I've been searching the forum and haven't found the answer yet, maybe a Colt expert can help me out.
What is the letter x at the end of the serial number about , if anything ? For example SP29900x
Thank's for any info.

Some people feel the need to hide their full serial number when posting.  You will notice that most gun magazines do the same.  For instance:

"I have a Colt 1911 in .38 Super, Serial Number 010XXX.  It is in near mint condition, and was a given to me by my aunt when my favorite uncle, the original owner, passed away.  Can you tell me if it has any collectors value,"

The author of the letter will include the entire serial number, when he writes to the magazine, but what gets printed in the magazine has the last 2-3 numbers "X"ed out to prevent any number of mis-deeds.  Basically, it is an unlikely crime that someone will report your gun by serial number as having been stolen from him. and easily disproved, but the magazines and some posters here would rather err on the side of caution.  

Anyways, thats why you see the X's.  

Quoted: Some people feel the need to hide their full serial number when posting.  You will notice that most gun magazines do the same.  For instance: "I have a Colt 1911 in .38 Super, Serial Number 010XXX.  It is in near mint condition, and was a given to me by my aunt when my favorite uncle, the original owner, passed away.  Can you tell me if it has any collectors value," The author of the letter will include the entire serial number, when he writes to the magazine, but what gets printed in the magazine has the last 2-3 numbers "X"ed out to prevent any number of mis-deeds.  Basically, it is an unlikely crime that someone will report your gun by serial number as having been stolen from him. and easily disproved, but the magazines and some posters here would rather err on the side of caution.   Anyways, thats why you see the X's.

I should have ask that a little better to rule that out . Sorry

The x is an actual x stamped at the end of the serial number, in my example number the SP299 is correct, I used the 00 to replace the last 2 numbers, so I have SP followed by 5 digits and the letter x at the end . the x is about half the size of the numbers.

Don't recall seeing a subfix letter in a SP serial number.

Lets start here, is the barrel marked C MP B, with a C and a bell shape on the right side of the front sight base?  And roll marked Patent Firearms rather then Firearms Division?   That is the barrel and roll mark you would expect to find on a high 29,000 series Colt SP1.

Don't think it is a 299,000 series, in that I never heard of one.

Barrel and front sight are marked as you state, also a small c stamped on upper rec. to the top right of the ejc. port dust cover, don't see any other markings on upper, bolt marked MPC , carrier has a small c on left side.



http://img.villagephotos.com/p/2006-1/1128588/sp29900.JPG

Quoted: Barrel and front sight are marked as you state, also a small c stamped on upper rec. to the top right of the ejc. port dust cover, don't see any other markings on upper, bolt marked MPC , carrier has a small c on left side. img.villagephotos.com/p/2006-1/1128588/sp29900.JPG

OK, just a regular old 1973-74 SP1 with a x at the end of the serial number.  Far as why and Colt goes, that can be real tough.  First guess pulled out of the hat is that they accidently made two SP1's with the same serial numbers, so put an x at the end of one of them.

I guess that could be possible .

Quoted:  Far as why and Colt goes, that can be real tough.  First guess pulled out of the hat is that they accidently made two SP1's with the same serial numbers, so put an x at the end of one of them.

I'm pretty sure your first guess is a good one.

Out of the mothballs of a memory that's older than dirt, I seem to recall a Colt workman telling me just that about a thousand years ago when I lived up there.

I believe this was a common practice when several companies were making Garands and carbines.  If a serial # was accidently duplicated they would add an "X" to one of them.  

I have seen other guns that this was done to when the serial numbers were duped. I believe they were S&W's.

Thank's guys, it sounds good to me.