It's not really bad, but what earned this my downvote are the following issues:
At least 50 guards are to remain on site at all times in event of attempted breach, with no fewer than five (5) Security personnel stationed on the catwalk at all times.
Security shouldn't be capitalized, fifty (50) guards should be using enumeration formatting, and honestly 50 is both rather suspiciously round and strangely high. Why precisely 50?
Agents demonstrating proficiency with antique and ancient weaponry are to be preferred.
Firstly, an agent and an armed guard aren't necessarily the same thing. We draw a lot of parallels from Men in Black, but we're much more reasonable. Secondly, this is silly. "Guard personnel must receive additional training in the use of antique firearms and fencing." would make much more sense.
[…] remains are to be searched for their source clipping, […]
Should probably be something like "original instance" or "initiating instance" rather than "clipping".
Under no circumstances is SCP-1297 to be transported by air, nor should it be allowed within 40 km of the nearest population center of 500 persons or more.
"should", not "is"
Five hundred (500).
[description snipped]
I can't help but wonder if this could be shortened, because it doesn't flow very well and it really, really needs to be simplified.
SCP-1297-1 refers to a defensive mechanism employed by SCP-1297 in perpetuating periods of activity, […]
Within five minutes of emergence, SCP-1297-1 will solidify around its source clipping in a radially symmetric pattern similar to an invertebrate of class Asteroidea.
You have inconsistent definitions of -1. One says it's a defense mechanism, the other says it's the ooze that comes out when said defense mechanism triggers.
Not to mention, "defense mechanism" is a misnomer because it's not actually defending itself, it's just forcing itself to activate. "an event that results in the autoactivation of SCP-1297's anomalous property that can occur during extended periods of inactivity" would be more accurate.
Addendum 1:
Normally addendum titles are something like "Addendum 1297-01: Incident Log, ██/██/██"
Early efforts on containment assumed the object to be of Euclid class, and were focused primarily upon preventing the emergence and manifestation of SCP-1297-1.
As Echo often points out, this is absurd. There is little to no connection between Euclid-class objects, and the containment for one Euclid-class object may have absolutely no effect on another. Rather than use one of the S/E/K classifications, you should state the specific false assumptions that caused this incident.
