Looking for XM-21 Expert - Page 4 - M14 Forum
M14 Forum Keeping the M14 tradition alive!  

Looking for XM-21 Expert

This is a discussion on Looking for XM-21 Expert within the The M14 forums, part of the M14 M1A Forum category; So I found my SAK-NM stash. I picked these up from a fellow a couple years ago hunting for m14 parts. I got both barrels ...


Go Back   M14 Forum > M14 M1A Forum > The M14

166Thanks
Reply
 
LinkBack Moderator Tools Display Modes

Old April 14th, 2020, 09:35 PM   #46
Designated Marksman
 
edgartwib's Avatar
 
Join Date: Aug 2012
Location: New Mexico
Posts: 595
So I found my SAK-NM stash. I picked these up from a fellow a couple years ago hunting for m14 parts. I got both barrels one with unitized gas cyl. and the NM reamed Flash hider with sight dovetail removed from the same guy who said they were from a M-21. The little baggie i have that the flashhider was in says m-25. A story is just a story who knows if they were from a M-21. The SEI gas block sight is one of my pick ups.














edgartwib is offline  
Remove Ads
Old April 15th, 2020, 04:17 AM   #47
Lifer
 
lysander's Avatar
 
Join Date: Apr 2015
Location: North Carolina
Posts: 4,182

Awards Showcase

Quote:
Originally Posted by grateful patriot View Post
Quote:
Originally Posted by M1Army View Post
lysander,

The XM21 used a standard weight NM barrel (TRW, SA & SAK) - the report above references

"Three Mann barrels"
"fired from the Mann barrels"
"In the event Mann barrels are used which exhibit large extreme spreads"

Do you know the definition of the term "Mann Barrel?" I am not familiar with this term.

Also XM21's - I thought were in service in 1969 so were these rifles that were in service and came back in and were tested? Based on the comments related to bedding I thought this might be the case?

I hope this isn't something I should know?

Thanks, M1Army
As I understand it, Mann barrels were mounted stationary 03 receivers with a full heavy profile (1-1/4 +-) possibly. The army used them for accuracy testing. These were even sold as surplus by Civilian Marksmanship Program a few years ago. Seems like they were about $500-550. Hopes this helps.
"Mann* barrels" is how the Ordnance/Picatinny folks refer to an accuracy test barrel and associated receiver. These are precisely made test barrels that can be easily changed on a universal receiver (back in the day an M1903, but increasingly today a more modern receiver is used). These are used to used throughout the industry to test ammunition accuracy.

Rifles #11 through #15 were XM21s that were returns from Southeast Asia (SEA) and were refurbished at Rock Island. Rifles #1 through #10 were rifles that were "built" as XM21s in 1969 and placed in storage, as the number built in 1969 was in excess of operational requirements.
__________
* named after pioneering ballistian Franklin W. Mann
Attached Images
File Type: png Test.png (249.3 KB, 9 views)

Thanks from m1sniper and M1Army

Last edited by lysander; April 15th, 2020 at 04:30 AM.
lysander is offline  
Old April 15th, 2020, 06:27 AM   #48
Automatic Rifleman
 
Join Date: Nov 2012
Location: FLORIDA
Posts: 134
Fantastic information Lysander. I’m amazed at the awesome information you dig up.
That list seems to verify that the ARTEL serial numbers are not matched to rifle serial numbers.
I’m getting the impression that maybe not all XM 21s were ex NM rifles, and not all were stamped XM21. It’s possible that The first batch of rifles built at the AMU were built not necessarily from NM rifles or stamped XM21. I once asked Hook if the XMs were stamped XM 21 and he said no. Some appear to have been electropenciled also.

PILTDOWNHOAX is offline  
 
Old April 15th, 2020, 06:47 AM   #49
Dodgin' The Reaper
 
XM25Ren's Avatar
 
Join Date: Dec 2012
Location: Land of the Free
Posts: 6,782

Awards Showcase

Quote:
Originally Posted by PILTDOWNHOAX View Post
Fantastic information Lysander. I’m amazed at the awesome information you dig up.
That list seems to verify that the ARTEL serial numbers are not matched to rifle serial numbers.
I’m getting the impression that maybe not all XM 21s were ex NM rifles, and not all were stamped XM21. It’s possible that The first batch of rifles built at the AMU were built not necessarily from NM rifles or stamped XM21. I once asked Hook if the XMs were stamped XM 21 and he said no. Some appear to have been electropenciled also.
The AR-TEL scope was matched to a specific rifle, the last four serial numbers on the receiver were engraved on the scope mount. I am unaware that the serial number of the scope was ever used to matched the scope to a specific XM21.

Both standard and NM M14s were used to build XM21 rifles.

REN

Thanks from PILTDOWNHOAX
XM25Ren is offline  
Old April 15th, 2020, 06:48 AM   #50
Lifer
 
Random Guy's Avatar
 
Join Date: Jan 2017
Location: No. VA
Posts: 2,201

Awards Showcase

Interesting report, thanks for sharing. It suggests that even the exotic epoxy impregnated stocks swelled in high humidty/high temps and developed cracks. Also the bedding compound didn't hold up all that well either:

Quote:
Although the stocks of the five weapons were sealed by vacuum impregnation with epoxy resin, this treatment did not prevent expansion of the wood grain and attendant separation of the bedding compound at the back of the stock - receiver area. There also was cracking of the bedding compound in the area of the frontal bridge of the stock. This appears to be caused by the compound in that area being of too thin a cross section to adequately support the front end of the receiver.
and..

Quote:
5. CONCLUSIONS:

b. Durability of the stock bedding compound is inadequate to prevent cracking
I will note that the two bedding compounds listed in the June 1971 AMU build guide are:

1. EPOXY-GLASS manufactured by Fewal Inc. Resin Systems Division, Ashland, Mass.
2. Bisonite Epoxy manufactured by: Bisonite Company Inc., Buffalo, New York

I think #1 ('Epoxy-glass') is commonly known as 'Accu-glass.' Perhaps Ted Brown or another long-time builder can comment, but my impression from one old time National Guard M14 builder is that bedding choice #2, Bisonite, is much more stable and more durable bedding compound compared to 'Accu-glass' aka 'Epoxy-glass', the later which exhibited more 'bedding-break-down'. He went through NM M14 school in 1990 and the US Army was using mostly Bisonite by that time, not the older 'Accuglass'. Moreover, by the 1980s newer and better bedding material came into use, most notably MarineTex, which is very stable/durable, and since then I've heard that Devcon-Titanium bedding compound is even more durable, but a pain to work with.

My point is the original XM-21 bedding material, if 'Epoxy-glass' is in fact 'Accu-glass,' probably contributed to these poor findings, esp if test conditions were + 125 to - 25 degrees with high humidity, etc. The original bedding compounds from 1969 have gotten much better, and I think the issue of 'bedding break-down' is/was a legitimate problem with the old Accuglass-based bedding compound(s).

To me the most interesting variable in the report is the topic of "foreend pre-load in lbs", which unfortunately was not explained as to how it was measured. (sounds like the 'draw pressure' voodoo topic...) The report notes that only 2 of the 15 rifles were within spec, which I think is 10 to 15 pounds. The rifles varied from 3 lb to 30 lbs of fore-end pressure, and the report noted this caused vertical dispersion issues. My suspicion is that this particular variability might be the root cause that contributed to the rifles not quite meeting the expected accuracy levels.

I didn't do any statistical analysis of course, but a cursory look at the vertical dispersion data seems to suggest that rifles at the upper end (over 20s lbs of forend pre-load) seem to have lower vertical dispersion levels - sort of....(rifles 2, 6, 8, and 12 were the only ones that showed 8.0 inches or slightly less vertical dispersion at 300 meters). I wonder how forend pre-load impacted accuracy?...

Quote:
The M14 National Match rifle rebuilt to USAMTU standards does not satisfy the rebuild criteria dimensionally.
Not sure what that means unless they were referring to the barrel bore diameter and grove uniformity. The footnote references this:

Quote:
a) The allowable maximum variations in dimension within a barrel (0.0003 of land and 0.001 for groove diameters, respectively) and/or direction of dimensional tapering were not within specification limits.
I have read somewhere that the XM21 barrel spec was 'loosened' somewhat from the original NM barrel specification, but I don't have that in front of me. I wonder if that decision was tied to this 1971 report?

Anyhow, thanks for the APG report. (Attached is a 1970 field report from XM21 usage in Vietnam, which I think showed its overall tactical effectiveness, despite the issues outlined in the APG report. Source: The Long-Range War (1994) by Peter Senich, page 91).
Attached Images
File Type: png XM21_report_May_1970_Senich_pg91_v2.png (1.17 MB, 3 views)

Thanks from XXIV Corps, XM25Ren, unkola and 1 others

Last edited by Random Guy; April 15th, 2020 at 10:01 AM.
Random Guy is offline  
Old April 15th, 2020, 07:15 AM   #51
Lifer
 
Random Guy's Avatar
 
Join Date: Jan 2017
Location: No. VA
Posts: 2,201

Awards Showcase

Barrel info

Quote:
So I found my SAK-NM stash.
That's a nice stash if the throat erosion on those 2 barrels is 2.0 or less. I will note that my XM21 replica has the exact same barrel as one of yours, an 8-69 dated SAK NM barrel (see pic 1).

On EDIT:

Quote:
The XM21 used a standard weight NM barrel (TRW, SA & SAK) - the report above references

"Three Mann barrels"
"fired from the Mann barrels"
"In the event Mann barrels are used which exhibit large extreme spreads"

Do you know the definition of the term "Mann Barrel?" I am not familiar with this term.
As a follow-up, attached is a picture of a Mann Device in 7.62NATO that was used for ammo accuracy testing. I think this was sold by CMP a few years back. 3rd pic is a Mann Device in 30-06.
Attached Images
File Type: jpg XM21_1969_barrel2.jpg (355.9 KB, 7 views)
File Type: png Mann_Device_7.62NATO_v2.png (350.1 KB, 9 views)
File Type: jpg Mann_Device_1.jpg (48.5 KB, 8 views)


Last edited by Random Guy; April 15th, 2020 at 09:04 AM.
Random Guy is offline  
Old April 15th, 2020, 07:53 AM   #52
Designated Marksman
 
edgartwib's Avatar
 
Join Date: Aug 2012
Location: New Mexico
Posts: 595


I also have this SAK barrel installed on my SEI match rifle I had Croc build years back. Its all USGI SA parts with NM mods. It would be a good M-21 clone canidate...








I do have this paperweight as well...


edgartwib is offline  
Old April 15th, 2020, 08:29 AM   #53
Old Salt
 
SPEEDGUNNER's Avatar
 
Join Date: Oct 2005
Location: Between the Brandywines
Posts: 1,027
Welcome to the Forum and thank you for your service. I sent you a PM, my son is currently at Benning as well for MCCC but the COVID-19 has put the training on hold.

SPEEDGUNNER is online now  
Old April 15th, 2020, 10:38 AM   #54
Lifer
 
lysander's Avatar
 
Join Date: Apr 2015
Location: North Carolina
Posts: 4,182

Awards Showcase

Quote:
Originally Posted by Random Guy View Post
Interesting report, thanks for sharing. It suggests that even the exotic epoxy impregnated stocks swelled in high humidty/high temps and developed cracks. Also the bedding compound didn't hold up all that well either:

and..

I will note that the two bedding compounds listed in the June 1971 AMU build guide are:

1. 'EPOXY-GLASS manufactured by Fewal Inc. Resin Systems Division, Ashland, Mass.
2. Bisonite Epoxy manufactured by: Bisonite Company Inc., Buffalo, New York

I think #1 ('Epoxy-glass') is commonly known as 'Accu-glass.' Perhaps Ted Brown or another long-time builder can comment, but my impression from one old time National Guard M14 builder is that bedding choice #2, Bisonite, is much more stable and more durable bedding compound compared to 'Accu-glass' aka 'Epoxy-glass', the later which exhibited more 'bedding-break-down'. He went through NM M14 school in 1990 and the US Army was using mostly Bisonite by that time, not the older 'Accuglass'. Moreover, by the 1980s much better bedding material came into use, most notably MarineTex, which is very stable/durable, and since then I've heard that Devcon-Titanium bedding compound is even more durable, but a pain to work with.

My point is the original XM-21 bedding material, if 'Epoxy-glass' is in fact 'Accu-glass,' probably contributed to these poor findings, esp if test conditions were + 125 to - 25 degrees with high humidity, etc. The original bedding compounds from 1969 have gotten much better, and I think the issue of 'bedding break-down' is/was a legitimate problem with the old Accuglass-based bedding compound(s).

To me the most interesting variable in the report is the topic of "foreend pre-load in lbs", which unfortunately was not explained as to how it was measured. (sounds like the 'draw pressure' voodoo topic...) The report notes that only 2 of the 15 rifles were within spec, which I think is 10 to 15 pounds. The rifles varied from 3 lb to 30 lbs of fore-end pressure, and the report noted this caused vertical dispersion issues. My suspicion is that this particular variability might be the root cause that contributed to the rifles not quite meeting the expected accuracy levels.

I didn't do any statistical analysis of course, but a cursory look at the vertical dispersion data seems to suggest that rifles at the upper end (high-20s lbs of forend pre-load) seem to have lower vertical dispersion levels - sort of....(rifles 2, 6, 8, and 12 were the only ones that showed 8.0 inches or slightly less vertical dispersion at 300 meters). I wonder how forend pre-load impacted accuracy?...

Not sure that means unless they were referring to the barrel bore diameter and grove uniformity. The footnote references this:

I have read somewhere that the XM21 barrel spec was 'loosened' somewhat from the original NM barrel specification, but I don't have that in front of me. I wonder if that decision was tied to this 1971 report?

Anyhow, thanks for the APG report. (Attached is a 1970 field report from XM21 usage in Vietnam, which I think showed its overall tactical effectiveness, despite the issues outlined in the APG report. Source: The Long-Range War (1994) by Peter Senich, page 91).
A coupl'a things . . .

User appreciation is not always tied directly to technical test data. There is another report on all sniper equipment sent to SEA in 1968, who got it, and their overall results and comments. I'll see if I can find that one again.

The method of establishing fore end pre-load was to attach a wire to the stock ferrule and another to the front band, this established an electric circuit. An ohmmeter measured the resistance of the circuit. Calibrated weights were hung on the gas cylinder at the front band until the ohmmeter recorded an opened circuit.

Oh, and #14 had zero pre-load.

Correlation between pre-load and group size is not good. probably due to other problems, like loose bedding.

rifle #, Lowest pre-loads and 300 ES:
#14 - 0 lb - 12.6"
#11 - 3 lbs - 8.4"
#15 - 8 lbs - 10.3"
#13 - 10 lbs - 10.8"
#3 - 13 lbs - 9.5"

Highest pre-load and 300 ES
#2 - 30 lbs - 7.5"
#4 - 30 lbs - 8.3"
#7 - 30 lbs - 8.1"
#8 - 29 lbs - 7.9"
#9 - 27 lbs - 10.2"

Aberdeen had nothing to do with specifications, they are only a test facility, so no they don't mention anything about relaxed requirements. However, REV P of DWG 7790190 (standard rifle barrel) gives the maximum bore and groove diameters as 0.3015" and 0.3095", respectively. These barrels do meet those requirements.

The addition of the word "dimensionally" is curious, as the only dimensions re the headspace and the bore/groove diameter. However, it is evident that these were not "match quality" rifles, only one having a 4.5 to 4.75 lbs trigger, half of them with receiver movement and many with other problems.

Thanks from m1sniper, M1Army and Random Guy
lysander is offline  
Old April 15th, 2020, 02:53 PM   #55
Lifer
 
m1sniper's Avatar
 
Join Date: Aug 2009
Location: USA
Posts: 4,405

Awards Showcase

AR-TEL scopes were never "matched" to any rifle. Scopes were totally interchangeable from rifle to rifle if needed. Scope SN is the Redfield serial number only and has nothing to do with the rifle or the mount.
Scope is installed into the aluminum mount.
The scope and mount "set" is then installed on a rifle. Being aluminum, the mount is, for the sake of argument, a "crush fit" to that rifle.
( Remember, it has been proven there can be and are some very slight tolerance differences between receivers.)
THEN the last 4 digits of the rifle are engraved into the mount. It is the mount that is "matched" to a specific receiver.
Per Bill Ricca many years ago.

m1sniper is online now  
Old April 15th, 2020, 03:18 PM   #56
Dodgin' The Reaper
 
Ted Brown's Avatar
 
Join Date: May 2004
Location: Jacksonville, OR
Posts: 7,389

Awards Showcase

M21

Here are a couple of pictures of one of my personal M21 rifles from my collection. It was built on LRB receiver number 3000 and includes a Krieger standard weight match grade barrel. The ART II scope is one of the custom assembled scopes from Iron Sight. All other parts are US GI and fully modified to NM specs.
Attached Images
File Type: jpg IMG_6523.JPG (1.08 MB, 18 views)
File Type: jpg IMG_6524.JPG (1.21 MB, 22 views)

Ted Brown is offline  
Old April 15th, 2020, 03:46 PM   #57
Lifer
 
m1sniper's Avatar
 
Join Date: Aug 2009
Location: USA
Posts: 4,405

Awards Showcase

Nice job on the transport box Ted. Looks great!! What info is typed on the label on the lid?

m1sniper is online now  
Old April 15th, 2020, 03:49 PM   #58
Dodgin' The Reaper
 
XM25Ren's Avatar
 
Join Date: Dec 2012
Location: Land of the Free
Posts: 6,782

Awards Showcase

Quote:
Originally Posted by m1sniper View Post
AR-TEL scopes were never "matched" to any rifle. Scopes were totally interchangeable from rifle to rifle if needed. Scope SN is the Redfield serial number only and has nothing to do with the rifle or the mount.
Scope is installed into the aluminum mount.
The scope and mount "set" is then installed on a rifle. Being aluminum, the mount is, for the sake of argument, a "crush fit" to that rifle.
( Remember, it has been proven there can be and are some very slight tolerance differences between receivers.)
THEN the last 4 digits of the rifle are engraved into the mount. It is the mount that is "matched" to a specific receiver.
Per Bill Ricca many years ago.
The mount was part of the total, I think it would be rare that they would switch out a scope from its original mount.

More often than not the two stayed together.

REN

XM25Ren is offline  
Old April 15th, 2020, 05:02 PM   #59
Dodgin' The Reaper
 
Ted Brown's Avatar
 
Join Date: May 2004
Location: Jacksonville, OR
Posts: 7,389

Awards Showcase

I put one of my best looking rifles up and you like the transit box? Oh well... I made the box using military hardware from a 105mm artillery shell box. The label on the inside of the lid is the Basic Issue Items list. I also have a nomenclature label on the outside:

1005-00-179-0300
US RIFLE CAL. 7.62MM M21 W/E
9386973
SER. NO. 3000
1.83 CF
36 LBS.

My plan is make a skinnier box for it. I'd like to get the total weight down some.

Ted Brown is offline  
Old April 15th, 2020, 05:12 PM   #60
Lifer
 
forceman's Avatar
 
Join Date: Dec 2007
Location: Arizona
Posts: 3,605
Beautiful rifle Ted,and yes I did notice the box but my eyes kept going back to that tiger striped hunk of Walnut.

Thanks from rallred
forceman is online now  
Reply

  M14 Forum > M14 M1A Forum > The M14


Search tags for this page

looking for xm-21 expert

,

rock island arsenal m14 match rifle

Click on a term to search for related topics.

Moderator Tools
Display Modes




Top Gun Sites Top Sites List