Deepening NMA Chambers?

[rodwha]

I’ve often read how modern guns do better with certain loads due to barrel harmonics. I have a ROA and a Pietta NMA that I curiously found both seem to do better with a certain powder charge despite the projectile used.

I’ve considered sending my cylinder to Clements (or someone) to have the chambers deepened on my ROA (and NMA?) and have wondered how that might change things. Though these don’t completely fill the chambers they come fairly close in my ROA, but I’d certainly like to stretch my projectile beyond the 195 grns it is now for hunting and still leave a little room as A) another found bullets loaded to the mouths get gas cut, and B) it leaves a little room for variances with loading.

I’d prefer to keep a universal bullet for both of these. Has anyone found a newer (mines a 2013) Pietta NMA has a little excess meat in the bottom to deepen one (I’m talking enough to add just 2-3 grns worth of space - guessing 1/16” of an inch at best and possibly half that)? I have slightly more excess then I do in my ROA. I see Clements claims their procedure adds 5-10 grns (guessing in my case we might be talking 5).

 

[whughett]

Sounds expensive. Just a thought, loading off gun with a good press, how much more could one gain with better powder compression. This comes to mind because I load a 45C case with 3f powder to the mouth, 40 grains. and then seat a 250 grain bullet to its crimping cannular. That black powder is compressed better than an 1/8 of an inch. I inertia pulled a bullet on one and the powder was a solid column.

 

[rodwha]

Sounds expensive. Just a thought, loading off gun with a good press, how much more could one gain with better powder compression. This comes to mind because I load a 45C case with 3f powder to the mouth, 40 grains. and then seat a 250 grain bullet to its crimping cannular. That black powder is compressed better than an 1/8 of an inch. I inertia pulled a bullet on one and the powder was a solid column.

I like the idea of using the loading system on the guns. First of all it’s something else I don’t have to take to the range, which my bag cannot handle anyway, and something I wouldn’t want in the field either.

It may well be expensive but so are the custom molds. It might be cheaper to modify the chambers than to order an additional mold. Plus I would much prefer to just have a universal bullet.

 

[paul harm]

I thought some of the guys enlarge the diameter to grove diameter or .001 larger. Would this be of any help for more powder ? And would it be more accurate ? I don't know, just a thought.

 

[rodwha]

I thought some of the guys enlarge the diameter to grove diameter or .001 larger. Would this be of any help for more powder ? And would it be more accurate ? I don't know, just a thought.

I’ve enlarged the chambers from 0.446” to 0.449” but have figured I’d bring it closer to groove diameter (0.452”). This isn’t to increase capacity (nor is deepening the chambers) as it likely wouldn’t add but a grain or two I’d think. It’s mostly to share bullets with my ROA without stressing the loading lever assembly. But if it will aid accuracy I’d be all in even more so.

 

[arcticap]

paul harm is right that many have reamed their chambers to make them larger.
Doesn't make sense to only make them deeper if they're not large enough to match or exceed the land measurements for best accuracy.
Some chambers may need it more than others, but many guns could benefit by being cleaned up and centered.
And some could benefit by having their forcing cones reamed too.
But it's not for me.

A lot of information & references about reaming the chambers of various models are contained in this single thread:

https://www.thehighroad.org/index.php?threads/cylinder-reaming.592634/

 

[LonesomePigeon]

The Pietta 1858 Remington "Shooter's Model" has .456" diameter chambers and .456" bore and the cylinder gap is very tight. The chambers do have a step in the bottom so they won't be too thin at the notches. I think the manual lists a maximum charge of 35 grains 3F but don't quote me on that. I've read that many people shoot them with .462" roundballs.

 

[arcticap]

That's interesting.
A quick search revealed that the Pietta Shooter's Model have their own parts which are not interchangeable with their regular production 1858's.
They are "Tiro" model parts.

 

[rodwha]

Installing the nipple and looking down into the chamber shows quite a bit of metal that could be removed. Placing the cylinder next to my ROA cylinder shows they are of identical enough length.

While loading it appeared to me as though a chamber or two might be a bit off center. How would one go about centering it if there’s not much metal to take off? And how would a reamer not center along the initial chamber hole?

 

[Mizar]

Hmmm, off center correlating to what - the bore, or the loading lever? If later, you might just have an improperly cut ratchet, which is of no big deal (Well, it depends actually, but let's just leave it that way for now). If the first, a slight misalignment is OK, as you have lateral slack in the locked cylinder to accommodate exactly this misalignment when the bullet enters the barrel. That and the forcing cone take care of this situation - it's not a problem.

You cannot simply "re-center", while widening, an existing hole with such dimensions - at best you will get an oval cross section. And if you try it with a reamer you will get a cone shaped hole to go with that oval because the reamer, as it enters deeper, will start to bend and try to follow the original center... If the misalignment is no more than (about) .004", just leave it alone - the revolver will shoot just fine.

 

[rodwha]

I had noticed the misalignment at the loading lever. I’ll have to pay closer attention next time I’m loading it.