Are there specific rules for modification of a registered receiver?

If one had a converted Colt SP1 RR, would there be any legal issue with adding the full fence to the receiver?  Take it a step further and do the A2 strengthening upgrades?  Or if it was an M16A1, now upgraded to A2 specs, does ATF care?

Of course, no modification done to the engraving or rollmark/ serial.

Thanks

The rules on what's allowable are not set in stone, or even particularly-well documented.

cosmetic mods have always been allowed, for the most part, as long as they leave the original mfg markings intact

mods which change the type of firearm or caliber have been variable and iffy - evaluated on a case by case basis

ETA: specifically addressing what you asked about - there's a difference between "adding a full fence" and "remaking the whole receiver" There have been times when ATF allowed the original manufacturer to remake or replace a receiver. It's generally not permitted any longer, and serious collectors are leery of the ones that were previously remade, fearing an administrative u-turn disallowing such exceptions in the future.

You could add anything you want as long as it does not change the original family weapon type of the receiver....for example..you can't make it into an M240, but you could make it into an M4A1 receiver spec  As long as it remains an M16 type receiver you are good to go.

Sterling and Sten tubes are an example to the same family

You would have to be a seriously talented welder to add all of that aluminum to an SP1 lower receiver, and a talented machinist to machine down those welds to the proper A1 or A2 profile. All without warping the lower receiver, or making it look like $h!t. This is doubly-true for any “un-weldable” 7075 AR lower receiver.

Most owners/welders/machinists would not dream of attempting such a project, because the “cons” (receiver destruction) far outweigh any potential aesthetic “pros”.

OP, what you’re considering is insane. Don’t do it. If you want an A2, sell your SP1 and buy an A2.

You're risking a RR for shits and giggles......Literally.

It's all fun and games to throw this out as a legal exercise but if you plan on doing this to a real RR then you might as well have burned tens of thousands of dollars for nothing.

So basically I'm saying you don't own a machinegun.  So why ask the question?

Just sell and buy one with an A2 lower

Can selector markings be redone?

Of course. There is no legal requirement/regulation for selector markings.

Thought so. I was thinking there must be some way to edit, fill in or remove the original selector markings (because they aren’t clean or symmetrical) and then re-engrave them. Unfortunately, Tar Heel State Firearms said they would absolutely not redo them because it “would look like shit.”

Colt and the military don't a couple ways. Some M4A1s I've seen have "XX" stamped through the "M4" and "burst" stampings, with new stampings next to them. The nicer ones have the old markings machined down to create a very shallow depression, and the new markings are stamped or engraved into the depression, replacing the old markings.

The latter method actually looked real good

That’s exactly what I was hoping to do.

run that through the Google translator...


if one had paperwork for an SP1 RR and took a blank A2-style receiver and remarked it with one's info, would one get into trouble with the ATF?


Answer - I would recommend not doing that

It would seem to me that over time transfers will tend to be more restrictive. Could cosmetic features be added or removed legally? I would think so. The biggest "but" concerning that is documentation. What if, in the future, pictures are required of the regulated item? A registered receiver with a SP-1 serial number that has a raised fence would be flagged to be inspected. Without pictures of the process, an antigun administration claims that the receiver was replaced and is contraband. How much would it cost to fight that in court? I'd be willing to bet that the legal costs would far exceed the market value of the registered receiver. That is true today and more than likely in the future. You could write the Technology Branch and get a determination that these cosmetic features could be added. Of course that could bring extra scrutiny in the future. Something that comes to mind, when did receivers start being made of 7075 instead of 6063? How about the alloy used in brands other than Colt? As previously posted, it would be so much less problematic to sell the lower and buy an A2 than to modify. YMMV.

Scott