M40 barrel contours as I know it for now.....

[Frank Green]

Been quite a bit of discussion on early M40 barrel contours. Here is what I know as of today based on originals and prints that I have been able to obtain/have.

The original M40 contour is nothing more than the Rem. varmint contour. An original that I measured had a .820" muzzle diameter. I've seen factory Rem. Varmint contours muzzle range from .820" to .845". We do our standard #13 rem. varmint contour with a .830" muzzle.

For the purist on wanting an original M40 contour... we do them at .820" muzzle.

I was supplied a real early M40A1 barrel made by Atkinson (assuming mid to late 70's from Ryan @USMCSGT0331 here on the hide). That barrel had the following dimensions and again this is a straight tapered contoured barrel. 1.159" x 4.5" and straight tapered to .909" muzzle at 25" finished length. So could this be a real early M40A1 barrel?

M40A1 contour.... just obtained a drawing yesterday. It's a straight taper contour barrel. These are the dimensions I have per a drawing that was sent to me and he will measure an original M40A1 barrel on a rifle that I've handled before and it's a HS precision barrel and the work was done by the RTE guys at Quantico back in the day. Think it was around 1980. The contour per the drawing (not a gov't drawing and no date on it etc...) is as follows....

1.200" breech diameter to 1.220" max diameter. Breech length is 3.000" then straight tapers to the muzzle of .890" min diameter to .900" max diameter. The spec'd blank length on the drawing is 26.5" before any finish work gets done.

Now I did find I did have a gov't drawing that was with the A1 stuff and it shows a contour of 1.200" x 4" +/-.25" not including the threaded section for the original .187" Rem. recoil lug. Add the lug and threads in that adds about .880" to the breech length. Which then the length could be anywhere from 4.880" to 5.13". Then it straight tapers to the muzzle which shows .875" for a 25" finish length overall. The funny thing is... this drawing is in the A1 packet but is dated Aug. 12,1999 just like the A3 drawing I reference below. This A1 packet drawing is the finished barrel drawing and it references the drawing from the A3 packet. So I'm assuming this is the last and final version of the A1 barrel contour which is the same as the A3. Just the recoil lug is different.

M40A2 barrel contour (even though there is no official M40A2 ever made... only prototypes possibly or preproduction A3) and again a straight tapered barrel with the following dimensions... 1.200" breech diameter +.010" / -.000" with a 3.5" breech length (in front of the lug so not including the threaded breech end) with a +/-.50" length tolerance then straight taper to .875" muzzle diameter +/-.005". Finished length of 24" from the front of the recoil lug. So if you wanted to get a blank prior to any finish work I would get a blank that is 1.200" x 4.5" breech length str. taper to .875" @ 25" / 27" blank so you have something to work with. This is a gov't drawing that is dated June 15, 1998.

M40A3 drawing with a date of Aug. 12, 1999 shows a blank contour of and again a straight taper barrel.

1.200" +/-.10" x 5.25" breech length +.50" / .10" for length tolerance and straight taper to .875" muzzle at 25.250". The muzzle diameter tolerance is +.050" / - .030". So the muzzle can be as big as .925" or as small as .845". If I were to order one from a barrel maker I would ask for 1.200" x 5.25" str. taper to .900" 25.250" and ask for a 27" blank so you have something to work with.

As you can see just with the tolerances on the gov't drawings they can vary quite a bit on the A1, A2 and A3.

Hope this helps everyone and trying to clear up any confusion but think there will always be some debate.

Later, Frank
Bartlein Barrels

 

[Frank Green]

What is interesting on the M40A3 barrel drawing when it came to the bore and groove sizes and the number of grooves and the twist.

Twist is spec'd at 1-12.
Right hand twist

Number of grooves per the drawing... 4 groove, 5 groove or 6 groove. Equally spaced.

Bore size = .2980" +.0022" / -.0000" so the bore could be as small as .2980" or as big as .3002".

Groove size = .3082" +.0004" / -.0020"... I think the minus tolerance is a typo on the drawing and should be -.0002"! So this would give you a groove size of .3080" to .3086"

The drawing for reference shows a 4 groove cross sectioned bore.

Later, Frank

 

[Frank Green]

Also keep in mind... the original M40 barrels and most likely even the A1's and early A3's where probably contoured on a tracer lathe and not cnc lathes. That would also make a variance on the contour dimensions as well.

 

[Frank Green]

Based on what I just found....

The A1 contour is the same as the A3 contour but just using a .187" Remmy recoil lug and not the later .312" lug on the A3.

So I'll say 1.200" x 5.000" str. taper to .875" @ 25" finish and I would make at least a 26" blank or a 27" for a customer to finish it up so you have plenty to work with.

Later, Frank

 

[Frank Green]

So for my A1 spec build. My barrel blank before finishing will be...

1.200" x 5.000" str. taper to .875" @ 25" finish / 27" blank

Later, Frank
Bartlein Barrels

 

[diggler1833]

Okay, I either ignored a shitload of people or Frank keeps coming back on here to drop "ah-ha!" moments of knowledge.

Now I am going to go measure all of the diameters on my barrels as all but one are M24/M40 contours (I understand the potential for difference). It won't make a bit of difference to me as they all shoot well...but it will be interesting to see how many differences I can find.

 

[Random Guy]

Frank, good luck with your build, and please show us some pics when it's done. I wanted one for years, and by 2019 I had collected the requisite parts.

 

[Frank Green]

Frank, good luck with your build, and please show us some pics when it's done. I wanted one for years, and by 2019 I had collected the requisite parts.
View attachment 8330890

I'll post up some pic's here when it's done.

GAP is going to assemble it for me.

My barrel will probably be done in a month or two. I cut the order back in early November. Could've had it done sooner but I'm making mine with a .299" bore. We don't run those all the time but standard min spec. .3000" bores run all the time.

Also I ordered a new chamber reamer for mine this month. It's a special designed reamer for the 169SMK. So it has a much shorter throat. That's not suppose to be done till April 8th.

So mine is a ways out yet! LOL!

 

[Smiley mountain]

Been quite a bit of discussion on early M40 barrel contours. Here is what I know as of today based on originals and prints that I have been able to obtain/have.

The original M40 contour is nothing more than the Rem. varmint contour. An original that I measured had a .820" muzzle diameter. I've seen factory Rem. Varmint contours muzzle range from .820" to .845". We do our standard #13 rem. varmint contour with a .830" muzzle.

For the purist on wanting an original M40 contour... we do them at .820" muzzle.

I was supplied a real early M40A1 barrel made by Atkinson (assuming mid to late 70's from Ryan @USMCSGT0331 here on the hide). That barrel had the following dimensions and again this is a straight tapered contoured barrel. 1.159" x 4.5" and straight tapered to .909" muzzle at 25" finished length. So could this be a real early M40A1 barrel?

M40A1 contour.... just obtained a drawing yesterday. It's a straight taper contour barrel. These are the dimensions I have per a drawing that was sent to me and he will measure an original M40A1 barrel on a rifle that I've handled before and it's a HS precision barrel and the work was done by the RTE guys at Quantico back in the day. Think it was around 1980. The contour per the drawing (not a gov't drawing and no date on it etc...) is as follows....

1.200" breech diameter to 1.220" max diameter. Breech length is 3.000" then straight tapers to the muzzle of .890" min diameter to .900" max diameter. The spec'd blank length on the drawing is 26.5" before any finish work gets done.

Now I did find I did have a gov't drawing that was with the A1 stuff and it shows a contour of 1.200" x 4" +/-.25" not including the threaded section for the original .187" Rem. recoil lug. Add the lug and threads in that adds about .880" to the breech length. Which then the length could be anywhere from 4.880" to 5.13". Then it straight tapers to the muzzle which shows .875" for a 25" finish length overall. The funny thing is... this drawing is in the A1 packet but is dated Aug. 12,1999 just like the A3 drawing I reference below. This A1 packet drawing is the finished barrel drawing and it references the drawing from the A3 packet. So I'm assuming this is the last and final version of the A1 barrel contour which is the same as the A3. Just the recoil lug is different.

M40A2 barrel contour (even though there is no official M40A2 ever made... only prototypes possibly or preproduction A3) and again a straight tapered barrel with the following dimensions... 1.200" breech diameter +.010" / -.000" with a 3.5" breech length (in front of the lug so not including the threaded breech end) with a +/-.50" length tolerance then straight taper to .875" muzzle diameter +/-.005". Finished length of 24" from the front of the recoil lug. So if you wanted to get a blank prior to any finish work I would get a blank that is 1.200" x 4.5" breech length str. taper to .875" @ 25" / 27" blank so you have something to work with. This is a gov't drawing that is dated June 15, 1998.

M40A3 drawing with a date of Aug. 12, 1999 shows a blank contour of and again a straight taper barrel.

1.200" +/-.10" x 5.25" breech length +.50" / .10" for length tolerance and straight taper to .875" muzzle at 25.250". The muzzle diameter tolerance is +.050" / - .030". So the muzzle can be as big as .925" or as small as .845". If I were to order one from a barrel maker I would ask for 1.200" x 5.25" str. taper to .900" 25.250" and ask for a 27" blank so you have something to work with.

As you can see just with the tolerances on the gov't drawings they can vary quite a bit on the A1, A2 and A3.

Hope this helps everyone and trying to clear up any confusion but think there will always be some debate.

Later, Frank
Bartlein Barrels

Yes, the first ones were built in R&D using 40x varmint/sporter barrels and I belive the first couple I built were actually 40x barreled actions pulled out of a truck full of them. They shortened and handed them to me along with a couple factory 700 stocks to open up and fit them. There was no reason to do anything else as they were only for in house testing. As soon as the military put in an order for I think about a dozen, I don't know if they made up a rollmarker (and I wasyearsagoin contact with guy that had the original rollmarker a )which was an expensive item, so more likely had the engravers in custom repair put on the proper markings. I do know that the other custom gunsmith and myself built the first dozen or so. It put us a little behind on the C grade Customs and Safari rifles we normally built so when they actually put in a larger order, they moved m40s over to the 40x guys and put on another guy to build them. Later when quantity orders came in, they were put into a separate production area and my son worked on those.
Smiley

 

[Smiley mountain]

Also keep in mind... the original M40 barrels and most likely even the A1's and early A3's where probably contoured on a tracer lathe and not cnc lathes. That would also make a variance on the contour dimensions as well.

Original m40 barrels definitely turned on Monarch Tracer Lathe in R&D as were 40x and 700 C grade Customs. I know well. When orders for C grades slowed, I'd go turn barrels or handload shells for 40x targeting.
Smiley

 

[RTH1800]

Smiley,

Was Mike Walker involved in this?
If so to what extent if you don’t mind saying.

Thanks,

RTH

 

[Smiley mountain]

Mike was definitely involved but I belive he was approached by the military to develop this project. My pay grade was not high enough to be invited to the meetings in Mike's office.
Because we were designing and building prototypes for the military including a 5 shot semi auto 40 mm grenade launcher, the full auto 1100 10 shot that I can't remember what model it was finally named and the mini gun that GE finally won the contract, It was not unusual to have military and sports/gun magazine writers touring R&D. The biggest name I met was Curtis LeMay who Leon, the senior gunsmith I worked with, built and repaired LeMay's firearms when he was stationed at Lackland AFB.
As I have said before, the first couple m40s were 40x sporter/varmint barreled actions on factory 700 stocks, that I opened the barrel channels to fit.
Smiley

 

[RTH1800]

Thank you so much for the time and information!
I would say Gen. LeMay was quite high up the chain.

 

[Smiley mountain]

I guess you can't get any higher than Chief of Staff!!

 

[Frank Green]

So I got another original take off M40a1 barrel. I got this from Maj Land. So the barrel is legit.

So to go back to Ryan's barrel first for comparison below this is what again that one measured......

I was supplied a real early M40A1 barrel made by Atkinson (assuming mid to late 70's from Ryan @USMCSGT0331 here on the hide). That barrel had the following dimensions and again this is a straight tapered contoured barrel. 1.159" x 4.5" and straight tapered to .909" muzzle at 25" finished length. So could this be a real early M40A1 barrel?

The Land barrel measures.... 25" overall length. Breech face to muzzle.

The barrel contour is... 1.168" x 4" then straight tapers to .924" @ 25" finished.

So you can see there is a variance in the barrels contour wise and vs the original USMC drawings etc....

The only markings on Lands barrel is RTE-P. No other markings or caliber designation are present. See the attached pic's.

Later, Frank

 

[kft101]

I need a proper barrel for my M40 build! Were the originals parkerized?

 

[Frank Green]

I need a proper barrel for my M40 build! Were the originals parkerized?

View attachment 8409898

I'll say parkerized from what I've seen.

Also the original barrels where made out of chrome moly steel and not stainless steel. The c.m. will take the parkerizing.... stainless won't.

The replacement barrel(s) we've made Mr. Land was c.m. steel, 6 groove and 10 twist.

 

[Random Guy]

So you can see there is a variance in the barrels contour wise and vs the original USMC drawings etc....

One book states that M40A1 barrels were sourced from the following: Atkinson & Marquart Rifle Company, Douglas Barrels, Hart Barrels, and Schneider Barrels. If that info is true, that might account for small variances seen circa 1977 to 2001.

FWIW, the crowns were also machined by a human, so plenty of variation existed there too…