With the combining of Caesar Guerini and Fabarm, the result is Italy’s second largest shotgun manufacturer, which now rivals the in-house design and manufacturing capabilities of any shotgun manufacturer in the world. The Fabarm XLR 5 has not been released in the United States, that I know of, until right now. The basic gas action used in this autoloading shotgun was released in 2003, the Fabarm “Pulse Piston” system. By now a well-proven system, the action bar design associated with this action was improved back in 2005.
The barrel design of the XLR 5 is the Fabarm “Tribore HP” also released in 2005, also improved from the original design from 2003 or thereabouts. The Tribore system was designed to handle lead and steel shotshells with equal aplomb, using the “Inner HP” parabolic choke system which allows for substantially tighter constrictions than allowable by the C.I.P. with conventional barrels, and commensurately tighter patterns to go along with the greater constriction. What the “hyperbolic” choke appears to be is a continous taper choke with a larger diameter, flared section at the muzzle. More marketing hyperbole than hyperbolic, there is no doubt about their excellent performance, regardless.
The idea of the Tribore barrel is that the area after the forcing cone begins at an overbored .740 inch diameter and tapers to .725 inch at the choke area. Here’s how Fabarm describes it:
SO, IN THREE WORDS TRIBORE® HP BARREL IS:
1. An over-bored area to reduce frictions and recoil ( diameter 18.80 mm ).
2. A long conical area ( 205 mm ) which reduce the bore diameter and which increase the pellets speed.
3. New and revolutionary choke tubes with HYPERBOLIC PROFILE.
I think I can describe it a bit quicker. It is simply a slightly tapered barrel that constricts a total of about fifteen thousandths along its length.
Like most all claims of this nature, the Tribore barrel notion contains more than a little bit of wishful thinking. One piece wads have such a low coefficient of friction in the first place that notions of reducing it have little basis in fact. For wads or wadding to have no friction, they wouldn’t be sealing in the first place. Increasing shot payload speed invariably increases recoil, unless a new branch of physics has also been discovered. Ed Lowry was able to show that increased choke constriction does increase muzzle velocity, but you hardly need any special barrel to achieve it.