M40a1 build guide

Jun 6, 2003
Well a couple of you have asked for a build guide for our M40a1 take off stocks. I am building an accurate clone, and learning as I go. I am by no means an expert, but I'm trying to find the right information just like many of you. Please post if it directly pertains to a the topic at hand or better yet just email me so we can keep the information condensed.

Jun 6, 2003
Re: M40a1 build guide

Matching Numbers:

The bottom metal doesn't necessarily need to be matching. I've spoken to George about this, and he mentioned that parts are just x'd out, and new numbers are engraved or stamped.


For those doing an accurate clone that means the Unertl 10X or the USO MST 100. According to John at USO the transition took place in late 1999. "I don't know how many M40A1 rifles saw our scopes on them. Just about all of the A1's were converted over to the A3 when they came back to Quantico. However, I have seen a couple."

I have a relatively new stock, and a C prefix action so I'm making a '92 or newer clone. I'm sure those of you doing the same are interested in when their rifle "could" have been issued.

I think the BDC dial for the Unertls was built using the old 173 SMK at a certain velocity. I don't think the BDC was changed when the switch from the 173 to the 175 took place.

This is the MOA drop for the Unertl/MST 100 for M118LR.


(MOA drops updated after shooting out to 700 yards dated 9/22/08)


This was from John at USO directly.

"The mounts that we are making are exact replicas of the original Unertl mount. These are a 0 moa down angle one piece mount with Redfield 1" rings silver soldiered to the base. These had 6-48 screws to mount the base to the receiver, unlike the M40A3's which use the 8-40 screws. The rings and base are made from 4130 or equivalent steel. So these mounts that we are making will be identical to the originals for historic purposes."


I bought an MRT sling. I think that's right, but not sure at all.


The U.S. mark over the Serial Number (for early 6 digit actions only) and Barrel mark

The marking on the bolt handle

The barrel, recoil lug, bolt, trigger guard, floor plate, and stock are all serialized.

Metal work:

Clip slotted mounts

The trigger has to be notched to clear the floor plate (updated with George's comments).

The factory recoil lugs are tapered 2 degrees. The recoil lugs were tack welded to the receivers on early rifles. This was stopped due to causing problems.

BDL Mag boxes were used and tack welded to the receiver.


It seems that the original actions for the M40a1 came from the M40's that were retrofitted, and were the 6 digit actions manufactured between '66 and '71. The numbers for the original actions were between 168,179 thru 322,769. These actions were replaced or augmented over time. About 100 additional C prefix actions were purchased from Remington in '92 for this reason. I also asked George about his, and he said that there were more E prefix actions in service than anything else.

The action screws used were 1/4X28 Hex Head screws with a black oxide finish. The front trigger guard screw is a 6X32 with the same threads as an electrical outlet screw.


There have been several barrels throughout the course of the M40a1 in varying lengths. The demensions are as follows: 1.2" for 4" then tapering to .91-.92" at the muzzel. These barrels were 6 groove, 1/12" twist, stainless steel and finished with a counter-bore crown. Hart, Schneider, Atkinson/H&S Precision all supplied barrels at one time, but I'd like to know when to get the time period clone right. The lengths vary from 26" to 24" measured from the expansion port.

The following quote was from another memeber:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I don't know if you'd be interested in this for your thread, but I got it during a conversation I had with Gary Schneider of Schneider barrels, back on 8-17-06 @ 3:30PM, via telcon.

I found he was a most pleasant person to talk to and surprisingly gave me information freely, considering he didn't know me from Adam, though I live not too far from his shop.

He said the M40A1 barrel dimensions were 1.10-1.210 +/- X4", straight tapering to .890-.910 +/- @ 26.5".

After cutting and threading the breach end you would end up with 1.20" X3", +/-.
Once it was threaded at the breech end they(the USMC armorers I believe) would trim the muzzle of the barrel to 24" from the front of the trued recoil lug, as is their method of measurement, making the muzzle approximately .920-.940, again +/- . ;\)
He stated there were variations of +/-.015", maybe more at times.

He also said the barrels had a rough turned finish when supplied to the Marines Corps initially as they were rushed to meet the deadline. He said he offered to make them smoother on production models if accepted(which he was), but the Marines liked the rough finish as they said it held paint real well, so he made all the rest of the contract the same way.

I was curious about the 1.20X3" finished breech end measurement as I was not used to that. Most civilian rifle barrels I had used or seen previous, had measurements of 1.25"X 4-5" X whatever length. He said that was strictly to facilitate the use of the night vision equipment they had/have. Any longer or thicker in the breech end would cause interference with the objective, or other parts of the NV equipment. So it wasn't just some outdated military quirk. This was info I hadn't known, and I learned a lot in that conversation. </div></div>


45 degree .090" deep

Special thanks to anyone who contacted me with information regarding this guide. I'd like to thank John at USO specifically for taking the time to answer my questions, and capture the images of his fine example of Marine Corp history. I hope this helps you guys.
Feb 25, 2007
Austin Texas
Re: M40a1 build guide

All I know about the M40A1 clones is that George has been to Quantico to examine and determine all of the markings and designs behind the A1 and A3. I do not know of any other builder who has done this unless they were a previous Marine Corps armorer. I would go to George for his knowledge of this sws. Good luck and I hope I get to see pics of the beauty when it is done.


Sergeant of the Hide
Jan 20, 2004
Re: M40a1 build guide

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CWSShooter</div><div class="ubbcode-body">unless they were a previous Marine Corps armorer. </div></div>

Actually GAP has one of those too. Eric was a USMC 2112

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Biography of Eric Reid, Senior Custom Rifle Builder, G.A. Precision


in 1994 he is recommended for the illustrious 2112 “Gunsmiths of the Corps,” 15 month OJT School at Precision Weapons Section, Weapons Training Battalion, MCCDC, Quantico, VA. There are no text books; the skills learned there are passed down from generation to generation, right there in the shop, right there at the bench. Upon completion of the school, he was assigned to Sniper section. Shortly thereafter, he was made section head, where his responsibilities included the training of new students, maintaining the rifles assigned to Scout Sniper Instructor School, and rebuilding the entire M40A1 inventory in the Corps. He got another medal. He was also instrumental in the research and development and building of the M40A3.</div></div>
Nov 14, 2006
Re: M40a1 build guide

I like the way you are going with this. It will eliminate a lot of previously asked questions/topics. Plus, as a sticky topic the information and experience shared is endless, available, and priceless.


Aug 4, 2006
Coast Range
Re: M40a1 build guide

I am building one also, cant afford a mst100 yet hovewer. Here from what i know to fill in the holes:

Douglas tubes also used at one time
“7.62 NATO” marked barrel (rebarrels)
deep Recessed Crown
Marked "U.S." on reciever above serial, 6 digit recievers
bdl box tac welded
tapered stock lug, only tac welded on very early ones, some tac welds were even grinded away they caused problems
Likes: Acer76
Jun 6, 2003
Re: M40a1 build guide


I'm getting conflicting information regarding the "7.62 NATO". I was at GAP a couple of weeks ago, and handled George's rifle when he was scuba diving. It didn't have the 7.62 NATO stamp. I've also been told that the M40a1's all had BDL mag boxes tacked in place on all of them. I'm veryifing this information so bare with me.

I've emailed George, John, and Dick Davis in an attempt to get as much info as possible in one searchable format. John has already returned my request for the above response. Thanks guys, and keep them comming.

Likes: Supersubes


Aug 4, 2006
Coast Range
Re: M40a1 build guide

Jeff, I believe the very very early ones did NOT have "7.62 NATO" stamped, when they were rebarreled the stamps took place. I am pretty sure George put together a rifle for himself that would clone the very first m40a1s since ive seen his stock and its one of the early ones. He would know better, i am going by what i have in a few books and such. I also understand that most of the original rifles have had so many things swapped around that some conflicting info will be present. If your bottom mettal does not match, just cross it out with a fine dremil bit and electroplate a new number thats what the Quaintico did!


Gunny Sergeant
Mar 26, 2002
N Kansas City, MO
Re: M40a1 build guide

7.62 NATO” marked barrel

Not on M40A1's Some M-40 rifles that were re-barreled by Remington were marked this way but never an M40A1. The Early ones were marked RTE - P the P is for Proof fired and was stamped by the Test Shed. The RTE stands for "Rifle Team Equipment" After 1998 The RTE became PWS "Precision Weapon Shop"

Deep Recessed Crown - Correct 45 deg .090 deep

Marked "U.S." on reciever above serial, 6 digit recievers only -

the C, E and now G are not marked U.S

bdl box screwed on later ones - Never Ever

tac welded on all others - All of them

tapered stock lug - Correct 2 deg taper

lug tac welded on very early ones - Correct

some tac welds were even grinded away they caused problems -

Correct, they were all ground away, none were left with welded lugs by 1995

The Picture above of the Modified Trigger is wrong. They were milled not dremeled, and the dimentions were .240 from the front, .290 Heigth. Cut away.
Jun 6, 2003
Re: M40a1 build guide

The information has been updated with George's comments. I'm still looking for info regarding the proper sling. Thanks to all.

Dec 18, 2001
Damascus, MD USA
Re: M40a1 build guide


The come-ups posted for the MST100 seem a little odd to me on the 400 yard value.

Here's what's posted:
<span style="font-weight: bold">
100 yards: 0 MOA
200 yards: 2 MOA
300 yards: 5 MOA
400 yards: 10.5 MOA
500 yards: 12.5 MOA
600 yards: 17 MOA
700 yards: 21.75 MOA
800 yards: 26.5 MOA
900 yards: 32.5 MOA
1000 yards: 39.5 MOA

I believe the 400 yard value could be in error, I'm thinking something in the 8.5 - 8.75 range rather than 10.5.

I have an MST100 but haven't used it just yet to verify. Would you mind a re-check those values, I'd appreciate it.


Sep 24, 2006
Mille Lacs, MN
Re: M40a1 build guide

Yep you were right the come ups was wrong....if you need anymore info besides technical dimensions and what not I still have all my books right here....just ask...its just a matter of flipping pages and typing stuff out....


Gunny Sergeant
Jan 26, 2006
Kennesaw, GA
Re: M40a1 build guide

We celebrate number 10 here in just a couple days!! Dated for 4 before that! I'm a very lucky fella!!! Took me 3 tries, but I definitely have a keeper!! Hope she still feels the same way when this month's CC bills come in!!!

#10 is glass right???
Sep 18, 2003
Gilbert AZ
Re: M40a1 build guide

I just had my tenth last weekend, all I got was a nice stay at a B&B in Laguna Beach.........
But she has facilitated me going from zero to 22+ firearms since we've been wed (including #1451 frankenfortyehwun)!
Feb 4, 2004
Vista, CA. U.S.A.
Re: M40a1 build guide

Trigger guard:
The one I have is smashed in, and I am opting for a replacement. Any recommendations for suppliers of a replacement would be appreciated. The modification to the length and the front screw position is not problem for me.
Re: M40a1 build guide

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bmbrzmn101</div><div class="ubbcode-body">Parga, Is there any way I could also get a copy of the clip slot dimensions. Your help is appreciated. Thanks Chris </div></div>

Um, no... I've changed my mind, no help for you.
Coming to you from rmp@redshift.com
Apr 22, 2007
Re: M40a1 build guide

Whats the difference between the USO and the Unertl MST 100 and witch one would be correct ? We have the real stocks might as well go with the right scopes . Also what is the ring height for the redfield rings and who makes the base . Man to many choices or lack of cash to hard to tell .
Semper Fi
Re: M40a1 build guide

Unertl was the first scope to go on the M40A1 but then USO got th contract for refurb and replacement as needed. If you see some pictures of the A1 and there's a access plug on the left hand side of the turret base that shows it was at USO at one time for refurb.

JBW#3 I am correct on this right?
Oct 18, 2004
Re: M40a1 build guide

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: usmcjones</div><div class="ubbcode-body">Whats the difference between the USO and the Unertl MST 100 and witch one would be correct ? We have the real stocks might as well go with the right scopes . Also what is the ring height for the redfield rings and who makes the base . Man to many choices or lack of cash to hard to tell .
Semper Fi </div></div>
JBW#3 at USO is making some replica base/ring sets and setting them up exactly like the USMC version to include the tackweld.
Re: M40a1 build guide

Very interesting ... I have a Remington 700 in 7.62 in a McMillan M40A1 stock and it's my favourite:

The McMillan is a superb stock, but recently the rear action screw, which I had been torqueing down to 65 inch pounds started to compress the stock (the bottom started to give way) and I remedied this with aluminum pillars.

Now this is not a shot at McMillan stocks, as mine's over 25 years old and everything needs maintenance, but wouldn't this have happened with USMC rifles, if only occasionally?

Likewise, I've had trouble with the Remington bolt release fouling occasionally, causing me to unintentionally pull my bolt out of my rifle when cycling it.

It happened enough that I got rid of it and fitted a Mauser/Ruger style bolt release on the side of my Remington 700's receiver.

Then I had constant trouble with the clip securing the shaft for the safety catch/bolt release slide guide though the trigger working loose and falling off to the point I replaced it with a stainless steel split pin and washer.

Seeing that the USMC saw fit to replace the trigger guard, were there any modifications to the bolt release and safety catch shaft?

I mean, if they failed this regular hunter/match shooter, surely they would give the USMC snipers trouble with the heavier and more intense use they give their rifles.