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October 16th, 2014

Big Sale on Ultrasonic Cleaning Machines — All Capacities

If you’ve never tried ultrasonic cleaning, you should. This process is great for cleaning small gun components, AR innards, carbon-caked suppressors, and even jewelry. Ultrasonic cleaning also transforms old, dirty brass, getting cartridge cases clean inside and out (including the primer pockets). With a big-enough ultrasonic cleaning tub, you can even clean complete AR uppers. One word of caution — we do NOT recommend ultrasonic cleaning for any blued parts or blued firearms.

Bullets.com Bald Eagle Ultrasonic Cleaning machine transducer Ultrasound

Bullets.com Bald Eagle Ultrasonic Cleaning machine transducer UltrasoundBald Eagle Ultrasonic SALE
Right now Bullets.com is offering very attractive introductory prices on the new Bald Eagle line of ultrasonic cleaning machines. There are five models to choose from, starting at just $34.95 for a 750 ml capacity small parts cleaning unit. The general-purpose 2.5 liter unit (which will hold hundreds of cartridge cases), runs $139.50.

A large-capacity 6 liter unit (that makes short work of big jobs) is $295.00. The jumbo, industrial-grade 7-liter unit, with a 25.5-inch-long dunk tank, is $495.00, marked down from $650.00. Compare these prices against those of other similar-capacity machines and you’ll see they represent good values. These introductory prices will be in effect through 12/31/14.


Bullets.com Bald Eagle Ultrasonic Cleaning machine transducer Ultrasound

Permalink Hot Deals, New Product No Comments »
October 13th, 2014

CUP vs. PSI — What’s The Difference in Pressure Measurements

by Philip Mahin, Sierra Bullets Ballistic Technician
This article first appeared in the Sierra Bullets Blog

The ANSI / SAAMI group, short for “American National Standard Institute” and “Sporting Arms and Ammunition Manufacturers’ Institute”, have made available some time back the voluntary industry performance standards for pressure and velocity of centerfire rifle sporting ammunition for the use of commercial manufacturers. [These standards for] individual cartridges [include] the velocity on the basis of the nominal mean velocity from each, the maximum average pressure (MAP) for each, and cartridge and chamber drawings with dimensions included. The cartridge drawings can be seen by searching the internet and using the phrase ‘308 SAAMI’ will get you the .308 Winchester in PDF form. What I really wanted to discuss today was the differences between the two accepted methods of obtaining pressure listings. The Pounds per Square Inch (PSI) and the older Copper Units of Pressure (CUP) version can both be found in the PDF pamphlet.

SAAMI CUP PSI Cartridge Copper Units Pressure PSI
Image by ModernArms, Creative Common License.

SAAMI CUP PSI Cartridge Copper Units Pressure PSICUP Pressure Measurement
The CUP system uses a copper crush cylinder which is compressed by a piston fitted to a piston hole into the chamber of the test barrel. Pressure generated by the burning propellant causes the piston to move and compress the copper cylinder. This will give it a specific measurable size that can be compared to a set standard. At right is a photo of a case that was used in this method and you can see the ring left by the piston hole.

PSI Pressure Measurement
What the book lists as the preferred method is the PSI (pounds per square inch or, more accurately, pound-force per square inch) version using a piezoelectric transducer system with the transducer flush mounted in the chamber of the test barrel. Pressure developed by the burning propellant pushes on the transducer through the case wall causing it to deflect and make a measurable electric charge.

Q: Is there a standardized correlation or mathematical conversion ratio between CUP and PSI values?
Mahin: As far as I can tell (and anyone else can tell me) … there is no [standard conversion ratio or] correlation between them. An example of this is the .223 Remington cartridge that lists a MAP of 52,000 CUP / 55,000 PSI but a .308 Winchester lists a 52,000 CUP / 62,000 PSI and a 30-30 lists a 38,000 CUP / 42,000 PSI. It leaves me scratching my head also but it is what it is. The two different methods will show up in listed powder data[.]

So the question on most of your minds is what does my favorite pet load give for pressure? The truth is the only way to know for sure is to get the specialized equipment and test your own components but this is going to be way out of reach for the average shooter, myself included. The reality is that as long as you are using printed data and working up from a safe start load within it, you should be under the listed MAP and have no reason for concern. Being specific in your components and going to the load data representing the bullet from a specific cartridge will help get you safe accuracy. [With a .308 Winchester] if you are to use the 1% rule and work up [from a starting load] in 0.4 grain increments, you should be able to find an accuracy load that will suit your needs without seeing pressure signs doing it. This is a key to component longevity and is the same thing we advise [via our customer service lines] every day. Till next time, be safe and enjoy your shooting.

SAAMI CUP PSI Cartridge Copper Units Pressure PSI

Permalink Reloading, Tech Tip 6 Comments »