Revolver throat reaming with drill press/mill

[MtGun44]

CONCEPT: Revolvers generally shoot the most accurately when the
throat diameter is about 0.001" greater than barrel groove (slugged)
diameter.

PROBLEM: My Ruger Blackhawk .45 LC/.45ACP had both cylinders
well undersized. Barrel groove diameter is .4515", ACP throat was .449"
and .45LC throat was .450". Ideal would be between .452" and .453".
Apparently this is a common problem with Ruger Blackhawks.

REAMER: Get from MSC at www.mscdirect.com. Go to page 170 of
their online catalog. US reamer in .452" was $36, foreign reamer is $26.
After the page loads change the 'quick search' type to "Big Book page #",
and put in 170 in the search box above to get the reamers in 0.001"
diameter increments. Buy 0.001" undersized and polish up to your desired
diameter.

SETUP: Machinist's vise with a V-block to hold cylinder vertical. Vise is
free to float on drill press/mill table. Drill press MUST be very accurately
square to table, check with dial indicator on arm mounted in the chuck, sweep
a circle (by hand!) to show constant reading for perpendicularity of quill to
table. Table and vise must be smooth steel, no burrs and lubricated to float
easily. Cylinder & vise will float to center reamer on existing throat, setup
holds parallelism, setup self centers. See pics. Hold vise by hand to absorb
the torque.

Ream slowly with lots of lube. Run a new reamer into a steel plate drilled
7/16" to smooth off cutting edges and get a true diameter. First ream will
NOT likely be true until sharpening burrs are worn off of a new reamer.
Run reamer at very slow speed, or turn by hand if no low speed is available.
Do not run at normal drilling speeds! You are only removing a few thousandths!
Never run reamer backwards even a short time will dull it.


FINISHING: Run 400 grit emery cloth in a split dowel in drill press to polish
the tool marks out. Pic greatly exaggerates the surface roughness from the
reamer, but shows smoothing from polishing with emery cloth. Measure
diameter and polish up to .4525" to .453" diameter. All dimensions for the
.45 LC/.45ACP with a .4515" groove diameter. See pics. One throat has been
polished the others just reamed. The reamed ones look rougher in the
photo than in real life, some digital effect.

NOTE: A machinist friend has recommended using a MSC adjustable lap
and lapping instead of reaming the throat to get a better finish. If you want to
try this, use the same setup but use the adjustable lap and 320 to 400 grit valve
grinding compound. I have NOT tried this but is sounds feasible and may well
produce a better surface finish. OTOH, most factory throat finishes are not
extremely smooth. Perhaps this would be better than factory work. Barrel lap
is on pg 892 of the MSC catalog and 7/16" expandable 15% is only $8.17 plus
shipping. I imagine 320 grit to cut and 400 or 600 grit to finish.

Hope this helps. I used a mill, but a decent drill press will work also if
the table is exactly perpendicular to the quill axis. This is very important.

Bill

[leftiye]

Great thread. especially for someone who like me who plans to ream a .41 mag out to get a proper (reads tight) chamber for his .44 mag S&W (can't ream out the mouths as they are already oversize on the .44 cylinder). I'm glad that you explained that the picture (lighting) exaggerated the reamer surface roughness! Reamers are generally used to obtain surface smoothness along with exact dimensions, and are pretty good at that point in the process as per roughness.

Or one could use your split dowel with sandpaper by hand to finish size the mouths (as long as only say one thou needs to be opened up). While you are at it use a sized (reads round) bullet of the proper diameter, and sand the throats to give a uniform push resistance fit , equally tight in all of the throats.

[MtGun44]

Thanks for the kind words, it worked well for me and I think
that most of the experimenters here have access to either a
mill or good drill press (own or friend's). Drill press must have
slop free quill bearings and be accurately adjusted to perpendicularity,
but will work fine as the loads are very low.

I'm a bit leary of using bullets as measuring tools but I suppose that
a push fit should be a way to see what the fit is like.

I worry that the lead will not make as good a gage as hardened
steel.

I bought a set of machinist's pin gages from Enco (get the minus tolerance)
for about $60, 250 gages in 0.001" steps from .251 to .500.
These are very useful for measuring holes, esp cylinder throats.
This is a lifetime tool investment and really useful for checking out
a revolver. For instance, I took the set to my gunshop and measured
the cylinders in my BH before I bought it, relaxed in the knowledge that
I could correct too tight throats pretty easily as opposed to too loose,
which I would have passed on. I also was able to find out why my
1917 S&W wouldn't shoot commercial .452 bullets worth a darn.
The throats were .454. Switch to .454 452423s and huge improvement.
I have trouble 'feeling' the fit with bullets, and do much better with
the steel pins. Others may have better skills and do fine with bullets
as gages.

Enco is at: www.use-enco.com and the set is part # 616-8131.

Bill

[Dale53]

Well done, MtGun44!

Rugers have the reputation for too small cylinder throats. I must be a lucky one. I had a 4 5/8 barrel Vaquero and now a Bisley Vaquero 5½" barrel (both in .45 Colt) that are dern near perfect. They both shot well.

In fact, I won a few silhouette and score matches with black powder with both of them. I, for one, would not hesitate to ream my cylinders if they needed it (and apparently, a lot of the early ones do).

As an aside, it flat amazes me that someone who obviously knows a lot about guns would have guns spec'ed out with undersize cylinders. Good Grief, Elmer Keith wrote about this problem in his first book written in 1936 (Sixgun Cartridges and Loads). Makes one wonder...

We can't let S&W off the hook, either. They have had their problems with incorrectly sized cylinders, also. I guess that is why tools are available to correct the factory errors...

Dale53

[MtGun44]

From what I see in my own new model (post lock) S&Ws (three)
they have the .44 throat diameters nailed. Two 629s are both
.430 and a 329 is .429+, just a few tenths short of taking the
.430 pin. All cylinders the same size. I hear (you re another one)
that the current Rugers are sized correctly too. A very experienced
part time S&W gunsmith (tool and die maker by trade) says that
the current S&Ws are the best they have ever made from a
tolerance and metallurgy standpoint.

I suspect that more of the knowledge that old timers have
known for years has slowly been seeping into the engineering
departments at the makers. Sites like this disseminate this info
far and wide and I believe raise the average level of knowledge
quite a bit. I read Keith's columns from the 60s on, but never
got his books until the 90s. Great that he wrote them and his
knowledge didn't die with him. I've learned a great deal on
this and other web sites, altho sometimes the signal to noise
ratio isn't too good. :) This site has by far one of the best
"knowledge factors" that I have seen, and I enjoy learning
from the real experts here, and am trying to give back a bit
when I have a bit of knowledge.

Another important issue is the low cost of carbide and ultra
hard coated cutting tools and CNC machines. Those of us that
play with precision machines are benefitting tremendously from
this dramatically improved manufacturing technology, so they
can hold the dimensions that they intend to more consistently,
and make shorter production runs affordable = more custom
models and cool variations at affordable prices. The King of
Siam has always been able to get what he wanted - but now
you and I can, too. Think Lee mold group buys ! :-D

Glad to hear your BH shoots good, I have an old SBH that has
a bit oversized throats (don't remember the size right now) and
I need to work out a big enough bullet for it. Haven't shot the
BH in the pix but about 2 groups yet, it's better -- but weather is
snowy and very cold and I fell on the ice and wrenched my
back yesterday, so it may be a while before I can report on
the results with a substantial number of groups. Watch out
for the ice if you are in the northern climes.

Bill

[Lee]

Quick question, and by no means an attempt to hijack the thread.
I've a Ruger 44Mag that besides damaging my hand every time I shoot it, won't shoot worth a darn, shots all over the place. Is THAT, can THAT be a symptom of undersize cylinder throat??
(Got the gun at an "excellent" price. Wonder that the previous owner couldn't make it shoot either?) If so, Ill have to check into that. Thanks.........Lee

[9.3X62AL]

Mtn Gun--

GREAT thread, sir.

I have a BisHawk in 45 that came with "choke boring" from the factory. I opened the throats manually, finish-polishing to .453" as you indicated. The revolver went from being a "one-booit wonder" to a castings-loving delight.

Who knows what the gunmakers are thinking at times? Often--we have to finish building the projects they start--and charge dearly for. Then, they thank us for finishing them by voiding their warrantee coverage. Ah, well......I think of most gun purchases as buying a "gun kit"--all the parts are there, but some assembly/finishing is required.

[MtGun44]

Lee --

Yes, too tight cyl throats is on the list of many things that could be causing this. Measure and see where they are as step 1. Use a bullet as a
gage if you don't have access to pin gages as mentioned above.

Could be too loose, too. Or wrong _______. Fill in blank with one of
25 other things.

Bill

[MtGun44]

Deputy Al,

It can be irritating, OTOH, what would us tinkerers do for fun? :-D

Makes me think of an article on setting up formula racecars for amateur
racing. Caroll Smith was a famous race car mechanic and he pointed out
something like "the only reason your racecar comes assembled from
the manufacturer is that that is the easiest way for them to know that
you got all of the pieces, not because it is put together right". Of course,
the myriad adjustments to a racecar suspension are a lot more than
on our guns, but sometimes makes you think like a bit like that.

Thanks for the kind words, sir.

Bill

[MT Gianni]

Quick question, and by no means an attempt to hijack the thread.
I've a Ruger 44Mag that besides damaging my hand every time I shoot it, won't shoot worth a darn, shots all over the place. Is THAT, can THAT be a symptom of undersize cylinder throat??
(Got the gun at an "excellent" price. Wonder that the previous owner couldn't make it shoot either?) If so, Ill have to check into that. Thanks.........Lee

Lee, make sure that the grip fits your hand. Ruger factory grips are the first thing I replace on a Blackhawk. If you have some jacketed bullets they should just slip through the cylinder holes. If not slug each one and go from there. Gianni.

[Bug]

altho sometimes the signal to noise
ratio isn't too good. :) " and "that is the easiest way for them to know that
you got all of the pieces, not because it is put together right

MtGun44:
Those two nuggets are absolutely worth the price of admission. Well Said!!!

[MtGun44]

Bug -

Thanks - I keep reading and learning on this site. Lots to
understand and I'm betting somebody here has either the
answer or a good hint at least for most of my questions.

Bill

[rvpilot76]

McMaster-Carr has the barrel lap in stock. AND it's cheaper than MSC. Since I need to open up the throats about .003", what grits would you recommend? I was thinking 320, 600, then 1000 grit?

4548A19
Expandable Through-Hole Brass Cylinder Lap for 7/16" Hole Diameter, 2-13/64" Barrel Length
In stock at $7.61 Each

For those with a printed catalog, page 2606.

There 'ya go fellas!

Kevin

[MtGun44]

I think you're well too far on the fine side. I'd say more like
240 or 320 to start and finish with 400, MAYBE as fine as 600,
but 600 will do essentially no material removal and 400 grit
is pretty well polished. You may be surprised how slowly
material is removed with 400 grit. I can't imagine using 1000
grit. I wet sand paint with 600, then 1200 before final buffing
and 1200 is REALLY, REALLY smooth and easy to bring up to
a mirror finish. Seems 1000 is much finer than you would ever
need for a cyl throat.

Now that I think a bit more on it, I am thinking in terms of
emery cloth on a spinning, relatively loosely fitted split dowel.
You may get more rapid results with the brass lap by adjusting
it to a relatively tight fit. What I'm thinking is that you may
get good cutting with 320 or even 400 grit due to the hard
surface and tighter fit of a lap compared to the emery strips
in a split dowel. Still doubt you'll need finer than 400 grit.

In any case, make sure your quill is square to the table, and
the cyl is also square, then let the machinist's vise float to
align with the lap. Work the lap in and out slowly.

Please report back your results this is a very interesting
project that will benefit many folks and pix do help.

Bill

[MtGun44]

Also - RVpilot76,

Is this like a Van Grunsven RV? If so, way cool. I have been
flying my Long EZ since '89 and have almost 1000 hrs on it now.

Bill

[rvpilot76]

The one and only! I fly with my friend Ken Miller. His RV6A has a Chevy 4.3 with a Belted PSRU driving the prop. Long-Ez eh? Burt Ruutan is one of my heroes. What are you running for an engine? 0-320? I am an aircaft mechanic here in Idaho. Here's where I work:

http://www.aerostaraircraft.com

I'm going to order the barrel lap today, and hopefully have the project completed by next weekend. I got delayed on picking up my Bisley, or I'd have it done this week. I'll post pictures on how everything turns out.

Kevin

[MtGun44]

I guess I can go way off topic on my own thread.

My Long EZ is totally stock. O-235-C2C 108 hp low compression, burn
mostly autogas (which used to be cheap!). Really fun airplane,
been to Sun-N-Fun many times, California for visits and vacations
three or four times, east coast and Fla many times for family and
friends visits. Great traveling machine. True 150 kts on 6.7 gph
or less at higher altitudes. I've never flown in or piloted an RV,
but have looked them over in detail at OSH and do really respect
VanGrunsven as an engineer and designer. Good looking birds -
kinda weird stuff that they're made out of tho.. . . . Some kinda
sheets of material pinned together with tiny pieces of the same
stuff and FAILED into position .. . . . Is this stuff safe?? :-D

I've got a C182, too, so I do understand tin airplanes. I have a
button which says "Friends don't let friends fly metal airplanes". [smilie=1:

Good luck with the lap, I would be very interested in how well it
works for you. Do a thread on it when you're done.

Bill

[MtGun44]

RVPilot76,

Looks like a nice place to work. I'd imagine that those are some
cool birds to work on, but in my experience with my brother's
Baron - the packaging on a twin is pretty tight every where.
Should be nice work, but I bet you have a few special tools
for access in tight place. We all have stories. . . .

Bill

[lar45]

You might want to put an empty case in the cylinder before you start running the lap. That way if the lap goes in too far as it's run in and out keeping the cutting even, then it won't accidentally give you a wide spot in the middle of the chamber.
Just something to think about.

[rvpilot76]

RVPilot76,

Looks like a nice place to work. I'd imagine that those are some
cool birds to work on, but in my experience with my brother's
Baron - the packaging on a twin is pretty tight every where.
Should be nice work, but I bet you have a few special tools
for access in tight place. We all have stories. . . .

Bill
About the only really tight place to work on them are in the turbocharger area, and the combustion heater if there is air conditioning installed. Other than those two places, they're great to work on. The bladder tanks and the bleed air shutoff valves from the turbine engines on the Twin Commanders were usually good for a few choice words. We are getting ready to mount Pratt & Whitney high bypass turbofan 615's on our jet project aircraft. Removing the recip engine and prop, and mounting the 615 directly under where they went. It'll look like a mini 737 when it's all said and done. Pretty cool.

Kevin