Will using Sweet's 7.62 on my Bushmaster xm-15 harm the chrome lined barrel?  What about the
barrel of my Beretta .40 or S&W .357 which are not chrome lined?  

The guy at the gun store left the impression that I would be a fool to clean the barrel of my ar15 with sweet's.  When I asked "Why?", he replied, "Because you don't want to do that".  

That doesn't tell me why I don't want to do that.  

So...my last question...Why don't I want to do that?

There's no issue with using Sweet's on any of the weapons you mentioned.  Just remember it's a copper buster.  Start off with a powder/carbon solvent and use it as directed.  Dry patch the bore when done.  Then apply Sweet's and don't let it sit for more than 15-20 minutes.  Patch it out and re-apply, let sit for 15-20, dry patch and look for blue on the patch.  If the dry patches keep coming out pretty drak blue, then repeat.  When they come out light blue, I would recommend stopping.  You could go another round or two, but I don't think there's any real benefit from continuing.  

Most importantly, when applying the Sweet's, don't use a brass brush because it will eat the bristles.  It's not that eating the bristles is a terribly bad thing, it's just that each time you patch it out, you'll come up dark blue each time, and the blue will be from your brush, not copper deposits in your bore.  Bottomline is you'll go stark raving mad trying to get your barrel clean when in reality you'll just be chasing your brush bristles.  either use a nylon brush or a loop jag and just "mop" the Sweet's on.  Let the chemical do the work, don't worry about scrubbing it on.

RoadDawg,

In a chrome lined AR, and handguns where the lower velocitys produce less copper fouling the use of Sweets should be infrequent.

Say every 1,000 rounds in the rifle and every 1,500 rounds in the handgun just for a roundabout SWAG.

Sweets is aggressive and CAN possibly be slightly damaging to the bore if not used properly as is the case with ANY copper solvent.

Copper fouling can be a problem that is more detrimental to the rifles performance if not kept in check however.

In all things, moderation.

Run the sweets with a patch only.
15 min. at the most in the bore.

Neutralize the sweets by patching out with 3-5 clean patches and then chase it with a couple patches that are wet with Rubbing alcohol, followed by a couple of clean dry patches.

If you shoot a lot, then you will need the Sweets on a regular basis.

If not, make an annual plan to remove copper fouling once a year.

It ain't Rocket science, but somehow, lots of wives tales have evolved around copper fouling and the use of ammoniated copper solvents.

In a chrome bore that is not used for competition, or as a precision rifle on duty, copper fouling is of little influence on accuracy to a point.

Same with the handgun that is not used at the olympic level.

Keeping the copper fouling at bay is the point in this regard and can be done with minimal risk by methodology.

Ignoring copper fouling with high volume use is ignorant as well.
have run a bore scope through barrels that show copper fouling to the point of causing measurable constriction.

Use the Sweets sparingly, and accept the copper fouling as normal to a point.

But do NOT be afraid to use the Sweets.
Properly used, the stuff is a godsend.

Just don't let the wife or girlfriend get a nostril full of the stuff inside the house, or you and the rifle will get banished to the garage!!!

Hope this helps.
S-28

Thanks guys.  You've been very helpful.