User Panel
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MN, USA
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Posted: 8/24/2020 1:33:55 PM EDT
[#1]
Quote HistoryOriginally Posted By CPshooter1: Take off from what, exactly? Is that "PMP" I see? Wonder if those are initials or just the equivalent to "MPC" in the Colt world... Quote HistoryOriginally Posted By CPshooter1: Originally Posted By Engineer5: These are the only markings on my take off barrel. https://www.AR15.Com/media/mediaFiles/84711/00100dPORTRAIT_00100_BURST20200606134513-1452191.jpg That barrel was taken off an original military Mk12 rifle, over a dozen hit the market a few weeks back and there's a few of us in this thread that own some. REV 3 stands for revision number 3, 5 03 is the date May 2003 and I have no idea what PMP stands for. My best guess is that it stands for something like Product Management Program or something similar. Crane uses a similar designation when making changes to some of their rifles, it's called PIP, Program Improvement Package. I have an original McMillan Bros M88 .50 cal receiver that's an overrun from Crane's Mk15 Mod 0 program and it's stamped PIP. My best guess is that PMP is the Army's version of the Navy's PIP, but someone with more knowledge will have clear this up for us. |
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Posted: 8/24/2020 2:28:32 PM EDT
[#2]
Quote HistoryOriginally Posted By CPshooter1: Take off from what, exactly? Is that "PMP" I see? Wonder if those are initials or just the equivalent to "MPC" in the Colt world... I'm definitely going to go with the NATO chamber. Not so much for clone correctness, but because I value reliability as much as accuracy in a platform like this. It was made to be a far-reaching 5.56mm service weapon, so I don't want to deviate too far from that original recipe by messing with custom chamber specs. That's just me though. It's good to have options! If I have a choice between "NATO" chamber or Wylde, I'll take the Wylde everyday and twice on Saturday. MK12s are supposed to be accurate rifles. |
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Posted: 8/24/2020 2:40:39 PM EDT
[Last Edit: kmcale]
[#3]
Quote HistoryOriginally Posted By ArmyPilot12: If I have a choice between "NATO" chamber or Wylde, I'll take the Wylde everyday and twice on Saturday. MK12s are supposed to be accurate rifles. In this case, CLE chamber is what i say to run. Just my 2 cents. As far as reliability, im not sure what is being sought out. No cleaning for a prolonged amount of time? I guess I'm confused, stainless steel barrels should be taken care of/maintained. CLE chamber will not disappoint in any way. Im not knocking the decision you end up with though, whatever works for you. My CLE chambered barrel does excellent, nothing weird using fiocchi 77gr, imi 77gr, hornady 75gr, and various handloads (75gr hornady match and 77gr smk) |
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Posted: 8/24/2020 2:54:03 PM EDT
[Last Edit: ArmyPilot12]
[#4]
Quote HistoryOriginally Posted By kmcale: In this case, CLE chamber is what i say to run. Just my 2 cents. As far as reliability, im not sure what is being sought out. No cleaning for a prolonged amount of time? I guess I'm confused, stainless steel barrels should be taken care of/maintained. CLE chamber will not disappoint in any way. Im not knocking the decision you end up with though, whatever works for you. My CLE chambered barrel does excellent, nothing weird using fiocchi 77gr, imi 77gr, hornady 75gr, and various handloads (75gr hornady match and 77gr smk) Concur. Pretty much any other chamber is going to be more accurate than the "NATO" chamber. NATO chamber is for running crap ammo, in a crap environment, at full cyclic rate of fire. I'm retired from the Army and don't have to do that crap anymore.  ETA When it comes to accuracy shooting, the Service Rifle guys are a wealth of knowledge. Go see what their using. CLE and Wylde chamber guns are all you'll see on the line unless it's a .mil "as issued" shoot. They put more rounds down range than most arfcommers and they don't seem to have any problems with "reliability". |
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Posted: 8/24/2020 3:36:05 PM EDT
[Last Edit: Duck_Hunt]
[#5]
Quote HistoryOriginally Posted By ArmyPilot12: Concur. Pretty much any other chamber is going to be more accurate than the "NATO" chamber. NATO chamber is for running crap ammo, in a crap environment, at full cyclic rate of fire. I'm retired from the Army and don't have to do that crap anymore. ETA When it comes to accuracy shooting, the Service Rifle guys are a wealth of knowledge. Go see what their using. CLE and Wylde chamber guns are all you'll see on the line unless it's a .mil "as issued" shoot. They put more rounds down range than most arfcommers and they don't seem to have any problems with "reliability". Quote HistoryOriginally Posted By ArmyPilot12: Originally Posted By kmcale: In this case, CLE chamber is what i say to run. Just my 2 cents. As far as reliability, im not sure what is being sought out. No cleaning for a prolonged amount of time? I guess I'm confused, stainless steel barrels should be taken care of/maintained. CLE chamber will not disappoint in any way. Im not knocking the decision you end up with though, whatever works for you. My CLE chambered barrel does excellent, nothing weird using fiocchi 77gr, imi 77gr, hornady 75gr, and various handloads (75gr hornady match and 77gr smk) Concur. Pretty much any other chamber is going to be more accurate than the "NATO" chamber. NATO chamber is for running crap ammo, in a crap environment, at full cyclic rate of fire. I'm retired from the Army and don't have to do that crap anymore. ETA When it comes to accuracy shooting, the Service Rifle guys are a wealth of knowledge. Go see what their using. CLE and Wylde chamber guns are all you'll see on the line unless it's a .mil "as issued" shoot. They put more rounds down range than most arfcommers and they don't seem to have any problems with "reliability". I always tend to opt for the wylde chamber on my 5.56 rifles, as all of my Ar platform rifles are tools I’d trust my life to. If I was to build a rifle for matches it would have a CLE chamber. It all depends on the intended use of the rifle IMHO. Let’s keep in mind the military went with the NATO chamber for a reason. On a hard use rifle in a war zone or shtf scenario(where that rifle will likely be neglected), in no way would I want a CLE or any other tight ‘match’ chamber. Here is a decent read From the link; “Remember those reliability issues the M16 suffered in Vietnam? When the rifle got dirty and gunked up, tight tolerances made chambering rounds and cycling the weapon difficult. To alleviate this problem, engineers redesigned the M16's chamber and barrel just slightly. They made the leade of the chamber slightly larger ("sloppier"), so it wouldn't bind up in battlefield conditions.” “The 5.56 chamber's longer, wider leade allows for longer bullets, higher pressure, and more reliability in the field when things get dirty.” |
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Posted: 8/24/2020 4:14:44 PM EDT
[Last Edit: lancecriminal86]
[#6]
The chambers used on the SPR program, and continuing with the rest of the Mk12 iterations, had a lot to do with the fact that they were designed around M855 originally and fielded as such before Mk262 caught up later on. And when Mk262 was used, the accuracy gains were still so plentiful there would have been little to no need to change it, considering 855 may still have been needed should supply of 262 run out.
There is a a lot of commentary here about "booo, 5.56 chamber baaaaaad", but the legit SPR upper belonging to at least one individual in here, not burned out like the ones sourced through PRI because it was barely used when acquired through other means, is still a well sub-MOA gun with current production issued Mk262, unlike their issued Holland. Y'all do your thing, but the modified 5.56 chamber used in the program produced a very accurate rifle. It probably was not the same chamber as on an M4A1, but was probably more generous than a Wylde. And I do believe CLE and others have a 5.56 Match chamber very much along those lines, maybe BCM had it on their SAM-R style barrels. Its almost like Gene Barnett knew what he was doing, but who the hell was that guy. 
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Posted: 8/24/2020 4:51:33 PM EDT
[#7]
Quote HistoryOriginally Posted By lancecriminal86: The chambers used on the SPR program, and continuing with the rest of the Mk12 iterations, had a lot to do with the fact that they were designed around M855 originally and fielded as such before Mk262 caught up later on. And when Mk262 was used, the accuracy gains were still so plentiful there would have been little to no need to change it, considering 855 may still have been needed should supply of 262 run out. There is a a lot of commentary here about "booo, 5.56 chamber baaaaaad", but the legit SPR upper belonging to at least one individual in here, not burned out like the ones sourced through PRI because it was barely used when acquired through other means, is still a well sub-MOA gun with current production issued Mk262, unlike their issued Holland. Y'all do your thing, but the modified 5.56 chamber used in the program produced a very accurate rifle. It probably was not the same chamber as on an M4A1, but was probably more generous than a Wylde. And I do believe CLE and others have a 5.56 Match chamber very much along those lines, maybe BCM had it on their SAM-R style barrels. Its almost like Gene Barnett knew what he was doing, but who the hell was that guy. Never said the .mil 5.56 NATO chamber was bad, it has it's place, just that there are better chambers for those that are spending their money (not Uncle Sam's) on a rifle built for accuracy. Do you have the specs for this "modified" 5.56 chamber? |
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Posted: 8/24/2020 6:35:23 PM EDT
[#8]
Quote HistoryOriginally Posted By ArmyPilot12: Never said the .mil 5.56 NATO chamber was bad, it has it's place, just that there are better chambers for those that are spending their money (not Uncle Sam's) on a rifle built for accuracy. Do you have the specs for this "modified" 5.56 chamber? Quote HistoryOriginally Posted By ArmyPilot12: Originally Posted By lancecriminal86: The chambers used on the SPR program, and continuing with the rest of the Mk12 iterations, had a lot to do with the fact that they were designed around M855 originally and fielded as such before Mk262 caught up later on. And when Mk262 was used, the accuracy gains were still so plentiful there would have been little to no need to change it, considering 855 may still have been needed should supply of 262 run out. There is a a lot of commentary here about "booo, 5.56 chamber baaaaaad", but the legit SPR upper belonging to at least one individual in here, not burned out like the ones sourced through PRI because it was barely used when acquired through other means, is still a well sub-MOA gun with current production issued Mk262, unlike their issued Holland. Y'all do your thing, but the modified 5.56 chamber used in the program produced a very accurate rifle. It probably was not the same chamber as on an M4A1, but was probably more generous than a Wylde. And I do believe CLE and others have a 5.56 Match chamber very much along those lines, maybe BCM had it on their SAM-R style barrels. Its almost like Gene Barnett knew what he was doing, but who the hell was that guy. Never said the .mil 5.56 NATO chamber was bad, it has it's place, just that there are better chambers for those that are spending their money (not Uncle Sam's) on a rifle built for accuracy. Do you have the specs for this "modified" 5.56 chamber? I was trying to figure out how anyone thought that they would be getting a straight NATO spec chamber for any clone SPR barrel in the first place. I dont believe CLE or any of the aforementioned ones use a straight 5.56 chamber on any of their match barrels. I believe CLEs chamber probably is close to what the SPRs used, but the actual SPR barrel prints arent exactly public posted. Monty at Centurion either has them or had access to them, and of course Gene Barnett had them. Im unsure Kevin at HCS actually had them on hand because they originally just used Gene himself. CLE has done SAM-R barrels as well and may have But I do believe it was a modified chamber from the get go because they were trying to squeeze everything they could accuracywise from M855 before Mk262 came online. Many teams didnt see 262 until a ways into Iraq. Add to that the SAM-R, and Lilja Recce barrels all set up to use M855, all known for being very accurate. Sounds to me like the tube and who cuts the chamber is the more important factor. |
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Posted: 8/24/2020 7:14:32 PM EDT
[#9]
Quote HistoryOriginally Posted By lancecriminal86: I was trying to figure out how anyone thought that they would be getting a straight NATO spec chamber for any clone SPR barrel in the first place. I dont believe CLE or any of the aforementioned ones use a straight 5.56 chamber on any of their match barrels. I believe CLEs chamber probably is close to what the SPRs used, but the actual SPR barrel prints arent exactly public posted. Monty at Centurion either has them or had access to them, and of course Gene Barnett had them. Im unsure Kevin at HCS actually had them on hand because they originally just used Gene himself. CLE has done SAM-R barrels as well and may have But I do believe it was a modified chamber from the get go because they were trying to squeeze everything they could accuracywise from M855 before Mk262 came online. Many teams didnt see 262 until a ways into Iraq. Add to that the SAM-R, and Lilja Recce barrels all set up to use M855, all known for being very accurate. Sounds to me like the tube and who cuts the chamber is the more important factor. LOL, agree with all. Most companies will cut what ever chamber the customer asks for though. They'll snicker and call their coworkers over to look at it, but they'll cut it. I didn't know about CLE being involved with the program. Maybe their CLE Match chamber is the "clone" correct chamber? The CLE chamber has a much shorter freebore length (jump) than both the nato and wylde. Which makes sense when firing .mil ammo (< 80 grs). The wylde chamber is more for shooting 80+grs that are seated a bit longer. 
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Posted: 8/24/2020 7:44:35 PM EDT
[#10]
Quote HistoryOriginally Posted By lancecriminal86: I was trying to figure out how anyone thought that they would be getting a straight NATO spec chamber for any clone SPR barrel in the first place. I dont believe CLE or any of the aforementioned ones use a straight 5.56 chamber on any of their match barrels. I believe CLEs chamber probably is close to what the SPRs used, but the actual SPR barrel prints arent exactly public posted. Monty at Centurion either has them or had access to them, and of course Gene Barnett had them. Im unsure Kevin at HCS actually had them on hand because they originally just used Gene himself. CLE has done SAM-R barrels as well and may have But I do believe it was a modified chamber from the get go because they were trying to squeeze everything they could accuracywise from M855 before Mk262 came online. Many teams didnt see 262 until a ways into Iraq. Add to that the SAM-R, and Lilja Recce barrels all set up to use M855, all known for being very accurate. Sounds to me like the tube and who cuts the chamber is the more important factor. Quote HistoryOriginally Posted By lancecriminal86: Originally Posted By ArmyPilot12: Originally Posted By lancecriminal86: The chambers used on the SPR program, and continuing with the rest of the Mk12 iterations, had a lot to do with the fact that they were designed around M855 originally and fielded as such before Mk262 caught up later on. And when Mk262 was used, the accuracy gains were still so plentiful there would have been little to no need to change it, considering 855 may still have been needed should supply of 262 run out. There is a a lot of commentary here about "booo, 5.56 chamber baaaaaad", but the legit SPR upper belonging to at least one individual in here, not burned out like the ones sourced through PRI because it was barely used when acquired through other means, is still a well sub-MOA gun with current production issued Mk262, unlike their issued Holland. Y'all do your thing, but the modified 5.56 chamber used in the program produced a very accurate rifle. It probably was not the same chamber as on an M4A1, but was probably more generous than a Wylde. And I do believe CLE and others have a 5.56 Match chamber very much along those lines, maybe BCM had it on their SAM-R style barrels. Its almost like Gene Barnett knew what he was doing, but who the hell was that guy. Never said the .mil 5.56 NATO chamber was bad, it has it's place, just that there are better chambers for those that are spending their money (not Uncle Sam's) on a rifle built for accuracy. Do you have the specs for this "modified" 5.56 chamber? I was trying to figure out how anyone thought that they would be getting a straight NATO spec chamber for any clone SPR barrel in the first place. I dont believe CLE or any of the aforementioned ones use a straight 5.56 chamber on any of their match barrels. I believe CLEs chamber probably is close to what the SPRs used, but the actual SPR barrel prints arent exactly public posted. Monty at Centurion either has them or had access to them, and of course Gene Barnett had them. Im unsure Kevin at HCS actually had them on hand because they originally just used Gene himself. CLE has done SAM-R barrels as well and may have But I do believe it was a modified chamber from the get go because they were trying to squeeze everything they could accuracywise from M855 before Mk262 came online. Many teams didnt see 262 until a ways into Iraq. Add to that the SAM-R, and Lilja Recce barrels all set up to use M855, all known for being very accurate. Sounds to me like the tube and who cuts the chamber is the more important factor. It would be nice to see some actual documentation on this rather than beliefs and hunches. Wonder if one of these fellas with a take off barrel would be interested in doing a chamber casting. |
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Posted: 8/24/2020 11:14:46 PM EDT
[Last Edit: lancecriminal86]
[#11]
Quote HistoryOriginally Posted By Honda4828: It would be nice to see some actual documentation on this rather than beliefs and hunches. Wonder if one of these fellas with a take off barrel would be interested in doing a chamber casting. Well, go dig up Gene Barnett then, or call Crane and get those prints. I don't know if youve noticed but in this roughly 10 year pursuit of SPR and Mk12 information, it takes a long time to dig up info and a lot of it really is hidden away in people's heads. Theres a ton of shit that will never show up in actual documentation, because it simply was never documented. Some of it was, but good luck figuring out the right FOIA requests to get it. While you're at it, start bugging people for Mk13 barrel prints. You'll find a lot of the same road blocks, plus those that do know or have them, that's what lets them charge a premium for that knowledge. The actual contract Mk12 barrel specs are no different. |
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MN, USA
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Posted: 8/25/2020 12:49:25 AM EDT
[Last Edit: USMCSGT0331]
[#12]
Quote HistoryOriginally Posted By lancecriminal86: While you're at it, start bugging people for Mk13 barrel prints. Quote HistoryOriginally Posted By lancecriminal86: Originally Posted By Honda4828: It would be nice to see some actual documentation on this rather than beliefs and hunches. Wonder if one of these fellas with a take off barrel would be interested in doing a chamber casting. While you're at it, start bugging people for Mk13 barrel prints. Mk13 Mod 5 barrel prints:    |
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Posted: 8/25/2020 7:59:46 AM EDT
[Last Edit: Duck_Hunt]
[#13]
Quote HistoryOriginally Posted By lancecriminal86: Well, go dig up Gene Barnett then, or call Crane and get those prints. I don't know if youve noticed but in this roughly 10 year pursuit of SPR and Mk12 information, it takes a long time to dig up info and a lot of it really is hidden away in people's heads. Theres a ton of shit that will never show up in actual documentation, because it simply was never documented. Some of it was, but good luck figuring out the right FOIA requests to get it. While you're at it, start bugging people for Mk13 barrel prints. You'll find a lot of the same road blocks, plus those that do know or have them, that's what lets them charge a premium for that knowledge. The actual contract Mk12 barrel specs are no different. Quote HistoryOriginally Posted By lancecriminal86: Originally Posted By Honda4828: It would be nice to see some actual documentation on this rather than beliefs and hunches. Wonder if one of these fellas with a take off barrel would be interested in doing a chamber casting. Well, go dig up Gene Barnett then, or call Crane and get those prints. I don't know if youve noticed but in this roughly 10 year pursuit of SPR and Mk12 information, it takes a long time to dig up info and a lot of it really is hidden away in people's heads. Theres a ton of shit that will never show up in actual documentation, because it simply was never documented. Some of it was, but good luck figuring out the right FOIA requests to get it. While you're at it, start bugging people for Mk13 barrel prints. You'll find a lot of the same road blocks, plus those that do know or have them, that's what lets them charge a premium for that knowledge. The actual contract Mk12 barrel specs are no different. Hey I get it that it’s hard to get info, but in the end Speculation is still speculation. I personally highly doubt that the Mk12 program used a CLE chamber, as that chamber is known to be really tight (to the point where some have had issues). If they deviated from the NATO chamber, It’s far more likely they used a Wylde(ish) chamber as it just has a shorter leade than the NATO. I’d love to be proven wrong though. My point is that since there is known take off barrels from the Mk12 program in the wild now.. Casting a chamber is cheap and easy. Even just measuring the Freebore would be easy.  https://www.brownells.com/gunsmith-tools-supplies/barrel-tools/barrel-chamfering-accessories/cerrosafe-chamber-casting-alloy-prod384.aspx |
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GA, USA
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Posted: 8/25/2020 8:39:07 AM EDT
[#14]
Was the original Mk12 barrel designed around the Mk262 mod1 cartridge or was the cartridge an afterthought?
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VA, USA
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Posted: 8/25/2020 8:52:24 AM EDT
[Last Edit: mra4523]
[#15]
Quote HistoryOriginally Posted By USMCSGT0331: Mk13 Mod 5 barrel prints: https://i.imgur.com/nErLL8B.jpg https://i.imgur.com/BaBispT.jpg https://i.imgur.com/sxjod2I.jpg Haha people are going to go nuts for that, even without the hard measurements. That one is actually a bit easier to read than the one I was given. |
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Posted: 8/25/2020 11:17:21 AM EDT
[Last Edit: lancecriminal86]
[#16]
Quote HistoryOriginally Posted By stainlineho: Was the original Mk12 barrel designed around the Mk262 mod1 cartridge or was the cartridge an afterthought? It was originally designed and tested around M855. Mk262 came about during the testing phases but was in limited supply when Afghanistan kicked off. Apparently the chamber did get adjusted to suit Mk262 a bit better at some point but we know it handled M855 just fine, as weve got @Stukas87 here who didnt get 262 until a ways into the Iraq invasion. And Ive had anecdotes from Marines about having to use M855. As a reminder, all of the early SPRs came with M855 calibrated turrets for an 18 inch barrel using whatever data Crane provided to Leupold. Well, except for the ones that apparently had 55gr dials, but we think those were from the testing phases. |
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USA
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Posted: 8/25/2020 7:45:33 PM EDT
[Last Edit: PerfectTurn]
[#17]
Anyone have a similar condition C AF upper in their stash that they would work a trade +/- cash accordingly for this Armalite that was seen on the FDNY gun? My 0 needs a C AF to be just about complete. If so email me, I'd fire up an EE ad for feedback/tracking purposes of course.
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OR, USA
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Posted: 8/27/2020 2:41:48 AM EDT
[#18]
I’ve been stashing Mk12 components away for a while and can assemble two uppers to run on one lower. I want the traditional 18” and a 16” with a LPVO. Do I go with the Mod 0 and SEAL RECCE or Mod 1 and Holland?
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Posted: 8/27/2020 8:18:03 AM EDT
[#19]
Has anyone spoken to Frank at Compass Lake in reference to the CLE chamber? He designed it when he first started building CMP legal AR rifles. The CLE Chamber was designed for the 80 grain projectiles due to the length. It works well for anything up to Sierra 80 MK's. His stuff is well built and has been tested over three decades. I'm sure if his stuff didn't live up to it both the Big teams wouldn't be using his parts.
Dan |
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Posted: 8/27/2020 5:48:57 PM EDT
[#20]
Quote HistoryOriginally Posted By Honda4828: Hey I get it that it’s hard to get info, but in the end Speculation is still speculation. I personally highly doubt that the Mk12 program used a CLE chamber, as that chamber is known to be really tight (to the point where some have had issues). If they deviated from the NATO chamber, It’s far more likely they used a Wylde(ish) chamber as it just has a shorter leade than the NATO. I’d love to be proven wrong though. My point is that since there is known take off barrels from the Mk12 program in the wild now.. Casting a chamber is cheap and easy. Even just measuring the Freebore would be easy. https://www.brownells.com/gunsmith-tools-supplies/barrel-tools/barrel-chamfering-accessories/cerrosafe-chamber-casting-alloy-prod384.aspx Don't take my comment as directly implying that the CLE chamber was used, it wasn't. I think BCMs 5.56 Match chamber would probably be similar to the Mk12 chamber based on their description, and I mean this IN SPIRIT, not in terms of direct dimensions. Here's a description from one of their uppers with the ionbond SS410 SPR barrel they make: --- 5.56 NATO Match Chamber (USMC SAM-R Chamber) The USGI 5.56 NATO chamber is the best choice for effective deployment, reliability, and compatibility, of higher chamber pressures of military or high quality personal defense ammunition. The SAM-R chamber is the precision version of the 556 NATO chamber. --- They used to have a better description of the BCM 5.56 NATO chamber but it seems to be lost to the internet. But going from a NATO chamber and tightening it up follows the progression of development from the SPR program as we know they had to design around M855, and we know the guns still worked with 855 even if the chamber was set up for Mk262 so it couldn't have been excessively tight. Or, maybe the started with a match chamber from AMU and worked backwards, we will see what my inquiries come back with. And to get directly at your point about casting a chamber, how much throat erosion and wear do you think these barrels will have, because that could throw the measurements off compared to what was originally cut afaik. If you're tired of speculation, even educated speculation based off of solid evidence and people who worked in the program, then please. Pick up a phone and start calling, and add some data to this thread. We have a lot of folks sitting back wondering about things or complaining about my answers, instead of getting answers for themselves. I've already asked in my avenues, lets see what some of yall can dig up. |
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USA
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Posted: 8/28/2020 9:38:50 PM EDT
[#21]
Sling folks, the goods are in, check your inboxes! If you don’t see an email from me, email me from here. Cheers!
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Posted: 8/29/2020 3:57:29 PM EDT
[#22]
Just a heads up I put my Nightforce 2.5-10x24 in the EE.
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Posted: 8/29/2020 4:47:37 PM EDT
[#23]
Quote HistoryOriginally Posted By -KentuckyWindage-: Just a heads up I put my Nightforce 2.5-10x24 in the EE. Just a heads up, I'll take it and I sent you a pm
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Posted: 8/29/2020 5:00:09 PM EDT
[#24]
Quote HistoryOriginally Posted By unstabl: Just a heads up, I'll take it and I sent you a pm 
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USA
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Posted: 8/29/2020 5:57:09 PM EDT
[#25]
I put the AR receiver from a couple posts above. Email me if you need it and we can talk. Thx!
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USA
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Posted: 8/29/2020 5:59:45 PM EDT
[Last Edit: Dobs013]
[#26]
So my tube came in. Threw the unmarked/unbeveled 3” rails on and the OG kac sling mount. I’m gonna work on filling the middle set of accessory rail mounting holes tomorrow. And as soon as I can get some time on a drill press or stop being cheap and buy a good cordless drill, I’ll be opening all the vent holes up to 7/16. Once all that is done I should be able to assemble my upper!
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USA
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Posted: 8/29/2020 6:17:42 PM EDT
[#27]
Quote HistoryOriginally Posted By Dobs013: So my tube came in. Threw the unmarked/unbeveled 3” rails on and the OG kac sling mount. I’m gonna work on filling the middle set of accessory rail mounting holes tomorrow. And as soon as I can get some time on a drill press or stop being cheap and buy a good cordless drill, I’ll be opening all the vent holes up to 7/16. Once all that is done I should be able to assemble my upper! https://i.imgur.com/9PKAVrA.jpg Love seeing someone else go through the effort here! Check your email, I have something else you might be interested in. |
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IN, USA
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Posted: 8/30/2020 10:32:21 AM EDT
[Last Edit: CPshooter1]
[#28]
Quote HistoryOriginally Posted By USMCSGT0331: That barrel was taken off an original military Mk12 rifle, over a dozen hit the market a few weeks back and there's a few of us in this thread that own some. REV 3 stands for revision number 3, 5 03 is the date May 2003 and I have no idea what PMP stands for. My best guess is that it stands for something like Product Management Program or something similar. Crane uses a similar designation when making changes to some of their rifles, it's called PIP, Program Improvement Package. I have an original McMillan Bros M88 .50 cal receiver that's an overrun from Crane's Mk15 Mod 0 program and it's stamped PIP. My best guess is that PMP is the Army's version of the Navy's PIP, but someone with more knowledge will have clear this up for us.  *edit* I also see my questions about the SPR chambers sparked some good conversation! I'm glad to see it. As mentioned, these were designed around both M855 and Mk262. CLE told me themselves that it was a NATO chamber in the original barrels. They didn't get more specific than that, however. I personally believe having the 18" tube and resulting increase in velocity will be enough of a gain over a 14.5" carbine for this rifle to serve its intended purposes. At least for me it will. I'm going to continue to try and figure out the details of the original barrel by doing more homework. I have no desire to rush this build, and now that there is so much uncertainty around the chamber specs, it makes me want to go that much further to try and find out what the deal is. If anyone with one of these rare "take-off" Mk12 barrels would be willing to loan one out under my extreme watch and care, I would be more than happy to pay a fee to borrow it and use as a reference for having a new barrel manufactured. I'm going to see if CLE, HCS, or Centurion have actual blue-prints on hand first, but if not, I am simply not going to rest until I find a real barrel that can be referenced. Thanks again for all the input, everyone! |
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USA
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Posted: 8/30/2020 11:16:42 AM EDT
[#29]
Took a before pic before I start hitting the tube with a cobalt bit....
 So based off the photo, from what I can tell, the bottom rail appears to be a 3” and not an 8.5”. Also I can’t tell if the handguard is the version with only 2 extra accessory rail mounting holes on the side or 3, so I’m gonna leave the third one open. Just saves work. Chime in on the bottom rail tho, not sure which direction to go in that one. Would prefer 3” bc I have an extra unmarked rail section but I don’t want to put it on if it’s not correct. 
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Posted: 8/30/2020 12:30:05 PM EDT
[Last Edit: KGLaw]
[#30]
Quote HistoryOriginally Posted By Dobs013: Took a before pic before I start hitting the tube with a cobalt bit.... https://i.imgur.com/5mzYiLP.jpg So based off the photo, from what I can tell, the bottom rail appears to be a 3” and not an 8.5”. Also I can’t tell if the handguard is the version with only 2 extra accessory rail mounting holes on the side or 3, so I’m gonna leave the third one open. Just saves work. Chime in on the bottom rail tho, not sure which direction to go in that one. Would prefer 3” bc I have an extra unmarked rail section but I don’t want to put it on if it’s not correct. https://i.imgur.com/YyEG10w.jpg Wouldn't be the only time someone ditched the long bottom and moved a side to its place. There's a couple pictures of Hollands like that. |
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USA
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Posted: 8/30/2020 4:52:30 PM EDT
[#31]
Regarding chambers (at least originally, I don't know what happened when it reached production status): It used a slightly modified 5.56 chamber as memory serves (I don't know the dimensions) but as was said above the gains in accuracy and keeping the reliability more than merited the choice.
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WV, USA
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Posted: 8/30/2020 5:00:27 PM EDT
[#32]
And the start of a Holland begins...
 
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FL, USA
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Posted: 8/31/2020 3:43:38 PM EDT
[#33]
Quote HistoryOriginally Posted By DStepec: Sling folks, the goods are in, check your inboxes! If you don’t see an email from me, email me from here. Cheers! Received the sling today. Outstanding work. Thanks! |
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USA
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Posted: 8/31/2020 3:57:42 PM EDT
[#34]
Quote HistoryOriginally Posted By rbgonoles: Received the sling today. Outstanding work. Thanks! Damn, “overnight parts from Japan”, that’s fast!!! Stoked for pics! |
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USA
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Posted: 8/31/2020 5:28:51 PM EDT
[#35]
Holes opened to 7/16, that was not fun...
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USA
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Posted: 8/31/2020 6:00:29 PM EDT
[#36]
Quote HistoryOriginally Posted By Dobs013: Holes opened to 7/16, that was not fun... https://i.imgur.com/wpgxf9w.jpg Haha glad I have someone to share this experience with |
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USA
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Posted: 8/31/2020 7:55:10 PM EDT
[#37]
Quote HistoryOriginally Posted By DStepec: Haha glad I have someone to share this experience with It was an experience for sure... |
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CA, USA
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Posted: 8/31/2020 8:09:02 PM EDT
[#38]
I once used a Mod 0 with the PRI round fore end. I used it just once and had a hand full of carbon fiber splinters. Do you run into that issue after adding or opening up the holes?
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Posted: 8/31/2020 8:09:43 PM EDT
[#39]
Received my slings today. I'm not sure if I should use these or put them behind a set of brass poles with a red rope across and just look at them. Amazing work. Thank you again. I'll try for pictures tomorrow.
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Posted: 8/31/2020 8:29:22 PM EDT
[#40]
Quote HistoryOriginally Posted By McCarron: I once used a Mod 0 with the PRI round fore end. I used it just once and had a hand full of carbon fiber splinters. Do you run into that issue after adding or opening up the holes? I'm not sure how that could've happened, was it super beat up? I took a chamfer bit to mine after opening up some new holes on my Gen II repro and smoothed it out even more by sanding it. Not once had that splinter problem. I like the PRI tube even more than the KAC RAS. |
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CA, USA
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Posted: 8/31/2020 11:35:59 PM EDT
[#41]
No, it looked very nice. This was about 20 years ago an pushed me towards the Knight’s rails for my working rifles. I like the look, weight, and balance of the PRI rails but just wondered if anyone else ran into that issue.
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Posted: 9/1/2020 1:12:33 AM EDT
[Last Edit: tamboi]
[#42]
Quote HistoryOriginally Posted By Dobs013: Holes opened to 7/16, that was not fun... https://i.imgur.com/wpgxf9w.jpg What did you use, I suppose when did they change the hole size, same time they omitted the extra hole in the middle. |
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USA
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Posted: 9/1/2020 7:02:27 AM EDT
[#43]
Quote HistoryOriginally Posted By tamboi: What did you use, I suppose when did they change the hole size, same time they omitted the extra hole in the middle. I took the redneck approach to mine, 7/16 cobalt bit and a Milwaukee 18v cordless. Then I went back and sanded and used jb weld to fill the couple of chips I got. Sanded again. Wet Sanded. Painted. Wet sanded again then painted again. The pic I posted was after the first coat of paint. Definitely would not recommend that approach. Only reason I took it was bc I don’t have regular access to a drill press and I didn’t want to wait a month to drill the holes out. Drill press with a carbide tipped bit or cobalt bit is the way to go for sure. |
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Posted: 9/1/2020 8:02:05 AM EDT
[#44]
Quote HistoryOriginally Posted By tamboi: I suppose when did they change the hole size, same time they omitted the extra hole in the middle. No. Hole size didn't change until later. After the Mk12 Mod 0s were done. The missing side rail hole happened earlier than that. PRi's tubes have all kinds of subtle variations... There's even tubes floating around with nine vent holes versus the standard ten. |
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Posted: 9/1/2020 11:02:55 AM EDT
[#45]
Quote HistoryOriginally Posted By Hunterex: No. Hole size didn't change until later. After the Mk12 Mod 0s were done. The missing side rail hole happened earlier than that. PRi's tubes have all kinds of subtle variations... There's even tubes floating around with nine vent holes versus the standard ten. Dobs, Hunterex thanks for the replies, does anyone know what the current hole size is compared to 7/16 .435. Actually must measure mine, if its easier with a drill press, I will wait till I have access to one, jesus a never ending process ti get these close. |
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Posted: 9/1/2020 11:37:26 AM EDT
[Last Edit: kmcale]
[#46]
Quote HistoryOriginally Posted By tamboi: Dobs, Hunterex thanks for the replies, does anyone know what the current hole size is compared to 7/16 .435. Actually must measure mine, if its easier with a drill press, I will wait till I have access to one, jesus a never ending process ti get these close. Drill press is 100% easier, especially if you make a little jig to hold the handguard. I used a scrap 2x6 and some dowel, stuck it in place through the handguard vent holes and went to town. Though for mine, I was adding holes and not expanding existing, so this may not work for you.. haha |
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USA
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Posted: 9/1/2020 7:17:07 PM EDT
[#47]
Have the upper half assembled. Still need to rocksett and loctite. Does anyone happen to know the size of the set screws for the fsgb and collar?
 
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Posted: 9/1/2020 7:28:43 PM EDT
[Last Edit: Engineer5]
[#48]
Quote HistoryOriginally Posted By Dobs013: Have the upper half assembled. Still need to rocksett and loctite. Does anyone happen to know the size of the set screws for the fsgb and collar? https://i.imgur.com/6X83CiB.jpg https://i.imgur.com/39HLomj.jpg It's not like you have to take them off a lot but I upgraded the size of the set screws in the collar. I had to remove one once and it was a bitch with the little allen and ended up having to carefully drill it out. I didn't want to ever worry about something like that again so I drilled and tapped mine to accept 10-32x1/8. ETA: Never noticed the different positions of the set screws.  |
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Posted: 9/1/2020 9:48:31 PM EDT
[#49]
Quote HistoryOriginally Posted By Engineer5: It's not like you have to take them off a lot but I upgraded the size of the set screws in the collar. I had to remove one once and it was a bitch with the little allen and ended up having to carefully drill it out. I didn't want to ever worry about something like that again so I drilled and tapped mine to accept 10-32x1/8. ETA: Never noticed the different positions of the set screws. https://www.AR15.Com/media/mediaFiles/84711/IMG_20200901_182046-1573127.jpg The one you drilled out is where they were located on the collars of the issued rifles. |
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PA, USA
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Posted: 9/1/2020 10:13:55 PM EDT
[#50]
i bet a 7/16 2 flute endmill woulda been much easier and cleaner cutting........ ;)
yep, mine is lower as well. from badger.  |
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