The modification consists of replacing the hammer nose, and hammer nose bushing.....and test firing. I have done dozens of them.
If the gun was left unmarked after a police armorer completed the modification, then it would be
the result of an error by the armorer.
The "M" stamp is applied to the frame near the serial number in the yoke cut-out.
Carter
L-Frame recall.......
SMITH & WESSON
MODEL 581, 586, 681, 686, or 581-1,
586-1, 681-1, 686-1 & 686CS-1, REVOLVERS
RECALL: Reports have been received from the field where the combination of a SMITH & WESSON L-FRAME 357 MAGNUM REVOLVER and some .357 Magnum ammunition has resulted in unacceptable cylinder binding. L-frame revolvers bearing model numbers:
581, 586, 681, 686, or 581-1, 586-1,
681-1, 686-1, 686CS-1
Cylinder binding can cause a failure to fire. Mishandling a revolver while freeing the cylinder can result in accidental discharge.
Cylinder binding can result from a number of causes, including characteristics of an individual revolver or the use of ammunition, which does not conform to industry pressure specifications or is particularly fast burning. Recent developments in ammunition manufacture emphasize the production of .357 Magnum ammunition with increased velocity and greater primer sensitivity.
Although there have been very few reported incidents of cylinder binding, in view of our concern for our customer's safety and the reliability of Smith & Wesson products in all circumstances, we issue the following warning:
In a situation where a failure to fire can be critical - such as law enforcement or personal protection - do not use .357 Magnum ammunition with an L-frame revolver bearing model numbers 581, 586, 681, 686 or 581-1, 586-1, 681-1, 686-1, 686CS-1 without an "M" over the model number until you have had the revolver modified.
Those who need to use their L-frame revolver under these conditions prior to modification can safely fire .38 Special caliber ammunition.
Smith & Wesson has developed a modification to improve existing L-frame revolvers. This improvement enables them to fire all .357 Magnum ammunition, without cylinder binding. Shipments of L-frame revolvers from our factory after August 21, 1987 already include this improvement.
You can check if your revolver includes this improvement by looking at the left side of the frame when the cylinder is fully open. If your revolver has been stamped either with a "2" or higher number after the basic three-digit model number or with an "M" above the model number, your revolver includes this improvement and does not need modification. If your revolver bears the model number 581, 586, 681, 686, or 581-1, 586-1, 681-1, 686-1, 686CS-1 without an "M" over the model number, it does not include this improvement and your should have your revolver modified.
Smith & Wesson will modify your L-frame revolver free of charge to eliminate the possibility of cylinder binding with .357 Magnum ammunition. Law enforcement agencies wishing to arrange for modification of L-frame revolvers should call 800-331-0852 between 9 A.M. and 6 P.M. Eastern time (MA residents call 413-734-8244). Other users should send their revolvers to a Smith & Wesson Warranty Service Center, specifying "L-frame improvement program" and enclosing their name and return address.
One of the modifications to improve the L-frame revolver is the installation of a new hammer nose. This obsoletes all old L-frame hammer noses (part numbers 4702 and 7513) and all old L-frame hammer assemblies (part numbers 3366, 3378, 3380, 3382, 3391, 4722, 4723, 4726 and 4728) in field parts inventories. Superseded parts should never be fitted into a modified revolver as this may result in malfunction. It is essential for safety that you return these obsolete L-frame hammer noses and obsolete L-frame hammer assemblies for a free exchange to:
Smith & Wesson
Service Department
2100 Roosevelt Avenue
Springfield, MA 01101
