Ruger SP101 binds when hot

[Coyote3855]

I'm an NRA Certified Instructor. In the current Personal Protection in the Home class, two students are shooting the same brand-new Ruger SP101. Last two classes, the revolver starts to bind up after 90-95 rounds in quick succession. The cylinder will not turn either double or single action when loaded. Will work unloaded.

Tolerances are very tight at both ends of the cylinder. Does not seem to be significant fouling at either the forcing cone, recoil shield or the back of the cylinder. No crud under the ejector star.

We speculate that when the gun gets hot, there is just enough expansion to cause the bind. We recommended the students put several hundred rounds through it and if there are still problems, send it back to Ruger.

Any other thoughts? Is there a way to "cool" the revolver between shooters so they can finish the class? They are an older couple and this is their first firearm.

 

[243winxb]

The cylinder will not turn either double or single action when loaded. Will work unloaded.

Rim thickness may make a difference. Have they tried different ammo?

 

[Coyote3855]

That's something I hadn't thought of, 243winxb. They were using American Eagle ammo. I did a bit of research and found that, as you suggest, rim thickness can vary from brand to brand. But I can't find data on which brands might have the thinnest rim. I'll break out the caliper. Anyone know which make of ammo might be the best in this situation?

 

[243winxb]

Rim thickness 357 magnum

You can look up rim thickness here, but not by brands. http://www.saami.org/specifications_and_information/index.cfm?page=CC For a 357 looks like .060" -.011" So the rim could be as thin as .049" if i understand the drawing correctly. http://www.saami.org/PubResources/CC_Drawings/Pistol/357%20Magnum.pdf

 

[rcmodel]

See this about rim thickness.

http://www.thehighroad.org/showthread.php?t=563715&highlight=colt+commando

rc

 

[WardenWolf]

I would send it back to Ruger. They'll make it right. They have some of the best customer service in the industry. They also have arguably the best revolvers in the industry right now, so if there's a problem with ANY in-spec ammo it should be rectified.

 

[Malamute]

See this about rim thickness

Good link.

 

[wbrco]

I hope they are using 38 spcl, id hate to do 100s of 357s in my 3" sp101.. ouch!

 

[Coyote3855]

Yes, they are shooting American Eagle .38 special FMJ as required by our range.

 

[retDAC]

With proper backlighting, gun empty and hot pointed in a safe direction, watch the relationship between the forcing cone and cylinder faces as you slowly turn the cylinder. You will have to have the hammer back far enough to disengage the bolt.

There may be an uneven forcing cone face, bent crane, or (rarely) an out of square cylinder face.

 

[BSA1]

Tolerances are very tight at both ends of the cylinder.

Elementary Dr. Watson.

Check the barrel / cylinder gap. Metal expands when it gets hot. It is not uncommon for revolvers with tight b/c gap to bind when the cylinder gets hot then function normally after it cools a bit.

We speculate that when the gun gets hot, there is just enough expansion to cause the bind

The solution is to open the b/c gap with a file. Brownells sells a tool designed just for this purpose. It will cut the rear of the barrel square and can also recut the forcing cone.

A good gunsmith should have this tool in their toolbox. It is a very simple and easy 10 minute fix. When checking the b/c gap check it from both sides of the barrel. I have a Ruger Vaquero that when new out of the box measured .003" from one side and only .001" on the other!

I like for my self-defense and competition revolvers to have the b/c set at .008" as I shoot mainly lead bullets. This leaves plenty of room for fouling from lead bullets. I believe the factory considers a b/c gap to be within specs out to .012".

It is much cheaper and much faster to have a gunsmith make this repair than sending it back to the factory. I think I paid my gunsmith $20.00 to fix mine.

 

[OilyPablo]

Check the barrel / cylinder gap. Metal expands when it gets hot. It is not uncommon for revolvers with tight b/c gap to bind....

This. I had a new Trooper Mk III that did the exact thing. One light brush with the stone is all it took. Tight is good, but it is ultimately a compromise. Too loose, too much gas escape. Too tight, binding.

 

[Coyote3855]

I very much appreciate the advice and suggestions. Thanks for the assistance.

 

[4v50 Gary]

Put empty cases in the cylinder. Put a feeler gauge (about .005" to .007" - I haven't checked my notes so I may be off) in the gap between the forcing cone and the cylinder mouth. Work the action for all six cylinders.

 

[Coyote3855]

4v50 Gary. I won't have access to the students' gun until Thursday night. I tried this with my old Speed Six. With Winchester empty cases, it will function with a .004 gauge but binds on two chambers at .005. Empty chambers, the gap is .006. I may run 100 rounds through the Six and measure again when it's hot.

My plan for the SP 101 is to measure the gap as you suggest. I don't want to tune on a gun that's not mine, so if the gap is too tight on one or more chambers, I will suggest either a return to Ruger or a local smith to take a bit off the forcing cone face.

Seems the consensus is the forcing cone is the problem.

 

[243winxb]

Not the forcing cone. In my experence, there is a high spot on the face of the cylinder or the gap between the cylinder face and barrel is to tight. S&W's run any where from .004" gap to .009" The cylinder is corrected by facing off, using a lathe to correct a high spot or tight gap. All it takes is some residue from firing to make it bind.

 

[Malamute]

Interesting. I've seen a number of forcing cones/rear of barrel that was uneven and had a high spot that rubbed, generally easily taken care of with some careful file work. I've not seen the cylinders be out of square enough to cause problems or high spots on them.

 

[243winxb]

The barrel face could also have a problem.

 

[BBBBill]

...I've seen a number of forcing cones/rear of barrel that was uneven and had a high spot that rubbed... I've not seen the cylinders be out of square enough to cause problems or high spots on them.

I've seen it both ways. In fact I've seen both on the same gun - A stainless King Cobra! That gun was a trip to get straightened out.

 

[TimSr]

Check the barrel / cylinder gap. Metal expands when it gets hot. It is not uncommon for revolvers with tight b/c gap to bind when the cylinder gets hot then function normally after it cools a bit.

^^ x2

 

[Coyote3855]

I checked the revolver at the class last Thursday. Unloaded, the barrel cylinder gap will take a .006 feeler gauge but not a .007. Did not bind on the .006 when cylinder was rotated single or double action. Mystery remains.