Question: Cylinder Throats & Bore Size

[mike44]

1) Do you WANT the cylinder throats to be a bit larger than the bore? I know you definitely don't want the chamber undersized.

After reading about Ruger Blackhawks and thread choke I decided to sit down and do some measuring. I have a Lipsey's/Talo SS convertible 45 Colt/ 45 acp. I used feeler gauges, pin gauges. dial calipers, and a micrometer, as well as slugging the bore. To say I was amazed is an understatement. First, I checked cylinder gaps with feeler gauges. The 45 Colt cylinder was .0015 and the gauge had a little resistance. Second, All the chambers in BOTH cylinders were the same .451 using the pin gauges. Then I slugged the bore with soft lead. I had groove measurements of .451 and lands of .443. Then I wanted to check for thread choke. The largest pin gauge that would fit was the .442 gauge. It slid all the way down with no thread choke. This is a production gun. A Belt Mountain base pin is the only part switched out on this gun. Uniformity is awesome! But, my real question is DO I WANT the cylinder throats to be the same size as the bore? Or, should it be .0005 to .001 larger?

I have not had the chance to run this gun through all the paces yet as I have been using my 500 JRH this hunting season.

[Deleted]

How does it shoot? While there are guidelines for such matters, each gun is an individual, and needs to be approached as such.

[dmize]

Throats sholud be larger than barrel. And I also agree with 358156...............BUT............ PROPER throats should be .4525 and proper pin gauge should not just be one that slides all the way through,but one that touches the lands at the muzzle and slides through freely.

[mike44]

10-4 thanks. I have not had a chance to shoot it much. None since putting the Belt Mountain base pin in. I will mainly be shooting 300 gr WFN or LWN either plain based a GC. Gonna look to run about 1100+ fps. Was just wondering. Thought the chambers should be a bit larger. I will definitely shoot it soon to see how it does.

[tek4260]

Throats larger than the bore, then bullets larger than the throats. The latter negates any variation in case neck tension.

[Encore64]

Mike44,  You have described my WSS Ruger 45 Bisley to the letter.  Mine shows the exact same throat and bore measurements.  It shoots great with cast bullets of .452 and jacketed bullets of any kind.  I think you will find the same thing.  The only time I have had a problem with revolver accuracy is when the throats are smaller than the bore diameter.

Even then jacketed bullets grabbed the rifling enough that it shot fine as long as cast bullets were avoided.  Referring back to my old 1937 Phil Sharpe loading manual, he stated that cast bullets needed to be the same size as the bore.  Today it is generally believed that they need to be .001-.002" oversized.  I have found with the hard cast bullets either way works similar.  You may find different results.  I look forward to hearing how this works out for you.

[bradshaw]

Mike.... when getting explicit on technical questions regarding revolver accuracy, we got to hone in on jargon. When you say "bore," I think you mean groove, as for asking whether chamber exits should match groover diameter. First of all, it is important to grasp REVOLVER ACCURACY continues to baffle the body of knowledge. Very simply because, aside from the fact that a finely dimensioned sixgun always shoots straight, there exist revolvers which dimensional irregularities do not prevent accuracy. Without digging too deep, let us set an accuracy parameter of 4-inches at 100 yards. Neither fantastic nor lousy. Now take the .44 with a bullet diameter of .429 or .430-inch. Providing a minimal forcing cone and groove diameter of .430", chamber exits of .433" will permit 4-inch groups at 100 yards. Or 4-1/2".

Can you squeeze a bullet in the chamber exit and still have accuracy? Yes, if it is a jacketed bullet. Cast bullets are more sensitive to squeezing.

If you have a choice, do not pinch the bullet in the chamber, especially a cast bullet. Some looseness in chamber exit is acceptable, more acceptable than loose groove diameter. While I try not to stray too far from your question, know that more bullets are doomed in the forcing cone than anywhere else. I played hard in this caper with Ruger and Smith & Wesson, lessons brutally learned on the firing line.

There is a world of difference between a revolver which groups five shots in 2" at 100 yards, and a revolver which groups five shots in 4-inches. And an other world of difference between a two inch revolver and a one-inch revolver.

This dope is just an etching of what is involved.
David Bradshaw

[mike44]

I really do appreciate all the feedback. I will shoot first then try to address any deficiencies after the fact, I do appreciate the info.