Just a heads-up, but if you guys need an alternate source for an M40A1 barrel, and don't want to use the new Schneider ones (I don't know how the new ones stack up to the old Schneider barrels), it might be possible to have Bartlein made some A1 barrels. I recently sent
@Frank Green an original 1970's vintage Adkinson M40A1 barrel to study. He's currently analyzing it and taking measurements for a personal project, but maybe he'd be willing to do a run of Bartlein M40A1 barrels if there was enough demand for them. He already makes the best reproduction circa 1966 M40 barrel you can currently purchase (measurements were taken from a real M40 barrel), so I think he could easily make an absolutely amazing reproduction A1 barrel!
What do you guys think about a Bartlein A1 barrel being offered to clone builders? Does anyone here have one of the new Schneider A1 barrels that was made by the new company owners? I've heard that the new Schneider barrels might have some changes, but I haven't been able to verify anything yet (I'll probably just have to order one and look it over). If anything has changed with the new Schneider barrels, I think a reproduction A1 barrel from Bartlein might be the best option. I'd really like to hear what you guys think, especially if anyone here has one of the new Schneider barrels that they could do a small review on.
So see the attached chicken scratch drawing. Sorry I did it quick! I was able to get my hands on a M40a1 drawing and I have the A3 drawing as well.
So here is what I'm seeing.... The Atkinson A1 barrels measures....
1.159" diameter on the breech end and almost 4.6" long (this includes the length of the breech threads) then straight tapers to .909" @ 25" finish (it's like just shy of 25").
The A3 drawing is showing 1.20" breech diameter +/-.10 on the diameter tolerance x 5.25" long with a +.050" / -.010" on the length tolerance of the breech (this is before any thread or chamber work etc...) then it straight tapers to .875" at the muzzle with a muzzle diameter tolerance of +.050" / -.030". So the muzzle could be as big as .925" or as small as .845" per that drawing. This drawing shows a blank length of 25.250" Ref. so if I was doing the install work... I'd make it a 24" finish length. I'm assuming they are cutting 1" off the muzzle end.
On the A3 drawing it shows a 24" finished measured from the front of the recoil lug. So basically a 25" finish length from the breech end/face of the barrel.
So the muzzle diameter is within spec...on the Atkinson barrel but the breech diameter is under by .040" approx. and the breech length is short. What we don't know is what blank length was supplied by Atkinson to the USMC and how the RTE shop guy did the work etc...I/we also don't know what tolerances Atkinson held on the barrels for length and diameter. Most likely the barrels contour was done on a tracer lathe. Not a cnc lathe.
If the one drawing I have is correct for the A1 (I don’t have the complete packet for the A1 and I can’t see the drawing # but is dated 1998 and I was just told that was a preproduction drawing and is from the A2 packet! Supposedly the USMC still built/rebuilt M40A1 spec rifles up to 1999 so I’m assuming this one drawing is a late standard for the A1? So who knows without seeing a drawing from the late 70’s or early 80’s for the early issued/conversion to A1 I’m guessing here a little bit) that shows a breech length on the straight portion of 3.5” +/- .50”. This does not include the breech threaded area. So you would be adding in almost another 1” for the breech length. So the overall breech length could be 4” or up to 5”.
So right now I’m looking at three different drawings. Two for sure are A3 drawings dated 1999 and 2000 and the other I’m guessing is a late A1 drawing which would become the A2 that never happened. The one drawing I have is in the complete drawing packet for the A3 rifle. That’s the drawing that calls out 4 groove or 5 groove or 6 groove rifling. The sectional view of the bore shows a 4 groove though.
The other interesting notes that I noticed on the 2000 dated A3 drawing... was the bore and groove sizes spec's.
Bore size was spec'd at .2980" +.0022" / -.0000"
Groove spec was .3082" +.0004" with a minus tolerance of -.0020" which has to be a typo on the drawing. They probably meant -.0002".
Number of grooves where spec'd as... 4 groove, 5 groove or 6 groove! Equally spaced right hand twist with a turn of 1-12 twist.
I measured the bore and groove of the supplied Atkinson barrel. My measurements are as follows:
Bore = .3008"
Groove = .3089"
Number of grooves = 6
So technically as I'm guessing and comparing the Atkinson barrel to the one of the drawings...it's out of spec. It's uniform on the bore and groove size but out of spec. Bore finish is decent/nice for a used barrel and what I'm looking at.
The Atkinson barrels muzzle crown is a variation of the stepped recess. The step is .040" deep. The width of the high portion is about .160" but it has a slight angle/taper going down at the step. Probably from the insert/turning tool the guy used. No real chamfer at the bore edge. Was probably a sharp edge crown. If it is chamfered it is real slightly done. The crown edge does have wear/light damage to it.
Later, Frank