Probably two thirds of all transactions in firearms cover used guns. I get a lot of questions about how to evaluate whether or not to buy a used gun; and valueprice questions aside; it's important to evaluate the mechanical soundness of a weapon before considering a purchase.
These are some simple tests that anyone should do before they buy a gun (new or used), after detail stripping, or while prepping a gun to be used after a period of storage.
Jim March has posted his famous "Revolver Check Out" for the wheelgun side, I thought I'd write somthing up for the semi-auto lovers among us.
The first step is a general inspection. Check the overall appearance of the gun and the finish; the grips/stocks (especially look for cracks around the grip screws), the sights, and the condition of controls, pins, and screws. Push on everything to make sure that everything that should move does so smoothly; and everything that shouldn't move doesn't. Excessive wear, play, or burrs, chewed up screws etc... are all indicators of a mistrteated or un/improperly maintained gun.
If a gun you are looking to buy from a private seller is dirty you can assume they don't care much about the gun, or about selling it for that matter; and they may not have taken care of it. Of course if you know what you are doing, this could also mean you can negotiate a better price for the gun (it's jsut like people who try to sell a dirty unwashed used car full of trash).
If the gun is so dirty that a comprehensive inspection cannot be made; either put it down and walk away, or if you are REALLY intersted, ask the seller to clean it for you (or if he minds you cleaning it yourself). If he won't clean it, or let you clean it, don't walk, RUN away.
Next step, you want to field strip, and carefully inspect the frame, slide, barrel and bore, hard parts (pins, safety, slide stop, hammer, firing pin stop etc...), and springs for cracks, inappropriate burrs, nicks, galling or abrasion, abnormal levels of discoloration (which may indicate detempering - some is normal on some guns, but too much is a problem), fatigue, work hardening, inapropriate finish damage, unexpected carbon or fouling buildup, and excessive corrosion (some very slight corrosion may be acceptable).
Pay careful attention to framerails, holes drilled in the frame, the bore, muzzle crown, and chamber face of the barrel, the breechface of the slide; and anywhere there is a metal to metal impact (like the hammer and firing pin), interference fit, sliding join, pin join, or butt join; like the barrel hood, locking lugs, barrel link or lug etc... as well as any part or location that handles high stress or pressure (which includes all of the above locations).
Use a bright light to highlight any cracks, burrs, or irregularities; and run your fingernal over sharp or broken edges to check for things you might not be able to see properly, or aren't sure of (your fingernail shouldn't snag on smoothe metal).
Use that same bright light, to inspect the chamber and bore. The bore should be clean with no (or minimal) corrosion or pitting, and the rifling lands and grooves should be clean and sharp. The chamber should slo be clean, without excessive pitting, and have a sharpe edge for the case mouth ot headspace on. Danger signals include deep or wide pitting, excessive corrosion, burrs, chips, cracks, galling, and inapropriate discoloration.
Again, if the seller won't let you inspect the gun properly, thank him for his time, and walk away; unless the gun is a difficult to find treasure, or some such... In which case, offer the seller a small deposit and promise to purchase assuming the gun passes your tests. If he still refuses, don't even think of dealing with him.
Assuming the weapon passes inspection, there is the more difficult section to deal with; function testing. For these, even a reasonable seller may balk; especially at a gun show (in fact these testes may not be possible at many gun shows depending on their weapon handling rules). Again I suggest offering the seller a deposit with a promise to purchase conditional on the weapon passing the tests.
The first test, hammer drops, is pretty simple:
1. Empty the weapon
2. Make sure it's really empty
3. Check one more time
4. Lock the slide back on an empty magazine
5. Release the slide and let the weapon return to battery
6. Pull the trigger. If the slide moves more than a barely perceptible amount, you may have lost tension in your recoil spring, or have too much slack in your recoil spring, even if there is enough tension.
7. Point the weapon down, cock the hammer, and see if the slide moves either forward or back more than a barely perceptible amount. If it does, you've probably lost tension as well. The hammer spring/main spring shouldn't be stronger (or that much stronger) than the recoil spring (well, in most guns anyway.
For slide drops, you need a mag full of snap caps, and an empty fired case.
1. Empty the weapon
2. Make sure it's really empty
3. Check one more time
4. Load a snap cap in a known good magazine
5. Slingshot the slide chambering the snap cap and run the hammer drop tests above
At this point the weapon should chamber the cap properly, and return to battery fully, without excessive play. You shouldnt be able to push the weapon out of batterry by pushing on the barrel hood; and it should require significant pressure to do so from the muzzle.
6. Eject the snap cap and make sure the slide locks back
7. reload the snap cap in the mag, and drop the slide using the slide release
Again, the weapon should chamber the cap properly, and return to battery fully, without excessive play.
8. Load the mag completely with snap caps, and repeat tests 5 and 7 for a full magazine each
9. lock the slide back and insert an empty fired case in the chamber. Drop the slide from lock on the round and ensure the extractor engages, and extracts properly.
10. Insert the fired round in the chamber, and gently lower the slide on the round. If the extractor doesnt engage the rim from recoil spring pressure (most won't and shouldn't), then slingshot the slide from there and ensure the extractor engages, and extracts properly. If the enctractor DOES engage, hold the slide off the round and slingshot it running the same test. Unfortunatley, if it does engage, you've probably lost extractor tension.
If your gun will feed empty cases (and if it's been set up and finished well many should, unless they have a very high feed ramp angle), re-run all the tests with empty cases.
At every step, I like to check the muzzle to slide/bushing fit and wobble; and push on the muzzel, and barrel hood checking for any wobble or weak engagement etc... Also checking the trigger, safety function, and magazine functioning in the process. Pushing lightly on the muzzle, or on the muzzel end of the lide, shouldn't result in more than perhaps 1/16th" of movement.
If the gun performs well in these tests, you can be reasonably assured you have a mechanically sound weapon.
