.41 mag - leading riddle????

[kevmc]

Now that I have my 3 SW629's (.44's) and my 3 SW.357's ( all revolver's) shooting well with cast and NO leading, I'm working with my SW 657 PC (.41mag hunter). Getting poor accuracy & some leading starting at (not in) FC and into the first couple inches of the bbl.

Here are the clues:
1. Using same alloy ( WW & 2% tin) and lube ( BAC or CR) in all, .44's, .357's and .41.
2. Unique used in all loads for around 1050 fps.
3. Bore slugs at .4085-.409 (that SW 5 groove thing), measured with a micrometer.
4. Cyl throats are uniform at .410 (measured by a Starrett small hole gage/ mic.), .410 jhp's (measured just under .410) soft push thru....bore slug falls thru or slight nudge, MP 258's (220K) sized to .410 (slightly +) cannot be pushed thru by hand.
5. boolit started into FC extends back well into cyl..
6. Shoots jhp's well......1" at 25 yds.....cast into 4" @ 25 yds. This using all 6 chambers.
7. Doesn't appear to be any thread crush...leading starts at front of FC and forward.

Anyone want to play as I work this out???

[OuchHot!]

I am getting old and senile and maybe not getting what you are saying. If there were thread crush, I would expect the leading to show right where you are finding it. Maybe run a cerosafe cast of the area fc and forward for an inch and mike that. Again, I may not be understanding....

[Doc_Stihl]

Did you clean the copper out REALLY well before going to cast? That's the only thing I can think of.

[kevmc]

Just checked for thread crush again....only the slightest more resistance when bore slug reaches frame.....slug thru the whole barrel measures maybe .0003 smaller than slug not run thru frame area.
I agree that leading position suggests crush........

"Did you clean the copper out REALLY well before going to cast? That's the only thing I can think of. "
Just now cleaned well with chore boy brush and #9, then, tight patch wrapped brush with Beartooth 320 lapping for 250 strokes with emphasis on frame area....

Out to shoot in 1/2 hr or so.......back then with results....

[OuchHot!]

Just seems to me that your alloy is adequate for the velocity and sizing seems on. Are the boolits skidding when they get to the rifling? Can you tell at the start of leading which side of the land (leading or trailing) you see the leading?

[geargnasher]

The leading position does suggest thread choke, but .0003" isn't going to cause a problem in my experience, at least. Unique and WW+2% tin ought to work and resist skid, you got me buffaloed.

Gear

[runfiverun]

I dunno that 408-9 barrel measurement sounds like a tight spot to me.
a small one perhaps, but small is all it takes.

[kevmc]

7.5 gr Unique, just now tried CR & BAC
4.5" patterns @ 25yds...scope/bench and too much leading to shoot well

Leading seems to be some on the leading edge of lands...also on top of lands.....

[kevmc]

Pulled boolits show they are NOT being sized down during seating/crimping....

[Guesser]

I suffered the same problem with S&W stainless revolvers; not 41, but 357. I tried everything from sizing to loob and loobing to varying alloys. I simply could not get that Model 66 or the model 65 to quit grabbing lead. Both guns did it with 38 Special and 357 magnum loads. I had a Ruger Security Six stainless and a stainless Python as well as a stainless Taurus. All loads worked well in all the stainless guns except the two S&W, after 2 years of aggravation I gave up and both of the Smiffs went to market. Is there some variation in S&W stainless alloy that causes this??

[Larry Gibson]

"MP 258's (220K)"

Could we get a picture of those bullets and the exact weight fully dressed?

Larry Gibson

[kevmc]

"Is there some variation in S&W stainless alloy that causes this?? "

No, My 3 629's (Stainless .44 mag) and my 686 (SS .357) shoot cast well with no leading

[kevmc]

"MP 258's (220K)"

Could we get a picture of those bullets and the exact weight fully dressed?

Larry Gibson

Sorry I wasn't more clear on the boolit....
Mihec's Group buy .41 - 258 ( copy of the HG #258)
Mine weigh 222 grs.
http://i1096.photobucket.com/albums/g337/Onty50/41H-GNo258CORR.jpg

[osteodoc08]

Larry. It's a copy of Keith's H&G design. I have that same mould and mine all weigh in at 222-223gr. I've used it for countless pounds of lead down range and never had issues.

[Piedmont]

If the revolver is new, maybe it just needs to be fired a while, cleaning all the lead out between sessions. I wouldn't venture into fire lapping until I had shot it for a while and problem just wasn't getting any better.

You could implement some JB bore cleaner after doing your regular cleaning for a polishing effect.

[kevmc]

In checking the chambers, they appear to be cut a little long.
This boolit has a .100" forward band, and it's still .055" short of reaching the throats.....???
An unsized boolit (.413) seated to 1.750 just touches throats and lets case rim seat to cyl. face. At this length, the boolit protrudes .015" out front of cyl.
Seated in the crimp groove, OAL is 1.695". So boolit has to jump .055" to get to the throats.
Rounds laying in the chamber short of the throats cannot help but be somewhat misaligned, then jump .055" to throats.....still round???..
.410 boolit to .409 bore, not centered in chamber......not much room for error......

I also have a RCBS 41-210 SWC mold, tomorrow I'll cast some to try. These have a shorter nose (.325 compared to the #258's .410). I may have to seat long to get the forward band into the throats......something to try.

[kevmc]

If the revolver is new, maybe it just needs to be fired a while, cleaning all the lead out between sessions. I wouldn't venture into fire lapping until I had shot it for a while and problem just wasn't getting any better.

You could implement some JB bore cleaner after doing your regular cleaning for a polishing effect.

I bought it many years ago......plenty of rounds thru it....mostly j-words, some cast.

[bruce381]

my 29 had about same problem. When I pushed a few SWC's through from firing pin side they shaved a little lead from the throats.

I polished the throats with?? 300 grit paper on a dowl in a drill press. And reduced the boolit size from .431 to .430 and leading is gone.

I guess if boolit is too soft it cannot make the jump sometimes from the thoats without sending some drbris into the forccing cone which build and then goes down the barrel.

Or not

[cbrick]

Here are the clues:

4. Cyl throats are uniform at .410 (measured by a Starrett small hole gage/ mic.), .410 jhp's (measured just under .410) soft push thru....bore slug falls thru or slight nudge, MP 258's (220K) sized to .410 (slightly +) cannot be pushed thru by hand.

leading starts at front of FC and forward.


In checking the chambers, they appear to be cut a little long.
This boolit has a .100" forward band, and it's still .055" short of reaching the throats.....???
An unsized boolit (.413) seated to 1.750 just touches throats and lets case rim seat to cyl. face. At this length, the boolit protrudes .015" out front of cyl.
Seated in the crimp groove, OAL is 1.695". So boolit has to jump .055" to get to the throats.
Rounds laying in the chamber short of the throats cannot help but be somewhat misaligned, then jump .055" to throats.....still round???..
.410 boolit to .409 bore, not centered in chamber......not much room for error......

I also have a RCBS 41-210 SWC mold, tomorrow I'll cast some to try. These have a shorter nose (.325 compared to the #258's .410). I may have to seat long to get the forward band into the throats......something to try.

You have answered your own question!

When the front driving band is not inside the throat when the round is chambered the entire cartridge lays in the chamber at a downward angle. Your boolits sized do not fit through the throats to begin with and then the downward angle of the cartridge has the edge of the front driving band striking the edge of the throat. It is then forced up into the throat at an angle shearing lead on it's way. The boolit travels through the throats at this angle and enters the forcing cone at this angle and then travels the bore at this angle. The result is a non-concentric boolit and poor accuracy. The leading is from the front driving band striking the edge of the troats.

Two choices, a shorter nose boolit seated out further as you suggested OR 414 Super Mag brass trimmed to fit the chambers in your revolver.

If it were my revolver I would do a chamber cast to determine the max brass length that will fit the revolver. Trim 414 brass to this length and the entire front driving band will be inside the throats, then size the boolits to A MILD SNUG FIT IN THE THROATS.

Rick

[kevmc]

The RCBS 41-210 SWC mold I have does have a shorter nose, but also the forward band is only .055". For this band to just reach the throats in THIS revolver, I'd have to seat the bullet .100" longer than if crimped in the crimp groove......maybe crimping in the lube groove!!! LOL!!!
For this idea to work I'd need a different boolit than the RCBS....any boolit with a forward band extending .200" (WIDE!) forward of the crimp groove would still only have .050" into the throat. Might be better off trading guns.....

414 brass is an interesting idea..........
I do like the idea of a chamber cast to verify my measurements/thoughts, will do so shortly.

[kevmc]

Chamber cast results.....have pics, but computer crashes when trying to upload...???
First I put a fired-unsized case into chamber, then poured a cerrosafe "boolit".
Measured throat at .4105, locked mic at this setting and turned the boolit with the case to throat taper lightly against mic. edge.
This made a nice light ring at start of throat.
case mouth to that ring measured .155" ....as expected....not going to get a forward band into the throat with .41 mag cases....

Interestingly, I did the same with a SW 629 and a SW 586.....same thing!!!
The 586 (.357) measured .115" from case mouth to start of the throat.
The 629 (.44) measured .170 from case mouth to start of the throat.
This might explain why I get better groups from my SW .44's and SW .357's with either a RNFP or a 429640 style (.44) as opposed to a SWC.

Leading???
The .357's have a .357 bore and are fed .359 sized boolits, leading when fed .357's none now at .359.
The .44's have a .429 bore and are fed .431 sized boolits, some leading issues at first, untill I opened the throats from .4280-.4295 to .431.
The .41?...4085-.4090 bore (SW 5 groove, it's in there somewhere) and .410 throats...tighter tolerance of just .001".
I don't have a 411640/412640 mold, but I'd bet sized to .411 with .411 throats it would shoot right.

[fourarmed]

If you have access to pin gauges, find the largest one that will enter the muzzle, and drop it down the barrel. If it hangs up at the frame threads, you have a choke problem.

[OuchHot!]

I have had revolver issues that started out similar as you describe. J types shot fine to great but various leading with boolits early in the bore. I have to agree with Rick. I have a couple of revolvers that cannot take keith configuration swc because I cannot get enough of the front ring into the cylinder throat. There are some "ogival wadcutters" an other designs that let you do what Rick says.....get the boolit into intimate alignment with the cylinder throat. Otherwise, you can be starting the boolit into the throat at an angle and the monkeys get loose. Nothing else jumps out at me. I have two j frames in 38sp and 32 (HnR "mag") that leaded like a bugger with all the right sizes and alloys an such. Now with designs that gently seat into the throat they are both very accurate.