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Posted: 10/27/2014 10:24:14 AM EDT
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i ordered one of BCM's blem uppers, i had a problem with the upper chambering my reloads using an RCBS small base die, it functioned fine with factory loads, i sent it back with an explanation of the problem, they checked and tested it then sent it back to me saying it was well within specs, last Thursday i bought a new set of RCBS SB dies, loaded 6 test rounds loaded them in a mag. then run them thru the chamber, they worked just fine.
i want to congratulate BCM for having their 5.56mm chambers to "MilSpec", while most others have a 5.56mm chamber that is "good enough"! a little history, i have been using a set of RCBS SB dies for reloading my 5.56mm ammo, ALL the ammo functioned in all my AR-15/M4 type rifles/carbines just fine till i got the BCM upper, THAT is when i found out that all my other 5.56mm chambers had to be "just good enough", i done extensive measurements with micrometers and calipers, the base of factory ammo measures .3730", the BCM chamber measures .3735", my new dies measure .3730", the old SB die sizes to .3745".., i then measured fired brass from my Colt, Bushmaster, LWRCI and some from friends from the range of unknown gun makers except for one was a LMT.., ALL the fired brass measured, .3745" to .3765"....., where the hell is the damn "MilSpec" from these chambers ?? BCM.., i applaud you for having a true MilSpec chamber, and thank you for producing a truly fine weapon. |
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The SAAMI Specification for 223 REM for the diameter of the case's rim is .378" – .010". The Military Specification for Part No. 11820451 (5.56MM Case) for the diameter of the case's rim is .378" – .007". The SAAMI Specifcation for 223 REM for the diameter of the case just forward of the primer pocket is .3759". The Military Specification for Part No. 11820451 (5.56MM Case) for the diameter of the case just forward of the primer pocket is .3759" – .0030".
The SAAMI Specification for the diameter of the chamber at the breech face is .3804". I do not have a blueprint drawing for a 5.56MM chamber to see how it compares with the measurements set by SAAMI. |
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Am I to deduce that these other manufacturers chambers have slightly larger chambers that did not produce a problem with original larger out of spec die? you deduced correctly, for over 10 years i have been reloading 5.56mm ammo with this set of dies and never had a problem with these reloads in any of my currently or previously owned rifles/carbines, with 5.56mm NATO stamped on the barrel.., even my old Coal Valley Eagle ! then i bought this BCM upper and not one of these reloads would cycle. thank you for the question, did i clear that up for you ? |
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The SAAMI Specification for 223 REM for the diameter of the case's rim is .378" – .010". The Military Specification for Part No. 11820451 (5.56MM Case) for the diameter of the case's rim is .378" – .007". The SAAMI Specifcation for 223 REM for the diameter of the case just forward of the primer pocket is .3759". The Military Specification for Part No. 11820451 (5.56MM Case) for the diameter of the case just forward of the primer pocket is .3759" – .0030". The SAAMI Specification for the diameter of the chamber at the breech face is .3804". I do not have a blueprint drawing for a 5.56MM chamber to see how it compares with the measurements set by SAAMI. Sir, i am aware of SAMI specs but factory ammo from the L.C. plant and commercial ammo measures much smaller to accommodate ALL chambers, that is why factory ammo functioned in my BCM upper. may i respectfully ask why you posted this info ? |
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may i respectfully ask why you posted this info ? Quoted:
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The SAAMI Specification for 223 REM for the diameter of the case's rim is .378" – .010". The Military Specification for Part No. 11820451 (5.56MM Case) for the diameter of the case's rim is .378" – .007". The SAAMI Specifcation for 223 REM for the diameter of the case just forward of the primer pocket is .3759". The Military Specification for Part No. 11820451 (5.56MM Case) for the diameter of the case just forward of the primer pocket is .3759" – .0030". The SAAMI Specification for the diameter of the chamber at the breech face is .3804". I do not have a blueprint drawing for a 5.56MM chamber to see how it compares with the measurements set by SAAMI. may i respectfully ask why you posted this info ? There are two sets of measurements listed there. The info highlighted in red is from a U.S. Government Blueprint. Also, the answer to your question; to show there is a tolerance range allowed in the "milspec".. |
| It sounds like you simply ran a bad batch of ammo. I would not lend much thought to measuring brass after it has been fired. It expands and contracts and depending on a lot of micro sized variances, the brass could expand and contract to a different point, but still work fine in almost all chambers. That fact should clue in that there is not really anything wrong with all of those guns you measured. |
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It sounds like you simply ran a bad batch of ammo. I would not lend much thought to measuring brass after it has been fired. It expands and contracts and depending on a lot of micro sized variances, the brass could expand and contract to a different point, but still work fine in almost all chambers. That fact should clue in that there is not really anything wrong with all of those guns you measured. there is a great advantage to measuring fired brass from different chambers, yesterday i fired 60 rounds from my new BCM upper that i resized/loaded with the new RCBS SB dies and my Colt 6920, today i will be measuring them. nothing wrong with the chambers of the guns, they are in my OPINION, NOT true MilSpec, they were reamed to allow any 5.56mm ammo of any manufacturers to function in any 5.56mm chambers, BCM reams their chambers to the tightest of Specs. which i find to be very desirable. had i known a long time ago my former RCBS SB dies were NOT true SB i would have never used them, it took the BCM upper/chamber to open my eyes to the looseness of all the 5.56mm chambers of my other rifles. in more simpler terms the ammo i cranked out using the old SB dies were in a general sense, "good enough" for most gun manufacturers chambers, e.g., Colt, Bushmaster, LWRCI, AND many, if not all others except for BCM..., again i applaud BCM for their dedication to high quality firearms. i hope this make sense to everyone ? |
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Quoted: there is a great advantage to measuring fired brass from different chambers, yesterday i fired 60 rounds from my new BCM upper that i resized/loaded with the new RCBS SB dies and my Colt 6920, today i will be measuring them. nothing wrong with the chambers of the guns, they are in my OPINION, NOT true MilSpec, they were reamed to allow any 5.56mm ammo of any manufacturers to function in any 5.56mm chambers, BCM reams their chambers to the tightest of Specs. which i find to be very desirable. had i known a long time ago my former RCBS SB dies were NOT true SB i would have never used them, it took the BCM upper/chamber to open my eyes to the looseness of all the 5.56mm chambers of my other rifles. in more simpler terms the ammo i cranked out using the old SB dies were in a general sense, "good enough" for most gun manufacturers chambers, e.g., Colt, Bushmaster, LWRCI, AND many, if not all others except for BCM..., again i applaud BCM for their dedication to high quality firearms. i hope this make sense to everyone ? Quoted: Quoted: It sounds like you simply ran a bad batch of ammo. I would not lend much thought to measuring brass after it has been fired. It expands and contracts and depending on a lot of micro sized variances, the brass could expand and contract to a different point, but still work fine in almost all chambers. That fact should clue in that there is not really anything wrong with all of those guns you measured. there is a great advantage to measuring fired brass from different chambers, yesterday i fired 60 rounds from my new BCM upper that i resized/loaded with the new RCBS SB dies and my Colt 6920, today i will be measuring them. nothing wrong with the chambers of the guns, they are in my OPINION, NOT true MilSpec, they were reamed to allow any 5.56mm ammo of any manufacturers to function in any 5.56mm chambers, BCM reams their chambers to the tightest of Specs. which i find to be very desirable. had i known a long time ago my former RCBS SB dies were NOT true SB i would have never used them, it took the BCM upper/chamber to open my eyes to the looseness of all the 5.56mm chambers of my other rifles. in more simpler terms the ammo i cranked out using the old SB dies were in a general sense, "good enough" for most gun manufacturers chambers, e.g., Colt, Bushmaster, LWRCI, AND many, if not all others except for BCM..., again i applaud BCM for their dedication to high quality firearms. i hope this make sense to everyone ? |
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the results from cold fired brass from Colt and BCM, is the Colt chamber measured .002" larger than the BCM from a random sample of ten (10) fired cases from each upper, i'll compare a Bushy to the BCM next week. SAYONARA ! Interesting thread Bud556MM, thanks for information and your research. |
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I think it's odd you find all those other manufacturers to have "out of spec"chambers, and BCM to have in spec. Quoted:
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It sounds like you simply ran a bad batch of ammo. I would not lend much thought to measuring brass after it has been fired. It expands and contracts and depending on a lot of micro sized variances, the brass could expand and contract to a different point, but still work fine in almost all chambers. That fact should clue in that there is not really anything wrong with all of those guns you measured. there is a great advantage to measuring fired brass from different chambers, yesterday i fired 60 rounds from my new BCM upper that i resized/loaded with the new RCBS SB dies and my Colt 6920, today i will be measuring them. nothing wrong with the chambers of the guns, they are in my OPINION, NOT true MilSpec, they were reamed to allow any 5.56mm ammo of any manufacturers to function in any 5.56mm chambers, BCM reams their chambers to the tightest of Specs. which i find to be very desirable. had i known a long time ago my former RCBS SB dies were NOT true SB i would have never used them, it took the BCM upper/chamber to open my eyes to the looseness of all the 5.56mm chambers of my other rifles. in more simpler terms the ammo i cranked out using the old SB dies were in a general sense, "good enough" for most gun manufacturers chambers, e.g., Colt, Bushmaster, LWRCI, AND many, if not all others except for BCM..., again i applaud BCM for their dedication to high quality firearms. i hope this make sense to everyone ? hummmm !, what is "odd" about it ? i have not found "all those other manufacturers", are out of spec, i have only compared two (2) different makes, also the "others" are within SAMI specs, it is a fact that BCM hold a much tighter set of specs...., and VALUES ! does this make sense now ?? |
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