Need advise from those experienced in fire lapping out a S&W bbl constriction

[Pistolero]

That should be "advice"......sorry, I do know the difference.

OK a friend has a really nice looking, new to him S&W 29. Does not shoot accurately, and
he is a "known good" pistol shooter, I have shot with him for decades.

Bbl stops a bore size gauge pin at the frame thread constriction, as expected. Tried to pull the
bbl - HOLY COW,even with proper frame wrench and heat had to give up for fear of damaging the
frame. So, it looks like fire lapping will have to be used, not what I prefer, and have never done it
on a revolver for thread choke. I pull the bbls turn the shoulder a hair and reset with red
loctite. Works great.....and all previous guns have let loose of the barrel with no major fight.

In any case, throats are already big (.432) so want to make sure not to open them up farther.

Here is my battle plan. Use commercial hard cast bullets, and Midway lapping kit, which I
have used in a couple of rifles, roll some coarse onto about a dozen bullets, load with
maybe 4 gr of Unique. I do NOT want them to slug up in the throats to leave them alone,
and since they are .429 the will cut only the restriction. Plan to fire 6 then regauge, the
more as needed, finish up with about 5 in fine grit.

The biggest question is how many shots have you guys found it to take to clean up a
thread constriction?

Any experience that shows a better way, I would like to hear.

I don't think I want soft bullets, will slug up and gut throats. Wonder if jbullets
might be good, although it seems like very little abrasive will be in each
bullet, leading to far more shots, but not sure.

After the restriction is removed, loading .431 or .432 cast should get good groups.

Bill

 

[Brad]

Here is my suggestion.
Use a soft bullet and very, very light charges. The bullet should leave the barrel and not much more. Always fire into a berm or something to ensure bullets don't stick in the bore.
Why a soft bullet? It doesn't spring back. We want to remove a constriction and nothing more. Bullet goes thru constriction, laps some of it, but barely touches bore rest of way down , or jacketed, will spring back some and lap the bore all the way down the barrel. Using soft bullets gives more lapping at breech, less at muzzle. A slight taper to bore like that is a good thing.

Using a hard .429 bullet will give you a .429 breech but what does the rest of the barrel measure?

I like a throats sized bullet cast soft and driven by a small charge of fast burning powder. This is a place where Trailboss is good. Easy to ignite and good at giving really low velocities. Think 650-700 fps.

Figure on lots of cleaning. Fire six, clean well, and check progress. Look at the muzzle for matching marks. When they are just starting to get touched you are good to go. Clean the chambers after every six shots. Don't need the grit causing issues. I like to use fired, unsized cases. Add a little flare and seat with a flat ended 7/8-14 bolt. Why get grit in your seating die?

I use Clover brand silicon carbide in grease. 320 grit works well. 240 grit for Ruger stainless guns as that stuff if tough.

Plan on 12-36 rounds most likely. My Ruger GP100 and SRH each took well over 50 with the first 36 being 240 grit. Both were done with unsized soft bullets.

Use a couple steel plate to embed the grit in the bullets. Use some pressure to get the grit into the drive bands.

That is pretty well how I do it. Rifle or handgun it is pretty much the same.

 

[Ian]

It will probably take fewer shots than you expect. I do six at a time, clean a d measure. Stupid question, but the barrel isn't pinned, is it?

 

[Ian]

+1 Brad. Embed soft bullets by rolling between two steel plates coated in vg compound. Smiffs are generally tight in the groove dimension anyway, so .429" is probably about right, at least to start.

 

[Pistolero]

Pinned does nothing at all preventing a S&W barrel from initial rotation if you have
pulled one. It doesn't work like you think, it sits in a big, precut groove, need
to turn bbl about 1/16-1/8 turn to hit the pin. S&W "pinned barrels" is really
a bit of a farce. Perhaps at some ancient time they were drilled after snugging
and held the barrel locked, but in the last 40 yrs or so, probably more, they
are pretty much cosmetic, will keep the barrel from falling out, but
not from turning enough to totally mess up sight alignment. I was quite
disappointed in what I saw when I watch my friend pull a pinned bbl. He
laughed, and said "Surprising, huh?" Convenience in assembly trumps
better retention. This is why the overtorque them in the first place, to keep
them from unscrewing, and because they won't take the time to fit them
properly any more.

I had always "assumed" that they drilled the hole to put the pin in after
the bbl was screwed in. Nope, hole drilled when frame made, top of
bbl slotted about 3/32 wide at top, flat cut straight across, screw in bbl,
drive in pin.

No pin, anyway.

OK, will switch to soft bullets, sounds good. Will load a dozen 240 grit, shoot
6, clean and measure, repeat as required. Blued gun, shouldn't be nearly as
difficult as a SS gun, I would think.

So, no trailboss, how about 2 or 3 gr unique? Worry it may not exit. Don't want
fast powder to slug them up to throats.

I have the Midway kit, has the steel plates, grit, etc. Have some swaged Hornady
.44 bullets, perfect for this.

 

[Brad]

I would use BE. With low enough charges slugging up won't happen. We are talking 3 -r gr of BE in a mag case. No crimp either.
I used unsized or throats sized bullets. Want to smooth the entire bore, not just the tops of the lands. Minimum use a bore size bullets.
Drill a small hole in a large sort bullet. Stick a small nail in the hole. Glue the head to the bullet. Use a rod with a hole that can slick over the nail to drive into the muzzle. Use the nail to pull bullet back out. Measure. You now slugged the muzzle with no chance of bore constriction giving a false reading!

 

[Brad]

I pretty much follow the instructions in the Beartooth Bullet guide. I have had very good results us far. Make lapped many rounds evolves and a few lever guns too.

 

[Pistolero]

Bore is .429. Will use .429, OK will try a pinch of TG, got a LOT more than
BE, pretty similar powders, functionally.

Thanks for the info, guys.

Bill

 

[JSH]

http://gunblast.com/FerminGarza-Firelapping.htm

Contact Fermin if you need too. He is a busy guy but will get back to you. https://fermincgarza.com
Jeff

 

[Hawk]

I've firelapped all my revolvers. Used Veral Smiths method and lapping compound.
If you don't have his book, you should get it.
It improved accuracy on all my guns.
And yes, the stainless steel guns were a booger to do. Amazed at how hard the stainless steel is!

 

[Brad]

Just read what Fermin Garza had to say and I agree with him entirely. I particularly like his comments on unsized brass and deep seating bullets.

 

[358156 hp]

Brad has pretty well nailed the subject down, and I'll only add a couple of points. Of course the bore must be absolutely clean before lapping, and inspect the bore between shots because I've seen slug loads lead bores slightly under some circumstances. I use three different grits of lapping compound for my lapping, 220 grit for coarse, 320 grit for medium, and 400 grit for fine, using soft slugs. Smiths steel never seems to be as abrasion resistant as Rugers (my primary lapping target), and I start out with six lapping shots with medium grit, cleaning out the bore with a solvent patch, followed by two dry patches. I do this primarily to keep the amount of residual compound in the bore to an absolute minimum. Otherwise shot #2 could potentially remove more metal than shot #1, and so on. I would view this as being more important with blued barrels than stainless ones.

After the first six, slug the barrel to see what sort of progress is being made. If you're already close to your dimensional goal, try six shots the same way using a finer compound to polish the bore a bit, using the same technique, then slug it again & inspect your results. Repeat as necessary, and don't be too concerned about the cylinder throats, they "lap" at a rate of 1 to 6 compared to the barrel, and with the low round cound I suspect the M29 will need, it's unlikely the throats will change much, if at all. It's pretty unlikely that a S&W blued barrel would require much, if any coarse lapping compound unless it's really messed up! Be glad it's not a stainless Ruger, their stainless barrels are tough! And I'm putting off lapping my stainless Redhawk for just this reason. I once lapped a Super Redhawk that....

 

[Rick]

Does Brad have any thread choke on his 624 44 spl?

 

[Brad]

Haven't checked as I haven't found any reason to suspect it is there. Once I found the right size bullet I haven't had a speck of leading and accuracy is good.

Why look for a problem you don't have reason to suspect exists?

 

[Rick]

Why look for a problem you don't have reason to suspect exists?

Because I did. That bore was fire lapped.

 

[Pistolero]

Thanks, everyone. Jeff - excellent link, thanks!

Bill

 

[Brad]

Can you do a before and after accuracy comparison Bill? Would be interesting to see the changes.

 

[Pistolero]

I'll have to borrow the gun, which should be possible. I have a lack of cases fired in it and
the best way to get them is to do some before groups. Maybe the best way is to have him
meet me at the range and shoot about around 8 six shot groups which will get us 48 cases
fired in that gun.

Probably better to have the owner shoot the gun, he is a very good shot, younger eyes than
mine.

Bill

 

[Ian]

BE and TG are quite different, actually. I would use BE if I had any, or Longshot.

I also use a tuft of Dacron under the bullet to mop the bore and prevent gas cutting.

 

[Pistolero]

Hmm. IME, BE and TG, in the .45 ACP, with similar bore diam and bullet weights to what
we are talking about create essentially identical velocities for identical charge weights.

Perhaps it may perform differently in smaller calibers, or very light bullet weights, but
please explain your point more.

Bill