m51 carrier

1970-1980
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.270 WIN
Posts: 422
Joined: Thu Feb 23, 2012 5:21 pm
Location: phila pa
PostPosted: Mon May 28, 2012 12:07 pm
i'm reposting a conversation had over at SGW,it might be relevent to someone coming here
it covers why 51s have carrier probs and how to get/keep it going.

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if you make sure the action spring is good ,you should never break the Acarrier.

there is a series of parts that go bad for the Acarrier to get overstressed and it starts with the action spring.
it does little to no good to replace the buffers without replacing the action spring
the good thing about this is you can still find the springs easily.
i'm not sure of the lifespan of the action springs ,but for $5 you can afford to change them at least once a year.if you start seeing buffer abuse , change it more often

after i clear out a few old projects , i'm gonna fab up a new Acarrier outa stainless.
the weakness in the OEM Acarrier has as much to do with bad maufacturing as it does design.
in other words if made properly , the design will work fine.

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Colonel26 wrote:

The carrier, was out a bad design our was it just made out of inferior metal. I'm wondering because if it it's just made out of inferior stuff it looks like you could get a machine shop to make one out of good stuff.

I've heard of folks having theirs welded up after they break. I wonder does that solve the problem? Any more trouble after that? All this talk about then handling like a model 37 has me wanting one myself


this is my take
i'm not a gunsmith , but i been working with steel and its alloys under extream conditions for 20 yrs.

the carrier itself is not much diffrent then any other carrier,under normal use it should not break
when it does break ,it always seems to break at the same spot ,a spot that is the weakest spot on the whole carrier.
why ..well beyond the obvious reason of having a poorly maintained gun....
Image
the carriers are made out of fairly cheap steel plate.
they punch cut the openings on flat plate then bend the rest to proper shape
in order to get a true bend ,the corners need to be opened up a bit to prevent the kinking .
this also prevents the start of stress cracks.
between the punch out for the bend and the machining for the shell stop action it leaves a very thin carrier rail at the highest stress point

Image
if you have access to a TIG welding set up it can be welded with normal 70.
if you do so cleanlyness is key ,no oil anywhere ,and no blueing anywhere near the weldzone.
the smallest blueing will suck into the puddle and cause porosity.
the above photo is shown rough finished
when i welded it up , i filled in the punch out at the top , increasing the thickness of the rail.
does it hold up?so far so good , i been told by a few with reputable ithaca credentials that they have welded them up with good results.
but welded or not , its lible to crack again if the action spring isn't maintained
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another point i should make is the carrier itself is 2 piece
the top part with the ring is accualy screw riveted on (phillips head screws with purposly buggered theads)

i'm sure they could be removed ,therefore only the bottom part of the carrier needs to be prefabbed , if you decided to make one.
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there are a few ways they could have been made ,
anything from milling the whole assembly from a solid blank to what i would do ..
weld the 4 peices together and shape to final dimentions.
each way has a diffrent cost in materials,manufacturing and man hours .

punch cutting and and bending are the cheapest.
when you say slots i'm guessing you mean the punch out where the crack occured?
the slots/punchouts are there to keep the bend level...the pad the bolt support is rivited too has to have the same hight dimentions as the top of the rail.
if you didn't add the slots/punchouts then follow up machining would be needed to get the correct specs.

i wouldn't touch a working carrier,i'd just keep good springs and buffers in it and ride it out.
you should be able to look at the crack point and see if its been abused,
there should be visable bulging from flexing
if it does or is cracked ,i'd weld it up ,filling in the punchout slot to level like i did.
the repair adds 1/8" to the thinnest point on the rail makes it as strong or stronger then any of the other rail stress points.

i've thought about filling in the other punchout areas but don't see the benifit of doing so until they might show stress signs

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