Ruger GP100 Cylinder Wobble...

[dwhaley]

Is this a problem?

Feels like the cylinder on this GP100 I purchased from a boardmember is a hair bit...loose on the rotational axis. Like a bearing isn't fully seated, or something.

Gun cycles and works fine...just this one issue. Seems like there's about 1mm or even less of play for the cylinder to buck around on its axis.

Thanks in advance for any answers.

 

[GNLaFrance]

When you push it around and then let go, does it go back to where it was by itself? If so, that's a good sign. Less than 1mm of rotational play doesn't seem like a problem to me, especially if the chambers line up with the bore with the trigger back and the hammer down (i.e., full lockup). How is the end shake (cylinder play forward and back)?

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REVOLVER CHECKOUT

So you're buying a revolver. New, used, doesn't matter, you want a good one, right? How do you check one over without firing it, right at the dealer's counter or gun show table?

This is how. All of this works with DA or SA wheel guns - "close the action" on most DAs means swing the cylinder in, on SA types, close the loading gate, on break-opens, close them. UNLOADED.

WARNING: Most of these tests require violation of the "finger off trigger" rule. Therefore, be extremely careful about safe muzzle direction and making sure the gun is unloaded ahead of time, PERSONALLY, as you begin handling it.
Note: Bring a small flashlight, something small and concentrated. A Photon or similar high-powered LED light is perfect. You also want feeler gauges if you're not used to eyeballing cylinder gaps; at a minimum, bring a .002", .004" and .006".

No dry firing is required or desired at any point. It just pisses off the gun's current owner.

Cylinder play

With the gun UNLOADED (check for yourself!), close the action.

Thumb the hammer back, and while pulling the trigger, gently lower the hammer all the way down while keeping the trigger back - and KEEP holding the trigger once the hammer is down. (You've now put the gun in "full lockup" - keep it there for this and most other tests.)

With the trigger still back all the way, check for cylinder wiggle. Front/back is particularly undesirable; a bit of side to side is OK but it's a bad thing if you can wiggle it one way, let go, and then spin it the other way a fraction of an inch and it stays there too. At the very least, it should "want" to stop in just one place (later, we'll see if that place is any good). The ultimate is a "welded to the frame" feeling.

Cylinder gap

Still holding the trigger at full lockup, look sideways through the barrel/cylinder gap. If you can get a credit card in there, that ain't good - velocity drops rapidly as the gap increases. Too tight isn't good either, because burnt powder crud will "fill the gap" and start making the cylinder spin funky. If you're eyeballing it, you'll have to hold it up sideways against an overhead light source.

My personal .38 snubbie is set at .002, usually considered the minimum; after about 40 shots at the range, I have to give the front of the cylinder a quick wipe so it spins free again. I consider that a reasonable tradeoff for the increased velocity because in a real fight, I'm not going to crank 40 rounds out of a 5-shot snub.

SAFETY WARNING: This step in particular is where you MUST watch your muzzle direction. Look, part of what's happening here is that you're convincing the seller you know your poop. It helps the haggling process. If you do anything unsafe, that impression comes completely unglued.

Timing

You really, REALLY want an unloaded gun for this one. This is where the light comes in. With the gun STILL held in full lockup, trigger back after lowering the hammer by thumb, you want to shine a light right into the area at the rear of the cylinder near the firing pin. You then look down the barrel. You're looking to make sure the cylinder bore lines up with the barrel.

Check every cylinder - that means putting the gun in full lockup for each cylinder before lighting it up. You're looking for the cylinder and barrel holes to line up perfectly, it's easy to eyeball if there's even a faint light source at the very rear of both bores. And with no rounds present, it's generally easy to get some light in past where the rims would be.

Bore

Swing the cylinder open, or with most SAs pull the cylinder. Use the small flashlight to scope the bore out. This part's easy - you want to avoid pitting, worn-out rifling, bulges of any sort. You want more light on the subject than just what creeps in from the rear of the cylinder on the timing check.

You also want to check each cylinder bore, in this case with the light coming in from the FRONT of each hole, you looking in from the back where the primers would be. You're looking for wear at the "restrictions" at the front of each cylinder bore. That's the "forcing cone" area and it can wear rapidly with some Magnum loads.

Trigger

To test a trigger without dry-firing it, use a plastic pen in front of the hammer to "catch" it with the off hand, especially if it's a "firing pin on the hammer" type. Or see if the seller has any snap-caps, that's the best solution. Flat-faced hammers as found in transfer-bar guns (Ruger, etc) can be caught with the off-hand without too much pain.

SA triggers (or of course a DA with the hammer cocked) should feel "like a glass rod breaking". A tiny amount of take-up slack is tolerable, and is common on anything with a transfer bar or hammer block safety.

DA triggers are subjective. Some people like a dead-smooth feel from beginning of stroke to the end, with no "warning" that it's about to fire. Others (myself included) actually prefer a slight "hitch" right at the end, so we know when it's about to go. With that sort of trigger, you can actually "hold it" right at the "about to fire" point and do a short light stroke from there that rivals an SA shot for accuracy. Takes a lot of practice though. Either way, you don't want "grinding" through the length of the stroke, and the final stack-up at the end (if any) shouldn't be overly pronounced.

Detecting Bad Gunsmithing

OK, so it's got a rock-solid cylinder, a.002" or.003" gap, and the trigger feels great. Odds are vastly in favor of it being tuned after leaving the factory.
So was the gunsmith any good?

First, cock it, then grab the hammer and "wiggle it around" a bit. Not too hard, don't bang on it, but give it a bit of up/down, left/right and circular action with finger off trigger and WATCH your muzzle direction.

You don't want that hammer slipping off an overly polished sear. You REALLY don't want that. It can be fixed by installing factory parts but that'll take modest money (more for installation than hardware costs) and it'll be "big-time" unsafe until you do.

The other thing that commonly goes wrong is somebody will trim the spring, especially coil springs. You can spot that if you pull the grip panels, see if the spring was trimmed with wire cutters. If they get too wild with it, you'll get ignition failures on harder primers. But the good news is, replacement factory or Wolf springs are cheap both to buy and have installed.

There's also the legal problems Ayoob frequently describes regarding light triggers. If that's a concern, you can either swap back to stock springs, or since you bought it used there's no way to prove you knew it was modified at all.

In Perspective

Timing (test #5) is very critical - if that's off, the gun may not even be safe to test-fire. And naturally, a crappy barrel means a relatively pricey fix.

Cylinder gap is particularly critical on short-barreled and/or marginal caliber guns. If you need every possible ounce of energy, a tight gap helps. Some factory gaps will run as high as .006"; Taurus considers .007" "still in spec" (sigh). You'll be hard-pressed to find any new pieces under .004" - probably because the makers realize some people don't clean them often (or very well) and might complain about the cylinder binding up if they sell 'em at .002".

The guns in a dealer's "used pile" are often of unknown origin, from estate sales or whatever. Dealers don't have time to check every piece, and often don't know their history. These tests, especially cylinder gap and play, can spot a gun that's been sent off for professional tuning - like my snubbie, the best $180 I ever spent.

As long as the gun is otherwise sound (no cracks, etc) a gunsmith can fix any of this. So these tests can help you pick a particularly good new specimen, or find a good used gun, or help haggle the price down on something that'll need a bit of work.

Hope this helps.

Jim March
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[Huckleberry]

Nice thing about Rugers, even used ones, is their warranty and customer service. You really worried about it, give them a call and see if they think you need to send your revolver in for a check up and service.

 

[lee2]

When you push it around and then let go, does it go back to where it was by itself? If so, that's a good sign. Less than 1mm of rotational play doesn't seem like a problem to me, especially if the chambers line up with the bore with the trigger back and the hammer down (i.e., full lockup). How is the end shake (cylinder play forward and back)?

excellent post!