sale for $699.99 at KYGUNCO in 6.5 Creedmoor or .308 Win, offers good performance for the price. It can serve as a competent starter rig for PRS/NRL competition, and also function well for hunting, with a weight of 9.9 lbs without scope. The Savage Axis II combines an accurate barreled action with a nice MDT chassis with adjustable comb and adjustable length-of-pull. For more info, read the very thorough Savage Axis II review in Guns America Digest.
2. Scopelist (EuroOptic) — Nightforce Clearance SALE
⏺ Save HUNDREDS on Nightforce ATACR and other NF optics
Right now ScopeList (a EuroOptic.com partner) is running a big Nightforce Clearance Sale. You can save up to $515 dollars on demo Nightforce optics with full factory warranty. Chose from the popular ATACR series or the advanced NX8 model with MOA or MilRad clicks. There are a variety of good FFP and SFP Nightforce optics on sale now.
3. Bass Pro — Garmin GPSMAP 64SX, $219.99
⏺ $130 Savings on full-featured modern GPS with TopoActive Maps
This rugged handheld Garmin GPSMAP boasts reliable satellite connectivity with Altimeter and Compass features. This 64SX model also comes pre-loaded with TopoActive Maps, which are great for backcountry hunters. This water-resistant design features button operation with a sun-readable 2.6″ screen.
4. Midsouth — SIG Sauer Optics Sale
⏺ SIGnificant savings on BDX scopes, BDX rangefinders, and red dot optics
SIG Sauer makes excellent products with notable features. SIG BDX Laser Rangefinders can communicate (via Bluetooth) to BDX series scopes. This allows calculated hold-over points to appear in the scope reticle. In addition, the LRF communicates with Ballistics Apps on your mobile device. Right now Midsouth has SIG Sauer optics products on SALE including scopes, rangefinders, Red Dots, and binoculars. Along with BDX scopes, SIG’s Whiskey5 SFP scopes are on sale. Many items also qualify for FREE Shipping.
5. Palmetto SA — AR15 Complete Stealth Lower (Blem), $139.99
⏺ GREAT deal on complete lower with full trigger group and adjustable stock
With changes to Federal law looming on the horizon, it may be wise to get your Black Rifle now. Here is a great deal on a complete lower with stock. The PSA AR-15 MOE Stealth Lowers include full, installed trigger group, plus a nice, adjustable MagPul MOE buttstock. The price is just $139.99 because these “blem” lowers may have a small scratch or blemish somewhere. For the same $139.99 bargain price, chose the Black Stealth Lower or the Flat Dark Earth Model as shown above.
6. MidwayUSA — Hoppes Gun Vise and Cleaning Kit, $39.99
⏺ Good basic gun vise at great price with bonus cleaning kit
The Hoppe’s Gun Vise is a good basic support for working on your firearms. Clamping brackets in the front and rear hold your rifle or shotgun securely without scratching. The vise is made out of a durable, chemical resistant polymer and has multiple compartments for your cleaning chemicals, tools, and accessories. Included with this vise is a 12-piece Cleaning Kit for rifles, pistols, and shotguns. Features include: Dual lockable no-scratch brackets, multiple compartments for tools, and adjustable feet.
7. Natchez — Bushnell Optics Sale, Save 35%
⏺ Great prices on hunting scopes and Red Dot optics
Hunting season is in full swing. If you need an affordable optic for your hunting rifle, check out the Bushnell Optics Sale at Natchez. A variety of scopes are 35% off. In addition, there are great prices on Red Dots you can use on a shotgun, pistol, or tactical rifle. And prices have been slashed on Bushnell binoculars and spotting scopes as well. Act soon — these Natchez sales don’t last long.
8. Midsouth — Forster Accu-Ring, $14.99
The new Forster Accu-Ring has precise markings so you can set your sizing dies with extreme precision in your press. The anodized ring has laser-etched precision markings in .001″ increments. This allows you to more easily set the amount of sizing and shoulder “bump” you get when you move a die up or down in your press. In addition, if you have a conventional seating die without a micrometer adjustment, this new Forster Accu-Ring can help you achieve more precise bullet seating. SEE Ultimate Reloader Review.
⏺ Owners say it is sharp with good features for price
This Sawback Bowie spring-assisted folding knife, just $9.70 on Amazon, has a 3.5″ blade. There is a curved cutting edge with a serrated section near the handle. Actual purchasers state: “This knife is very well made with a tight feel. No play at all. The assisted open is excellent [and] they come very sharp too”, and “This is a good quality knife. It’s solid and a bit heavy, really good looking and comes pretty sharp. Overall its a great knife.”
⏺ Quality name-brand shooting eyewear — buy multiples at this price
Every shooter needs eye protection EVERY TIME you go to the shooting range. Right now Midsouth has the good Radians clear Lens Outback Shooting Glasses for just $5.88. These ANSI Z87.1 Radians Shooting Glasses provide 99.9% UVA/UVB protection with the coated lenses. These offer excellent wrap-around protection and are fairly light and comfortable. A handy neck cord is included. With this low $5.88 price, you can buy 3 or 4 sets and keep spares for yourself and your shooting buddies.
Share the post "Bargain Finder 319: AccurateShooter’s Deals of the Week"
One of the most important aspects of precision reloading is setting the shoulder bump during the full-length (FL) sizing process. You want the amount of “bump” to be precise and identical for every loaded round. However, when you switch brands of brass you may need to change the die position to get the desired bump and case body sizing. And even with the same brand of brass, you may find that you need to adjust your FL die as the number of brass load cycles increases. Brass that has been fired many times will behave differently than new or near-new brass.
Also, even with the same cartridge type, brass loaded for a semi-auto rifle may need more bump than brass fired in a bolt gun. For example, with .223 Rem ammo, you’ll normally want to push the shoulder back farther if the ammo will be shot in a AR15 as opposed to a bolt-action rig.
So how do you make all these needed adjustments for your full-length dies? You can move a conventional locking ring up and down, but that can be a tedious, trial-and-error process. Some guys use shims in one-thousandth intervals, but that still requires taking your dies in and out of the press. Well there is a better way now…
PMA Tool Micro-Die Adjuster
Wouldn’t it be great if you could precisely adjust your FL die up and down in half-thousandth increments, with a simple indexed click. That is now possible with products offered by PMA Tool and Whidden Gunworks. PMA Tool offers a Micro-Die Adjuster that replaces your existing lock ring and can be used with nearly any 7/8-14 full length sizing die. The engraved marks correspond to approximately .001″ of shoulder bump adjustment. Splitting the engraved marks is therefore approximately equal to .0005″ (half a thousandth). Users love this product, saying it adds precision and saves time.
Whidden Click-Adjustable FL Sizing Die System
Whidden Gunworks offers a complete click-adjustable FL sizer die with a special, indexed ring. With Whidden’s patented Click Adjustable Sizer Die system, the die and lock ring work together to allow rapid, precise bump adjustments. One click changes the bump .001″. It’s simple and fast. Included with the Click Adjustable Sizer Die is a shoulder bump gauge. John Whidden explains:
“There has become a need for an easier way to adjust the sizer die properly. Until now there have been few options other than trial and error to get the shoulder setback correct. Anyone who has done this can attest that it’s a slow and imprecise job! Our die and lock ring work together to give the user a clicking feel to the adjustment. Each click moves the shoulder bump .001” so you can easily find the exact shoulder bump that you desire.” — John Whidden
New Universal Click Adjustable Lock Ring for Standard Sizing Dies
Whidden Gunworks also now offers a Universal Click Adjustable Lock Ring for all brands of standard sizing dies. If you don’t need a complete die, this special Lock Ring provides the functionality of the Whidden click-adjustable sizing dies for the standard 7/8-14 dies you already own. Lock Ring Instructions PDF.
John Whidden explains: “With our Universal Click Adjustable Lock Ring (Patent No: 10,393,488) you can instantly turn your sizer die into a Click Adjustable Die. Our ring works with any 7/8 OD sizer of any brand with adjustable shoulder bump. The inner and outer ring can rotate independently of each other. Each click is metered in true 1 thousandths adjustment and has .100″ total available travel. Those loading for two rifles with different headspace can easily optimize the shoulder bump for each rifle.”
General Tips on Setting Up and Using Sizing Dies
Share the post "Click-Adjust Die Options from PMA Tool and Whidden Gunworks"
Photo 1: Three Near-Equal-Weight 7mm Bullets with Different Shapes
TECH TIP: Bullets of the same weight (and caliber) can generate very different pressure levels due to variances in Bearing Surface Length (BSL).
Bullet 1 (L-R), the RN/FB, has a very slight taper and only reaches its full diameter (0.284″) 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!
This article from the USAMU covers an important safety issue — why you should never assume that a “book” load for a particular bullet will be safe with an equal-weight bullet of different shape/design. The shape and bearing surface of the bullet will affect the pressure generated inside the barrel. This is part of the USAMU’s Handloading Hump Day series, published on the USAMU Facebook page.
Beginning Handloading, Part 13:
Extrapolating Beyond Your Data, or … “I Don’t Know, What I Don’t Know!”
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.
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. These 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 length (BSL) is often overlooked when considering maximum safe powder charges and pressures. In photo 1 (at top), note the differences in the bullets’ appearance. All three are 7mm, 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.
Bearing Surface Measurement Considerations
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 deceiving.
Photo 2: The Perils of Measuring Bearing Surface Length with Comparators
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.]
Share the post "TECH TIP: Bullet Bearing Surface Length Can Affect Pressure"
You can learn about all these metals (and more) in the online archives of RifleShooter magazine.
