Super Blackhawk woes-Parte Deux, eh

[BCRider]

Greetings from the Great White North. Well.. more like the Great Wet North. In my area we've only had a couple of inches of snow so far this winter. Lots of rain though.

Some time back I posted my tale of woe with my Ruger Super Blackhawk that had three small chamber throats and three normal throats.

Well I got that fixed a while back and loaded up some reduced power lead bullet loads to check for accuracy. Rested shooting still didn't show the sort of accuracy that so many here write about. Like 4 inches or so at 20 yards at my club's indoor range.

So just tonight I slugged the bore to check things out. A .490 round ball was hammed down the muzzle with a block of 2x4 and an aluminium cleaning rod used to bump it the rest of the way down the bore. The slug was pretty consistently a snug push fit the entire trip down the barrel until it got to the area where it's threaded into the frame. THEN it got quite tight and needed a few good palm thumps to get it by.

Re-engaging the slug in the muzzle and pushing it in still showed a lot of drag to passing down the majority of the bore. Not quite as much as the first time, but close. Again I needed a couple of good palm thumps to get the slug to pass through the area bounded by the threading in the frame.

So it would appear that the bore is a little snug as it passes through the frame. Could this be the reason why I'm not seeing the sort of accuracy that I am able to get with my other revolvers? And the sort of accuracy that so many here are getting?

The fact that the slug was stil snug going down the bore the second and third time suggests that the part at the threading isn't much smaller. I'm thinking that I may set up a threaded rod and make up a few slugs like this that are drilled down the center and use them as lapping tools to open up the area bounded by the frame and perhaps a little ways up the bore so the overall bore is SLIGHTLY tapered to a smaller size as it reaches the muzzle.

Thoughts on this idea?

 

[Coal Dragger]

Fire lap it.

 

[hardluk1]

Let ruger fix it again on there dime.

 

[rcmodel]

Your plan to lead lap the tight spot is sound.

Fire lapping it isn't, because that will lap the whole bore, not just the tight spot that needs lapping.

And probably sending it to Ruger from Canada would be a major PITA???

rc

 

[buck460XVR]

I've never had the best of luck regarding accuracy with low power loads. My best accuracy generally comes once I get to the middle of a load recipe and above for a specific powder/bullet combo. I've also found that some guns just don't like a specific bullet or load. I would shoot the gun with some other loads, even jacketed factory loads to see if there is any improvement in accuracy before I do anything more drastic.

 

[CraigC]

Taylor throating or a new barrel are typically the fix for this but neither is something you can do at home and I don't know if you'll find any good revolversmiths in Canada or not. Lapping may be your only option and I agree that the threaded shank is the only area that should be lapped.

 

[murf]

i don't think your accuracy problem is a bore restriction. i don't know what your new throat diameters are, but your slow lead bullets are probably not expanding to fill those throats. try a full power load through the gun before you go to all the trouble of "fixing" the problem.

i vote for taylor throating, if you have the money and a knowledgeable gunsmith and lead lapping if you don't (i'd ask rcmodel for detailed instructions and advise if choosing the latter).

all ruger single-action pistols have crush-fit barrels. many of these guns are very accurate out-of-the-box. i only mess with taking the restriction out if there is a barrel leading issue.

good luck with your project.

murf

 

[highlander 5]

I've fire lapped several Ruger SA and DA revolvers with good results. The man who is most knowledgeable on this topic is Veral Smith of LBT. What the problem with revolves to day is that the barrel is a "crush" fit as opposed to the old way of securing a barrel by pinning it. My first attempt at fire lapping was a Ruger Bisley in 45 Colt,the area in front of the forcing cone was .450" and the rest of the bore was quite rough. Using LBT's bore lap kit per instructions the bore on the Bisley is .451 and smooth as a baby bottom. Took about a hundred rounds to smooth out the bore but it was worth it. Mr Smith has the fire lap kit down to a science.

 

[BCRider]

Yep, being in Canada makes sending anything back to the Ruger parent factory a non starter. I'm stuck with the Canadian rep, my own local gunsmith or my own efforts.

Buck, on shooting the gun with less than full power loads I had the same thought as you originally. So I checked the Ruger information on the .44Mag vs .44Spl barrel twist rate. Seems that Ruger uses the same twist rate for both. And more than likely the same barrels off the same machines. So I don't see why I should not be able to shoot reduced power loads and get decent results.

Chamber thoats might be an issue that I can't do anything about. My last hiccup with this gun that had it's own thread last fall found me with three throats at .432 and three at around .423. Since my own shop is still being reno'd I had my local smith open up the undersize throats so they all match at .432. I know that this still seems rather open for shooting .429 to .430 size bullets but I figured better all the same than three at an ideal .430 to .431 and three that are a little more open. At least at .432 I know that the bullets aren't being swaged down before entering the forcing cone....

Oh, the slug I pushed through the bore measures the groove diameter at .428 to a hair over at around .4285'ish depending on which lands I measure the slug.

Murf, I did try full power jacketed loads with it last summer. Results at the time where less than stellar which was likely due mostly to the three sub size chamber throats. Since matching the thoats up at least it's shooting what could be fairly called a group. It's just that the group size is significantly more open than my other revolvers.

Given that all the information I've seen points to the best accuracy coming from tapered bores where the muzzle is the tightest spot I have to think that having a tight area at the threaded fit is likely part of the lack of optimum accuracy that I'm seeing with this gun. It's bad enough that at this point if I can't fix it to shoot as well as my S&W's then it'll be up for sale.

The fire lapping looks highly interesting. And I've got a mold and some dead soft lead that I was going to use for round ball casting which would be perfect for making a few bullets to use for both hand lapping and for fire lapping.

I'm thinking that I'll likely hand lap the tight spot to first clear the obstruction. The greater degree of control I'd have with a hand lap seems like the safer alternative. Once the tight spot is relieved and a slug passes down the bore with consistent drag I'll choose between fire forming and hand lapping to produce a slightly tapered bore and finish polish.

Likely all this will need to be put on hold for a few months until my shop renos are done and the machine shop is fully back up and running. And at that point I've got this slick idea for a rig that will allow me to hold a complete revolver frame in my lathe to allow me to cut precision muzzle crowns....

 

[CraigC]

Unless your bullets are too hard or too soft, there's no reason why reduced loads shouldn't be accurate. My custom flat-top .44Spl doesn't care if it's shooting sedate factory loads or the 1200fps Keith load.

 

[BCRider]

Craig, you mean based on the twist rate or despite the apparent bore tight point?

If you mean based on the twist rate I agree. Since Ruger has a good reputation for shooting well with the same barrel twist rate on their .44Spl models I SHOULD be able to get good results with my SBH running at what is roughly the top end of the .44Spl range or slightly into the +P sort of territory.

I'm not sure what the hardness is on the cast bullets. I'm using commercially cast bullets from a local outfit. They aren't dead soft but they are known for doing well which the guns that they are intended to be used in. I've been trying various loads using 200gn RNFP and 240gn RNFP with various powders and loadings over the 900 to 1000 fps range.

 

[murf]

bcrider,

the accuracy issue may be a bad crown.

lapping out a .001" barrel restriction is going to take a lot of work. as per highlander5, fire lapping will probably take between 75 and 100 bullets down the barrel to remove the restriction (i have done three blackhawks this way). i don't know how much work is involved doing the lapping by hand.

it is still worth the effort, imop.

murf

p.s. running a .430" diameter bullet through a .432" diameter bore may not be good for accuracy.

p.p.s. also check your forcing cone. the one on my 44spl blackhawk was almost nonexistent (i just stick a bullet in there and see if it is the same as my "accurate" blackhawks).

 

[BCRider]

Murf, the .432 is the chamber throat size. Not the bore. The slugging showed the groove diameter as .428 to maybe .4285 depending on where i measured the slug.

I did notice that the forcing cone is rather minimalist on my SBH compared to my S&W's and even my Pietta SAA clones. So you may be onto something in that regard. The major diameter of the forcing cone is just barely bigger than the groove diameter.

So it looks like I've got a few things to do to "blueprint" this SBH;

• Slightly open up and re-angle the forcing cone to a longer angle and slightly larger mouth.
• Lap out the restriction at the crush threading area.
• Cut an accurate muzzle crown.

None of these is un-doable for me. I've got a long history of machine work hobby time behind me. And I've already come up with ideas for tooling to make that will do the forcing cone and muzzle crown accurately.

But this project will need to be put on hold for a few months while I finish off my retirement shop renos. The wood working/model airplane/firearms/reloading area in the basement is almost done. Then I need to unpack my life from storage in the garage and finish off the machine shop in there. So it'll be mid summer or a little later before I can look at this work.

Guess the SBH will remain a safe queen until then. As it shoots now I'm just not interested in taking it out.

 

[CraigC]

If we were talking about rifles with the unbelievably slow 1-38" twist, it may be an issue but the 1-20" twist Ruger uses is not a problem for any load that makes it past the muzzle.