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-   -   How to Measure Locking Shoulder? (http://www.falfiles.com/forums/showthread.php?t=190114)

william013 January 08, 2007 22:29

How to Measure Locking Shoulder?
 
I was checking my locking shoulder when I noticed that the measurement from
top to bottom (long flat facing up) was .266.5. However, the measurement
from forward and back (short flat facing forward) is .263. What is the proper
way to measure it. BTW, the rifle headspaces with a .263 pin gage

Also, when I was checking the fit of the locking shoulder into the Century receiver. the left side is extremely tight. Should I relieve this area or just try to pound it in and hope for the best?:uhoh: :cool:

Plucky Purcell January 08, 2007 22:43

Ok, First do NOT pound in the locking shoulder. They should be pressed in. Pounding on them may cause them to fracture during use resulting in the bolt and carrier impacting in your forehead. Locking shoulders come in different OD sizes as well as locking sizes. You need one that will allow for a press fit and have the correct shoulder dimension. The measurement is from the locking flat to the OD. The flat that the bolt would come in contact with.

william013 January 08, 2007 22:58

Thanks for the info Plucky. BTW, you said the LS have different OD's. If you had a LS that the OD was very tight in a Century receiver ( Don't flame me please, I'm a working man on a budget.) Would it not be easier to open up the hole in the left side of the receiver or would you grind the LS ? :cool:

Plucky Purcell January 09, 2007 00:19

Quote:

Originally posted by william013
Would it not be easier to open up the hole in the left side of the receiver or would you grind the LS ?
I always go by the rule to alter the cheapest part, but rather than try to grind a LS you would be better off getting the correct one if at all possible.

Here's a list of the locking shoulders made possible by NZ L1A1 COLLECTOR.

TABLE 2 - LOCKING SHOULDER DETAILS

Designation
Number NSN Locking Shoulder
Size (inch) Locking Shoulder
Diameter (inch)
(a) (b) (c) (d)
1. 1005-66-029-6872 0.261 0.0009 0.2978 0.0008
2. 1005-66-029-6873 0.262 0.0009 0.2978 0.0008
3. 1005-66-029-6874 0.263 0.0009 0.2978 0.0008
4. 1005-66-029-6875 0.264 0.0009 0.2978 0.0008
5. 1005-66-029-6876 0.265 0.0009 0.2978 0.0008
6. 1005-66-029-6877 0.266 0.0009 0.2978 0.0008
7. 1005-66-029-6878 0.267 0.0009 0.2978 0.0008
8. 1005-66-029-6879 0.268 0.0009 0.2978 0.0008
9. 1005-66-029-7041 0.269 0.0009 0.2978 0.0008
10. 1005-66-029-7042 0.270 0.0009 0.2978 0.0008
11. 1005-66-029-7043 0.271 0.0009 0.2978 0.0008
12. 1005-66-029-7044 0.272 0.0009 0.2978 0.0008
13. 1005-66-029-7045 0.273 0.0009 0.2978 0.0008
14. 1005-66-029-7046 0.274 0.0009 0.2978 0.0008
15. 1005-66-029-7047 0.275 0.0009 0.2978 0.0008
1/1. 1005-66-029-7052 0.261 0.0009 0.2982 0.0008
2/1. 1005-66-029-7053 0.262 0.0009 0.2982 0.0008
3/1. 1005-66-029-7054 0.263 0.0009 0.2982 0.0008
4/1. 1005-66-029-7055 0.264 0.0009 0.2982 0.0008
5/1. 1005-66-029-7056 0.265 0.0009 0.2982 0.0008
6/1. 1005-66-029-7057 0.266 0.0009 0.2982 0.0008
7/1. 1005-66-029-7058 0.267 0.0009 0.2982 0.0008
8/1. 1005-66-029-7059 0.268 0.0009 0.2982 0.0008
9/1. 1005-66-029-7060 0.269 0.0009 0.2982 0.0008
10/1. 1005-66-029-7061 0.270 0.0009 0.2982 0.0008
11/1. 1005-66-029-7062 0.271 0.0009 0.2982 0.0008
12/1. 1005-66-029-7063 0.272 0.0009 0.2982 0.0008
13/1. 1005-66-013-2792 0.273 0.0009 0.2982 0.0008
14/1. 1005-66-013-2793 0.274 0.0009 0.2982 0.0008
15/1. 1005-66-013-2794 0.275 0.0009 0.2982 0.0008
1/2. 1005-66-029-7068 0.261 0.0009 0.2990 0.0008
2/2. 1005-66-029-7069 0.262 0.0009 0.2990 0.0008
3/2. 1005-66-029-7070 0.263 0.0009 0.2990 0.0008
4/2. 1005-66-013-7961 0.264 0.0009 0.2990 0.0008
5/2. 1005-66-013-7962 0.265 0.0009 0.2990 0.0008
6/2. 1005-66-013-7963 0.266 0.0009 0.2990 0.0008
7/2. 1005-66-013-7964 0.267 0.0009 0.2990 0.0008
8/2. 1005-66-013-7965 0.268 0.0009 0.2990 0.0008
9/2. 1005-66-013-7966 0.269 0.0009 0.2990 0.0008
10/2. 1005-66-013-7967 0.270 0.0009 0.2990 0.0008
11/2. 1005-66-013-7968 0.271 0.0009 0.2990 0.0008
12/2. 1005-66-013-7969 0.272 0.0009 0.2990 0.0008
13/2. 1005-66-013-7970 0.273 0.0009 0.2990 0.0008
14/2. 1005-66-013-7971 0.274 0.0009 0.2990 0.0008
15/2. 1005-66-013-7972 0.275 0.0009 0.2990 0.0008
1/3. 1005-66-029-7075 0.261 0.0009 0.2998 0.0008
2/3. 1005-66-029-7076 0.262 0.0009 0.2998 0.0008
3/3. 1005-66-029-7077 0.263 0.0009 0.2998 0.0008
4/3. 1005-66-013-7973 0.264 0.0009 0.2998 0.0008
5/3. 1005-66-013-7974 0.265 0.0009 0.2998 0.0008
6/3. 1005-66-013-7975 0.266 0.0009 0.2998 0.0008
7/3. 1005-66-013-7976 0.267 0.0009 0.2998 0.0008
8/3. 1005-66-013-7977 0.268 0.0009 0.2998 0.0008
9/3. 1005-66-013-7978 0.269 0.0009 0.2998 0.0008
10/3. 1005-66-013-7979 0.270 0.0009 0.2998 0.0008
11/3. 1005-66-013-7980 0.271 0.0009 0.2998 0.0008
12/3. 1005-66-013-7981 0.272 0.0009 0.2998 0.0008
13/3. 1005-66-013-7982 0.273 0.0009 0.2998 0.0008
14/3. 1005-66-013-7983 0.274 0.0009 0.2998 0.0008
15/3. 1005-66-013-7984 0.275 0.0009 0.2998 0.0008


Kevin Adams

Rifle, 7.62mm L1A1 Collector & Researcher
NEW ZEALAND

Powderfinger January 10, 2007 00:22

[QUOTE]Originally posted by Plucky Purcell
[B]Ok, First do NOT pound in the locking shoulder. They should be pressed in. Pounding on them may cause them to fracture ]

Ok_First of all I'm not trolling, I seriously don't understand this POV. Is there any ACTUAL data supporting this? I have seen this before on the Files and for the life of me, I don't savvy how a locking shoulder can withstand the EXPLOSIVE IMPACT of a 7.62 NATO round igniting THOUSANDS of times and not fail, but a dozen TAPS with my 12 oz. ball peen hammer to seat it will fracture it.
I'm all ears.:?
Metalurgists, Mechanical engineers? What say you?

gibsonguy909 January 10, 2007 22:35

I'm not an expert either, but this is my personal train of thought;

Locking shoulders are heat treated to be very hard, which means they are brittle. True; they can withstand thousands of rounds of 7,62 ammo, but the strike created by firing the round is distributed by a bolt that is engineered to engage the locking shoulder in a very specific way. Randomly striking the locking shoulder with a punch, ball peen hammer, or anything else could create a hairline fracture or other stress point that could cause it to fail at the most inopportune moment. When it comes to a locking shoulder, pretty much any moment is an inopportune one for the thing to fail! Me personally; this is not something I'm willing to bet my life on. :D

I also would love to hear of any documented evidence of this, because this is just my paranoid self talking to me . My job requires a certain level of paranoia, so this just happens to be a personal trait of mine... ;)

Plucky Purcell January 11, 2007 10:24

I seem to remember NZ L1A1 COLLECTOR (who I consider to be an authority)said that it's OK to remove a worn locking shoulder by hammer and drift as long as it will then be discarded, but that installation was always done with a press. The illustration only indicates removal of the LS with no mention of installation. Is there more to that diagram that does mention installation?

Depending how the LS is made, heat treated, and the grain of the material may make a big difference in fracture resistance between basically non-supported longitudinal impacts from the small surface area of a punch being struck by a hammer and lateral fully supported impacts with the larger surface area of the bolt.

Like everybody else here I've always heard from reliable sources that hammering in of a LS is BAD. If there is content in a manual showing the installation of a LS that way I'd like to see it. What's on page 66? :)

Powderfinger January 12, 2007 12:55

1 Attachment(s)
Quote:

Originally posted by Plucky Purcell
If there is content in a manual showing the installation of a LS that way I'd like to see it. What's on page 66? :)
It's actually on pg. 92. It refers back to fig. 87 on pg. 65 as seen above.
I use a 1/4" punch with a flat true face to engage the shoulder and use a 12 oz. hammer. You don't have to kill it, just tap it in with the punch centered on the shoulder preventing bending the dogbone ear.

Plucky Purcell January 12, 2007 14:27

Well sure enough, there it is. I stand corrected. Thanks for going to the trouble of finding and posting those pics. :bow:

I was typing my reply up to the point above when it occured to me that those pics might have come from the "Light Automatic Rifle - CAL. 7.62 mm" (C 24)manual by FN that is sitting on the shelf six feet from my head. Sure enough...turn to pages 65 & 92 and there they are.

And to think I wasted that money on a press. ;)

cliffy109 January 12, 2007 15:07

I'll admitt that I have pouned the living crap out of locking shoulders. I've also broken the ear off a couple and had to start over. Hell, I even bought a bigger hammer to do it. What I will usually do is put a little oil on before it makes that last little movement into the far side hole. That reduces the amount of pounding required.

Now... if I had a press, that's how I'd do it. I really think the press is a better method, but I have had no negative consequences by pounding.

gibsonguy909 January 13, 2007 00:40

I too stand corrected. But notice the instructions say "carefully hammer it into position"... So it's a matter of how hard can you hammer while still being careful. :beer:

Powderfinger January 13, 2007 14:17

I am no expert and have installed 8-9 or so LS. (Some on mine, some on friends, some redos when swapping a barrel or reciever). If you need a bigger hammer or have to "pound the living crap out of it", something is too tight IMHO. I have started driving them in and when it seems obvious my little hammer ain't cuttin' it, I backed it out and regrouped. I have had to polished the hole clean of parkerizing or tooling marks with crocus cloth, polished the LS, maybe added some Never-Seize. You may need to "set" the LS as it starts to enter the hole on the opposite side also with your punch (to line it up). I used a flat, true faced punch as mentioned before to distribute the tap squarely on the LS. Not tilted or off center. Notice I have said "tap". I hope this has met the definition of careful.:fal:


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