Oversize Redhawk Throats and Bore Restriction

[tacotime]

This 1987 blue Redhawk leads up the bore near the cone terribly using a .431 hard cast and 9.5gr UN or 18gr 2400 (in less than 6 shots). 
 
Later found it has a terrible rough forcing cone and throats that are .4325 using pin gauges and an obvious tight spot at the frame while slugging (but surprising to me, slugged at .4295).  The bore will pass a .4175 pin but the .418 hangs up about 1/2 in. into the muzzle.  I can't access the breech with the pin. I plan to fire lapp this weekend. 
 
My question is, do you think I will end up needing a .432 bullet or a .433 bullet for these throats, or what size? I do not cast.

What is the most bullet size over the bore size do we consider safe and allowable?
 
Thanks.

[Veral]

  In revolvers always fill the throats, no matter how much oversize compared to the barrel.

  Regarding the rough forcing cone.  Ignore it if you are lapping, as the lap will smooth the part where bullets will hit.  Throats are already too large in diameter and deep in modern revolvers, so slicking it up with the popular 11 deg reamer will make matters worse.

  The above applies for using hard bullets.  If one is using soft bullets which expand with the loads being used, a rough forcing cone can cause such a wad and drag that the barrel can be split.  Poor quality lube makes the matter worse.

  When you purchase bullets request at least 16 bhn and harder is better, though I've found that few commercial casters sell bullets with a hardness over 16 , regardless of what they claim.   I've learned this from testing hardness of many sample bullets sent in by customers over the years.

  If your leading problem doesn't go away after lapping the barrel and getting bullets which fit the throats, insist on gas checked bullets and if you can, find a caster, insist on LBT bullet lubricant.
  Montana Bullet Works is the only commercial caster that I'm aware of who is using LBT bullet lube, though I do know there are a few smaller producers who are but I can't remember their names.  I don't think anyone selling bullets would lie about what lube they use, so trust them, at least until you see if your leading problems go away. 

[tacotime]

Thanks for the guidance!  Hopefully the larger bullets and lapping will put this Redhawk in order.  It was impossible to shoot with cast bullets.  Six shots and then 15 minutes to clean it. Pretty disappointing to say the least.
 
Any suggestion for a proper lapping load for 44 mag?
 
I've got a few .432 and .433 to try.  Once I see what works, I will order some that fit and look for LBT lube.
 
I enjoyed the post on coffee, interesting...

Just noticed the LBT address.  We were up by Moyie last Summer and really enjoyed ID (1st trip) and will be coming back.
 
Thanks again.

[Veral]

  I was finally able to answer your other post a few minutes ago.  The one worrying about the bore getting oversize and ruining jacketed accuracy.

  Always.      Make the cylinder throats a little bigger than groove diameter of the barrel
                    Make the bullets a close fit to the cylinder throats.
  Always.

  Oversize cast do not change chamber pressure enough to be dectected by a realoader, but undersize bullets always make them well aware of poor accuracy and leading.

  If one has the ability, which means in fact custome swage dies, reswaging factory jacketed handgun or rifle bullets to fit an oversize barrel will produce incredible accuracy.

  I wrote a very detailed two part artical for Rifle magazine back in the 80's on this very subject, giveing solid irrefuitable proof, and explaination of why.  That artical went into Rifles first printing which contained a handgun artical, and because it was so large the editor broke it down for two different months.

[tacotime]

Exactly what I needed to know - I will be back at work on the Redhawk this weekend.  Thanks!

[Veral]

  Not knowing what rifling depth is, makes groove diameter a mistery,  which we can't afford to live with for the final fitting.  Bullet diameter must fill the cylinder throats closely and be larger than barrel groove diameter of optimum accuracy.
 
  So, once you barrel is lapped and you are content that it is straight, slug the barrel with a soft slug, and try inserting it into the cylinder throats.  It must drop in freely.
 
Order bullets to suit throat diameter.  I believe Montana Bullet Works will probably supply a suitable size,  and they use LBT lube.

  The big problems with purchasing cast bulletss from major suppliers  are as follows.
 1.  Few use what I would call a good bullet lube, and most use just a colored wax which is abominable.   Their bullets will not do well if whatever they put on for lube doesn't stay between bullet and barrel when the pressure is on.
 2.  Most of the designs are built to drop into any gun, which leaves them too week for good cast bulet performance.
 3.  Quality is generally very poor compared to hands on hand casting and inspection.
 4.  Bullet diameter is slightly over jacketed bullet size, which makes bullets way undersize for most revolvers.
5. Bullet hardness is fixed with whatever alloy the make uses, and non that I've checked hardness on in the last 15 years or so came up to what was promised.  Not that a high hardness really matters because the bulk of commercial  cast bullet shooters do not want to shoot at high velocity/pressure, and for that use , with all the above factors included, bullets MUST be soft enough to swell up and seal off gas blowby or they will not  give satisfactory performance.

  Which leaves a bad taste in many peopls mouth regarding cast bullet performance.    It did me for many years until I learned what the problems with cast were.

  So to get the best performance possible with inexpensive /high volume commercial cast bullets, try playing with powder charges till you wring the best possible accuracy you can from them.  That will be far inferior  from most revolvers, to a good design well fitted to the gun with quality lube, but at least you'll be able to make your gun bang affordably.

  A trick that helps commercial casst perform, is to smear the thinest film of LBT bue soft lube on with a finger, just before loading.  If lube quality can fix them this will do it, even though it is just a thin film.

[tacotime]

Veral, I just got back to this thread late and saw your post.  Thanks for the word.  I've just about got the choke out of this barrel and am going to try some .433 bullets with the throats very close to .433.  Thanks for your lapping compound which seems much more effective than the one I had before I saw yours.
 
And to combat the oversized cylinders, I happened onto a replacement cylinder with .431 throats and if I can get it fit, I may be set with the .4295 bore.
 
I'll post results, but it may take me a while...
 
Thanks again.
 

[facetious]

How many rounds did it take to lap out the choke and did it help smooth the forcing cone?

[tacotime]

148 rounds.  Way more than the 24 to 30 I expected.  I think the compound on the first 96 was not very effective.  Maybe the grease was too thick, giving too much lube.  Progress increased with Veral's compound. It is thinner and looks to have more grit.  The cone now appears pretty smooth to the naked eye, but I have not looked at it magnified yet.

[Veral]

  I formulate the compound which I sell myself, with an extreemly high concentration of abrasivie so it gets the job done fast as possible without undue throat wear.