None.
The present invention relates to sound moderators for airguns. More particularly, the present disclosure relates to airgun sound moderators that employ a stack of acoustic baffles made from fibrous polymeric felt, which rapidly deteriorate in the presences of gunpowder combustion products and temperatures, thereby reducing their potential effectiveness for suppression of firearms.
In the field of firearms, given the high impulse sound pressure levels generated during firearm discharge, the use of sound suppressors, or “silencers”, is well known. Gunpowder combustion products, discharged gases, high temperatures, and the fired bullet all contribute to the generation of this impulse. Firearm silencers greatly reduce the peak sound pressure levels in firearms. Certain combinations of firearm caliber and silencer can reduce the acoustic impulse to such a low level that the need for hearing protection is obviated. Pneumatic airguns also produce significantly high acoustic impulses upon discharge. This is particularly true in the case of pre-charged pneumatic (“PCP”) airguns, in both rifles and pistol configurations. PCP airguns commonly operate with up to 4,500 PSI air pressure, which result in acoustic impulse levels that are potentially not “hearing-safe”, so the use of hearing protection is recommended. “Sound moderators” are known, and are employed to reduce the acoustic impulse to hearing-safe levels.
The use of firearm silencers on airguns can be effective in reducing the airgun acoustic impulse to hearing-safe levels. However, firearm silencers are subject to tight control under state and federal law, and are subject to criminal penalties if such laws are violated. According to the Gun Control Act Definitions on silencers (18 U.S.C., § 921(A) (24)), the term “Firearm Silencer” or “Firearm Muffler” means any device for silencing, muffling, or diminishing the report of a portable firearm, including any combination of parts, designed or redesigned, and intended for the use in assembling or fabricating a firearm silencer or firearm muffler, any part intended only for use in such assembly or fabrication. Furthermore, any device that meets the definition as stipulated above in 18 U.S.C. § 921(a)(24) is also subject to controls of the National Firearms Act 26 U.S.C., Chapter 53 (“NFA”). Thus, the lawful use of a firearm silencer is subject to the NFA, including criminal background checks for any purchaser, payment of a substantial tax, extended waiting periods for approval, as well as a wide range of state laws and regulations. The NFA does not cover airguns or airgun sound moderators. For these reasons, the use of firearm silencers on airguns is not a favorable option.
In the case of products designed to be used for sound moderation in airguns, there is a legitimate legal concern about their potential use on firearms. In the case where the transfer or use between airguns and firearms exists, then interpretation the NFA language becomes critical to providers and users alike, as it may be a criminal act to make, sell, transfer or use an airgun moderator on a firearm. Airgun moderator providers have striven to produce airgun moderators that cannot easily be used on firearms, to avoid such legal liability. This often manifests itself as an incompatibility in the means for connecting the airgun moderator to a firearm. However incompatible the designs may be, the ability to conceive of and produce some sort of adapter always clouds the legal questions at issue. Thus is can be appreciated that there is a need in the art to address the forging problems in the prior art.
The need in the art is addressed by the apparatuses and methods of the present invention. The present disclosure teaches an airgun sound moderator assembly for attachment to an airgun that has a barrel defining a bore axis, where the barrel is fixed to a frame member, and that has a moderator engagement fitting adjacent a muzzle end thereof. The assembly includes an elongated housing that has an interior profile, and that has an airgun engagement fitting at a first end, and that has a moderator muzzle cap at a second end, and wherein the airgun engagement fitting is selectively attachable to the airgun moderator engagement fitting. A stack of plural acoustic baffles are located within the elongated housing between the airgun engagement fitting and the moderator muzzle cap. The plural acoustic baffles are each fabricated from a fibrous polymer felt, which inherently defines a polymer softening temperature and a polymer melting temperature, where the specific polymer is selected to provide sufficient rigidity of the felt to maintain structural shape below the polymer softening temperature, and where the polymer softening temperature and the polymer melting temperature are both less than three hundred degrees celsius, such that the plural acoustic baffles will rapidly deteriorate if exposed to gunpowder combustion products and temperatures. Each of the plural acoustic baffles are substantially planar, and have a thickness in the range of 0.5 to 4.0 centimeters, with an outer profile that at least partially conforms with the interior profile of the elongated housing, and each have a bore hole formed therethrough, which is aligned with the bore axis when the airgun engagement fitting is engaged with the moderator engagement fitting.
In a specific embodiment of the foregoing assembly, the fibrous polymer felt is fabricated from polyethylene terephthalate fibers. In a refinement to this embodiment, the polyethylene terephthalate fibers are substantially heterogeneous in size, and the plural acoustic baffles are thermally cut from sheet felt material, which partially fuses the cut edges to enhance rigidity.
In a specific embodiment of the foregoing assembly, where the moderator engagement fitting is fixed to the airgun frame and internally threaded, the airgun engagement fitting is externally threaded for selective attachment to the moderator engagement fitting.
In a specific embodiment of the foregoing assembly, where the airguns discharges a projectile of predetermine caliber, the plural acoustic baffles includes a first portion of baffles interleaved with a second portion of baffles, and the first portion of baffles have round boreholes with a first diameter that is larger than the predetermined caliber, and the second portion of baffles have a second bore hole size that is larger than the first diameter.
In a specific embodiment to the foregoing assembly, the second bore hole size is cut to reveal a zigzag edge profile. In another specific embodiment, the second bore hole size is cut to reveal an undulating edge profile. In another specific embodiment to the foregoing assembly, a portion of the plural acoustic baffles are cut such that the outer profile reveals a concave scalloped edge. In another specific embodiment of the foregoing assembly, a portion of the plural acoustic baffles are cut such that the outer profile reveals a castellated edge.
The present disclosure teaches an airgun sound moderator assembly for insertion into an airgun that has a barrel that defines a bore axis, where the barrel located within a frame member by a barrel support member, and where the frame member has an interior profile and is enclosed at a muzzle end by a muzzle cap. The assembly includes a stack of plural acoustic baffles that can be located within the frame between the barrel support member and the muzzle cap. The plural acoustic baffles are each fabricated from a fibrous polymer felt, which inherently defines a polymer softening temperature and a polymer melting temperature, and, the polymer is selected to provide sufficient rigidity of the felt to maintain its structural shape below the polymer softening temperature, and where the polymer softening temperature and the polymer melting temperature are both less than three hundred degrees celsius. This assures that the plural acoustic baffles will rapidly deteriorate if exposed to gunpowder combustion products and temperatures. Each of the plural acoustic baffles are substantially planar and have a thickness in the range of 0.5 to 4.0 centimeters, with an outer profile that at least partially conforms with the interior profile of the frame member, and each has a bore hole formed therethrough, which is aligned with the bore axis when inserted into the airgun frame.
In a specific embodiment, the foregoing assembly further includes a baffle spacer located between the barrel support member and the stack of plural acoustic baffles to provide separation between the barrel and the stack of plural acoustic baffles.
In a specific embodiment of the foregoing assembly, the fibrous polymer felt is fabricated from polyethylene terephthalate fibers. In a refinement to this embodiment, the polyethylene terephthalate fibers are substantially heterogeneous in size, and the plural acoustic baffles are thermally cut from sheet felt material, which partially fuses the cut edges to enhance rigidity.
In a specific embodiment of the foregoing assembly, where the airgun discharges a projectile of predetermine caliber, the plural acoustic baffles include a first portion of baffles interleaved with a second portion of baffles. The first portion of baffles have round boreholes with a first diameter that is larger than the predetermined caliber, and the second portion of baffles have a second bore hole size that is larger than the first diameter. In a refinement to this embodiment, the second bore hole size is cut to reveal a zigzag edge profile. In another refinement to this embodiment, the second bore hole size is cut to reveal an undulating edge profile.
In a specific embodiment of the foregoing assembly, a portion of the plural acoustic baffles are cut such that the outer profile reveals a concave scalloped edge. In another specific embodiment, a portion of the plural acoustic baffles are cut such that the outer profile reveals a castellated edge.
The present disclosure teaches a method of fabricating an airgun moderator assembly, including a stack of plural acoustic baffles, which are for insertion into an airgun or into a separate moderator elongated house that is attached to an airgun. In the case of a separate housing, the airgun has a barrel fixed to a frame member that defines a bore axis, and has a moderator engagement fitting adjacent to its muzzle end, for attachment of an elongated housing that has an interior profile, and that has an airgun engagement fitting at a first end, and a moderator muzzle cap at a second end, and where the airgun engagement fitting is selectively attachable to the airgun moderator engagement fitting. In the case of an integrally located moderator assembly, for insertion of the plural acoustic baffles into an airgun that has a barrel located within a frame member by a barrel support member, and where the frame member has an interior profile and is enclosed at a muzzle end by a muzzle cap, which enables location of the stack of plural acoustic baffles within the frame member between the barrel support member and the muzzle cap. In either case, the method includes selecting a substantially planar sheet of fibrous polymer felt within the thickness range of 0.5 to 4.0 centimeters according to its inherent polymer softening temperature and polymer melting temperature, which are both less then three hundred degrees celsius. As such, the polymer will rapidly deteriorate if exposed to gunpowder combustion products and temperatures. The fibrous polymer felt is also selected according to its rigidity, which provides structural strength below the polymer softening temperature. The method further includes cutting the plural acoustic baffles from the sheet of fibrous polymer felt, such that each of the plural acoustic baffles have an outer profile that at least partially conforms with the interior profile of the elongated housing or the interior profile of the frame member, and each has a bore hole formed therethrough, which is located to align with the bore axis of the airgun. This arrangement moderates the acoustic impulse emitted by the airgun upon discharge of a projectile.
In a specific embodiment of the foregoing method, the fibrous polymer felt is fabricated from polyethylene terephthalate fibers. In a refinement to this embodiment, where the polyethylene terephthalate fibers are substantially heterogeneous in size, the method fourth includes thermally cutting the plural acoustic baffles from sheet of polymer felt, thereby fusing the cut edges and enhancing rigidity. In a refinement to this embodiment, where the airgun discharges a projectile of predetermine caliber, the cutting step further includes cutting a first portion of the plural acoustic baffles and cutting a second portion of the plural acoustic baffles, and interleaving the first portion and second portion of the plural acoustic baffles. The first portion of baffles are cut with round boreholes having a first diameter that is larger than the predetermined caliber, and the second portion of baffles are cut with a second bore hole size that is greater than the first diameter.
Illustrative embodiments and exemplary applications will now be described with reference to the accompanying drawings to disclose the advantageous teachings of the present invention.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope hereof, and additional fields in which the present invention would be of significant utility.
In considering the detailed embodiments of the present invention, it will be observed that the present invention resides primarily in combinations of steps to accomplish various methods or components to form various apparatus and systems. Accordingly, the apparatus and system components, and method steps, have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the present teachings so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the disclosures contained herein.
In this disclosure, relational terms such as first and second, top and bottom, upper and lower, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.
The present disclosure advantageously teaches assemblies and methods for employing fibrous polymeric felt in the form of a stack of acoustic baffles for both detachable and integral airgun sound moderators. Suitable materials are presented that provide sufficient strength and rigidity to maintain shape and acoustic performance when exposed to repeated compressed air muzzle blast from an airgun, yet, which will quickly deteriorate if exposed to the temperatures and combustion products of gunpowder firearms. In addition to the use of polymeric felt itself, the present disclosures teaches methods of cutting acoustic baffles from sheet polymeric felt material using thermal cutting techniques, including laser cutting, which effectively fuses the fibers exposed along the cutting lines. This technique further reinforces the strength and structure of the polymeric felt acoustic baffles.
As a point of reference, gunpowder typically has a burn temperature of at least 700° C., with maximum temperatures typically exceeding 1400° C. Thus, a firearms silencer must be fabricated from materials that endure such temperatures, and pressures for that matter, for a reasonably large number of repeated exposures in order to be regarded as an effective silencer for firearms applications. In fact, most quality firearms silencers employ a first internal baffle, often referred to as a “blast shield”, that is fabricated from a material and shape (thickness) that is particularly effective at enduring such exposure. Synthetic polymers, on the other hand, have considerably lower softening and melting temperatures. So much so, that most will melt or be destroyed when exposed to gunpowder combustion products, temperatures, and pressures.
The list of synthetic polymers (and their respective melting temperatures), roughly in the order of those most often utilized, includes polyethylene (115-135° C.), polypropylene (130-171° C.), polystyrene (240° C.), polyvinyl chloride (100-260° C.), phenol formaldehyde resin (220° C., decomposition), nylon (190-350° C.), polyacrylonitrile (300° C.), silicone (250° C., decomposition), and others. In addition to the melting or decomposition temperatures of such polymers, it is also necessary to consider the rigidity and strength of such materials, as well as available techniques for implementing an acoustic baffles from the materials. For example, synthetic rubbers and silicones are soft and flexible, making them largely unsuitable for airgun sound moderator applications. With respect to the physical structure of polymeric acoustic baffles, felt has been tested and determined to be an effective option for implementation of airgun sound moderator baffles.
Felt is a textile material that is produced by matting, condensing and pressing fibers together. Felt is often referred to as a non-woven fabric, where the fibers engage with one-another through the process of entanglement. Felt can be made of natural fibers, or from synthetic fibers such as petroleum-based polymeric fibers. Felt dampens vibration and absorbs sound, hence its suitability for use as an acoustic baffle in an airgun sound moderator. Testing by the inventors of the present disclosure has established that polymers in the polyester category provide sufficient rigidity and strength to effectively endure applications as acoustic baffles in airgun sound moderators.
Polyester is a category of polymers that contain the ester functional group in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). PETs have low less fire-resistant and can melt when ignited. Polyethylene terephthalate is a strong, stiff synthetic material that can be spun into fibers for various applications. PET is produced by the polymerization of ethylene glycol and terephthalic acid. Ethylene glycol is a colorless liquid obtained from ethylene, and terephthalic acid is a crystalline solid obtained from xylene. When heated together under the influence of chemical catalysts, ethylene glycol and terephthalic acid produce PET in the form of a molten, viscous mass that can be spun directly to fibers Under the influence of heat and catalysts, hydroxyl and carboxyl groups react to form ester (CO—O) groups, which serve as the chemical links joining multiple PET units together into long-chain polymers. The presence of a large aromatic ring in the PET repeating units gives the polymer notable stiffness and strength, especially when the polymer chains are aligned with one another in an orderly arrangement by drawing (stretching). The stiffness of PET fibers makes them highly resistant to deformation, a characteristic particularly suitable for airgun sound moderator acoustic baffles. PET has a low softening temperature, approximately 70° C., and a melting temperature of approximately 250° C., this it will quickly deteriorate in the presence of gunpowder combustion temperers and pressures.
Polyethylene terephthalate felt materials are commercially available, and particularly configured for sound absorption applications. In an illustrative embodiment of the present disclosure, Acoufelt™ AP12 acoustic panel, which is prepared from 100% polyester, its employed. See www.acoufelt.com for further information on the AP12 product. The AP12 polyester felt product is available in 0.47″ thick sheets having a density of 0.49 pounds per square foot, employing substantially heterogeneous fiber sizes with good acoustic absorption properties, meeting the AS ISO 354-2006 NRC sound absorption standard.
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Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications and embodiments within the scope thereof.
It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention.
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