I have a couple of revolvers that shoot pretty good, a 5 inch 629 classic and a 4 5/8ths stainless blackhawk in 45 colt.

The smith probably shoots as good of groups as I can shoot with a 5" barrel and the ruger while having shot some above average groups at 25 yards. I have not been able to get it to shoot as good as I would like at longer ranges.

I am considering opening the cylinder throats on both these guns because they are under size. the smith measures about .429 or .4295 and the ruger .451 plus or minus 5 ten thousandths.

My question is, and this might be heracy on this board but how does opening the cylinder throats affect accuracy with jacketed bullets.
For better or worse I have not convinced myself that cast are all I will ever want to use in my revolvers and want to know all the facts about bigger cylinder throats before I take the plunge.

Has any of you done before and after tests with jacketed bullets, if so I would sure appreciate some good data.
If no before and after just tell me how well it will shoot now with jacketed after haveing the throats opened.

Thanks for your time: J Sanders

J Sanders

I have not opened cylinder throats on my revolvers, but I do know why one has it done: if your cylinder throats are smaller than your barrel diameter, cast bullets will be sized by the cylinder, and then be undersized while passing through the barrel. This can cause gas cutting on the bullet, which can ruin accuracy and lead the barrel. The only way you can know if the operation may be valuable is to slug your barrel, then compare the diameter of the slug to the diameter of your cylinder throats. Jacketed bullets tend to be more “springy”, and slug back up to fill the bore. When measuring the throats, you may find that they vary in diameter. Throating them will make them uniform, which nearly always adds to accuracy.

Darrel

A little oversized should not hurt jacketed accuracy, at least not to a great degree.

I have a 1976 Blackhawk in .45 Colt / .45 ACP; both cylinders have throats measuring about 0.456" with the barrel groove diameter being between 0.451" and 0.452". Both cylinders shoot surprisingly well, under 2 inches at 25 yards. The .45 Colt cylinder still shoots well with hard cast; 300 & 335 grain WFNGC bullets shoot just as well as jacketed as a matter of fact. Recoil, however, is brutal and I switched to the Bisley model and have sort of retired that gun, although it is accurate.

I'd go 0.001" over groove diameter, you won't go wrong with that.

Mike G,

That is just the kind of info I was looking for. If yours shoots jacketed and cast equally good with throats that big I should not have anything to worry about. I appreciate your time, Thanks: J Sanders

A the risk of sounding ignorant, wouldn't the firelapping mentioned on this forum size the throats to the proper diameter to match the bore. I have a SBH that seams to lead a little more than it should with tight throats to boot and was considering this as a solution. Any thoughts??

Don't want to lap until the cylinder throats are at least as big as the barrel groove diameter. So open them up first, if need be.

Otherwise the lapping bullet gets squeezed down and then only hits the tops of the lands.

Been thinking about your question of opening up the cylinder throats for cast bullets and trying to get accuracy from the smaller jacketed ones.

All I can offer is that Ruger is selling their Superblackhawks and Redhawks now adays with .432+ cylinder throats. I have not experienced any frank loss of accuracy from these "large" cylinder throats. I would also expect that if Ruger's did not shoot jacketed bullets in .429 well, with these larger throats, they would have smaller cylinder throats. It's kind of reverse thinking but I have not experienced or heard of problems with throats .003+ larger than the bores with jacketed bullets.

Kinda makes sense... I think............ Bill

Any suggestions on where to go or DIY tips. I read on one of these forums about an outfit that takes 44 cylinders and bores them to 45, eliminating the slop. As my cylinders are loose, if I have to pay to open up the throats, I would like them to just build new for the additional accuracy benifits. Again folks, thanks for all the help and paitience. Been a member for a while but just trying to absorb all the info on this forum is overwhelming with 1 - 3 hours a week on the box and still have time to torch some powder. Amazes me that this many folks can get together, even if long distance, and have as few major differences as there are and all with such helpfull attitiudes.

J Sanders,

I have two .45 Colt revolvers. One a S&W 25-5 with grossly oversized throats. They measure out at .457". No I'm not guessing I slugged each one of them and miched the slugs. The grove diameter is around .4515".
Because of the oversized throats this gun is a leading fiend. It will lead with any bullet, at any velocity, EXCEPT factory lead or oversized cast bullets. These shoot well. Jacketed bullets shoot well also, but I rarely buy them.
There is no cure for this gun except a new cylinder and those are virtually impossible to find.

The other one is an Old Model Blackhawk that had very undersized throats. They measured out in the .450" area. The grove diameter is .452". This gun leaded with any lead bullets, didn't matter what they were, and the accuracy even with jacketed bullets was pathetic.
I had the throats opened up to .4525" and the leading problem was reduced by 90%.
Accuracy increased dramatically with both lead and jacketed bullets.
It was more than worth the money to have it done.

My guess is you Smith wouldn't benifit too much by haveing the throats opened up, but your Ruger would.
Here are two people who do the work you can contact for additional information.
The Cylindersmith at; http://www.cylindersmith.com/
and the .45Throatdoctor at; http://45throatdoctor.com/

The 45throatdoctor did my cylinder and I can vouch for his work. I've also heard many good reports for the cylindersmith.

Joe

Bill M , Joe and everyone else. Thanks a bunch for answering my questions.
I'm convinced by your responses I will be risking nothing in jacketed accuracy and will be gaining with cast. Thanks again JS

J Sanders, I have a .45 colt Bisley Ruger that had cylinder throats that were .449-.450 and I couldn't even get LBT bullets into them. I had them opened to .452 and the accuracy with LBT bullets increased greatly and their was no loss in accuracy with the jacketed bullets; if anything their accuracy increased. It definitely helped my gun as did the firelapping of the barrel. Best of Luck! Pistolpete

If you only have one revolver requiring the throats sized, then it's probably cheaper to have a gunsmith do it......but then you have the shipping cost that can really raise the cost. I've done three Ruger .45LC and the only problem I had was I didn't adequately clean the drill before backing it up and slightly scratched one cylinder. I paid about $100 for the equipment and it was easy to use. A set of guides of various diameters were furnished and I simply used the one that fit the current throat to guide the bit (by hand). It wasn't a particulary lengthy job and I enjoyed it. But by all means, do firelap the revolver as it is so much more fun shoothing lead bullets when they don't lead (minimum leading is worse case) the barrel, not to mention the improved accuracy.

Dan

Dok, does Brownells carry the kit yhat you speak of and is it for just the one model??

Dok, does Brownells carry the kit yhat you speak of and is it for just the one model??

Let me jump in here, if you will. I just happened to have my Brownells catalog open and there it was on page 130. Clymer's Cylinder Sizer for .45 Colt cylinders only, cost $199.00 (not discounted for FFL's). I seem to recall reading somewhere that this tool was rented by the job, like chamber reamers. Maybe give Clymer's a call. If you could rent it then return it, the economics would be better for a single job.

Brownell's also offers the Manson Precision Throating Reamer set. The reamer is $70.00 and the Pilot Pack is $44.00. This is also a hand turned tool. Manson also offers a .44 cal set.

Happy gunsmithing - nothing satisfies like learning to do something new - and getting it right.

axlenut

I have two new S&W 629-6 44 mags. Both have cylinder throats of .4294 diameter, all holes. I talked to S&W about it.

For jacketed bullets they said to stick to bullets advertised as .429 diameter. Speer has them, so that's what I buy. They mike about .4293 to .4297. That's within the tolerance I got from S&W.

With lead bullets, I size them to .4295 with an RCBS Lubrisizer. Good accuracy and no leading.

I know I'm supposed to find out what size the barrel is and size the throats accordingly. But these things are working good, so I'm going to stick with them.

Sometimes I shoot bullets as big as .4315 diameter in these guns - the 210gr Silvertips. I wonder how they can squeeze down so much so fast. Says something about the nature of pressure I guess. adk

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I have a Ruger 200th year (1976) .45Colt/.45ACP convertible, 7-1/2" bbl. When the subject of subdiameter cylinder throats became widely mentioned a few years ago, I took measurements of my gun, purely out of curiosity. I'd never worried, as the revolver is very accurate: sub-two inch groups in .45 Colt with the hardcast 260-grain Keith which is all I use in that cylinder; and an inch or LESS with the ACP cylinder and .45 Hardball or Hardball-equivalent handloads (groups at 25 yards). My ACP cylinder measures .452-.4525 all around. The long Colt cylinder measures .453-4535. Bore slugs a tight .451+. I let well enough alone, and praised the good fortune that sent this particular gun my way.

You did good! My 200th model has both cylinders at about 0.456".... although it shoots fairly well with either.

I think the big throats somewhat compensate for the chambers not lining up perfectly.