April 28th, 2020

Vihtavuori Explains Powder Grain Shapes

Vihtavuori loading propellant reloading powder N133 N150 N140 N550 ball flake stick extruded perforated powders

POWDER GRAIN SHAPES — What You Need to Know

The shape of powder grains has a profound effect on the performance of the powder charge, as it concerns both pressure and velocity. There are multiple powder shapes including flake, ball, and extruded or “stick” (both solid and perforated).

All Vihtavuori reloading powders are of the cylindrical, single-perforated extruded stick type. The differences in burning rate between the powders depend on the size of the grain, the wall thickness of the cylinder, the surface coating and the composition. Cylindrical extruded powders can also have multi-perforated grains. The most common types are the 7- and 19-perforated varieties. A multi-perforated powder grain is naturally of a much larger size than one with a single perforation, and is typically used for large caliber ammunition.

Other types of powder grain shapes include sphere or ball, and flake. The ball grains are typically used in automatic firearms but also in rifles and handguns. The ball grain is less costly to produce, as it is not pressed into shape like cylindrical grains. Flake shaped grains are typically used in shotgun loadings.

Vihtavuori loading propellant reloading powder N133 N150 N140 N550 ball flake stick extruded perforated powders

Web thickness in gunpowder terminology means the minimum distance that the combustion zones can travel within the powder grain without encountering each other. In spherical powders, this distance is the diameter of the “ball”; in flake powder it is the thickness of the flake; and in multi-perforated extruded powders it is the minimum distance (i.e. wall thickness) between the perforations.

The burning rate of powder composed of grains without any perforations or surface treatment is related to the surface area of the grain available for burning at any given pressure level. The change in the surface area that is burning during combustion is described by a so-called form function. If the surface area increases, the form function does likewise and its behavior is termed progressive. If the form function decreases, its behavior is said to be degressive. If the flame area remains constant throughout the combustion process, we describe it as “neutral” behavior.

The cylindrical, perforated powders are progressive; the burning rate increases as the surface area increases, and the pressure builds up slower, increasing until it reaches its peak and then collapses. Flake and ball grains are degressive; the total powder surface area and pressure are at their peak at ignition, decreasing as the combustion progresses.

So how does the shape affect pressure and muzzle velocity? In general, it can be said that powder that burns progressively achieves a desired muzzle velocity at lower maximum pressure than a powder that burns neutrally, not to mention a degressive powder. As grain size increases, the maximum pressure moves towards the muzzle, also increasing muzzle blast. Muzzle velocity and pressure can be adjusted by means of the amount of powder or loading density, i.e. the relationship between the powder mass and the volume available to it. As the loading density increases, maximum pressure grows.

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Vihtavuori loading propellant reloading powder N133 N150 N140 N550 ball flake stick extruded perforated powders


This article originally appeared on the Vihtavuori Website.

Permalink Bullets, Brass, Ammo, Reloading, Tech Tip No Comments »
April 28th, 2020

Tuesday Trivia: Can You Over-Stabilize a Bullet?

spinning bullet stabilizationOn the Applied Ballistics Facebook page a few seasons ago, Ballistician Bryan Litz posed a “Tuesday Trivia” question about ballistics. This being Tuesday we thought we’d bring back this interesting brain-teaser — a true/false question about bullet stabilization. On shooting forums you often find heated arguments about “over-stabilization”. Bryan wants readers to consider the issue of over-stabilization and answer a challenge question…

Is This Statement TRUE or FALSE?

“The problem with ‘over-stabilizing’ a bullet (by shooting it from an excessively fast twist rate) is that the bullet will fly ‘nose high’ on a long range shot. The nose-high orientation induces extra drag and reduces the effective BC of the bullet.”

True or False, and WHY?

Click the “Post Comment” link below to post your reply (and explain your reasoning).

Bullet Movement in Flight — More Complicated Than You May Think
Bullets do not follow a laser beam-like, perfectly straight line to the target, nor does the nose of the bullet always point exactly at the point of aim. Multiple forces are in effect that may cause the bullet to yaw (rotate side to side around its axis), tilt nose-up (pitch), or precess (like a spinning top) in flight. These effects (in exaggerated form) are shown below:

spinning bullet stabilization

Yaw refers to movement of the nose of the bullet away from the line of flight. Precession is a change in the orientation of the rotational axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle (nutation) is constant. In physics, there are two types of precession: torque-free and torque-induced. Nutation refers to small circular movement at the bullet tip.

Diagram from the University of Utah Health Sciences Library Firearm Ballistics Tutorial
Permalink Bullets, Brass, Ammo, Reloading, Tech Tip 14 Comments »
April 28th, 2020

Rebate Central: Great Spring/Summer Factory Rebates

summer Factory rebate programs

We’ve found eight great discount/rebate programs. These can save you money on ammunition, security safes, optics, or a new firearm. Some of these rebates are worth $75 or more. For example you can save $75 on a Rem varmint rifle or $75 on a Savage rifle. Note: most of these promos are good through summer, but some deals expire April 30, 2020 — just two days away. So don’t delay if you want these deals!

Remington Rifle Shotgun $100 Off rebate gun

Remington Rifle and Shotgun Rebates
Get $100 rebate on Remington Versamax Shotguns. Receive a $75 rebate on Rem V3 Shotguns and Model 700 Varmint Rifles. Get $50 rebate on Rem Model 870 Super Mag Shotguns.
Start Date: 2/1/2020
End Date: 4/30/2020 ACT SOON!!

Savage Rifle Shotgun $100 Off rebate MSR gun

Get up to $75 Back From Savage
Purchase any Savage MSR and receive $75 back with a mail-in rebate. Or, buy any Savage A or B series rifle and receive $50 back with a mail-in rebate.
Start Date: 2/27/2020
End Date: 5/1/2020

CCI Rimfire Rifle Ammo Rebate free ammunition

Free Ammo with Rimfire Gun Buy
Buy any brand rimfire rifle or handgun plus 2 boxes of CCI rimfire ammo and CCI will rebate the purchase price of one box of ammo up to $20.
Start Date: 1/1/2020
End Date: 12/31/2020

Federal Varmint Predator Rifle Ammo Rebate free ammunition

Get up to $100 BACK ON Federal Ammo
Receive $5 back per box when you purchase select Federal Premium varmint and predator ammo. Minimum of 4 boxes and maximum of 20.
Start Date: 1/1/2020
End Date: 4/30/2020 ACT SOON!!

Spring field M1A Rifle magazine scope mount Free deal

Springfield M1A Mags + Scope Mount
Receive a FREE Scope Mount and 2 additional magazines with the purchase of any new M1A rifle. This is a $265 Value!
Star Date: 3/1/2020
End Date: 5/31/2020

Browning Ammo Rebate free ammunition $20 Off

20% REBATE on Browning Ammo
Receive 20% back on all Browning ammunition with mail-in rebate. Maximum rebate of $25.
Start Date: 4/16/2020
End Date: 5/12/2020

Leupold Rebate free pack binoculars

Leupold Binocular Bonus
Here’s a nice bonus that hunters can really use. If you buy Any Leupold BX-4 Pro Guide Binoculars and receive a FREE Leupold Binocular Chest pack, a $99 value. These packs are nicely may and comfortable, and can also be used to carry a Laser Rangefinder, Kestrel or more.
Start Date: 3/30/2020
End Date: 5/31/2020

Hornady Safe gunsafe security free ammo rebate

Free Ammo with Hornady Security Products
Hornady is offering FREE Critical Defense® Ammo (value $68) when you purchase Hornady Security products: RAPiD Safe 4800KP RFID, RAPiD Safe 2700KP/2600KP, RAPiD Safe AR Wall Lock or AR Gunlocker, RAPiD Safe Shotgun Wall Lock, RAPiD Safe Night Guard, RAPiD Safe Ready Vault, RAPiD® Safe 2700/2600, and RAPiD® Vehicle Safe RFID.
Start Date: 1/1/2020
End Date: 12/31/2020

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