cylinder throats / under sized

[Luke Duke]

Bought a New 629-6. Cylinder throats measure .425 according to my Starret Calipers. Seems on the small side. Thinking .429 to .430 is more like it. Can't push a .429 bullet through the throat. Has anybody reamed a cylinder? Should it go back to S&W? Other than that this gun is awesome tight.
Any thoughts on this?

 

[armorer951]

Some addn forum info here:

http://smith-wessonforum.com/s-w-re...el-29-mountain-gun.html?629073=#post140902152

 

[series guy]

Shoot it. I bet you will find it very accurate. I sure wouldn’t be reaming a new gun without using pin gauges to get an exact measurement. I have found that smaller throats improve accuracy.

 

[Luke Duke]

New 629-6

Found my cast bullets started to lead up quick. Had to clean after 18 rounds. There all sized to .430. Jacketed bullets seem to shoot real good. Seemed to be a bit of copper fouling though. Tried a different caliper. Was getting more like.4275 to .428

 

[Protocall_Design]

You really want the throats to be bore size to .001 over. You want the bullet to go from larger to smaller. If the bullet gets sized down going through the throats, it won't be tightly controlled in the barrel. Same thing if the bullet gets sized down by a choke point just ahead of the forcing cone.

 

[StrawHat]

Calipers are not good for directly measuring round holes. To get an accurate measurement, drive an oversized bullet through each chamber (6 bullets) and then use your calipers. Or, get a set of pin gauges.

Kevin

 

[venomballistics]

Found my cast bullets started to lead up quick. Had to clean after 18 rounds. There all sized to .430. Jacketed bullets seem to shoot real good. Seemed to be a bit of copper fouling though. Tried a different caliper. Was getting more like.4275 to .428

calipers aren't great for this kind of measurement. you could slug the throats and mic the slug.
However, something I've found that worked is the pig pen powder coating method.
boil the lube off your cast bullets then hit em with some brake parts cleaner.
Mix up a slurry of powder coating powder with some acetone.
Shake the cleaned bullets in this slurry, let dry then bake them at 400 degrees in any toaster oven you might find at Goodwill.
Repeat the shake and bake till your happy with the coverage.
They dont have to be pretty ... just covered.
Load, pack and fire.
If you really like these results, Horrible fright has a cheap powder coating gun that'll make coating bullets a snap and you wont have to butcher your gun

 

[Protocall_Design]

Making a gun to the correct specs does not constitute butchering. They don't all come perfect from the factory.

 

[series guy]

Bullets will still obturate (expand) to fill the rifling even if the throat is smaller than the barrel. There is a lot of pressure behind that bullet.

 

[venomballistics]

Making a gun to the correct specs does not constitute butchering. They don't all come perfect from the factory.

true, but any such work by the wrong hands certainly can be.
An underlying theme in this thread is the classic cast lead merry go round.
Guy buys some cast bullets, lead lines the bore and ends up someplace like right here asking why.
He's told to size and lube correctly ..... useless, because he does not have the means to do either since he bought them.
next hes told to slug the bore .... this might confirm the issue, but not solve it, because its outside his wheelhouse....

We're at the slug the throats portion of the ride, and I'll wager size and lube is still outside his wheelhouse .... but shake and bake isn't.

 

[venomballistics]

Bullets will still obturate (expand) to fill the rifling even if the throat is smaller than the barrel. There is a lot of pressure behind that bullet.

yes ... eventually they will. but till they do, they are making a contribution from the forcing cone right on up to that point where it rectifies itself.

 

[Luke Duke]

I've been casting for years and never had leading problems. I'm considering sizing down to throat size and getting a gas check design. Been doing with the 358156 for years. I'm just kind of a cheap guy and if I can cast a bullet why would I buy jacketed. Now days if you find gas checks there getting expensive. I've shot the RCBS 250Gr for years in my Rugers and never scrubbed Lead. Rugers always had generous throats though.

 

[Luke Duke]

Calipers are not good for directly measuring round holes. To get an accurate measurement, drive an oversized bullet through each chamber (6 bullets) and then use your calipers. Or, get a set of pin gauges.

Kevin

that's a good idea. may have to fire up the furnace

 

[steelslaver]

If you have some soft lead cast some bullets from it or go to a gun store and get some 45 caliber muzzle loader balls. Take you cylinder out and remove rod and ejector star. Set the cylinder on a piece of hardwood, throats up and tap a soft bullet through each throat and measure. Use an under size flat faced punch for the last bit so you do not strike the cylinder face with the hammer. I had a new 44 mag cylinder with under sized throats. You can rent a throat reamer from 4DREAMER Rental Cylinder Throater Archives - 4D Reamer Rentals.
It comes with 7 pilots ranging from .4275 to 4300 to keep you centered and straight

I am assuming you know how to take cylinder apart correctly without messing it up. If you keep the reamer clean and well oiled only turn it clock wise with very light pressure you will not mess the job up. It just isn't that hard.

On the other hand if Venomballistics is right and you don't know much. Leave it to others.

 

[Luke Duke]

yes, I do and I'm a mechanic. 38.00 bucks isn't a bad price to rent the tools either.

 

[BLUEDOT37]

My 396NG had .428" throats & I bought a Manson Reamer throater with the removable pilot pack because not all of the factory throats were just one size.

A pin gage set can be invaluable.

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