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.
Scope:
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.
100-0
200-2
300-5
400-8
500-12
600-16
700-20.5
800-25
900-31
1000-37.5
(MOA drops updated after shooting out to 700 yards dated 9/22/08)
http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=764571#Post764571
Mount:
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."
Sling:
I bought an MRT sling. I think that's right, but not sure at all.
Markings:
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.
Action:
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.
Barrel:
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>
Crown:
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.