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Author Topic: Problem slugging the bore.  (Read 829 times)

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Offline Dusty Miller

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Problem slugging the bore.
« on: November 27, 2004, 08:08:30 PM »
I slugged the bore on my 629 today and much to my dismay there appears to be an odd number of groves and therefore I've got a raised part on one side and a flat spot on the other.  WHAT TO DO?
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Offline Cat Whisperer

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Problem slugging the bore.
« Reply #1 on: November 28, 2004, 02:53:44 AM »
That's good news and bad news.  
The good news is that odd number of grooves is a better barrel.

The bad news is that it will take some calculations and special equipment to do the measurement.

A vee-block of the correct angle is needed.  The angle is matched to the number of lands and grooves.  Then one uses a height gauge and does some calculations.

How many lands/grooves?
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Offline Duffy

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Problem slugging the bore.
« Reply #2 on: November 28, 2004, 01:18:51 PM »
Typical S&W 5 land, you can fudge a bit and just catch the edges of the lands while measuring. Kinda of a pain but will get you in the BP.
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Offline Dusty Miller

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Problem slugging the bore.
« Reply #3 on: November 29, 2004, 10:42:43 AM »
I did fudge and came up with .428  and I'm thinking that's bogus.
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Offline Trapper-Jack

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Problem slugging the bore.
« Reply #4 on: November 29, 2004, 02:11:59 PM »
Cat Whisperer,
Quote
The good news is that odd number of grooves is a better barrel.


Just out of curiosity, why does a barrel with an odd number of grooves make a better barrel?
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Offline Cat Whisperer

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Problem slugging the bore.
« Reply #5 on: November 29, 2004, 02:21:45 PM »
The groove being cut or pressed by the button is located by the opposite land, not the opposite groove.  Even numbered grooves/lands tend to wander more, odd number grooves/lands tend to be straighter.
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Tim K                 www.GBOCANNONS.COM
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Offline Lead pot

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Problem slugging the bore.
« Reply #6 on: November 29, 2004, 03:44:51 PM »
Dusty you need a special V anvil micrometer.
Kurt
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Offline Cat Whisperer

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Problem slugging the bore.
« Reply #7 on: November 29, 2004, 04:34:55 PM »
Or a vee-block of 90 degrees for 4 groove rifling (and a height gauge).
Or a vee-block of 120 degrees for 3 groove rifling...
Or a vee-block of 72 degrees for 5 groove rifling...

But if you really want to get fancy, a CMM will do them all.

(coordinate measuring machine)
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Tim K                 www.GBOCANNONS.COM
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Offline Duffy

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Problem slugging the bore.
« Reply #8 on: November 29, 2004, 05:02:16 PM »
You may not be that far off if there's a bit of thread crush in the frame.  Try slugging again and pay attention when the slug goes by the frame area. Two bit's says it get's tighter there. I oil the bore to make things slide a bit better too.
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Offline Trapper-Jack

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Problem slugging the bore.
« Reply #9 on: November 29, 2004, 07:10:35 PM »
Cat Whisperer
Thanks for the explanation.  I never thought about it before, but it makes sence.  Just goes to show that if youre not careful, you can learn something new every day.
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Offline J.Solo

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Problem slugging the bore.
« Reply #10 on: December 22, 2004, 09:25:31 PM »
Speaking of thread to frame crush.... I tried slugging my .357 S&W Model 686 and .44 Special S&W Model 696 and the slugs were smaller in Dia. than the measurements I took at the bores with a set of Taper Feeler Depth Gages.

I borrowed some Gage Pins from work and the pins that slipped easly into the bore and down the barrel got hung up when trying to pass the barrel thread to frame fit. The slugs were becoming smaller as they passed through the barrel to frame areas of the bores.

I'm debating now if I should Fire Lap the bores or just try to work the thread/frame crush areas with J&B Bore Past to remove the tightness.

J.Solo
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Offline kenjuudo

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Problem slugging the bore.
« Reply #11 on: December 22, 2004, 11:41:17 PM »
J. Solo; I've found JB paste to be rather slow going in either type of lapping. Something in the 300 grit range gets the job done a little quicker, then finish off with the JB, Simicrome or whatever.
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Offline haroldclark

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Firelapping a S&W
« Reply #12 on: December 23, 2004, 06:23:02 AM »
I have a 686 and 624 S&W 6" barrels.  Both were severely crushed at the frame.  JB Bore paste can be used for toothpaste without much if any damage to the enamel on your teeth compared to what is needed for this job.

I have varying coarseness grades of valve grinding compound and I started with coarse, then fine and then LBTs lapping compound.  I thought I was going to set the dry weeds on fire with the sparks flying out of both guns.  However, I was at a point that I didn't have anything to lose with either gun.  They wouldn't shoot to my satisfaction anyway.

I sized the bullets to bore diameter at the muzzle and let um rip.  I have two of the finest shooting revolvers now.  I ran a total of 100 rounds through each gun.  I don't recall how many of each, but I used less of the coarse than the others.  The LBJ Fire Lapping compound will not wear as quickly as the carborendum valve compound and therefore, it polishes the barrel to the end of a 6".

Harold Clark
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Offline Duffy

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Problem slugging the bore.
« Reply #13 on: December 23, 2004, 07:58:07 PM »
My brother has a M15 S&W target 38 that had a .002 crush at the thread. It shot pretty good as it was but after about 125 lap bullets it smoothed out the crush and it's a real tack driver now. You have to remember that once the lap bullet goes through the "tight section" is is sized down so it doesnt really touch the larger section of bbl. Thus the entire bbl is straightend evenly.
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Offline Haywire Haywood

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Problem slugging the bore.
« Reply #14 on: December 24, 2004, 03:51:07 AM »
If you have a tight spot in the middle of the barrel, say where they stamped the labeling into a rifle barrel,  a lap bullet would be lapping everything till it got to the tight spot, then it would get squeezed there.  Wouldn't you end up with a tapered bore up to the former tight area?

I have a bottle of LBT's lapping compound on my loading bench but haven't gotten around to using it yet.  I was going to lap my 357 Max Handi barrel.

Ian
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Offline Dusty Miller

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Problem slugging the bore.
« Reply #15 on: December 24, 2004, 07:33:05 AM »
Hey, great information guys.  I appreciate the input.
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Offline Duffy

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Problem slugging the bore.
« Reply #16 on: December 24, 2004, 02:52:17 PM »
Ian,
Yes to some extent, but it's better to have a bore that tapers from the chamber to muzzle(ie.bigger at chamber end) than the other way around. I have noticed tight spots under some stampings too but they are usually very slight and don't have too much effect. Only thing I don't like is the fact that it rounds off the lands at the throat but it doesn't seem to have hurt the guns I've done.
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