New M40 receiver information

USMCSGT0331 · Mar 7, 2023

It's pretty rare that new information about the M40 comes out, but ever so ofter we get to learn something interesting. In past threads people have asked if there's a difference in the US markings between the 6 digit serial number M40's and the 7 digit serial number M40's. Everyone who commented said yes, the US markings and placement are the same on both types of M40's. I never thought this was correct, but without having a 7 digit M40 in hand I wasn't able to provide anything and be able to give a definitive answer. I did notice a difference in the US placement when looking at photographs of the 2 types of M40's, but those are just photos,what I saw might not have been reality.

I recently won an auction for a 6257xxx 7 digit serial number and I picked it up from my FFL a few hours ago. As I was waiting for the 4473 to clear, I took a sheet of paper and held it's edge to the left rail of the rifle. If you try this with regular USMC 6 digit serial number M40 receivers, the piece of paper will follow the left rail cut, extend past the end of the cut and the US rollmark will be above the edge of the paper. I discovered this method of check US rollmarks when I got my first M40. The paper test is now one of the ways to quickly and easily check the authenticity of a supposed M40, since most people stamp their clones too low. If it's not above the edge of the paper, it's not a 6 digit M40 (my friends and I have tested this on at least a dozen original M40's, all with the same outcome).

This is all well and good for a 6 digit M40, but what about a 7 digit M40? Until now I've only seen photos of the 7 digit M40's online, but to my eye the US rollmark looks like it was applied slightly lower. With my new 7 digit M40 in hand at my FFL's shop, I was finally able to do the paper test! It turns out that what I had seen in the photographs online was real, the US rollmark is applied a little bit lower than the US rollmark on the 6 digit M40's! The edge of the paper followed the left rail cut and then cut right through the lower pats of the US rollmark.

When I got home I was able to use a caliper to see how high the US rollmark is above the serial number on each type of M40. I also measured the height of the US rollmark letters to see if there were any differences between the 2 types of M40's. As it turns out, the height of the US rollmark letters on both types of M40 are the exact same. So, we're just looking at a difference with the placement of the US, not the size or font.

Here are both of the M40's, if you look very closely at the US rollmark's location above the serial numbers, you can see a different in placement. Once you know what to look for, it becomes quite obvious.

First up is the 6 digit serial number M40, the US rollmark is approximately .26" above the serial number.

Here's the 7 digit serial number M40, the US rollmark is approximately .2" above the serial number. Since the serial numbers on the 2 rifles are in the same location, the closer distance to the serial number means it was rollmarked further down.

Now that you've seen the actual locations of the US rollmark using a caliper, let's take a look at the paper test. The top photo is the 6 digit serial number M40, notice how the entire US rollmark is above the edge of the paper, when the paper runs along the edge of the left rail cut. Now compare that to the paper test on the 7 digit serial number M40. The edge of the paper is also following the left rail cut, but it cuts across the US rollmark right at the top of the periods in the U. S.

So, we now have definitive proof that the location of the US rollmark on each type of M40 is in a slightly different location and that the letter sizes are the same. Next time your at a gunshow and a dealer has an "M40" on their table, do a quick paper test and see if it passes. If it passes that test, then look for other known features, like the left rail being cut back to the center of the Redfield scope base's rear left windage screw (this will only work with the correct type of Redfield base, such as the 40X base). If the rifle doesn't pass the paper test, move along, it's probably not an M40.

I say "probably" just to give the opportunity for the "exception to the rule" to show up. However, 100% of all original USMC 6 digit serial number M40's have these features. Remington had very tight quality controls on the production of these M40's and the US rollmark was set into a device where neither it nor the receiver could move out of place. I don't know for sure why the 2 types of M40's have a different location for the US rollmark, but it had to have been deliberately moved. Maybe the receiver jig broke and a new one was made. Maybe it was done for an aesthetic reason or make it easier to see when looking at the serial number. I have absolutely no idea why Remington changed the location, I just know that they did do it.

Hopefully this post wasn't too long and boring, but new information is always exciting! And the only place you can find this information is right here in the Vintage Section!

parkhurstta · Mar 7, 2023

That’s great information! Good to know a way to identify the real thing vs a fake!

Random Guy · Mar 7, 2023

Thanks for the pics. One possible explanation for the roll mark positions being different is that Remington revised the original 1966 drawings two times during the M40's production history, once in 1968 and again in 1969. This resulted in various small differences regarding the machining of the bolt, trigger/sear?, and the shape of the safety. (Fwiw, According to the former manager at Remington Defense, the SSA and Chuck Mawhinney rifles were built 10 to 15 years ago used the 1969 dated M40 drawings, as that is what Remington had on file. That upset some customers as they were expecting the 1966 version of the M40 with the "flat" or "tombstone" style safety on their SSA commemorative, and not the later "round" safety, which is what late M40 used).

One other pet theory is that perhaps when Remington went to a 7 digit serial number number, perhaps they ordered new roll stamping dies?, as one can see the "2" is a slightly different shape between the early and late M40s shown in this link. At least to my eyes, not only are the numbers stamped deeper, but it was definitely a different die to stamp that number "2" on the later rifle. The replacement dies could have changed the relative location b/t the "U.S." and the numbers? or maybe that was reflected in the revised engineering drawings? Only way to be sure would be to compare the 1966 drawings to the 1968-69 drawings, which is likely impossible at this point in time...

(As an aside, one can also see a similar pattern with the serial numbers stamped on M1 Garands made during WWII at Springfield Armory, they periodically changed the worn-out dies. The 1940-42 Garands have somewhat deeper roll marks than the serial numbers seen on the 1943-1945 Garands, and the font changed slightly when they went from 6 digit serial numbers to 7 digit serial numbers. I just assumed Springfield Armory changed the dies at that time...maybe Remington did too? I have no idea how long these roll dies/stamping dies last, but they are replaced from time to time).

Mike Sullivan · Mar 11, 2023

Thank you for sharing this information about the differences between the US markings on the 6 digit serial number M40's and the 7 digit serial number M40's as well as the paper test. I’ve always been nervous about confirming authenticity on m40 parts but this is the kinda thing that has me thinking about getting into it more.

mjmd11 · Sep 25, 2023

Great string . Have been researching this for a few years and I concur. The positon of the the left side of the U. as it relates to the serial on the vertical axes is also critical. They are in different place on the six digits vs the 625's. on legit weapons. Although you have .260 above the serial i would think it may be a little less than 6.8mm (.260") I think it may be the quality of your instrument? It would be most helpful if we could also confirm the width, height and period placement measurments of th U.S. stamp. please email me if you have time.

mjmd11 · Sep 25, 2023

An after thought..There are other unique qualitys that have been noted in that factory roll stamp too. like the appearence of a slight tilt on the U because the stamp was hitting a bit heavier (making a wider impresion) on the left side when it rolled through.

RemCustom6 · Sep 25, 2023

The factory roll stamp machine that produced all of the roll stamps in Ilion made its way to South Dakota when Remington moved the Custom Shop to the Dakota Arms factory. When Remington went bankrupt, we sold most all of the old machinery including the roll stamp machine which included several of the original stamp dies. The stamp machine was a finicky unit and if an untrained operator ran it, the stamp depth and location could be different on one receiver to the next. It was more about timing (pushing 2 buttons at the same exact time), part placement X axis vs. Y axis and set height of the physical part. While we did try to place the US stamp in the same location on receivers like the M24’s, M40’s, and some Defense prototypes, there was no guarantee we were able to place them exactly from one run to the next. We made M24’s in 40 unit lots roughly 2-3 months apart. We even experimented with using a laser, especially on titanium actions that were used on various Defense submissions. Even some RR prefix M24’s got the laser treatment.

AND THEN………. Everything took a crap and BIG GREEN went belly up. You guys would not believe the amount of old documentation, photos, historical data that we were told to just throw away. We filled up about 18 large dumpsters with filing cabinets, parts, you F’ing name it. That all went to a recycling center. There was a private security company hired to ensure that nothing was taken out of the dumpsters. Yes, it was that bad!!

Sorry to derail the thread a bit. On a good note, I happen to know exactly where that old roll stamping machine is!

USMCsean · Sep 27, 2023

Sad when you have to destroy things that such a part of history of something. I've been in your shoes destroying drawings from the teens that were on waxed linen. Works of art. Someone's life spending hours upon hours making a dwg that was used for one reason or other and they were works of art. Told to scrap them.

mjmd11 · Sep 27, 2023

Odd that the limited number of (8) early original (listed) receivers I have seen and measured would have all been so consistent in placement. Must have been a good couple of years (1966-68) on the roll stamp at Remington. All right on the same measurement (+/- .5mm) above from the serial number on the horozontal axis and consistent, placement wise, on the vertical axis too. There was an unlisted 262 I also had in hand and measured, that was roll stamped and consistent too. Do you remember who was running the machine in 1966-68? I want to send him a good bottle of wine is he is still alive!. A list of what the Navy got would be great to see if somebody ever finds one.

RemCustom6 · Sep 27, 2023

66-68 was WAY before my time at Big Green. A lot changed throughout the years (roughly 12)I was there at the Custom Shop. Keep in mind, we went through 5 CEO’s in 4 years at one point. Turnover was a disaster, you would just get done training people and they would up and leave.

mjmd11 · Sep 27, 2023

RemCustom6 said:
66-68 was WAY before my time at Big Green. A lot changed throughout the years (roughly 12)I was there at the Custom Shop. Keep in mind, we went through 5 CEO’s in 4 years at one point. Turnover was a disaster, you would just get done training people and they would up and leave.

You are one of the most helpful people I know Rem Custom 6 and are always willing to freely share your knowledge. (We do know each other) My experience in M-40 stampings is limited to the early listed 168xxx's- 224xxx's ( only one in 322xxx range) runs . My hypothesis is they were very consistent with the U.S. in those ranges and in those days, but i would love to see an original listed reciever from that era to disprove that if anyone has one here. You were very helpfull on the M40a1's and I can't express enough gratitude for that.

mjmd11 · Aug 26, 2024

An update . I have now seen ten or so original and listed M-40's serials between 221xxx's through 224xxx's.
These ranges are pretty consistent stamp wise. in the dimension of the letters, width of the stamp and the U.S. roll stamps placement above the serials.
The left side of U consistently splits the second digit of the serial number and the bottom of the letters in the U.S. are placed approx .240-260 above the top of the serial numbers. The minor variation in this range I attribute to whomever was running the machine that day in the custom shop. It appears that the placement above the serial, measurment wise, seems to change when they got into the 314 range . I am also very confident that there was a 262 M-40 serial range. It is interesting to note the out of allignment of the last three digits on the horozontal axis in the serial number stampings on the early six digit M40's.

the 625's are also pretty consistent in the placement of the U.S. , although the stamping is closer to the serial as described in the post above.. M-40A1's appear to be all over the board .

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