taiwanluthiers
Cast Iron
- Joined
- Dec 6, 2016
- Location
- Xinjhuan District, New Taipei City
So my machining of a Remington 700 action from scratch is a success. I do not have a broach, EDM, or any fancy machines. Heck, I do not even have a lathe!! All I have is a modified Grizzly G0704 benchtop mill. Not the best but it's adequate for the job assuming carbide tool is used.
I started with this:
414 pre heat treated bar stock 1.575 4 MM x 249 MM 9.82 long ground OD 38-42RC | eBay
I can attest that this material is hard, and not the easiest thing to machine either. It's just the right size for a receiver however. This is the operations I took:
Bore out a .700" hole - not the easiest thing to do and it actually took a long time due to not having the right tool. The material eats HSS drill bits for breakfast. The hole must be drilled in increments.
Form the bolt locking abutment - While the receiver is clamped vertically, I used a short boring bar to bore the front of the receiver to 1 inch in diameter. The problem with a boring bar is the abutment will not be even... so use a counterbore or a 1" end mill to smooth that out.
Thread the receiver - I used a very cheap 1 1/16" - 16 tap I found from an ebay seller in China (similar tap can be bought for around 35-45 dollars). I didn't care about the spec as long as it was 1 1/16" -16 (and it fits a stock Remington 700 barrel properly). If you are not using a tap wrench (recommended, make sure you put even pressure on BOTH sides) you must take care to put pressure on BOTH sides or else it will cut at an angle, which happened to me. I corrected it by flipping the receiver and chasing the thread by putting pressure on the OPPOSITE side. That fixed it but the thread is looser than I like... but the receiver held up fine.
Mill out ejection port - Yes, VERY counter-intuitive, however this step is necessary because it forms a good portion of the bolt raceway. The idea is, use standard machining process to form the bolt raceway however by milling the raceway through the ejection port, you cut the length that you must broach from over 8 inches (for short action) or 9 inches (for long action) down to 2 inches or less (doesn't matter the action length).
Broach the raceway - Stand the receiver straight up again. Using a 4 flute 3/8" end mill (you may want a ball end or corner radius end mill for this), DRILL down into the abutments. Do this until you cut into the raceway made in the precious step. Take light cuts, use SHARP end mills, and high-ish RPM. You don't need to take off a lot of material but you do need to take off a steady amount of material. Some deflection is possible here. When you get done making semi circles approximately the width of the bolt locking lugs, switch to a smaller end mill and make that corner smaller. You need end mills that are at LEAST 4 inches long for this so don't get too carried away with small end mills, 1/4" is the smallest you can do before you start breaking them. When you get done with one end, flip it over and repeat.
FILE the raceways - Yes, use a GOOD file to file the raceways until the bolt fits. This is going to take quite some time but keep at it. Good things come to those who are patient. After enough elbow grease the bolt will start fitting... do this until it slides in and out without difficulty.
Cut both the extraction and chambering cam - This is where I messed up... I cut a good chambering cam by using a dremel bit and a 4 flute 1/8" end mill until I get a good ramp. However I completely forgot about the extraction cam and as a result, I do not really have one. I may wind up gluing a piece of steel to the back of the receiver for this but I can still extract the bolt by pulling HARD on it after opening.
Finishing touches - Now you can drill for the scope mount, mill for the magazine, chambering ramp, hatcher hole, etc. and blue the metal with whatever... I didn't mill out a magazine pocket because this will be a single shot rifle. I will try again and see how it works.
As you can see from the bottom pics, I have test fired it by loading a starting load of 30-06, and fired 2 shots at the range. I didn't go with a "proof" load because I'm not able to secure the rifle in a vise and fire remotely... so far there are no pressure signs on the cartridge (it didn't know it was fired by a homemade gun), there are no difficulty with extraction, and there are NO sign of abutment setback (I took the rifle apart and looked).
This receiver isn't perfect... I messed up on a lot of things, for example the stock mounting screw is off by about 1/8 of an inch because I had bad blueprints (the blueprint is for a short action), I had to modify the stock to fit. I also made the receiver square instead of round since I did not have a lathe. So the stock had to be modified to fit. It also does not have a bolt stop... I will probably make one eventually by drilling and tapping a hole and using a small bolt as a "bolt stop". I can't make the factory bolt stop work (I need to mill a very narrow slot in the bottom of the receiver) and the "external bolt stop" is very expensive.
I started with this:
414 pre heat treated bar stock 1.575 4 MM x 249 MM 9.82 long ground OD 38-42RC | eBay
I can attest that this material is hard, and not the easiest thing to machine either. It's just the right size for a receiver however. This is the operations I took:
Bore out a .700" hole - not the easiest thing to do and it actually took a long time due to not having the right tool. The material eats HSS drill bits for breakfast. The hole must be drilled in increments.
Form the bolt locking abutment - While the receiver is clamped vertically, I used a short boring bar to bore the front of the receiver to 1 inch in diameter. The problem with a boring bar is the abutment will not be even... so use a counterbore or a 1" end mill to smooth that out.
Thread the receiver - I used a very cheap 1 1/16" - 16 tap I found from an ebay seller in China (similar tap can be bought for around 35-45 dollars). I didn't care about the spec as long as it was 1 1/16" -16 (and it fits a stock Remington 700 barrel properly). If you are not using a tap wrench (recommended, make sure you put even pressure on BOTH sides) you must take care to put pressure on BOTH sides or else it will cut at an angle, which happened to me. I corrected it by flipping the receiver and chasing the thread by putting pressure on the OPPOSITE side. That fixed it but the thread is looser than I like... but the receiver held up fine.
Mill out ejection port - Yes, VERY counter-intuitive, however this step is necessary because it forms a good portion of the bolt raceway. The idea is, use standard machining process to form the bolt raceway however by milling the raceway through the ejection port, you cut the length that you must broach from over 8 inches (for short action) or 9 inches (for long action) down to 2 inches or less (doesn't matter the action length).
Broach the raceway - Stand the receiver straight up again. Using a 4 flute 3/8" end mill (you may want a ball end or corner radius end mill for this), DRILL down into the abutments. Do this until you cut into the raceway made in the precious step. Take light cuts, use SHARP end mills, and high-ish RPM. You don't need to take off a lot of material but you do need to take off a steady amount of material. Some deflection is possible here. When you get done making semi circles approximately the width of the bolt locking lugs, switch to a smaller end mill and make that corner smaller. You need end mills that are at LEAST 4 inches long for this so don't get too carried away with small end mills, 1/4" is the smallest you can do before you start breaking them. When you get done with one end, flip it over and repeat.
FILE the raceways - Yes, use a GOOD file to file the raceways until the bolt fits. This is going to take quite some time but keep at it. Good things come to those who are patient. After enough elbow grease the bolt will start fitting... do this until it slides in and out without difficulty.
Cut both the extraction and chambering cam - This is where I messed up... I cut a good chambering cam by using a dremel bit and a 4 flute 1/8" end mill until I get a good ramp. However I completely forgot about the extraction cam and as a result, I do not really have one. I may wind up gluing a piece of steel to the back of the receiver for this but I can still extract the bolt by pulling HARD on it after opening.
Finishing touches - Now you can drill for the scope mount, mill for the magazine, chambering ramp, hatcher hole, etc. and blue the metal with whatever... I didn't mill out a magazine pocket because this will be a single shot rifle. I will try again and see how it works.
As you can see from the bottom pics, I have test fired it by loading a starting load of 30-06, and fired 2 shots at the range. I didn't go with a "proof" load because I'm not able to secure the rifle in a vise and fire remotely... so far there are no pressure signs on the cartridge (it didn't know it was fired by a homemade gun), there are no difficulty with extraction, and there are NO sign of abutment setback (I took the rifle apart and looked).
This receiver isn't perfect... I messed up on a lot of things, for example the stock mounting screw is off by about 1/8 of an inch because I had bad blueprints (the blueprint is for a short action), I had to modify the stock to fit. I also made the receiver square instead of round since I did not have a lathe. So the stock had to be modified to fit. It also does not have a bolt stop... I will probably make one eventually by drilling and tapping a hole and using a small bolt as a "bolt stop". I can't make the factory bolt stop work (I need to mill a very narrow slot in the bottom of the receiver) and the "external bolt stop" is very expensive.