M40a1 build guide

Re: M40a1 build guide

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TWO MAN ATTACK</div><div class="ubbcode-body"> The cuts are comepletely different. One of the barrells has is 0.90" depth and the other is 0.75" depth. Both specs call for a 45 degree cut, but barrell lenght and the 2112 building the rifle would determine how "square" the cut would look. Hope the following pictures and explanation helps. The owner of GA Precision had posted some pictures of used USMC issued barrells that had been removed from the M40A1s at Quantico. They have since been deleted. Perhaps he can repost them to show the variance in the crowns?

Crown:

45 degree .090" deep

icrbf8.jpg




".075 deep and at a 45 degree angle to leave an approximate final width of .750 at the widest portion of the crown" The 45 degree was not critical so some looked more "square cut than others."

2vi2y61.jpg

</div></div>

Ummmm........ What crown??? LOL!
 
Re: M40a1 build guide

Does anyone know the official name of the bottom metal inlet for the M40A1 spec stocks?

Searching through 23 pages on this thread, and don't see it actually mentioned.

Figure I'd place an order in for a spec stock before McMillan raises their prices at the beginning of the year, and wanted to know what the details to give them when ordering.

Thanks!
 
Re: M40a1 build guide

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: firesniper27</div><div class="ubbcode-body">WILLIAMS DOSENT MAKE THE TWO PEICE BOTTOM METAL ANYMORE I DON'T THINK </div></div>

Are you sure about that I just ordered some directly from Williams about 2-3 months ago. I know GAP uses Williams on the spec builds. If I had it to do over again I would just get it from GAP or TBA as it will already be modified.....
 
Re: M40a1 build guide

Since the M40A1s were built in the 70s, I believe the Win bottom metal used was post-64 and not pre.

Does anyone have any before and after photos of the mill work they had to do to the Win bottom metal?
 
Re: M40a1 build guide

I picked an unmodified post 64, M70 two piece bottom metal on gunbroker a while back. If I had it to do over again, I would just send the rifle to GAP or TBA and have them supply it, neither of them seemed to have an issue with supply when I asked each about it. I am pretty sure I could handle modifying the bottom metal, but the trigger modifications to make it work are a little beyond my scope of gunsmithing. If you look around on Ebay or gunbroker you will probably come up with something.

 
Re: M40a1 build guide

confused.gif
Here's the true scoop..........

The original M40A1 bottom metal was <span style="font-weight: bold">pre-64</span> Winchester Model 70. Like everyone else, the Marines preferred the forged and milled parts to the cast crap. They only switched to the cast, post-64 parts when the pre-64 parts were becoming too difficult to source on a consistent basis. The only advantage to the cast, post-64 parts was that it was found the steel around the floorplate screw hole was beefier and less prone to breakage than on the pre-64 floorplates.

I haven't been able to determine precisely when the change ocurred, but I understand the later runs (1992 and later) were made with the post-64 bottom metal.
 
Re: M40a1 build guide

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rainier42</div><div class="ubbcode-body">This trigger guard/bottom metal issue is the only thing really stopping me from going ahead with my own build. </div></div>

If you can thread, chamber, and crown a barrel blank, clip slot the receiver, true a bolt face, lap lugs, glass bed, drill and tap for sling swivels, mill the trigger housing, TIG weld the magazine, and hot blue the works, then fitting the bottom metal should be a breeze. It was one of several things I found I <span style="font-weight: bold">could</span> do on mine.

The most critical step is in milling the shoulders in the bolt holes true to the angles of the receiver bolts. If they are not true (flat and perpendicular to the axes of the bolts), the shoulders on the bolts will not have full bearing, and that will affect accuracy to some degree.
 
Re: M40a1 build guide

Dude, please stop spamming this thread with multiple posts when you can put them into one, either originally or by editing a post.

And there are rules on this forum on selling stuff, which you're breaking with these last couple of posts. Please read up on and follow them, otherwise moderators and the forum elders will start being mean to you.
 
Re: M40a1 build guide

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rainier42</div><div class="ubbcode-body">10x ... it's not that I can do the above, it's just 1 less thing that I was hoping I would need a gunsmith for.</div></div>

Okeedoke. If you have a new stock from McMillan inletted for the M70 bottom metal, here's how I remember doing mine....

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Install the trigger guard (either cut or uncut) and measure from the center of the front action bolt hole in the stock to the front of the shoulder on the trigger guard where the end of the floor plate should end up. Then measure from the center of the hole in the floor plate hinge to the centerline of the floor plate and scribe a small line , where it will be cut to length. Then scribe a line across the floor plate at that line for your cut line. Make sure you have the cut line straight across, i.e. do not use a square to make the line, as the sides of the floor plate are not parallel.

Clamp the floor plate and either band saw or hack saw across the floor plate to make your cut, leaving the scribe line showing. Then, use a fine flat file to dress the cut straight across.

Install the floor plate and check for fit. It should need a bit more shortening to bring it to length. Use the file to remove a little metal at a time and adjust the angle of the cut until there is a small and even amount of clearance between the trigger guard shoulder and the end of the floor plate.

---------------------

Remove the floor plate release pin, spring and plunger from the trigger guard. Install the trigger guard in the stock with the action in place with its magazine. Scribe a cut line on the front of the trigger guard flat at a point where the rear of the magazine sits, leaving enough clearance between the two so they will not touch when completed, but leaving as much of the flange as possible for enough space to drill and countersink for your front trigger guard screw. Cut or mill the front of the trigger guard flange off at the line, and dress as needed.

Drill and countersink for your front trigger guard screw.

--------------------------------------

Tape your receiver and bottom metal in place in the stock, leaving the action bolt hole areas free. Make sure the trigger guard is all the way to the rear, and the floor plate all the way to the front. Get a 1/4"-28 bolt about 5" long, and cut the head off. This will be your indexing bolt to index the parts at the proper angles for milling the bolt holes in the trigger guard and floor plate so the shoulders of the bolts mate properly in the countersinks.

Screw the bolt into either action bolt hole, and leave the bolt's headless shaft end sticking out through the trigger guard or floor plate hinge, whichever you are working on at the moment (The bolt <span style="font-style: italic">should</span> center in the holes if the inletting is good to go). Carefully lift the rifle and chuck the shaft in a drill press, lower the chuck and clamp the stock enough to hold it securely in place at whatever angle it ends up being. Make sure, though, that the shaft is not being flexed in any way, or the cut will not end up square to the axis of the bolt.

Loosen the chuck and raise it from the indexing bolt shaft. Remove the bolt from the receiver and chuck up a 3/8" end mill. Turn the end mill at slow speed into the bolt hole to remove the tapered countersink and cut a square shoulder to match the square bottom of the bolt head. Only cut enough as needed to provide sufficient surface for the action bolt to torque against, leaving sufficient metal for strength.

I cannot honestly remember if I hand turned the chuck, or ran the end mill under power, but slow speed and careful is key here. It helps to have the trigger guard cut and the front screw in place to help hold it during milling, so have that step done before doing this. Everything needs to be taped really well and solid so it doesn't shift during the process.

Repeat the process for the other action bolt.

The same can be done carefully with a mill under power, but I didn't have access to one at the time.

-------------------
You will need to mill or carefully file the trigger opening in the trigger guard to provide clearance for the Remington trigger and bolt release.



Measure twice and cut once. Check and recheck everything along the way. Go slow and be carefull. But, I'm sure that all goes without saying.

Do at your own risk, or send it out to have done. Good luck.
 
Re: M40a1 build guide

I had to modify the post because I couldn't remember if I hand turned the end mill in the drill press, or if I had it turning under power at slow speed. Afterall, that was over 20 years ago. I suspect I would have had to turn it under power as I don't think I would have been able to cut the steel by hand. Maybe, like a reamer, but I just don't know. Maybe try it by hand first, and go to power if you need to. Using power is a potentially dangerous way to do it, so be sure everything is tight and solid, and go slow.
 
Re: M40a1 build guide

Thanks for the update, 10X. I did a side-by-side between my pre-64 M70 and my M40 Repro last evening to better vision what you were talking about. May take off the bottom metal from both this weekend to better see.
 
Re: M40a1 build guide

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rainier42</div><div class="ubbcode-body">Thanks for the update, 10X. I did a side-by-side between my pre-64 M70 and my M40 Repro last evening to better vision what you were talking about. May take off the bottom metal from both this weekend to better see. </div></div>

Now, an M40 should have stock Remington bottom metal. But you should be able to see how the front of the Winchester trigger guard will have to be shortened, and a new front screw hole drilled.

The action bolts (some say screws) in your M70 will be oval headed. The M40A1 uses allen bolts, which have square shoulders. That is why the tapered countersinks in the trigger guard and floor plate hinge need to be milled flat to mate with the square shoulders of the allen bolts.
 
Re: M40a1 build guide

Couple more questions ... and I appreciate all of the patience you all have extended to me here ... 1. Why was the Winchester bottom metal used and not a standard or upgraded Remington? 2. Does the box magazine have to be welded to the receiver? Thought I read somewhere that they started out with the welding but stopped the practice after a bit.
 
Re: M40a1 build guide

I dont believe you have to weld it. If i remember right they stopped welding it pecaus it was problematic. you could use a adl mag box cut to fit the bottom metal it is attached via a screw so you wont have to weld it.
Think i read that in this thread.
 
Re: M40a1 build guide

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rainier42</div><div class="ubbcode-body">Couple more questions ... and I appreciate all of the patience you all have extended to me here ... 1. Why was the Winchester bottom metal used and not a standard or upgraded Remington? 2. Does the box magazine have to be welded to the receiver? Thought I read somewhere that they started out with the welding but stopped the practice after a bit. </div></div>If u look on page 1 of this thread george explains some of this on there about the welded box mag, it doesnt say y the marine corp used the win. mod70 floorplates, theres also some pictures of a box mag welded up to a reciever on page 2 if that helps,, i dont think there were any box mag that was screwed on ever. they used to weld the recoil lug,, but stop doing this becacause of problems
 
Re: M40a1 build guide

MWhite ... got it and thnx! This is a resource rich thread and very easy to miss things. I confused the tac welding of the box magazine with the recoil lug.

Regarding the Win Mod70 Floor plate, everything I've read says it was used. Is also discussed throughout this thread. What am I missing?
 
Re: M40a1 build guide

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rainier42</div><div class="ubbcode-body">MWhite ... got it and thnx! This is a resource rich thread and very easy to miss things. I confused the tac welding of the box magazine with the recoil lug.

Regarding the Win Mod70 Floor plate, everything I've read says it was used. Is also discussed throughout this thread. What am I missing?
</div></div>I dont think your missing nothin, im like u, ive study this my self and still dont know it all. The win mod70 floorplates was used on these guns for reasons i dont know other than maybe there wasnt a solid piece made or produced then that was good enough,, then so they modified these cause they were strong,i read some where on here where they welded them to the reciever because the box mag would rattle if they didnt and even tape the latch to floorplate so it would not open. there are some solid pieces floorplate out there now that work better than this set up, but if u r building a clone mod70 floorplates is what u need. good luck.
 
Re: M40a1 build guide

MWhite ... yes, Williams as an example, makes an excellent steel floor plate. Have to decide how close I actually want to get. Am actually seeing a pretty clear path now on how I want to proceed with a build.
 
Re: M40a1 build guide

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rainier42</div><div class="ubbcode-body">Couple more questions ... and I appreciate all of the patience you all have extended to me here ... 1. Why was the Winchester bottom metal used and not a standard or upgraded Remington? 2. Does the box magazine have to be welded to the receiver?</div></div>

O.K.
The Winchester 70 bottom metal was used because a) it is MUCH, MUCH stronger than the Remington bottom metal, and b) the floor plate latch inside the Remington trigger guard was terribly prone to accidental actuation and inadvertant dumping of the ammunition from the magazine.

The magazine must be welded to the receiver to prevent vibration during firing. Any vibration, and accuracy suffers.
 
Re: M40a1 build guide

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 10Xview</div><div class="ubbcode-body">

The magazine must be welded to the receiver to prevent vibration during firing. Any vibration, and accuracy suffers. </div></div>

They were welded in because the modded Win bottom metal had no way of retaining the mag box when it was opened up whereas the 1pc Remington bottom metal held it otherwise. On the Win 70 the mag box is retained with the trigger guard extending over the mag box and the front held with the ears on the front piece of floorplate! Remington had the same shit metal in 62 (or in 66 with the M40) that it does now!

As for "accuracy suffers" how many factory rigs or custom actions nowdays use a welded in mag box to enhance accuracy??? It was welded because there was no other way of keeping it in place!
 
Re: M40a1 build guide

SD ... thanks for the explanation. In terms of the magazine used, I assume it is the standard issue magazine that comes with the action?

Yes, the bottom metal on Remington is pretty crappy and is why I am upgrading the bottom metal on my M40 to a Williams.
 
Re: M40a1 build guide

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SDWhirlwind</div><div class="ubbcode-body">
As for "accuracy suffers" how many factory rigs or custom actions nowdays use a welded in mag box to enhance accuracy???</div></div>

For that matter, how many factory rigs or custom actions use a welded recoil lug? Leave it to the Marines to try anything to squeeze every posible ounce of accuracy out of a sniper rifle!

Yes, you are absolutely correct about a BDL magazine dropping out through the floorplate if not somehow secured. I thought that went without saying. Of course, that being the case, they could have simply used easily removable, modified ADL magazines, but they didn't. I wonder why.



 
Re: M40a1 build guide

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 10Xview</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SDWhirlwind</div><div class="ubbcode-body">
As for "accuracy suffers" how many factory rigs or custom actions nowdays use a welded in mag box to enhance accuracy???</div></div>

For that matter, how many factory rigs or custom actions use a welded recoil lug? Leave it to the Marines to try anything to squeeze every posible ounce of accuracy out of a sniper rifle!

Yes, you are absolutely correct about a BDL magazine dropping out through the floorplate if not somehow secured. I thought that went without saying. Of course, that being the case, they could have simply used easily removable, modified ADL magazines, but they didn't. I wonder why.



</div></div>

Yes, but it was the recoil lug that they stopped welding I believe because it just didn't work out.
 
Re: M40a1 build guide

Just in case anyone frequenting this M40A1 thread is interested

http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=3740604#Post3740604

Also cut down a new bolt shroud to the old pre 68ish short length like on original M40 bolts. Did it for a guy planning on building a rig and found out after I did it he didn't even have the rifle bought yet. Sold the rifle a few weeks later cause he needed money and never bothered to tell me. After 3 months waiting I PMed him to find out I altered a new shroud for 'my entertainment' I guess. Anyone wants it @ $25. Just cold blued on the rear. Also can cut yours down if needed for M40 or early M40A1 build. Pictured between an original '64 shroud and newer longer shroud.

P1010006-1.jpg


Thanks
Respectfully,
Dennis
 
Re: M40a1 build guide

Great thread guys, thank you for the information on all of these. I will be trying to assemble one of these for my dad who was a jarhead in Vietnam and one of the most incredible rifle shots I have witnessed. I will attempt to outshoot him with my 300 win this summer. Thanks again guys, y'all are great!