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Subsonic & Specialty Ammo   
 • 5.56/.223 Ultra Stealth Match Subsonic
 • 7.62/.308 Thumper Subsonic

 • 7.62/.308 PBS-Precision Bonded Subsonic

 • .300 Winchester Magnum Subsonic
 • .338 Lapua Magnum Subsonic
 • 7.62x39 Jackhammer Subsonic
 • 9mm Tactical Subsonic
 • .40 S&W Subsonic
 • .44 Magnum Subsonic
 • 7.62x39 Tracer

 • 12-ga KlinkMeister

Frangible Ammo
 • 12 ga. Frangible ENTRY Slug

 • 9mm Tactical Frangible
 • .40 S&W Frangible

 • .45 ACP Frangible Reduced Hazard
 • .223/5.56 Frangible

 • .308/7.62 Frangible
 • .300 Winchester Magnum Frangible

Government & Military
 • 40mm CQB
 • 7.62/.308 Limited Penetration
 • 7.62 x 39 Facility Protection Frangible

 • 5.56/.223 Subsonic

 • .50 cal Anti Ricochet
 • 6.5 EBR

Weapons and Related

 • For Sale

"The Straight Dope" Information and Tools
 • READ ME Proper Use of Subsonic Ammunition
 • Why use Phosphate Removal for Subsonic Ammunition?
 • Instructions on how to use EBR Phosphate Removal

 • Ballistics Calculator
 • Greenhill Formula For Rifling Twists
 • Twist Rate, continued

 • First-Round Pop
 • Subsonics Do Not Like Long Barrels!
 • The Use of Mil-Dots & Subsonic Ammunition
 • 7.62 Thumper vs. 7.62 PBS?
 • Speed of Sound Chart
Use of Subsonic Ammunition
 • Verifying Stability
 • FAQ - Frequently Asked Questions

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First-round Pop

It doesn't take long, particularly with subsonic ammunition, for the operator to notice that the first round fired is considerably louder than subsequent rounds. It is only 2-3 decibels on a good sound meter, but since decibels are logarithmic rather than linear, to the human ear, this is a lot. If there is a "cooling period" of more than a few minutes, FRP rears its ugly head again. Operationally, this can be a very undesirable thing, so here are two methods of combating this phenomenon.

1. If your suppresser is of the "Quick Detach" type, perhaps the easiest and most effective method is removing the can and spitting in the rear (blast chamber) end.

2. A more technological solution is canned Nitrogen gas. Available at any computer store outlet, this is the stuff with which you dust your monitor screen. The method is to chamber a cartridge to seal the rear of the barrel, and BEING CAREFUL WHERE YOU POINT THE LOADED WEAPON fill the bore and suppresser with the Nitrogen gas. A squirt of several seconds does the job. Put a piece of tape over the muzzle to hold the gas in. This method is good for several hours, until the Nitrogen slowly leaks out the back around the unexpanded cartridge case.

3. As well as the phenomenon of first round pop, the first round out of a cold barrel is often slower than succeeding shots due to energy - that would otherwise be used to propel the projectile, being soaked up and used to heat the steel barrel. This is exacerbated by a long barrel, as discussed in the article "Subsonics Do Not Like Long Barrels".


Engel Ballistic Research, Inc.
Phone (512) 360-5327 | Fax (512) 360-2652
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