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I am looking for advice in what to look for when buying a used M1 Garand op-rod. I am looking for a post war HRA and have found several but each discussed the piston diameter and I am unfamiliar on where to measure and what number is within specs. Are there any other areas too check when buying? Does the piston diameter of a Garand op rod equate to the tab thickness of a M14 op rod when it comes to the primary wear point? Thanks.
 

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You need a jig for the contour, use a Mic for piston dia (.530? new, .525 Min), good sharp edges, early op rods were squared at the transition to the rod tube, later radius to prevent cracking... I look for pitting also in the tube. Tab square. Piston can be replaced, a total op rod rebuild from a company in Ohio...I forget the name...someone jump in...is like 100.00
 

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The CMP will recondition an oprod for $75. This includes new tab, new piston, straightening, and reparking.

They'll even swap it out for an already done one if your in a hurry.

Justin
 

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You need to make sure the seller measures the tab as well as the piston. There is no reason to pay topdollar for a op rod then having to send it off for a rebuild
Needs to be measured with a Micrometer not Calipers
Piston Diameter: .5260 to .5253 (under .5245 calls for rejection)
Piston Thickness: .190 to .155
Tab/Lug Height: .320 to .317 (under .310 calls for rejection)
Tab/Lug Thickness: .100 to .095
Tab/Lug Width: .265 to .235
Tab/Lug Hang .070 to .055
 
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