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September 6th, 2023

Hunters — Determine Your Cold Bore Point of Impact (POI)

USAMU Cold Bore Video Browning X-Bolt Hell's Canyon Cold-bore zero
Photo of Browning X-Bolt rifle courtesy Browning.

Hunting season is coming up, so it’s time to get your rifle squared away. You’ll want to zero that rifle before the hunt, and you need to know how your shots will impact with a cold barrel.

Commonly, hunters won’t have the ability to fire one or two fouling shots before heading out on a hunt. Therefore it’s important that a hunter understands how his rifle shoots with a “cold bore shot”. Both the point of impact (and possibly velocity), may be different with a cold bore than with a barrel that has been warmed and fouled with a series of shots. In this video from the U.S. Army Marksmanship Unit (USAMU), you’ll learn how to determine your cold bore point of impact (POI) for a rifle that just been cleaned, as well as the cold bore POI with a barrel that has already been “fouled in”.

SGT Joe Hein of the USAMU shows how to plot cold bore POI with both a clean bore and a fouled bore. Note that the “cold bore” shot from a fouled barrel was closer to the follow-up shots than the cold bore shot from a clean barrel. This is typical of many factory barrels. SGT Hein provides a simple way to understand your rifle’s cold bore performance. Hein’s advice can keep you from missing that long range shot at that big buck on opening day. A little time spent on the range before that critical first shot will help ensure you have meat in the freezer this season.

Permalink Hunting/Varminting, Shooting Skills No Comments »
June 7th, 2023

How Ammo Temperature Affects Velocity, Pressure, and POI

Sierra Bullets Ammunition Ammo temperature temp test hot F-Class Ammo cold
In this .308 Win test, 70° F ammo shot 96 FPS slower than ammo heated to 130.5° F. And the 130.5° ammunition was 145 fps faster than ammo taken right out of the freezer (at 25.5° F). That’s a huge difference…

summer heat ammunition temperature velocitySummer Solstice is just two weeks away, so most parts of the country will soon be encountering peak summer heat. Some ranges in the Western states have already recorded temperatures well over 100 degrees F during matches. When dealing with extreme summer heat, you should make a serious effort to keep your ammo at reasonable temperatures. When possible, keep ammo in a cooler in the shade.

Never leave boxes of ammo out in the hot sun. Even with powders advertised as “temp stable” you can see significant velocity increases when ambient temps reach 90 degrees and above. This article explains how temperature extremes (both hot and cold) can alter bullet velocities. The velocity differences between very cold ammo and very hot ammo can be very large, as this article explains.

EDITOR’s NOTE: The Sierra tester does not reveal the brand of powder tested here. Some powders are much more temp sensitive than others. Accordingly, you cannot extrapolate test results from one propellant to another. Nonetheless, it is interesting to see the actual recorded velocity shift with ammo temperature variations in a .308 Win.

Written by Sierra Chief Ballistician Tommy Todd
This story originally appeared in the Sierra Bullets Blog
A few weeks ago I was attending the Missouri State F-Class Match. This was a two-day event during the summer and temperatures were hot one day and hotter the next. I shot next to a gentleman who was relatively new to the sport. He was shooting a basically factory rifle and was enjoying himself with the exception that his scores were not as good as he hoped they would be and he was experiencing pressure issues with his ammunition. I noticed that he was having to force the bolt open on a couple of rounds. During a break, I visited with him and offered a couple of suggestions which helped his situation somewhat and he was able to finish the match without major issues.

He was shooting factory ammunition, which is normally loaded to upper levels of allowable pressures. While this ammunition showed no problems during “normal” testing, it was definitely showing issues during a 20-round string of fire in the temperatures we were competing in. My first suggestion was that he keep his ammunition out of the direct sun and shade it as much as possible. My second suggestion was to not close the bolt on a cartridge until he was ready to fire. He had his ammo in the direct sunlight and was chambering a round while waiting on the target to be pulled and scored which can take from a few seconds to almost a minute sometimes.

This time frame allowed the bullet and powder to absorb chamber [heat] and build pressure/velocity above normal conditions. Making my recommended changes lowered the pressures enough for the rifle and cartridge to function normally.

Testing Effects of Ammunition Temperature on Velocity and POI
After thinking about this situation, I decided to perform a test in the Sierra Bullets underground range to see what temperature changes will do to a rifle/cartridge combination. I acquired thirty consecutive .30 caliber 175 grain MatchKing bullets #2275 right off one of our bullet assembly presses and loaded them into .308 Winchester ammunition. I utilized an unnamed powder manufacturer’s product that is appropriate for the .308 Winchester cartridge. This load is not at the maximum for this cartridge, but it gives consistent velocities and accuracy for testing.

I took ten of the cartridges and placed them in a freezer to condition.

Sierra Bullets Ammunition Ammo temperature temp test hot F-Class Ammo cold

Sierra Bullets Ammunition Ammo temperature temp test hot F-Class Ammo cold

I set ten of them on my loading bench, and since it was cool and cloudy the day I performed this test I utilized a floodlight and stand to simulate ammunition being heated in the sun.

Sierra Bullets Ammunition Ammo temperature temp test hot F-Class Ammo cold

I kept track of the temperatures of the three ammunition samples with a non-contact laser thermometer.

The rifle was fired at room temperature (70 degrees) with all three sets of ammunition. I fired this test at 200 yards out of a return-to-battery machine rest. The aiming point was a leveled line drawn on a sheet of paper. I fired one group with the scope aimed at the line and then moved the aiming point across the paper from left to right for the subsequent groups.

NOTE that the velocity increased as the temperature of the ammunition did.

The ammunition from the freezer shot at 2451 fps.

Frozen FPS

The room temperature ammunition shot at 2500 fps.

Room Temperature FPS

The heated ammunition shot at 2596 fps.

Hot 130 degree ammo

Sierra Bullets Ammunition Ammo temperature temp test hot cold

The tune window of the particular rifle is fairly wide as is shown by the accuracy of the three pressure/velocity levels and good accuracy was achieved across the board. However, notice the point of impact shift with the third group? There is enough shift at 200 yards to cause a miss if you were shooting a target or animal at longer ranges. While the pressure and velocities changed this load was far enough from maximum that perceived over pressure issues such as flattened primer, ejector marks on the case head, or sticky extraction did not appear. If you load to maximum and then subject your ammunition to this test your results will probably be magnified in comparison.

Sierra Bullets Ammunition Ammo temperature temp test hot cold

This test showed that pressures, velocities, and point-of-impact can be affected by temperatures of your ammunition at the time of firing. It’s really not a bad idea to test in the conditions that you plan on utilizing the ammo/firearm in if at all possible. It wouldn’t be a bad idea to also test to see what condition changes do to your particular gun and ammunition combination so that you can make allowances as needed. Any personal testing along these lines should be done with caution as some powder and cartridge combination could become unsafe with relatively small changes in conditions.

Permalink - Articles, Bullets, Brass, Ammo, Reloading, Tech Tip No Comments »
June 28th, 2018

Avoid Canting Your Rifle to Improve Your Long Range Shooting

rifle level canting shooting rifle Ryan Cleckner

In a helpful NSSF video, Ryan Cleckner explains why you normally should avoid canting your rifle — rotating it clockwise or counter-clockwise. Cleckner explains that canting the rifle in one direction or another will change the point of impact: “When you rotate the rifle, not only does the [POI move] in the direction that you’re rotated, [but] it also loses some of its elevation as it rolls down.” This, Cleckner explains, can make you miss on one side or the other:

Cant to the Left — You’re going to miss low and left.
Cant to the Right — You’re going to miss low and right.

rifle level canting shooting rifle Ryan Cleckner

In this video, starting at the one-minute mark, Cleckner shows the effect of rifle canting when engaging a 600-yard target. A few degrees of cant (either to the left or to the right), moves the shot POI completely off the steel silhouette target. The POI change occurs mainly because you are lowering (and laterally shifting) the scope sight-line relative to the bore axis, effectively changing your zero.

David Tubb has explained: “Every 1 degree you are off on a cant, is about six inches of difference laterally at 1000 yards”.

Position Shooting with Sling — Rifle Cant Considerations
Cleckner’s discussion assumes that the scope or sights are set to hit center with the rifle level and plumb. That works for most situations when shooting prone off bipod, front mechanical rest, or front sandbag. However, many sling shooters, including David Tubb and John Whidden, do tilt or cant their rifles slightly inward because this allows a more comfortable hold with sling, or allows better eye-to-sight alignment. Holding the rifle at an angle can work — but the angle of cant must be consistent for every shot. Canting the rifle is not a sin by itself. However, after you confirm your zero on your target, the degree of cant must be the same for EVERY shot. You must maintain that exact same degree of rotation on each shot or you will experience the shot POI movement Cleckner illustrates. Consistency is the key.

John Whidden
John Whidden, 5-time Nat’l Long Range Champion, holds a Palma rifle. John now shoots a match rifle with an Anschutz stock which he holds more upright, but still with some counter-clockwise cant. John also installed his iron sights at an angle so that the adjustments are correct (and plumb) even with his canted hold: “While it may not be obvious in the picture, the sights on my rifle are set up so that they’re straight vertical and horizontal while I hold the rifle canted. Making sure your adjustments (scope or sights) are vertical and horizontal is a critical piece of the pie.”

Inexpensive Dual-Diameter Scope-Mounted Bubble Level
The best way to avoid inconsistent rifle canting is to use a bubble level fitted to rail or scope. One very affordable and versatile product is the Jialitte Scope Bubble Level. This features a 30mm milled inside diameter, plus an inner insert ring so it will also fit 1″-diameter main tubes. The Jialitte unit is nicely radiused, and has a low profile in the middle. User reviews have been very positive. You could easily pay $35.00 or more for a 30mm scope level. This costs just $10.99 on Amazon.

Scope Optic bubble level 30mm 1

Permalink Shooting Skills, Tactical 6 Comments »
September 6th, 2017

Hunting Tip: How to Plot Your Cold Bore Point of Impact

USAMU Cold Bore Video Browning X-Bolt Hell's Canyon Cold-bore zero
Photo of Browning X-Bolt rifle courtesy Browning.

Hunting season is coming up, so it’s time to get your rifle squared away. You’ll want to zero that rifle before the hunt, and you need to know how your shots will impact with a cold barrel.

Commonly, hunters won’t have the ability to fire one or two fouling shots before heading out on a hunt. Therefore it’s important that a hunter understands how his rifle shoots with a “cold bore shot”. Both the point of impact (and possibly velocity), may be different with a cold bore than with a barrel that has been warmed and fouled with a series of shots. In this video from the U.S. Army Marksmanship Unit (USAMU), you’ll learn how to determine your cold bore point of impact (POI) for a rifle that just been cleaned, as well as the cold bore POI with a barrel that has already been “fouled in”.

SGT Joe Hein of the USAMU shows how to plot cold bore POI with both a clean bore and a fouled bore. Note that the “cold bore” shot from a fouled barrel was closer to the follow-up shots than the cold bore shot from a clean barrel. This is typical of many factory barrels. SGT Hein provides a simple way to understand your rifle’s cold bore performance. Hein’s advice can keep you from missing that long range shot at that big buck on opening day. A little time spent on the range before that critical first shot will help ensure you have meat in the freezer this season.

Permalink - Videos, Hunting/Varminting 7 Comments »
January 13th, 2011

Point of Impact Target Shooting Game from Guns & Ammo

Point of Impact App GameNeed a diversion? Looking for an interesting shooting game you can play on an iPhone or iPad as well as your home computer? The Guns & Ammo Point of Impact Shooting Game lets you select a firearm type, then shoot it for accuracy in “virtual ranges” modeled after the Scottsdale (AZ) Gun Club. No this is NOT another Zombie Game, or First-Person-Shooter kill-fest. It is NOT based on the Point of Impact book by author Stephen Hunter. Point of Impact is a skill-oriented, arcade-style gun simulator presented by the National Shooting Sports Foundation (NSSF). It lets you test your skills in target shooting scenarios, with a wide selection of virtual firearms and targets.

*WARNING: We are not aware of any issues with this software and it passed multiple virus scans for us. However, as with any software, installation of this program can take resources and slow your machine down. Also, a software conflict could cause other programs to crash or run more slowly. For these reasons, we recommend that you NOT install this software on a work computer. If you choose to install the computer version on your home computer, and you don’t like it, or you get bored with it, you should uninstall the program from your home PC or laptop.

Credit Research Assistant Edlongrange for sourcing this game report.

Permalink Shooting Skills 1 Comment »