Wednesday, February 28, 2007


Perry , when you said you did the caculations for the L.A.R. , what did you caculate and how did you know what to caculate , say for the 45 Winchester Magnum , what was going on in your mind ? Where do / did you start and how did you know what to start with , numbers , pressures etc . Paul


perry said...

Hi Paul,
Interesting question... A long story - but let me try to condense it a bit.

In the interest of accuracy(!), if you mean by your question, the calculations I did on the "Arnett Patent System Grizzly Multi-caliber Magnum Semiautomatic Pistol", I can address that. [I don't know what an "L.A.R." is.]

I did do the calculations on the "Grizzly Pistol", which were incorporated into the manufacture of that product by LAR Mfg. Co. under license for me.

The initial impetus for the conception and creation of the "Arnett Patent System Grizzly Multi-caliber Magnum Semiautomatic Pistol" ["the Grizzly Pistol"] was generated by the large amount of .45 Win Mag and 9mm Win Mag ammo Winchester had in inventory at the time. I got some ammo samples, and the published data on the cartridges from Winchester, and from that, I began the calculations for the Grizzly Pistol. Known pressure data always has to come first.

I had expressed the thought to others, that I could design and build a firearm based on the Browning 'lock' of the Colt/Browning 1911-A1 caliber .45 ACP Semiautomatic Pistol, that would handle BOTH the .45 Win Mag, and the 9mm Win Mag cartridges, interchangeably, with no replacement of the slide or receiver being required. That was the initial challenge I gave myself. My #4,253,377 patent had already been applied for (and may have been already issued), so I was going to incorporate that extant Multi-caliber technology into the new firearm.

My first concern [naturally], was the barrel burst pressure and Safety Factor. Having owned and operated a gunsmithing business since 1968, I had seen and handled plenty of firearms of all types with burst barrels and blown mechanisms. [A friend had even given me a slide from his Browning P35 High Power that he had literally beaten to death with ~10,000 rounds of Czech 9mm machine gun ammo. The slide is cracked in two or three places along the firing pin hole.] I was not about to let that happen in this experiment.

So I first 'calculated' whether the chamber/barrel wall thickness of a standard 1911-A1 Government Model Pistol in .45 ACP caliber would be strong enough to hold the elevated pressures contained within the .45 Win Mag cartridge. My ~2,000 volume technical and firearms library contains among other things, the SAAMI Pressure Data and Chamber Drawing Spec Books and other engineering books and references; these, and the knowledge of how to use them allowed me to do that.

I already owned a set of government drawings for the 1911-A1 Pistol, so I knew the requirements specified by the military for the barrel, the slide and the frame. By checking the Materials Data Handbook, I knew the allowable loads of the materials under stress. Once I knew that, I was able to determine that using the correct steel alloy, of the required grain size, that was heat-treated to the proper specs, of the proper dimensional section, that a barrel could be made to safely contain the pressures generated by the .45 Win Mag cartridge in the form suitable for use in a 1911-A1-style firearm.

In fact, my calculations showed that a standard government issue 1911-A1 barrel would contain those .45 Win Mag cartridge chamber pressures safely. [By actual count of the empty boxes, the original Grizzly Pistol prototype I hand-built using that government issue .45 ACP barrel has had more than 1,000 rounds of .45 Win Mag factory ammo though it!]

That knowledge inspired me to order a chamber reamer for the .45 Win Mag cartridge.

There are three ways by which one can create a barrel suitably strong enough to contain the pressures generated by a known cartridge: 1) using a stronger alloy; 2) heat-treating the alloy to a harder condition; or 3) using a thicker section. Using one, or a combination of all these factors, one can create the barrel proportions required to generate a safe barrel - or not! If the outer dimensions are constrained by the form or size of the firearm, then one is left with only the materials selection and/or the heat-treatment as options.

I reamed the .45 ACP G.I. barrel to ".000" headspace dimension for the .45 Win Mag cartridge.

Once I had the barrel, then I decided to build the magazine. If I was going to have a semiautomatic pistol that would feed the .45 Win Mag cartridge, I needed a magazine long enough to hold and feed those rounds. So I then built a magazine large enough to feed .45 Win Mag cartridges. I did that by cutting and silver-brazing two magazine body shells of suitable dimension together.
Having the magazine, I knew then how large the magazine cavity in the handle portion of the receiver had to be.

So I then built a receiver to match the magazine's length. I used a 1911-A1 G.I. receiver that I cut vertically through the magazine well, then added a ~3/8 inch spacer to both sides, then silver-brazed that assembly all back together. That required making a 3/8" longer trigger bow, and a 3/8" longer firing pin, extractor, etc. I did all that by hand. [I had learned long before that, how to do very precise silver-brazing on very thin sections. ]

After having the barrel, the magazine, and the receiver to fit the .45 Win Mag cartridge, I then built the slide to match all those parts.

I cut a government model 1911-A1 .45 ACP slide in the 'right' places to make it match those parts, elongated it the proper amount, then welded it back together. In so doing, I added the fishplates to the sides and the top of the slide to both strengthen the slide, and to give it some additional weight which I knew it needed to counteract the faster slide-recoil-velocity that would be generated by the .45 Win Mag cartridge. Thus, the 'fat' and 'tall' slide dimensions of the Grizzly Pistol slide. In order to give the slide some aesthetic shape I used a 3/8" diameter ball mill to machine the scallops between the sides and the top flats.

Once I had the slide, I tried feeding dummy rounds through the assembly and they worked!
As mentioned elsewhere, I fired the first few rounds of .45 Win Mag ammo (12 rounds, I believe) through the first Grizzly Pistol in the "locked breech mode". This was done on a board I built to hold the gun.

That is, I designed and built a tool steel 'device' that allowed me to purposefully lock the breech at the moment of firing so as to accomplish two things: 1) to see if the combined barrel, slide, receiver and slide stop pin and link, all of which comprise the locked 'breech' for that 1911-design, were sufficiently strong to satisfactorily contain the pressures and the bolt-thrust of the fired cartridge; and, 2) to keep the brass from flying out of the gun if the slide retracted, so that I could extract it manually, after it was fired, so I could examine it under magnification in a pristine condition - if the breech held.

The breech-locking device worked, so I proceeded with further testing.

I had previously filled an export contract with a company in Italy for some caliber 30 Luger Colt 1911-A1 Pistols, so I had to run those tests, and had gained an intuitive hands-on, internal ballistics experience from that.

I had also been building .38 Special Wadcutter Interchangeable-caliber Conversions for 1911-A1 .45 ACP pistols, so I gained some hands-on experience with internal ballistics from that activity also. And, I had designed and built some open-bolt, Multi-caliber SMG's around this time, so I knew the failure points of cartridge cases, how they looked, how they responded, what variations in bolt velocities were, and how they reacted, etc.

So, I had both an intuitive sense and hands-on experience, but also, the books and the rational mind capable of running the numbers.

I was prepared to abandon the project if it was unsafe, and I knew that that was always a possibility. But having done the math first, and having had what I considered to be enough hands-on experience in the firearms design field, I was able to put the two together and create the product now known as the "Arnett Patent System Grizzly Multi-caliber Magnum Semiautomatic Pistol".

After having granted a License to L.A.R. Manufacturing Inc., in which they were to build the Grizzly Pistol in quantity for me under that License, I did the calculations for 'fit and finish' to establish match-grade-performance from a production gun. I had built a number of match grade 1911-A1 pistols for others, so I knew the inherently wide 'fit and finish' tolerances called for in the 1911 design. It was, after all, a firearm designed for military use under combat conditions, so the fit tolerances were spec'ed for functionality, not necessarily accuracy. I knew that with proper compromises of 'fit' dimensions, I could tighten the tolerances in such a way that the pistols could be made to be fully interchangeable, so that when any slide, or barrel or bushing was mated to any receiver, they would perform with 'custom' match grade accuracy and reliability of function - and at a production level that would allow for this to be done at a profit.

My signature is on all those Machine Drawings used for the manufacture and production of the Arnett Patent System Grizzly Multi-caliber Magnum Semiautomatic Pistol, AND Multi-caliber Conversion Units.

After having created the Grizzly Pistol in .45 Win Mag caliber, it was then basically a repeat of the process to create the 9mm Win Mag Conversion Unit for the same Pistol, and then all the other Multi-caliber Conversion Units that came after, with which I am associated.

I conceived my first invention at age 9 [a multiple-bogeyed wheel arrangement for the rear of a bicycle, to even out the bumps], and my first electro-mechanical machine for factory automation at age 17 [a fully automated, computer-controlled production ice cream freezer designed specifically to reduce and recover the amount of butterfat then inherently lost in the commercial ice cream manufacturing process; this was in 1957, BEFORE computers were commonly available], so I have always had an intuitive sense of mechanics [my father was a machinist/mechanic/inventor/musician] and a sense of 'how things work', and what can be done with various materials and shapes and forms.

Don't know if this is the answer you had in mind. I appreciate your interest in all this! I'm recalling here, events that happened some ~27 years ago or so, so I cite this "to the best of my recollection".

If Cam will permit a bit of blatant self-promotion:

Am I still available to do similar work for others? Sure! I'm currently semi-retired, and always looking for new opportunities to stretch my mind and serve others with useful devices or improvements and high profits. My current IP Portfolio of new products, processes and other conceptions, designs, and inventions numbers more than 300, some of which include highly innovative state-of-the-art firearms. I'm available for long or short term consulting, and my Intellectual Property Portfolio is available for licensing or outright sale. I've appended URL's for my issued U.S. Patents below.


Perry Arnett

- sole conceiver, inventor, designer, engineer, patent-holder and licensor of the technologies incorporated in the Arnett Patent System Grizzly Multi-caliber Magnum Semiautomatic Pistol, and Multi-caliber Conversion Units for the same []



frankenfab said...

What a great story! Thank you, Perry, for sharing it!