Wednesday, August 26, 2020

Converting a Pre-64 30-06 to 300 H&H Part 2

A majority of machine work has now been completed to the magazine cavity and feed well but the rail width modification is still required.  The OD of the belted case as well as the shoulder OD is larger than the 270/30-06 class of cases so additional room through the rails must be made to accommodate for these larger case diameters. 

It is the height of the case that protrudes above the rails and allows the lower edge of the bolt face to engage the protruding case and then allow the bolt to shove it towards the chamber. The case must stick up through the rails ENOUGH as its pushed forward or the bolt face will override the case head and cause a jam. Most 270/30-06 Model actions are approximately .545 to .550 in width from one feed lip or rail to the other side at the very rear of the feed well opening directly above the magazine box and then widens to .600 to .610 directly above the bottom of the bullet ramp. This geometry has work since the 1st Pre-64 stepped off the bus so it's hard to argue that it isn't adequate, is it prefect? well...............

All the next cuts will be made from the center-line of the receiver so you must establish the best means to do so. Again the fixture I use allows me to do this very easily. Finding the center-line I start off and finish using only a 3/32" carbide end mill. I widen the existing width at the rear of the rail from the original .545  to .610. Taking a photo of this operation is difficult at best due to the close proximity of the mills spindle being so close underside of the action. 

With the help of the DRO I will now cut stepped flats into the rails in incremental lengths from the rear forward and later on file and blend these transitions. If you had a CNC you could write a program to do this parabola shape, push start and step back. 

You can just make out the stepped width progressional flats cut into the rails 

Cutting the width and or SHAPE of the rails becomes a matter of interpretation and just how anal retentive you choose to be and still live with yourself. I would say that every Pre-64 70 I have ever worked on left the factory with the rails being straight in nature and wider across the front of the rails above the feed ramp. What I prefer to do today is the widen the rails in the partial parabolic fashion. Tom Burgess referred to this as a candle flame shape. Wider in the mid section of the rails than in the front and in the rear sections, How much you say ? at the widest point .620 to.625 seems to work out pretty well for me for the 300 H&H. When the parabola cuts are blended you also need to file or stone a radial profile to the top and bottom side of each rail. Failure to so will cause the brass to hang up as each case if rising out of the feed well and mag box. Time spent polishing the blended rails will pay off 

The ejection port is next and again carbide is your only reasonable option. I make a pass or two usually removing .006 to .010 of steel to clean up the leading edge of the ejection port and back of the front ring. I then begin opening up the ejection port to the rear. 

The number 3 scope base screw hole will always be cut away in this operation so you'd better have plans for repositioning that screw hole and what rear scope base you will ultimately use after this conversion.

How far you go to the rear is up for considerable debate and much of the next series of cuts will depend on your extractors length. The Standard OEM Pre-64 extractor is approximately 4.420 in over length. Some gun smith's will insist that the tail end of the extractor MUST be tucked under the right side of the rear bridge with the bolt turned down into full battery so the extractor's tail has no possible way of becoming jammed in ejection port. If you follow this as a rule then you can really only open up the ejection port to approx. 3.400. 

So if this is a concern you can modify the rear bridge as shown below, similar to the original factory receivers leaving a standing wall and blending an angular cut from the 3.600 opening you've established from the center line of the action out to the edge of the standing wall. 

This Pre-64 30-06 length action below has been chambered and set up for a 7mm Mashburn with an extended throat and uses up most the 3.600 real-estate in over all loaded length. To keep the 4.420 OEM extractor tail under the rear bridge I needed leave some standing wall as shown at the arrow. The OAL of the new opening is 3.600 but the port length is still 3.400. This still requires snaking the rounds in though the ejection port and under the scope mounts. While this takes some finesse and practice for rapid loading the extractor stays contained 100% of the in time in or out of battery. I've done many conversions in this manner especially when chambered for heavy calibers and are iron sight dedicated rifles. 

Then along came the Willams Firearms Company and their version of a M-70 retro fit extractors. The beauty of this Williams extractor is some of these were machined with an extra .130 in extractor length. I can't remember what date these came to my attention but I've used a dozen or so of these and still have a few squirreled away. This now gives us another option if you have one of these longer Williams units. To my knowledge Willams has ceased production and these are no longer available. 

Jim Wisner from time to time will make a run of an even longer extractor 4.900 as seen below for both right and left handed current production model 70 actions and these are also of excellent quality.

Williams Long Extractor 

Wisner Long Magnum M-70 

Provided you have on hand 0ne of the Williams longer than normal Extractors you can now open the ejection port to 3.600 completely. "But," you say "the tail will not be buried under the rear bridge !!!! " Well Yes and No as you lift the bolt out of the battery position and the bolt body rotates up the extraction cam the rearward movement in rotation places the LONGER Williams extractor tail under the rear bridge well before the bolt has completed its rotation.

To confuse the issue even more below is a standard Pre-64 action and OEM follower that is chambered for 280 Remington that has the ejection port opened up the 3.416. Note the tail of the extractor showing with the bolt in full closed battery and then the tail tucked under the rear bridge as the bolt is opened. The result is a longer loading port and a captured extractor tail. 

The wonder of it all !

A lot depends in any conversion or modification on the the materials at ones disposal. You will see similar adaptations of this on many of the Magnum length actions chambered for long cartridges. Note the visible exposed tail on this extractor fit to this H&W magnum 98 action, lift the bolt and the tail end slips under the rear bridge before the bolt rotates completely up the extraction cam, no fuss-no muss.

Time for lunch 

Sunday, August 9, 2020

Converting a Pre- 64 Mod-70 action from 30-06 to 300 H&H Part 1

In the late eighties as I began to set up or build more 375 H&H's for hunters and finding suitable actions/rifles to do so could be a challenge. By this time I had used quite a few original Pre-64 Model 70's that had left the factory as 300 H&H and 375 H&H rifles and while they all mechanically worked except-ably there were a few things that seemed to crop up over and over again with these factory long-magnum receivers that could use some attention to detail and revision.

I began to consider using the standard 270/30-06 receivers as they came from the factory and modifying them to remove the factory idiosyncrasies that I felt I could correct. Do they need correcting ? Yes, No, Maybe, so let's see.

The one area of contention is usually the 300/375 magazine cavity that holds the magazine box in place just under the feed well is usually cut with a gross amount of clearance. In short most mag boxes rattle in place. Not always a great feature to have a full magazine migrating in recoil as it will begin to distort the mag box over time and use. Then there's the amount of material removed from the lower recoil lug seat as the actions underside is by design opened up forward to allow the 3.600 length cartridges to be used. Yet another major issue is the way the factory then changed the bullet ramp angle and usually left a razor sharp edge at the top edge of the bullet ramp. There had to be a better way.

A radial notch was then cut into the rear edge of the front ring and another large radial cut was added to the front of the rear bridge to allow loading the rifle quickly from the top side of the action with these longer rounds. All was great when those rifles were fit with the Lyman or Redfield receiver sights or even kitted out with the shallow V's found on many older Model 70's. You had an opening in the top of the receiver you could fill the magazine as you back peddled away from danger.

Scope use changed this paradigm radically. Once the 1 piece scope mount became vogue you then had to really practice to load that rifle quickly. A fault ???? not in the original design idea but the system still worked day in and day out. Especially by those that had to make a living with these Model 70's.

Thousands of standard length 98 actions have been altered too except the 300/375 H&H and those suffered the same fate. It works, no doubt about it and still does.

Where was I ? 

So in an effort to make a "better" mouse trap can we use a a Standard Model 70 chambered for a 270 Win or 30-06 ? You bet.

I going to assume you have already opened up the .473 bolt face to .538 or what ever you deem the right Magnum bolt face size and fit and chambered the 300 H&H barrel. At the same time you've also modified your standard extractor hook to a magnum hook. As you're going to need that H&H chamber to use for feeding trials sooner than you think. 

You also need to understand that this is not a one hour conversion, requires a milling machine, carbide tooling and a very secure way of holding the receiver while it is being modified. The barrel should be removed and in this case the rifle receiver was also going to be fit with my scope mounts. So the 1st course of action for me was to true up the underside of the receiver as my fixtures for fitting a set of my mounts are made to work with the underside of the action being machined flat, so we're now killing two birds with one sledge. With the underside of the action leveled off the feed rails I then make a number of passes along the bottom of the receiver with usually with a 4 Flute 1/2" carbide end mill until the bottom side of the feed well and trigger area and tang are of the same level. Then I insert a 1/2" end mill into the collet that has a .030 corner ground onto the end mill. I then cut the recoil flat pocket behind the recoil lug so it is also flat. At the same time the recoil flat pocket is being cut the back face on the contact surface of the recoil lug is also being machined 90 degrees to the the recoil flat. The pic below illustrates why this alone should be done.

While not the same Pre-64 we're going to open up the photo below display's a very common occurrence with all Model 70's and that is the recoil Lug being originally machined into a wedge shape unfortunately being wider or thicker depending on your perspective at the BOTTOM of the lug. All with complements from New Haven.

Below .006 has already been removed from the back of this G -series recoil lug face and were still not cleaned up or perpendicular. Tightly Glass Bed such an action with this integral wedge into a stock and you risk breaking the stock before you get the barreled action back out of your bedding job. This issue is more common than you think with the Model 70 having machined a couple hundred of them I can guarantee this anomaly. 

Since we're converting a 270 action to 300 H&H the next step is to carefully begin to open up the feed well originally set up for the 3.400 width and length magazine box. Now we're making room for the longer and more tapered 3.630 length 300/375 OEM mag box.

Since the client supplied and original 300/375 magazine we begin fitting the new box into the feed well cavity. We measure the thickness of the back wall of the magazine and note its .030 thick. The box will rest on the lip at the rear of the mag well. Usually this lip is recessed approx. 200 deep into the feed well just ahead of the middle guard screw. The 270/30-06 magazine box back wall is approx. .050 thick and the 300/375 box is .030 in wall thickness. So we can move the back wall of the feed well even further to the rear by another .015 to .025 usually. 

The lip that the rear of the box sits on is machined to the same thickness as the back of the 300/375 mag box. There must be a seamless transition for the base of the belted mag cases to slide up the magazine and into the feed well. As the 300/375 magazine is wider at the back of the feed well the width on our 270 action must also be modified to reflect this new width. Measure the width at rear of the 300/375 box and cut away for the center-line of the action accordingly on either side at the rear.

Note the 2 red arrows as they show other areas I will need to machine to allow for the proper width in the feed well with the new 300/375 magnum box.

But first the forward end of the receiver must be cut away to the overall extend length of the longer mag box. The cavity being cut will also serve as a Depth Stop for the forward end of the mag box like the shelf in the rear of the feed well. So it will also be cut to the same depth as the rear shelf at .200.

This OP is best done with a 1/2" end mill to match the radius on the front of the 300/375 magazine box. Cutting away from either side of the actions centerline establishes the front cavity shape. Again care must be taken to the cut this overall length to the numbers, now is not the time to be sloppy

The area inked in red will also have to go but not just yet.

If I have done my math correctly the new 300/375 length box should now PRESS into place. I have controlled the amount of steel removed to a minimum to try and arrest box migration in recoil.

Sweet!!!!!! you say, but the job is far from over. Now we have to remove steel from the feed well that is currently still set up to facilitate the 270/30-06 box geometry and over hanging the the newly installed longer box. To do this OP we need to be able to rotate the action as well as off set the taper to make these cuts. As the fixture I use will allow me to pivot the action this it's not at all difficult. The taper is generated by running an indicator done the inside wall of the feed well with pivoted offset until it reeds as close to as you can get  to ZERO front to back. Being gang milled in the factory nothing on a 70 is every super  precise from one action to the next, frankly they didn't need to be. 

So the action is rotated on its axis and then locked down with which ever side of the action you chose to start on at an 8 degree angle. It is best not to guess. 

Then the new magazine box is place back into the feed well and you need to determine of much additional  steel to remove that is overhanging the new magazine box. This transition BEHIND the feed rib needs to be flush with the top or opening of the new box. This is done one side at a time and in this case with a 1/4" ball nose carbide cutter to match the original radius as cut into the action at the factory. The steel was removed .005 at a time until the top of the box and feed well blended seamlessly up to the rib in the box. DO NOT remove any material above the rib or there will be hell to pay.

With a smooth transition at the junction of the mag box and the feed well to the rear of feed rib we can now work on area ahead of the mag box rib. This feed well width in this area should allow clearance for just the loaded necks of the 300 H&H rounds and no more. Again a 1/4" ball end mill ties the 8 degree side wall cuts into the 1/2" ball mill cuts I will now make to finish up at the front end of the feed well. Confused yet ??? 

Remember the front of the 300/375 mag box has a 1/4" radius and feed well must reflect the same radius at the not only the front of the magazine on the level but also on the 8 degree taper in the feed well itself. Here a picture is worth a 1000 words. Now that we have one side done we rotated the action and re-adjust taper to cut the opposite side of the feed well. If you've gotten this far, take break for lunch you've earned it.

So far so good