Slugged my barrels, now have more questions


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AK Eggy
April 4, 2010, 03:27 AM
So I'm going to try casting some bullets. We decided to start with .44 mag and melted down some wheel weights and cast some ingots. We're getting ready to cast some bullets and decided maybe we should slug the barrels of the different guns. Of 5 guns, all were the same (.428)...except for one which measured .424. I slugged it twice and measured the slugs several times with the same result. Even had someone else measure the slugs and he got the same measurements.

According to what I'm reading I should size to +.001" over the measured diameter (for a starting point). No biggie as I see there are sizer dies available to accomplish that. But now I have questions about what are the effects of a "tight" bullet in the bore? I've been shooting .429 bullets through this gun for as long as I've owned it (jacketed bullets).

So...What happens if the bullet is that much larger (.005") than the measured inner diameter of the barrel? Is it hard on the barrel? How does it affect the quality of the shot?

Seems like the more I learn, the less I know :banghead:

Thanks for any ideas you can share.

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Sport45
April 4, 2010, 04:54 AM
You will have higher pressure behind the bullets in the smaller bore but I don't imagine it will hurt the barrel. It will just deform the base a bit more because extra material is being displaced. This will have an effect on accuracy, but if you shoot like me you won't notice it. ;)

Did you slug the cylinder throats as well? If they are less than bore size (not likely with you're .424 bore gun) you may get leading. In any case, I'd size the bullets so they're a snug fit in the throats without regard to bore diameter. If the throats are too small they can be reamed to barrel diameter or just over.

Myke_Hart
April 4, 2010, 05:20 AM
Whats the model on the one with a tight bore?

Robert Palermo /Penn Bullets
April 4, 2010, 06:19 AM
Did you use a caliper or a micrometer to get those measurements? A caliper will not give you exact measurements and can be off by a few thousanths of an inch.

You do need to slug the cylinder throats and size to those dimensions. those measurements should also be done with a micrometer.

NuJudge
April 4, 2010, 08:01 AM
For a revolver, the cylinder throat diameter is important, the barrel groove diameter is important, and you want the cylinder thoat diameter to be maybe a shade larger than the barrel groove diameter.

For a revolver, if the cylinder throat is smaller than the barrel groove diameter it will not shoot Lead bullets well, and you're stuck with jacketed. It will also probably Lead like mad.

Before you go any further, check your caliper or micrometer against a known quantity to make sure of its accuracy. The cheap electronic vernier calipers are usually off by .002" in my experience.

There are other things that might cause inaccuracy with Lead bullets in revolvers. In my experience, the threading on the outside of many barrels causes a slight constriction on the inside of the bore. For accuracy, if there is to be a constriction on the bore, it is best that it be at the muzzle end, not at the rear. I have a Ruger Speed Six .357 revolver that appears to have this, and bad, and it will not shoot Lead worth a hoot, except for gas checked bullets. This kind of problem can be lapped out.

For best accuracy, Lead bullets shoot best without sizing. I will typically use a mold which produces a bullet of the diameter I need, and a die in my Lubricator/sizer that is .001" larger than what the bullet is. Bullet diameter will vary with the Lead alloy composition you use, and learning to deal with this comes with time. I like to cast all my bullets hard, and drop them from the mold into water, mostly for material handling reasons, but it does make Lead-Tin-Antimony bullets even harder. My smaller diameter bullets "ring" when you drop one. I like gas check designs, mostly because they are more forgiving of any of the problem situations mentioned here, but they increase costs about 3 cents a bullet. I like NRA lube because it always works, even if it smokes a bit, but the Lee Liquid Alox works also.

See some of the comments here:
http://castboolits.gunloads.com/showthread.php?t=21598

. . . and yes, the more you learn, the more questions you will have.

CDD

fecmech
April 4, 2010, 12:33 PM
As others have said throat size is the most important consideration with revolvers and as long as the barrel groove size is smaller than the throat you should be ok. With .428 grooves I'd be surprised if your throats are smaller. My Ruger Super Blackhawk has .434 throats and .429 groove. With close to max magnum loads it doesn't lead and is very accurate with wheel wt bullets sized .430 but those same bullets loaded light to about 800 fps will lead badly and are not accurate. To get rid of the leading in the light loads I have to cast larger and size to .434 which also gives slightly better accuracy with the mag loads.

Steve Marshall
April 5, 2010, 09:28 AM
I'd be very curious as to the make of the barrel that slugged .424". Is it possible that you have an odd number of grooves? If so, you'd need a special micrometer to measure the diameter. It's also possible that the grooves are atad deeper and your lead slug didn't upset properly. Did the groove impression come out sharp and clear? I've heard of groove diameters being larger than spec. but never that small.

Remo-99
April 5, 2010, 12:18 PM
So...What happens if the bullet is that much larger (.005") than the measured inner diameter of the barrel? Is it hard on the barrel? How does it affect the quality of the shot?

Lead is soft, so it will swag down several thousands no problem, pressures will be a little higher, so unless these are max pressure loads for 44mag then no problem, and if the cylinder throats are larger than the barrel groove diameter is also good for accuracy.
Lead bullets that have to squeeze down a few thou. in the barrel tend to shoot better than those that are sized to match a barrel diameter. imo.

918v
April 5, 2010, 12:40 PM
Reference the .424" figure, it could be you have a constriction where the barrel meets the frame and that is causing your slug to come out .005" smaller. This constriction will hurt accuracy and needs to be removed either by lapping or Taylor Throating.

243winxb
April 5, 2010, 01:03 PM
Standard bullet diameter is .430" for cast. Do a test run with the tight barreled .424" gun, see how accuracy is, or if it leads first. I would only worry about pressure if your loading a maximum load of WW296

AK Eggy
April 5, 2010, 01:50 PM
The tight barrel is a S&W Alaskan Backpacker (model 329 I think). Steve was right...only 5 grooves on that barrel and the others had 6. It looks to me as though the slugs bottomed in the groove though, the edges were nice and sharp anf you can see on the high point of the slug that it displace material as well. Don't know why I didn't think to look at that earlier :o.

SO.....Is there a way to measure or calculate the diameter of the slug with an ordinary caliper or micrometer? Without sounding too ignorant, what's the special micrometer you mentioned Steve?

The caliper I was using is a dial caliper and I like it alot better than an expensive digital one I have. It's much more consistent. I haven't checked it against a standard though, so I guess I should do just that.

As far as the sizing die. I was thinking just the opposite. I was thinking bullets that were only cast and lubed wouldn't be as consistent as those run through a sizer die that was smaller than the cast dimension of the bullet. What's the reason for those not run through the sizer die shooting better than those that were? Not arguing, just trying to learn.

I went to order the Lyman casting manual but noticed that the 4th addition is supposed to be out shortly, so decided I would wait for that. Most of my questions would probaly be answered there, but I truly appreciate the help you guys offer.

Thanks for everone's help, and if there's more please chime in if you would.

fecmech
April 5, 2010, 05:27 PM
SO.....Is there a way to measure or calculate the diameter of the slug with an ordinary caliper or micrometer? Without sounding too ignorant, what's the special micrometer you mentioned Steve?


Yes there is. One way is gently close the calipers on the slug and then gently rotate the slug and it will open the caliper to the high point which will be very close to groove size(you will be just catching the two edges of the rifling). Another way is to use some thin shim stock .002-.004 and wrap the slug with the stock and subtract 2X the thickness of the shim stock used. If you do it gently the first method works just fine. As I said in the previous post the groove is not all that important as long as it is smaller than the throats and you size to the throats.

As far as the sizing die. I was thinking just the opposite. I was thinking bullets that were only cast and lubed wouldn't be as consistent as those run through a sizer die that was smaller than the cast dimension of the bullet. What's the reason for those not run through the sizer die shooting better than those that were? Not arguing, just trying to learn.

A general rule is the less sizing the better but that is not always hard and fast.

Steve Marshall
April 6, 2010, 07:32 AM
It's called a V-micrometer. They come in 60 and 120 degree versions. With the 120 degree version, you'd get reasonably close. Ideally, you'd need 144 degrees. 360/5 =72 degrees times two for the two anvils, = 144 degrees. Simple.... not. Anything flexible enough to wrap a bullet with, is flexible enough to sink between the "flutes" of the bullet. That's what V-mics are used for, primarily. Measuring tools with non-standard number of flutes. What happens when you try to measure something like this with typical
parallel anvils, is you hit one flute top-dead center but the other anvil snuggles between two flutes. Therefore the small reading. For my money, I'd accept that S&W gave you close to a .429" barrel, or, if you really need to know, you could send it to me or another inspector and have it measured. I'm certain that some old-timer has a trick or two on how to measure this that I'm not aware of. I'd also wager that many many slugged bullets were measured improperly.

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