How to tell if bullet size is matched correctly to throat?

[chutestrate]

I just read a couple of posts on sizing the throat. I have a Ruger SRH which will stop a J slug when I drop it through. It requires a gentle push with a rod to go all the way through the cylinder. Is this the correct diameter I should size for?


TIA!!!

[Larry Gibson]

Many consider that just fine. However, in my experience the so called "perfect fit" for a tapered throat (most Ruger revolvers have tapered throats) dictates the front driving band of the cast bullet be a snug slip fit in the throat right in front of the chamber (the largest diameter of the tapered throat) when the loaded round is chambered. Thus the bullet is larger than the smallest diameter of the throat at the front end of the cylinder. Truth be known you probably could tell by shooting any difference between a cast bullet sized as such or if it was sized for the slip fit through the cylinder as you have.

Larry Gibson

[DougGuy]

Yup, Larry nailed it. It should go in the front of the cylinder with a slight drag fit. The perfect drag fit will be pushing the boolit into the front of the cylinder, slowly turning it vertical and the boolit stay in the cylinder throat until you shake it and it should drop free. That is about .0005" clearance. If it falls out easily, it's closer to .001" clearance which is still acceptable.

If you have a j word sized .451" and it's that tight, you would not want to size cast any larger than .451" but how even are your cylinder throats? Does the j word hang more in one or two than it does in the rest? Are one or two holes a loose fit that let the j word drop through easily? If they are all pretty even I would size to fit the cylinder. If they are uneven, I would hone the tight ones until they all have about the same amount of drag fit as the largest one, and size to fit that.

[gray wolf]

OK, first let me say I am not trying to disrupt this thread,
but I am finding some conflicting thought about this.
Here we have said that on the tapered throat rugers a snug fit into the throat with the front drive band is a good thing. There is another thread going about this and the OP is getting beet up for having to use a slight thumb pressure to seat his bullets, cause being that he is seating long and the front drive band is snugged up into the throat. He wants to do this so the bullet is better aligned with the barrel and does not slump in the chamber.
The complaint from the members is that the throat will get all clogged up after a few rounds and will have to be cleaned to often in order to seat bullets. Hope I explained that right.
Can we have clarification please.

[Larry Gibson]

OP should shoot the bullets he has and let his Ruger answer the question. Anything else said is speculation.

Larry Gibson

[Cherokee]

The proof is in the shooting performance.

[rodsvet]

I would slug the bore and match the throats to the bore. I'm no gunsmith but every revolver that I own has been done this way and they all outshoot me. Rod

[DeadWoodDan]

Not meaning to add or confuse to the OP question, but i too am attempting to get better accuracy and no leading in my revolvers. When we refer to "tapered throats" I am assuming each cylinder throat? I was not aware of this....shooting Ruger BH's in .357 and .41

I purchased a pin gage set in .001" increments so i have a fairly good idea what each cylinder measures within this tolerance. Next I am going to slug the barrel and compare to the smallest cyl. throat. and hope i don't have to ream anything. Of course i did watch(read?) that i could attempt to open up a cyl. with emmery cloth and drill? Ideally i want my cyl. throats to be .001-.002" bigger than the slugged barrel?

I just fired 25rds through the .41magnum and leaded up the barrel pretty good using Unique, not a full load either.

thanks for the direction

DWD

[DougGuy]

Best case scenario, the dimensions should be decreasing throughout the path the boolit will take, kinda like a funnel. Boolit should be .001" to .002" larger than bore diameter, cylinder throat diameter should be .0005" to .001" larger than boolit diameter. This will ensure the boolit is being swaged down in size as it enters the bore so it will have a good seal in the bore, and nothing between the case mouth and the muzzle is under-dimensioned causing the boolit to be undersized as it enters the bore, as this will cause leading, and a fairly noticeable loss of accuracy.

The bore should be checked for consistency as well, and all too often the threaded portion of the barrel where it screws into the frame winds up being slightly smaller in diameter than the bore, because of thread crush as the barrel is tightened in the frame. This will undersize the boolit as it is fired, again causing leading and a loss of accuracy.

The harder the alloy used, the more apparent and noticeable any tight cylinder throats or thread constriction will be. This is because the harder alloy boolit has no choice to be swaged down on firing, and forced through the tight spot by burning powder gas, and the alloy is too hard to obturate and seal the bore once it is in the bore. Softer alloys and J word boolits will go through a tight spot and then swage back up to seal the bore, -IF- there is sufficient gas pressure behind them.

This is why a badly dimensioned cylinder or a constricted barrel will still shoot "good enough" to make muster and pass range tests at the factory with no problems. The factory builds a gun that will function safely and reliably with SAAMI spec'd ammunition, tight dimensions will go totally unnoticed under these test conditions. It's only when we as shooters get one in our hands and start feeding it hard cast handloads that any problems become noticeable, like leading and poor groups.

If you have a cylinder with undersized throats, don't match the boolit to the throats, match the throats to the boolits you want to shoot. Problem fixed.

[oldfart1956]

Excellent post Doug. Audie...the Oldfart..

[chutestrate]

All of this has been most helpful. Thank you