XM-3 on CMP, what’s the story behind these?

why did the US upgrade the M40A3s into M40A5s instead of adopting the XM-3?

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XM3 parts photo dump. I sold this rifle to a friend last year and I disassembled the XM3 so he could see each part of the rifle in detail. This was one of the IBA shop guns they used for testing, it's not a DARPA prototype or USMC used. However, it's an original IBA XM3 that was built about the same time as the USMC rifles and it's in the same serial number range. Since it's a test rifle, the barrel is a slightly different length than the USMC rifles and the scope adjustments are also different. Chandler told me that this particular scope came off 1 of the 2 XM3's they sent to the Army for testing and that this is what they requested for the scope turrets. I just thought a detailed parts breakdown might be beneficial for anyone attempting to clone one of these rifles.

Here's all the parts in one photo:

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The barreled action:

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Remington 700 short action receiver close-up. The receiver has an "S" prefix serial number, the S indicates that this is a stainless steel receiver. This serial number is right in the middle of the USMC XM3 serial number range. The rear right of the scope base is marked "XM-3" and the rear left of the scope base is marked with the rifle's serial number. The top of the scope base is marked "IRON BRIGADE ARMORY". This is unique to this specific test rifle, the issued USMC XM3's have a shorter scope base which doesn't have any markings on it:

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The underside of the receiver, the magazine well is welded to the receiver:

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The bolt with a large bolt knob and the last 4 digits of the rifle's serial number stamped on the handle:

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The right side of the barrel is marked "P XM-3," the "P" is the proof mark. The left side of the barrel is marked "H-IBA 308 4019." I can't remember what the "H" stands for, so if anyone knows what it is, please post it in this thread. The "IBA" is obviously the maker, "308" is the caliber and "4019" is the last 4 digits of the rifle's serial number.

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The muzzle brake is made by SureFire, but is completely sterile. All of the issued USMC rifles have these sterilized SF brakes. This is a small detail that most people overlook when building their XM3 clones.

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The McMillan A1-3 stock that was developed specifically for the XM3 program and the Eagle Industries cheek pad:

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The entire barrel channel and inletting is filled with a bedding compound in order to seal the exposed fiberglass. The last 4 digits of the rifle's serial number is stamped in the barrel channel. The bottom part of the Colorado Micro Precision EFR is also embedded in the barrel channel:

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Anychance you know the serial number range of these or a source that might? Thanks and sweet setup, hope your buddy is making great use if this one.
 
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Anychance you know the serial number range of these or a source that might? Thanks and sweet setup, hope your buddy is making great use if this one.

I have all 52 of the USMC XM3 serial numbers, here's the serial number ranges that you want to look for when choosing a donor rifle. My suggestion is to just get something relatively close, or even just the very basic "S6" portion of the serial number. I recently tried to help a friend find an XM3 donor rifle, and trying to find a good donor receiver for these builds is challenging. My friend was able to get a good receiver with the correct bolt face, but it's not within one of these serial number ranges (his receiver is an S639, that's as close as we could find).

Here's the 4 serial number ranges for the 52 USMC XM3's, and the number of how many XM3's are in each of the serial number ranges:

S652xxxx - 4 rifles
S653xxxx - 29 rifles
S654xxxx - 7 rifles
S655xxxx - 12 rifles

I hope this helps!
 
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Can anyone with an XM3 let me know how long the shank is and muzzle diameter after being fit to the action? My understanding is the blank starts @ 26", and both the shank and muzzle are cut back some. Likewise, does the barrel follow the standard surefire print for their reflex muzzle devices like the CA762SSAL/RE?

Thanks in advance!