M1 Rifle receiver inspection points-
1. Barrel torque shoulder (front receiver face)- This surface must lie at 90° to receiver axial centerline in both the vertical and the horizontal planes. Specification for this surface (and for the receiver locking lug bearing surfaces) is 90° 5’ +/-0°5’. If the receiver face is not at 90°, installed barrel centerline will diverge from the receiver axial centerline. Centerline disagreement grows worse with distance from the receiver and, in turn, causes gas cylinder misalignment and corresponding operating rod fit and sight zero problems. Because receivers were detail gauge inspected during manufacture, it is probable that very few, if any, got by with off-specification torque shoulder s or barrel threads. It’s likely that a receiver found this far downstream with an off-specification torque shoulder was probable commercially refaced to remove pitting. Two relatively easy ways to check this are: (1) install the receiver or barreled receiver in an aligned 6”, or larger, mill vise; measure right lug face to receiver face distance (specification is 1.2720” + .0035”); zero a quill mounted dial indicator on the receiver face at that point; and then comparison read the front of the receiver at the top and at the opposite side; and (2) although subject to error due to barrel nonconcentricity, secure the barreled receiver in an aligned mill vise, as above, locate barrel O.D. forward of the receiver at the left, right, and top and compare with similarly indicated points at the front gas cylinder ring mounting diameter (also see plug gauge indication on page 196). If necessary, remove the barrel, install it between lathe centers, and dial check runout. If the problem follows the barrel, the barrel is at fault-and, if not, the receiver is the cause of the problem. With the above in mind, limit M1 receiver torque shoulder surface preparation to fine bead blasting.
2. Receiver barrel threads- Receiver threads must be in as close to original condition as possible. Thread specifications are: minor dia. .918” + .004; major dia. .975” + .005”; and basic pitch dia. .9455”. Note: The ordnance M1 receiver thread gauge shown in figure 27 enabled assemblers and armorers to be certain before barrel installation that: (1) an ordinance specification replacement barrel would turn to correct hand tight position against the receiver torque shoulder and draw correctly, and (2) that after torquing to final position, the barrel’s rear breech ring and breech recess surfaces would not be so far to the rear that either would contact or interfere with the bolt. The position of the breech ring on a currently installed barrel will usually indicate whether or not a G.I. replacement barrel will also fit. After barrel removal, check by installing the replacement barrel hand tight and estimating final draw position. Removing metal from the receiver torque shoulder, as discussed in paragraph 1 above, will change barrel draw and can make custom lathe adjustment of the barrel breech ring and/or breech recess necessary.
3. Receiver left lugway and cartridge extracting cam- Receiver lugway and lug bearing surfaces should be in as close to original condition as possible. Both surfaces should show light wear polishing, only. Reject the receiver if the lugway or extracting cam surfaces are pitted, altered, or damaged.
4. Receiver bolt locking lug engagement surfaces- Receiver bolt locking lug engagement surfaces should be in as close to original condition as possible. Both surfaces should show light ear polishing, only. Reject the receiver if the bolt lug bearing surfaces are damaged, altered, or pitted through the case.
Note: The purpose of the original ordnance receiver gauge (see figures 19 and 20) was to enable armorers to measure the distance between the front receiver locking lug engagement surfaces and the flat, primary (bolt closing) firing pin retracting surfaces on the back of the receiver bridge. Sufficient wear and/or seating at either, or both, of these surfaces would produce an unserviceable receiver reading. A gauging system capable of measuring aggregate three way receiver bolt and firing pin wear was not available to armorers. See hand simulated firing pin retraction check on page 30. If firing pin retraction is insufficient with a serviceable bolt and firing pin, reject the receiver or install a shorter than standard extension length firing pin. See firing pin gauging on page 34.
5. Receiver bridge primary (bolt closing) firing pin retracting surface- This surface should show only light wear polishing and should be in as close to original condition as possible. Replace receiver if excessively worn, peened, pitted, altered, or damaged. Also see item #4 above.
6. Receiver bridge secondary (bolt opening) retracting surface- This helically cut camming surface should show only light wear polishing and should be in as close to original condition as possible. Corner wear can shorten firing pin retraction timing. Replace the receiver if this surface, including the corner and/or the right side of the clearance slot is excessively worn, pitted, altered, or damaged. See simulated firing pin retraction check on page 30.
7. Receiver bridge bolt passage and bridge rear bolt support surface- Must be in as close to original condition as possible. Diameter specification is .730” + .005” (.735” max.) with center of the passage coincident with receiver/bore axial centerline. Reject the receiver if the passage is worn oversize or the bridge support surface is peened or battered.
8. Receiver right cartridge guide rib (opposite left rib, C, in sectional illust.)- The top edge must not be worn to the extent that cartridge chambering is affected. His critical surface directs cartridges stripped from the right side of the clip to the left (to center the bullet on the chamber mouth) as the bolt moves forward. The right guide rib is similar to the left, but considerably smaller at the top and more susceptible to damage and abrasion. Although most have been withdrawn from service, some early M1 receivers are found with low right cartridge guide ribs. Low ribs, typically, became nonfunctional with very little wear.
9. Receiver operating rod lug guideway slot- Must be in as close to original condition as possible. Replace the receiver if the slot is pitted, altered, or damaged. Specified inside slot dimensions are: width .102” + .006” (.108” max.) and height (not including dismount notch) .330” + .008” (.338” max.).
10. Receiver follower arm pin hole- Must not be damaged or oversize. Specified I.D. sizes are: pin shaft passage .149” + .003 (.152” max.); pin head recess .205” + .008”. A #24 drill shank (.152” dia.) can be used as a shaft passage max. gauge and a drill rod ground to .153” dia. Can be used as a no go gauge.
11. Receiver clip latch pin holes- Must not be damaged and should not be oversize. Specified I.D. sizes are: pin shaft passage .123” + .003” (.126” max.); pin head recess .162” + .008”. A #30 drukk sgabj (,1285” dia.) can be used as a shaft passage no go gauge.
12. Receiver elevation indexing serrations (on left receiver ear)- Specifications call for 60 serrations not less than .006” deep. Tops must be sharp enough to maintain positive sight elevation adjustment. Reject the receiver (or use it for a display rifle) if serrations are rounded off, altered, or damaged. See page 253.
13. Receiver rear sight mounting ears- Must be undamaged, elevation index mark on left ear intact, and windage/elevation know alignment holes unaltered. I.DS. specification .375” + .002” (.377” max.).
14. Receiver rear sight cover installation slots- Must be in original condition and free of dried oil and dirt. Reject the receiver if cover slots are pitted, altered, or damaged.
15. Receiver rear sight base bearing surface (recessed flat surface between the receiver ears)- This critical surface should show no more than very light wear polishing at tops of machine marks. A few strokes with a fine stone to level the tops of machine ridges permissible only. Surface alteration will reduce sight cover tension and permit sight base movement (base rotation or wobble).
16. Receiver stock bearing surfaces- Flat and 10° angle receiver bearing surfaces must not be altered or damaged. Light pitting on receiver bearing surfaces that can be removed with a wire wheel and/or fine bead blasting are acceptable for reparkerizing. Receivers with deeper bearing surface pits usually have occluded rust pockets and should not be used.
17. Receiver leg detail- Includes trigger guard lug slots, magazine follower slots, clip guide slots, and bullet guide mounting slots – all should be in original condition. Reject the receiver if slots are altered or damaged or pitted through the case. Light pitting on exterior/interior surfaces that can be removed with a wire wheel or brush and/or fine bead blasting is acceptable for reparkerizing. Receivers with deeper leg area pits usually have occluded rust pockets and should not be used.
18. Overall receiver condition and exterior surface condition (above stock line)- For best, and most original, appearance, receiver exterior stamping imprints and machine lines should be clearly visible. Although grading is subjective and always a judgement call, mechanically serviceable receivers with above the stock line exteriors that have been bead blasted, sand blasted, and/or heavily etched by poor reparkerizing work, do not look original and shouldn’t be used in building first quality M1 Rifles. Depending on appearance, I would suggest limiting the use of such receivers to basic shooter grade or display grade (wall hanger) rifles. Receivers must not be warped, tweaked, or action wrench scarred. While this kind of damage isn’t commonly found, it’s almost always caused by improper barrel removal/installation tooling that doesn’t support the receiver properly and/or by twisting force applied to the receiver, improperly, behind the front receiver ring.
19. Receiver integrity- An important question: is the receiver being inspected one piece, as originally manufactured, or is it an assembly of demilled front/rear sections that have been welded back together? In this regard, although the actual number is unknown, various sources have estimated that between 5000 and 20,000+ M1 receivers may have been reassembled from demilled scrap. Those who maintain that welded M1 Rifles receivers are acceptable because the welds are located well behind the lug seats have glossed over a number of important details discussed on pages 82 – 84. Close examination of welded Ml receivers always reveals the telltale misalignment, remachined areas, weld/fill bubbles, and weld bead/edge cracks. As I see it, welded receivers should be used only in nonfiring display rifles and cutaways.
Note: Riflesmiths who build or work on M1 Rifles should keep at least one as-new M1 Rifle receiver and a full set of as-new parts on hand for visual and dimensional comparison with parts being inspected at the bench. Reprints of M1 Rifle receiver and parts drawings are also helpful references. See reprint publisher source listings on page 60 and 234.
