StrangeRanger Posted December 29, 2020 Report Share Posted December 29, 2020 (edited) Inside my M1 receiver just behind the magazine slot there is an oval shaped depression machined into the interior top surface. It does not appear to have any function. What is it for? Edited December 29, 2020 by StrangeRanger Link to comment Share on other sites More sharing options...
benedw60 Posted December 29, 2020 Report Share Posted December 29, 2020 Its for a place for debris If you are running your gun dirty Link to comment Share on other sites More sharing options...
bob241 Posted December 29, 2020 Report Share Posted December 29, 2020 It was machined there so when the tooling used to machine the radius on the front of the receiver where the bolt enters would clear the top of the receiver. Link to comment Share on other sites More sharing options...
Bridgeport28A1 Posted December 29, 2020 Report Share Posted December 29, 2020 I also recall seeing a narrow channel running the length of the receiver as well on some M1 receivers. The AOC M1's seem to have a more pronounced oval at the front location when compared to Savage plant M1's. Link to comment Share on other sites More sharing options...
StrangeRanger Posted December 29, 2020 Author Report Share Posted December 29, 2020 It was machined there so when the tooling used to machine the radius on the front of the receiver where the bolt enters would clear the top of the receiver. That's pretty much what I thought it might be. Thanks for the confirmation I also recall seeing a narrow channel running the length of the receiver as well on some M1 receivers. The AOC M1's seem to have a more pronounced oval at the front location when compared to Savage plant M1's.Mine is a Savage and Got Uzi's M1A1 is a Bridgeport but the cuts are very similar. Without actually measuring, his appears to be very slightly deeper Link to comment Share on other sites More sharing options...
Bridgeport28A1 Posted December 29, 2020 Report Share Posted December 29, 2020 Was there a different cutter or tool used on 1928 receivers to machine the front radius? Link to comment Share on other sites More sharing options...
anjong-ni Posted December 30, 2020 Report Share Posted December 30, 2020 (edited) 7) BREECH ENTRY COUNTERSINK This is a custom made, piloted, HSS, 50 degree included angle countersink designed to be driven by an arbor through the receiver pilot hole. This cutter is used to form the cone at the front end of the bolt channel on all Receivers which guides the bolt shank into the breech. From Doug's catalog, page 40:It's the clearance channel for the breech entry bevel cutter which is driven through the spring-pilot hole with a 1/4 extension....Phil RichardsonCatalog72A.pdf (sturmgewehr.com) Edited December 30, 2020 by anjong-ni Link to comment Share on other sites More sharing options...
StrangeRanger Posted December 30, 2020 Author Report Share Posted December 30, 2020 (edited) The pilot hole on an M1 is at a different height from the one on a '28. The tool that works on one won't work on the other. On the M1 it is in line with the bore, on a '28 IIRC (don't have one to measure) it's .10" lower. Sounds like the tool you're describing is for an M1. Its greater proximity to the inside top surface of the receiver must be what necessitated the relief cut for the tooling. That brings up another question: how did they machine the feed ramps on a '28? Edited December 30, 2020 by StrangeRanger Link to comment Share on other sites More sharing options...
anjong-ni Posted December 30, 2020 Report Share Posted December 30, 2020 The little cutter itself centres on the bolt-path hole in either receiver. It drives with a (5/16?) socket. The clearance slot is for the socket. They used to be in the D.R. catalog...Phil Link to comment Share on other sites More sharing options...
Zoltar Posted January 8, 2021 Report Share Posted January 8, 2021 Can this oval shaped depression machined into the interior top surface be of any benefit for running your gun dirty? Link to comment Share on other sites More sharing options...
deerslayer Posted January 8, 2021 Report Share Posted January 8, 2021 I believe the feed ramp was machined from the front through the barrel hole. Link to comment Share on other sites More sharing options...
benedw60 Posted January 8, 2021 Report Share Posted January 8, 2021 No the feed ramp is machined through the mag well Link to comment Share on other sites More sharing options...
laurencen Posted January 8, 2021 Report Share Posted January 8, 2021 could be machined thro the ejection slot Link to comment Share on other sites More sharing options...
StrangeRanger Posted January 8, 2021 Author Report Share Posted January 8, 2021 Can this oval shaped depression machined into the interior top surface be of any benefit for running your gun dirty?Probably not. Most of the crud seems to accumulate in the area of the feed ramps and is blocked from getting into the main part of the receiver by the wall at the rear of the mag slot - the one through which the front of the bolt passes Link to comment Share on other sites More sharing options...
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