I bought a police trade-in Smith and Wesson 66-7 last weekend. I inspected it and function tested it and everything looked good. The only thing I'm a little concerned about is headspace. I don't have an empty case, only live rounds, so I didn't want to measure headspace with my feeler guages. I don't have actual headspace gauges either. I'm wondering what the headspace measurement should be if I used a case and feeler guages. Is it .060"? What concerned me was from looking at the air gap between the case and frame on a new Taurus revolver that I've only put 50 rounds through and comparing that to my used Smith. The gap is definetly wider, but not sure if it's too much.
I haven't had a chance to shoot it yet so not sure if it will have light strikes or any of that. I suppose I could try and find a gunsmith and see if he could real quick check the headspace. Wonder what that would cost? What is rememedy for having too much headspace?
I'm not real concerned about it, but I thought I'd run it by you guys and see what you thought.

Found article on web saying that on a 38/357 revolver it should be between .060 adn .075 to meet Sammi specs. Sound right?

This is from S&W.......

I added the gage specifications below for each particular caliber (from the armorer's manual):

38,357,41,44 .060"-.068"
22 magnum .004"-.008"
45 ACP .090"-.094"
45 Long Colt .060"-.068"

38,357 w/cylinder Counter Bore .012"-.018"

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NRA Benefactor Member

Thanks for the specs. My feeler gauges are too wide to fit inbetween the case and the frame so I guess I'll just shoot it and see what happens. From looking at the firing pin stickout and comparing it to the air gap I don't think I'll have any problems with light strikes or buldged cases. I'll talk to a gunsmith if I do.

Haven't had a chance to shoot it yet, but If I do have a problem what is my best course of action?

As long as the center part of the ejector is not filed down, I doubt you will have any issues with head space.

Try your gun with new ammo to rule out any bad reloads. If you have sticking, split cases or primers pushing out then we could help you further.

To measure the head space, measure it with a cartridge in the chamber. First measure the rim, then add feeler gauge then add both values up.

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NRA Benefactor Member

Looks like I was concerned over nothing. I took it out yesterday and ran 50 rounds of blazer 158 lrn 38 sp. through it with no trouble. Then I ran 12 rounds of expensive +p self defense ammo without a hitch. Gun is very accurate. I'm extremely happy with my purchase.
Just for curiousity sake, how is headspace adjusted on a revolver? Does the cylinder need to be moved back and the barrel moved closer? That would be a nightmare if it had to be done that way.

Headspace "cartridge rim-to-recoil shield clearance", barrel-to-cylinder gap, and cylinder endshake are all related. Change one, and the other two will also change.

At the time the revolver is fitted, the extractor hub is ground to provide headspace within specifications. The cylinder endshake is regulated to specification, and the barrel is fitted to provide b-c gap to specification.

Any after-market changes (adding endshake washers, replacing barrel, fitting replacement cylinder or extractor) must be done properly to make the revolver function correctly.

Hi everyone, new member here.

Regarding headspace, I noticed that the cartridge case used, also has an effect on headspace.

I noticed slight pressure marks on the primers when using Sellier&Bellot .357 cases. The pressure marks were not present in other brands of cases (Lapua, Magtech, Winchester). I measured the case rims, and the S&B case rims were a tenth of a mm thicker than the other brands. Load used was a mild 7gr VV N340, 158gr Ares polymer coated bullet. Gun is a four inch model 66, no dash.

With rifles, tight headspace is fine, excessive headspace leads to higher and sometimes dangerous over pressure.

Not sure about revolvers.

On S&W revolvers headspace is either in spec or it isn't; a go/no-go gauge is used to determine clearance for minimum and maximum specs. So long as the revolver's headspace accepts the "go" side and rejects the "no go" side of the gauge, all is in order.

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Pickpocket

A no go gauge is longer, so it is the same wrt S&W revolvers.

I’ve used feeler gauges, as explained in Kuhnhausen’s book.

A gun can reject (close all the way on) a NO-GO gauge and still be in spec.

You have to check the gun further with a Field gauge to see how much more the HS is before a pronouncement of rejection is given

If the same gun will not close all the way on the Field gauge, it is considered to be still in spec and not to be rejected.
It is at the lower end of the acceptible HS spec range,,but still within it.

If the gun DOES close all the way on the Field, then it is considered 'Out of Spec' and is rejected.

We like to have the actions not close on a No-GO gauge. That shows that the action is still very 'tight' and has a long way to go before it is loose and wear takes it out of spec.
But everything isn't always perfect and some actions are tighter than others, some worn more than others, some just not fitted as well to begin with.

Being able to use the set of 3 gauges properly is important.
Keeping everything clean in use, not forcing the action closed on them and learning to read the gauges and what they are telling you by how far the gun closes on a specific gauge all helps.
The gauges are precision known quantities (lengths).
With that and the SAAMI specs for Max and Min you can get a very good idea for what the actual reading of the HS clearence is in a particular firearm.