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Author Topic: Frame opening for loading conicals NMA58  (Read 187 times)

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Offline Rebel Dave

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Frame opening for loading conicals NMA58
« on: February 08, 2019, 11:12:08 AM »
Hi all
Can someone, who has an original NMA58, measure the opening between the barrel, and cylinder for me. I have two NMA's and want to open that area up to accomidate loading conicals. I would like to know the lenght from high point in barrel, to the cylinder. I have the Lee, and Johnson,and Dow molds. I don't want to just start grinding.
Thanks   Rebel Dave
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Offline Hawg

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Re: Frame opening for loading conicals NMA58
« Reply #1 on: February 08, 2019, 12:41:38 PM »
Neither one of those bullets should require modifying the frame. The Lee is a tapered bullet and the J&D is rebated.
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Offline Omnivore

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Re: Frame opening for loading conicals NMA58
« Reply #2 on: February 08, 2019, 12:54:56 PM »
First, let's be clear on our nomenclature.  "The opening between the barrel and cylinder" is commonly known as the "cylinder gap" and has nothing to do with loading.  That gets a bit uncertain on a Colt however, being that the loading window is actually part of the barrel.  Therefore I don't say "barrel" but rather "loading window".  On a Remington the loading window is a feature of the frame, so I don't know why we're talking about a barrel here at all, unless the NMA you're discussing is a Colt (Colt actually did refer to the 1960 and later percussion guns as "New Model" [Army, Navy etc.]).

The size and shape of the loading window will depend on who made the gun.  Original and Uberti Remingtons should be ready to handle most conicals without modification.  Both of my Piettas have needed modification to load even the Lee 450-200-1R, whereas even the wider nose, heavier conicals that I have will load easily in both my un-modified Ubertis.

Handing you measurements would not help you.  I've modified a number of guns, Remingtons and Colts, and never measured anything, nor would having measurements in-hand have helped me in the slightest.

They way to do it is to insert your chosen bullet, up to the front of the heel, or as far as the bullet would normally go into the chamber prior to ramming.  You do that in a chamber that's alongside the frame, on the right-hand side of the gun, then rotate the cylinder so the bullet is going toward the loading window and under the rammer.  Where ever the bullet hits the frame, take metal away at the location.  Repeat until there is no interference.  Then you're done.  Measurement numbers are irrelevant because you can clearly see where the bullet it hitting and where it isn't hitting, and that is what matters.

It may be useful to use a strip of cigarette paper as a feeler gauge, to verify exact points of contact along the way through the process.  Another technique I've used is to shove the bullet hard enough into the interference point so as to make a mark on the bullet.  Another method is the transfer dye method, where some black grease is used on one part to mark the point of interference on the other part.  Last time I did this however, all I did was look, remove metal, look some more, etc., until done.  This photo of the cut being made in progress will give you some idea of what needs to the done.  Though it shows a Colt, the concept is the same.

A Colt is a bit different in that no conical can be inserted straight into a chamber that's clean out to the right hand side, as can be done on a Remington.  So on a Colt one must tip the bullet into the chamber, with that chamber a bit closer to the ramming position.
« Last Edit: February 08, 2019, 01:06:21 PM by Omnivore »
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Offline G Dog

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Re: Frame opening for loading conicals NMA58
« Reply #3 on: February 08, 2019, 02:33:34 PM »
Using Omni’s photo I have indicated what for my Pietta Colt’s and Remington’s seems to be the critical contact point.  My sons have reshaped that particular area on their Pietta Rems and can load many conical types without the bullet making contact with that corner. 

I’ve not made that modification on my own Piettas but using Accurate Molds  45-190R (by DD4) I get only a small line of friction there on the 1860's but not enough to prevent the cylinder from easily turning the bullet under the rammer.  That bullet fully clears the corner on Remington's. When I expand to using other longer conicals I’ll need to make that modification too.

« Last Edit: February 08, 2019, 02:51:34 PM by G Dog »
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Offline Omnivore

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Re: Frame opening for loading conicals NMA58
« Reply #4 on: February 08, 2019, 05:32:58 PM »
Here's a photo of a modified Pietta loading window.  The whole top side of the window has been opened up (as it comes from the factory, the bottom side already clears the cylinder's major diameter, so there's more than enough room there), but note the same location that G Dog circled on the Colt is also substantially ground away on this Pietta Remington.  For one of the newer conical molds I have, this window could be opened up even a bit more, from that location on up a little higher.  It all depends on the bullet style, length and nose shape (and what we will call the bullet's initial insertion depth, as controlled by heel length or tapered base profile) you're trying to accommodate.

This is one of the reasons why I've begun to prefer a generous length heel, or base taper; the deeper the initial insertion, the less clearance you tend to need at the loading window. 
« Last Edit: February 08, 2019, 05:49:10 PM by Omnivore »
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Offline mike116

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Re: Frame opening for loading conicals NMA58
« Reply #5 on: February 08, 2019, 07:12:52 PM »
Concerning the Johnston & Dow Bullets the problem on a Pietta NMA is not the height of the loading window.  The loading window accommodates the height of the bullet but is obstructed by the extra metal at the side of the loading window closest to the barrel. 
      

By the way,  the name is Johnston & Dow, not Johnson & Dow (notice the "t").

Offline scrubby

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Re: Frame opening for loading conicals NMA58
« Reply #6 on: February 08, 2019, 10:11:31 PM »
Hi all
Can someone, who has an original NMA58, measure the opening between the barrel, and cylinder for me. I have two NMA's and want to open that area up to accomidate loading conicals. I would like to know the lenght from high point in barrel, to the cylinder. I have the Lee, and Johnson,and Dow molds. I don't want to just start grinding.
Thanks   Rebel Dave
 {?(
I would also note the slight notching in the edge of the plunger, allowing a tiny bit more room for the tip on a conical to slip under. Just about .60" from cylinder face to edge of plunger on my NMA