Send parts from abroad

I am a new member from Sweden and am wondering if there are any problems with sending, for example, sights, grips, tools and springs for guns to private buyers in the USA. Problem for the buyers is what I mean.
Grateful for answers

AFAIK, certain countries in Europe (notably Germany) have some restrictions on sale of gun parts to the USA. I have bought grips direct from Thomas Rink in Germany, so no problem for grips. Also bought other small items from other EU countries. Small components should not be a problem. Even complete air pistols, not a problem.

But frames, etc, with a serial number, definitely no.

Not sure about barrels.

Red dots and other optics should not be a problem clearing USA customs, but you would have to research your home country's export control laws to be sure that you are not breaking their law.

I recently contacted the USA "customs" department regarding importing small quantities of lead bullets in checked bags when returning from a trip to Europe. Despite several emails I was unable to get any kind of definitive answer. The only comment was that it would be down to the officer at the point of entry who would apply the local laws in the jurisdiction of the airport - Aaaarrrggghhh! I shall probably not bother.

It depends entirely on both the local country’s regulations and the destination country’s regulations they have enacted in response to the Wassenaar Arrangement and other treaties ( for ease of speaking I’ll use ITAR).  These can be quite granular depending on the individual country.  As soon as you use the term “Firearm Accessories”, ITAR gets involved and if you don’t comply it can get ugly real fast.

ITAR specifically regulates items in the US Munitions List, and Category I reads as follows:

Category I—Firearms and Related Articles
* (a) Firearms using caseless ammunition.
* (b) Fully automatic firearms to .50 caliber (12.7 mm) inclusive.
* (c) Firearms specially designed to integrate fire control, automatic tracking, or automatic firing (e.g., Precision Guided Firearms).
Note 1 to paragraph (c):
Integration does not include only attaching to the firearm or rail.
* (d) Fully automatic shotguns regardless of gauge.
* (e) Silencers, mufflers, and sound suppressors.
(f) [Reserved]
(g) Barrels, receivers (frames), bolts, bolt carriers, slides, or sears specially designed for the articles in paragraphs (a), (b), and (d) of this category.
(h) Parts, components, accessories, and attachments, as follows:
(1) Drum and other magazines for firearms to .50 caliber (12.7 mm) inclusive with a capacity greater than 50 rounds, regardless of jurisdiction of the firearm, and specially designed parts and components therefor;
(2) Parts and components specially designed for conversion of a semi-automatic firearm to a fully automatic firearm;
(3) Parts and components specially designed for defense articles described in paragraphs (c) and (e) of this category; or
(4) Accessories or attachments specially designed to automatically stabilize aim (other than gun rests) or for automatic targeting, and specially designed parts and components therefor.
(i) Technical data (see § 120.33 of this subchapter) and defense services (see § 120.32 of this subchapter) directly related to the defense articles described in this category and classified technical data directly related to items controlled in ECCNs 0A501, 0B501, 0D501, and 0E501 and defense services using the classified technical data. (See § 125.4 of this subchapter for exemptions.)
(j)–(w) [Reserved]
(x) Commodities, software, and technology subject to the EAR used in or with defense articles.
Note to paragraph (x):
Use of this paragraph is limited to license applications for defense articles where the purchase documentation includes commodities, software, or technology subject to the EAR (see § 123.1(b) of this subchapter).
Note 1 to Category I:
The following interpretations explain and amplify the terms used in this category:
(1) A firearm is a weapon not over .50 caliber (12.7 mm) which is designed to expel a projectile by the deflagration of propellant;
(2) A fully automatic firearm or shotgun is any firearm or shotgun that shoots, is designed to shoot, or can readily be restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger; and
(3) Caseless ammunition is firearm ammunition without a cartridge case that holds the primer, propellant, and projectile together as a unit.

So for grips and springs etc, these are not regulated by ITAR.  That said, a lot of the regulations for commercial guns are now regulated by the Department of Commerce, so a lot easier to comply with.  I confess ignorance on what we are allowed to import.  I don't think there is much regulation, other than CFR 922.  However when you read it, it pertains primarily to firearms and ammunition.
https://www.law.cornell.edu/uscode/text/18/922

It fully depends on the laws that have been passed by both the home country and the destination country in response to the Wassenaar Arrangement and other accords.

The United States also has the Arms Export Control Act, which applies to imports into the United States, as well as exports, and applies to every part of a weapon, firearm, or arm of just about anything that could be a weapon.  Penalties are up to $1 Megabuck & years in Club Fed.  There is an exception in the Rules that implement it, for sales less than $100.

Hmmmm....
Multiple bits of legislation presumably ultimately enforced by different agencies, but for dumb civilians (including me) policed by Border Control.

Tricky!

One has to hope that common sense prevails, but, that is not guaranteed. I know of a recent case in Thailand where a European guy got put in jail after Customs discovered one single live round of 9mm ammo in his checked bag. I am now super careful checking my bags before travelling overseas.