determing cut depth for m16 extractor install

[thisguy65]

I'm doing this for school project. First I model a Remington 700 bolt and processed to start modifying to make sure it would be right. This is .308 bolt

1st I pulled the prints off PTG and Badger sites (PTG uses a 45 degree off set, Badger uses 30 degrees)

For the bushing I'm going to use .625 OD which is stated for magnum. But since there is no measurement called out for .308 or .223 I'm left to use this one. Or go with a slightly smaller bushing like .500 OD

If you look at the print: (download here: https://www.badgerordnance.com/wp-content/uploads/2013/10/306-90_91_92_Extractor.pdf)

Of the pocket view

The issue is the cut of .115 doesn't appear to be deep enough.

Here is to show my reference point (OD of the bolt) and depth is correct per the drawing. The bolt body is .696 OD and the bolt nose is (lugs forward to bolt nose) is 0.693OD. I'm measuring the bolt I have off my factory rifle.

It seems the correct way is to mill the slot deeper, but how deep? In the model I could use guess and check to find it would take .145 cut to get completely through bolt body to rid the area in pink squares above.

 

[SGS]

I have one in the shop with a mini m16 extractor cut in.308. I would recommend you use the smaller size (approx. 3/16 wide) for a non magnum. The front of the slot is .160 deep from a nominal .700 bolt diameter. The deep rear pocket is about .230 deep give or take. The drawing only shows the basic dimensions for the large extractor and magnum bolt face. I suspect that you should increase both the front and back of the pocket an equal amount. You may also need to lower the pin hole position.

Based on your drawing, I would probably add the difference between the standard magnum bolt face and the .308 to the depth dimensions shown on the drawing. .545 - .484 = .061 / 2 = .0305. So just move everything about .030 toward the center of the bolt.

Your bushing size should be based on the diameter you need to bore the bolt face recess to mostly clean up, and it will be smaller for the .308.

 

[thisguy65]

I have one in the shop with a mini m16 extractor cut in.308. I would recommend you use the smaller size (approx. 3/16 wide) for a non magnum. The front of the slot is .160 deep from a nominal .700 bolt diameter. The deep rear pocket is about .230 deep give or take. The drawing only shows the basic dimensions for the large extractor and magnum bolt face. I suspect that you should increase both the front and back of the pocket an equal amount. You may also need to lower the pin hole position.

Based on your drawing, I would probably add the difference between the standard magnum bolt face and the .308 to the depth dimensions shown on the drawing. .545 - .484 = .061 / 2 = .0305. So just move everything about .030 toward the center of the bolt.

Your bushing size should be based on the diameter you need to bore the bolt face recess to mostly clean up, and it will be smaller for the .308.

I'm glad you posted this because as I study the drawing and saw a few articles that use the mag bolt. I got me thinking. I was thinking to take the difference in the bolt dims of the mag and standard but didn't have any one to confirm.

 

[SGS]

I see that PTG only has a drawing for the large (1/4") extractor and magnum Bolt face in the downloads page of their website. Sometimes if you call them they may have a drawing they can email. It works for reamer drawings. Another note: If you are doing a barrel install, they suggest an oversize recess for the bolt nose to allow the extractor enough clearance to pop over the case rim. This is usually only needed for magnums. With the extractor set deeper into the bolt it can open enough to pop over the case rim without requiring an oversize bolt nose recess. I think this is the best and safest way to go.

 

[msalm]

First, depending on your attachment method, I usually counterbore the bolt nose until the existing extractor groove is cleaned up completely. If using solder I like clean metal all the way around. After soldering the bushing in and boring out to size, I found the easiest method is to measure the thickness of the nose of the bolt from the outside to the boltface. Take this measurement and add the depth of the extractor groove, that should be the depth you need the extractor to be. In the deeper pocket leave the far rear portion a little shallow where the spring will be by maybe .010" as on the standard bolt face the deep pocket will cut into the firing pin hole (on occasion).

 

[SGS]

I received an email from Badger after I posed the question about the depth of the extractor cut. Their response is that the cut is the same for all calibers. Assuming that the hook on the extractor is considerably longer for the std. bolt face than the magnum, this would still leave the extra material to be machined from the bushing which would be best done from the front, another setup.

I think you will be glad that you decided to use the mini M16 extractor. It is the one that Jerry Stiller and others are using for .308 and .223 bolts. I did also send an email to PTG about the vagueness and error on the drawing they have posted on their website. Hopefully, they will respond.

 

[thisguy65]

Thanks SGS. Are you still in NC? If you allow I may have to spot by sometime. Parents have a place in Holly Ridge.

I did order a badger extractor to compare it to my defiance.

 

[SGS]

I am still in Hubert, NC. Send me an email. Address is in my profile.

 

[thisguy65]

I went and bought badger extractor so I have the part to measure and comparing it to the defiance (other than the defiance being a mini) the claw is considerably deeper.