Some builders are assembling .17 HMR rifles from our MAGNUM Receivers. Due to the high pressures, thin bullet cases and receiver tuning required with this round we no longer recommend building a .17 HMR.
The RAZOR MAGNUM receiver is a variant of the Ruger 10/22 Magnum Semi-automatic rifle. Unlike the Ruger with the Tungsten bolt that was discontinued due to bolt cracking issues. Our bolt is made from 4140 steel. We harden our bolts and then draw them back so we don't experience and cracking. They are not brittle like the tungsten bolts. Ruger had no choice but to use this exotic metal (Tungsten) due to the weight /mass that it offered. It was 1.5 times the weight of a standard steel bolt. They needed this extra weight in the bolt to slow the bolt recoil due to the hotter more powerful magnum load. However, tungsten is a very brittle metal it doesn't last long under impact stress. Eventually all the bolts will develop stress cracks and break apart during normal firing of the rifle. That is why Ruger no longer supports or makes the 10/22 Magnum Rifle.
Select Fire re-engineered the receiver and bolt design. We overcame the bolt recoil inertia issue with heavier bolt recoil springs. The bolt cracking issue was resolved by getting away from exotic metals like tungsten and using a 4140 base metal that is then hardened. We even were able to change the receiver from a cast steel to a CNCed aluminum unit, making it much lighter and offering tighter tolerances. This was accomplished by reducing the bolt recoil rate with a main spring and installing our R25P bolt buffer to absorb any residual bolt recoil rather than the old steel pin and receiver.
There are 7 parts unique to our MAGNUM receiver that Select Fire LLC manufactures. We make the MAGNUM Receiver, Bolt Assembly, Charging Handle, Main spring, Main Spring Follower, Main Spring Retention Plug and R25P Bolt Buffer. The MAGNUM uses a standard 10/22 trigger group, standard 10/22 cross pins, standard 10/22 V-Block assembly and Take-Down screw. There are several suppliers that manufacture the 22 MAGNUM (WMR) barrels along with a large supply of stock manufactures to include Boyds and Hogue.
The Magnum Rifle shoots a 30 to 40 grain projectile that is almost 2 times the speed (2200 fps) of a stock .22 caliber bullet (1150 fps). We add or remove spring length to compensate for the recoil cause by different rounds.
Our MAGNUM receiver is sold at the 80% level so no FFL transfers or paperwork are required. You finish the last 20% of the receiver, just like our RAZOR receiver. We supply a drawing with every receiver that calls out hole locations and drill size. We also sell a drill fixture that allows for precise hole location and drilling. In addition, we sell a tool kit (Same kit Used for RAZOR) that provides you with the necessary drills and tap to help complete your MAGNUM receiver. MAGNUM Kit and or individual parts can be purchased from our ORDER / PURCHASE page.
Unlike the standard RAZOR receiver this MAGNUM receiver is less forgiving when it comes to building it. You must get all the holes in the right locations. Being close is not going to cut it. Don't even try and drill the barrel hole to size. Find someone with a milling machine and have it bored or drilled then reamed to size. I am not saying that someone can't build a working MAGNUM with basic hand tools, I am simply stating that this Receiver works with larger ammunition, greater breach pressure and much tighter tolerances. Why take a chance on damaging an expensive part when you can do it right the first time with the proper/recommended tools. The drill jig was designed to put the holes in the exact locations. I recommend using it if you do not have a mill or you're not sure of your skill level.
NOTE: The Magnum requires fitting and tweaking of the parts. It is not meant for the first time builder. It requires the ability to troubleshoot little issues and correct them with polishing, grinding, and filing. It is not going to be a like the RAZOR (Drill the holes and go shooting). It will require you to build the rifle and make small adjustments to fit and function. You will need to polish the bolt, remove burs, clean up surfaces and make the necessary adjustments to build a quality well functioning firearm.
There is a great place to get firearm building expertise. I am providing the link for those of you that may want to use it. http://www.prexis.com/sten/homebuilder/index.php
There are only 2 unique tools to support the Magnum Receiver. The first one is the Drill fixture, easily identified by the words MAGNUM and the RED color. The second tool is the Main spring Plug Wrench. Used to remove and install the the Plug that secures the main spring to the receiver
MAGNUM RECEIVER PARTS
The Parts used on the MAGNUM receiver are shown above. There is our new Bolt Assembly made from 4140, with our Black Diamond firing pin, spring, Extractor Claw, spring and plunger. All manufactured by Select Fire. Then the new Charging handle assembly with the larger more robust and aggressive handle, Drill Rod Shaft and Stainless Steel spring. The Brass Spring Follower , Main spring retention Plug and Main Spring used to apply additional mechanical static pressure to the bolt assembly.
Clean all sharp edges to include the radius around the barrel hole, The edges should be rounded .020
Purchase a Dremel tool to assist with the build process
Remove all sharp edges on the bolt face where the bullet rim seats.
Remove sharp edges and polish the sides of the extractor claw (Don't polish the tip)
Make sure the bullet ram profiled on the bottom of the bolt fits between the magazine feed lips, If it does not remove material from sides as necessary.
If the buffer gets chewed up add more spring to the main spring. The bolt should eject rounds but not to the extent of contacting the buffer. The goal is to get the rounds to just eject, not to fly out the side of the rifle.
Use premium ammo like CCI to break the gun in.
Take your time, drill the holes in the right locations, use the correct tools, do not be in a hurry!
Link to Video of a Select Fire MAGNUM Receiver being test fired by the builder