1858 throat and barrel size/ reaming questions

[dledinger]

So far so good. I ended up doing a bit more than the cylinder.

First, the cylinder alignment was WAY off. I opened up the bolt window and shimmed the bolt tight, along with necessary fitting. It took opening up the window .030" to get it close. Second, I reamed the cylinder to .4531. Third, the muzzle was not square, so I trued it up with a file and cut a new crown. And finally, I polished up the forcing cone to take out the chatter marks (mostly).

Before I could not keep 6 balls on an 8.5 X 11 copy paper target (at 25 yards), and now I'm doing about 4".

I think there is still some room for improvement with tweaking the load, but so far so good, and I'm only down time and $20.37 for a reamer.

My other realization....my guns are not Piettas. I believe they are Armi San Paolos. I've never really bothered to look, I bought them used as Piettas and always assumed they were.

 

[rodwha]

How much meat do you have between the chambers now?

My 2013 Pietta NMA had 0.446" chambers new. I sent it to a fellow who reamed them to 0.449" and chamfered the mouths. I've wanted to ream them a bit more to get closer to my 0.452" groove diameter but the walls just look a bit too thin as it is.

I've had a couple of others ream to 0.453" as well with only one who uses energetic powders and conicals with substantial loads (not the weaker target loads).

 

[dledinger]

Yeah, visually they pathetically thin even before reaming. I won't be shooting full loads of Swiss behind a conical any time soon. LOL.

I'll measure them and let you know.

FWIW, I've shot a max of 30 grains of Graf's FFF behind a roundball, and I doubt I'll go any higher.

I went ahead and chamfered my cylinder as well, hoping to swage a bit more lead into the cylinder.

Next thing I am working on is the plunger. I'm not sure if they're all this way, but mine mangles roundballs when loading. I'm hoping a better shape will keep that from happening and lead to a bit better accuracy.

 

[rodwha]

I need to figure out what to do with mine as it mangles the meplat on my WFN conicals.

 

[dledinger]

Not much new to report on this as I haven't had much time to invest in my revolvers.

To recap:

- I fixed the cylinder indexing by opening the bolt window and tightening up the slop with a shim made from a feeler gauge.

- I cut a new crown with a round head bolt.

- I reamed the cylinder to .4531.

Groups improved with this arrangement substantially, even if the numbers would suggest that it isn't ideal. I'm not terribly happy with the amount of lead shaved from a .457 ball.

I ended up borrowing a forcing cone reamer and gauges. Using the gauges, I found that both pistols, while totally inconsistent, already had oversize cones. Way over size.

I set it up anyway and used it to remove the final chatter marks that I couldn't fix with the lapping.

Fact remains, however, the only way I'll ever get it right is by setting the barrel back. Given the still-oversize bore, that's just not worthwhile.

Anyway, it's been a very fun project which gave me a lot of opportunity to learn!

 

[rodwha]

A few questions come to mind.

1) What is the diameter of your cylinder?

2) What is the wall thickness between chambers?

3) What load(s) are you shooting?

There's another who owns a Pietta NMA who has opened his chambers to .453". As I use a more energetic powder with 30 grns (about 33 on a scale) and conicals I wasn't sure about this. But asking him he does the same thing. Those thin chamber walls keeps me from going beyond the .449" they've been reamed to.

 

[dledinger]

Rodwha...you're on the mark in being conservative, IMO.

I'll get the measurements for you, but there's absolutely no way I would consider shooting 30 grains of an "energetic" powder in this revolver..assuming you mean Swiss, Old E or anything similair.

The stiffest load I've fired is 25 grains of Graffs 3f...and I cringed every time I pulled the trigger.

 

[rodwha]

Indeed I do. Mostly 3F Olde Eynsford or occasionally Triple 7.

I've certainly put plenty of lead down range so far with .449" chambers. But those walls sure look thin enough which gives me pause to take them to .453" as you and this other fellow have and continue as I am.

The load I use has shown to be the most accurate with a useful load for hunting. Compared to chronographed results of the same powders and similar projectiles I'm likey getting standard .45 ACP performance (375-425 ft/lbs) with that 195 grn conical.

 

[dledinger]

I've wondered at times about the safety of perusing this. Sure, in my hands it is my risk and I am totally comfortable with that. I worry, however, that if something were to happen to me someone might grab the old gun and look up loads for an 1858, without knowledge of what was done. I would definitely NOT want anyone to to load a conical over 30 grains of Swiss or T7.

There reaches a point where the juice is no longer worth the squeeze, and one needs to abandoned their efforts and chalk it all up to a learning experience.

I think I've crossed that line.

 

[rodwha]

Yea. I value my digits. It works just fine as is. I'd certainly prefer better but not at the expense of those digits. And that has given me pause of going further.

Besides my ROA would be my hunting arm were I looking for a primary hunting arm anyway. It's more accurate, prefers a slightly heavier charge of 35 grns (about 38 weighed), and has a better sight radius.

Clearly I didn't recall the actual measurements of mine. I thought the grooves were .452". In fact they are .455" with a land diameter of .444"

 

[Grenadier1758]

Are the photos above showing measurements from one ball that you cast or purchased? I have that kind of variation with old molds from the 19th century.

Are you showing us measurements from a ball pushed through the barrel and the measurements indicate the land to land (0.442") and the groove diameter (0.453")?

 

[rodwha]

That is a .457" cast ball from a Lee mold. It was run down my bore to check dimensions to those people stated with older models. I knew mine differed when I saw 6 lands/grooves and found the twist to be about 1:16" instead of 1:30.

 

[dledinger]

Rodhwa, Sorry. I meant to get back with you on this sooner. I've recently started casting bullets for some cartridge guns and have myself chest-deep in alloys and new moulds.

I've played around trying my best to get a good measurement. The best I have to do so is a digital caliber. It's easy to tell right off the bat that both cylinders - factory and modified - are all over the map. While my measuring technique is probably not the best, a bit of finesse seems to make it possible to get a fairly decent and repeatable read.

I'm seeing the following minimums:

Modified cylinder: Smallest = .0480
Factory Cylinder: Smallest = .0520

That's a variance of .004....when I removed about .005 of metal. Seems reasonable accurate.

 

[M. De Land]

The gauge will pick up the slight helix angle of the rifling pitch imprinted groove (land) on the slug over it's length thus increasing the width of the measuring surface on the two lower points so the mic only has to pick up the center of the top groove or land on the slug. The bottom of the gauge orientates the top of the mic jaw or caliper to TDC each time.
For this reason it is one of the more accurate try mic gizzy's.

 

[Blizzard of '93]

good surmise may well explain the accuracy of the knurled pattern driven band slugs.

 

[nkbj]

Pietta 1858's make me think that someone could have quite a bit of business if they produced replacement barrels with .444" groove diameter.

Their .36 calibers might be a great opportunity to rebore to use .44 revolver molds (that are really .43, go figger ) and the .433 ball molds that nowadays nobody much has a use for.

 

[Eras Gone]

This is an interesting subject. I cant understand why the Italian makers produce the guns as they do. Here is a video I did on the subject. Chamber vs Bore Diameter

 

[dledinger]

Nice video. I regret I didn't see it sooner.

When I bought my pistols they were the only two I'd ever looked at up close. I've since had the opportunity to look at many, and have concluded that mine were some absolutely horrific reproductions. That's much of what motivated me to work on them, knowing they could hardly be made worse.

It was certainly fun to see some improvements along the way. I need to get back to them one of these days and see what else I can do.

And then, maybe one day I'll buy a nice one!

 

[M. De Land]

Barrel constriction under the frame thread is common in production revolvers and needs lapped out for best accuracy. It can be cleaned up with fire lap slugs just like any revolver but is best done by hand with formed lap slugs and lapping compound with a bearing-ed lap rod and muzzle guide. The latter is better affording more control.
I reamed out each chamber throat in my Pietta 1858 to .450. I removed the barrel and made a tight fitting reamer spud that went into the barrel hole through the frame to hold the reamer in perfect alignment as I indexed each chamber and reamed it out to .450. This method is called line boring as it insures perfect alignment with each chamber in relation to the bolt position lock up.

 

[Billy Boy]

Where does the 'slugging up' of the ball due to having its' inertia overcome by the explosion, and further, slugging up at the instant of contact with the forcing cone fit into the diameter equation?