As an Amazon Associate, this site earns a commission from Amazon sales.











January 10th, 2023

Five Cool Tools to Measure Shoulder Bump on Your Cases

shoulder bump headspace gauge comparator tool whidden manson

The Tactical Rifle Shooters Facebook Group recently showcased tools used to measure case headspace before and after “bumping” the shoulder. After a case is fired, hand-loaders who full-length size their cases will typically bump the shoulders back anywhere from .001″ to .0035″, depending on the rifle and application. With our 6mmBR and Dasher cases we like about .0015″ bump.

You want the amount of case sizing and bump to be the same for all your brass. To ensure uniformity, it makes sense to measure your cases before and after the FL sizing process. When we have time, we check every case. Other folks will simply check the first 3-4 cases coming out of the FL sizing die to ensure the FL die setting is correct and delivering desired headspace/bump.

1. Whidden Gunworks Shoulder Bump Gauge

shoulder bump headspace gauge comparator tool whidden manson

There are a variety of tools that can be used to measure shoulder bump. Our favorite is a special cartridge-specific bushing made by Whidden Gunworks. The Whidden Shoulder Bump Gauge enables you to adjust your sizing die to the desired measurement. The bump gauge is attached to your calipers with a set screw and determines the measurement from the base to the shoulder of the case. The photo below, from Tactical Rifle Shooters, shows the Whidden Bump Gauge for the .375 CheyTac cartridge.

2. Dave Manson Vertical Comparator with Dial Read-Out

shoulder bump headspace gauge comparator tool whidden manson
Background image courtesy Tactical Rifle Shooters; inset photo from Manson Precision Reamers.

Dave Manson states: “This tool was designed to make life easier for the advanced shooter and re-loader by allowing precise measurement of ammunition, case, and chamber headspace. With this information, the re-loader will be able to fine-tune clearances and fits between his ammunition and chamber, with resultant improvements in accuracy and case life.” The functions of the Manson Comparator are:

1. Measure headspace of factory or reloaded ammunition
2. Quantify chamber headspace by measuring headspace of a fired case
3. Ensure minimal shoulder set-back when setting up re-loading dies
4. Compare base-to-ogive length to ensure consistent bullet-to-rifling relationship.

In addition to the Dial Indicator and Stand, the $150.00 Vertical Comparator is supplied with multiple Datum Blocks of precise length and inside diameter (.3300″/.3750″/.4000″/.4375″). MORE INFO HERE — Catalog page 29.

3. Hornady L-N-L Headspace Comparator System

shoulder bump headspace gauge comparator tool whidden manson

Hornady’s Lock-N-Load Headspace Comparator system is easy-to-use and handy. You can get a kit with Red bushing-holder body and 5 bushings for $43.43 at Midsouth. Hornady explains: “The Lock-N-Load® Headspace Comparator… gauge measures variations in brass before and after firing or re-sizing. It allows for headspace comparison between fire-formed brass and re-sized brass.” IMPORTANT: Hornady states: “To determine the proper bushing diameter for your cartridge, simply add the neck diameter and the shoulder diameter and divide that number by two. Use the bushing closest to that number.” Hornady offers five: .330″, .350″, .375″, .400″, and .420″.

One tip — We have found the Hornady gauges may vary a little from unit to unit even with the same nominal size. If you have more than one gauge for the same cartridge, test each on your brass — you may then note a slight difference in your bump measurements. Mark one and use that consistently. There is also an Anvil Base Kit that mounts to the opposite blade on the caliper. This provides a more stable surface for the base of your case.

4. L.E. Wilson Case Gage Depth Micrometer

shoulder bump headspace gauge comparator tool whidden manson

If you are looking for precise “bump” measurements without having to mess with calipers and clamp-on gauge blocks, you may want to consider the L.E. Wilson Case Gage Depth Micrometer (currently $130.00). This takes very precise, repeatable measurements, but you need to know your starting point. The manufacturer explains: “Every reloader should know exactly how much your Full Length Sizing Die is pushing back the shoulder. With the NEW Case Gage Depth Micrometer you can do just that! It has never been easier to measure you cases headspace before and after sizing. The Depth Mic allows you to slip the micrometer perfectly over the top of the Gage with your case inserted into the Gage and take a measurement. Micrometer has graduations of .001″. The Case Gage Depth Micrometer is set to a zero of .100″ on the scale at our factory. Because of differences in ‘feel’ and temperature, we include a the Gage Block for you to test Zero and to adjust if necessary.”

5. Pistol Brass Case DIY Bump Gauge

Last is a “field expedient” set-up if you do not have any of the comparator tools shown above. A sized .45 ACP case (or other suitable pistol case) can be used to measure shoulder bump. The mouth of the pistol case sits on the shoulder of your rifle cartridge brass.

Make sure the .45 ACP case is trimmed square and that it is round. We recommend you first run it through an expander, then size it, trim it and chamfer. Next, take the .45 ACP case and slip it over the neck of a fired, unsized rifle case with the primer removed. Align the two cases between the jaws of your calipers and note the length from rim to rim (See left photo below).

OK, now you have the length for a fired rifle case BEFORE sizing. Next, take a full-length sized rifle case (without primer) and do the same thing, placing the .45 ACP case over the neck of the FL-sized case (Right Photo). The difference between the two numbers is the amount of “bump” or set-back you are applying to the shoulder. Here the difference is .0015″. The amount of bump you need varies with your chamber and your load, but .0015-.002″ is a good initial setting.

Permalink Bullets, Brass, Ammo, Gear Review, Reloading, Tech Tip No Comments »
January 10th, 2023

The Rifle That Shot 3000 Bullseyes — Sam Moore’s Win Model 52

Samuel Sam Moore Calvin Coolidge 3000 Bullseye NRA Museums

Here’s a rifle that earned a Presidential medal and a visit to the White House. This rifle has a unique heritage, having been used to shoot 3000 consecutive bulleyes in a single day. The year was 1926 and a high school shooter named Sam Moore hoped to set a record. With his trusty Winchester Model 52 rifle in hand, Moore fired 3,000 rounds downrange, only stopping when his rifle became too hot to hold and daylight was fading fast. But he had fired 3,000 consecutive bullseyes in NRA Junior Rifle competition (target at 50 feet). The event, which set a world record, received national attention.

Samuel Sam Moore Calvin Coolidge 3000 Bullseye NRA MuseumsMoore was summoned to Washington, DC on April 26, 1926 to meet President Calvin Coolidge. At the White House, President Coolidge met the young marksman and presented Moore with a gold medal. The engraving on the back reads: “Presented to L.S. Moore by the President of the United States [on] behalf of the National Rifle Association. Junior Rifle Corps World Record — 3000 — consecutive bullseyes.”

Editor: Consider how times have changed. In 1931 the U.S. President was proud to honor a junior marksman for a great achievement. Today the White House condemns everything gun related. And the State of California has passed legislation imposing $25,000.00 fines for promoting youth marksmanship (AB 2571).

Marksman Moore Went to the U.S. Naval Academy and Served in WW II
After high school, Sam Moore earned admission to the U.S. Naval Academy, and graduated in 1931. Later, Moore helped develop the Fairbairn-Sykes fighting knife, served in WW II as a USMC aviator, and maintained his interest in shooting until his passing in 1982. Moore’s rifle and engraved gold medal were donated to the National Firearms Museum by his son David.

Photos and story from NRA Museums Facebook Page

Permalink Gear Review, News, Shooting Skills No Comments »
January 10th, 2023

Eye on Optics — How Riflescopes and Spotting Scopes Work

Accurateshooter.com optics rifle scope Swarovski

For many years, the Swarovski Optik website featured a blog with interesting technical articles. (Unfortunately some of these articles have been taken offline.) In the “On Target” series of blog stories, Swarovski provided a handy explanation of how optics systems work, with exploded diagrams of rifle scopes, spotting scopes, and binoculars. We’ve reproduced the key diagrams here. CLICK HERE for Swarovski On Target Archive.

Accurateshooter.com optics rifle scope Swarovski

Scope Terminology
Focusing Lens
The focusing lens is an adjustable lens inside the optical system for focusing the image at different distances…. In the case of rifle scopes, apart from focusing, the focusing lens also facilitates parallax compensation.

Objective Lens
The objective lens is the optical system’s front lens group facing the object and operates like a converging lens. Its purpose is to display an image which, at the image plane, appears upside down, laterally transposed and reduced, and which is subsequently displayed correctly again by the reversal system.

Diopter Adjustment
For rifle scopes, the reticle can be focused using the diopter adjustment on the eyepiece, thereby correcting any visual impairment. [Editor’s Note: Movable eyepiece diopter adjustment is not offered on all rifle scopes. It is a useful feature on Swarovski and other premium scopes. This allows shooters who need eyeglasses to get a sharply focus image even without wearing corrective lenses. Of course shooters should always wear ANSI-certified eye protection. With the diopter, folks who need correction can use inexpensive, non-Rx safety eyewear instead of expensive prescription safety glasses.]

Reversal System
The purpose of the reversal system is to reverse the image by means of prisms in binoculars and telescopes, and lenses in rifle scopes….The lens reversal system is needed in rifle scopes to control the variable magnification and move the exit pupil[.]

Resource tip by EdLongRange. We welcome reader submissions.
Permalink - Articles, Optics, Tech Tip No Comments »