Best way to measure slug

[texas tenring]

I just picked up an Enfield No. 4 Mk I with a five groove barrel. The first thing I did was clean and slug the barrel, got out my mike and calipers and went to measuring. Only problem is at 180 degrees of a groove is a land on my slug, best I can do is estimate the exact groove diameter unless someone can enlighten me.:???:

[AkMike]

I spin the slug and take the higest measurement given. I's not exact but pretty close. To be absolutely correct takes a special micrometer that I don't have and I'm not going to buy!

[texas tenring]

I spin the slug and take the higest measurement given. I's not exact but pretty close. To be absolutely correct takes a special micrometer that I don't have and I'm not going to buy!

Yeah thats what I did and best guess is about .310 groove dia. but I want to know the bore dia. also.

Like AkMike, the only equipment I have to measure with is a micrometer and a dial caliper. I was hoping there was some trick I have'nt thought of.

[KCSO]

For bore diameters I use a plug gauge set or a hole gauge. I never thought about doing it any other way. I'll have to give this some thought.

[Phil]

Really the groove size is not what you want to measure for fitting a lead bullet. Measure the throat diameter. It is certain to be bigger than the grooves and thats what the bullet has to fit anyhow.

Cheers,

Phil

[texas tenring]

Really the groove size is not what you want to measure for fitting a lead bullet. Measure the throat diameter. It is certain to be bigger than the grooves and thats what the bullet has to fit anyhow.

Cheers,

Phil

I agree the throat dia. is the most important measurement but I want to know the bore dia. also. I think the nose dia. of the cast boolit should be a fit to the bore for the best accuarcy in my limited experience?

I get the impression there is no way to easily measure a five groove barrel.:(

[Phil]

Hi Texas,
Aha! Now I see what you want to do. I do it the simple way, just stuff the nose of the bullet I want to shoot into the muzzle and if I can't get it much more than started I know thats what I want. To correct a too small nose I made a die that holds the bullet body snugly. The die is shorter than the bullet and a series of washers is placed on top of the die with a bullet in it. Then the whole mess is set in a small arbor press and the ram depressed until it hits the washers. Measure the nose and adjust washer stack as needed to expand the nose to the size you want.

To measure a barrel with odd numbers of grooves you need a micrometer with two anvils (triangular spacing with the spindle). Or, slug the barrel. Then place a bullet (I use a jacketed bullet) of known diameter in a machinists X block. Measure from the top of the block to the bullet with a depth micrometer. Then measure your slug. The difference in measurements between your standard and cast bullet is the diameter of the grooves. Some guys wrap a piece of feeler gauge (.003 or .004, around there) half way around their slug and measure that, then subtract twice the thickness of the feeler gauge. I've never tried that since I have micrometers and X blocks to do it with.

I have measured a LOT of 303 British barrels and they seem to run from .314 to .318, the average barrel being more on the order of .315 or so. I've never seen one as tight as .310, the smallest I've ever seen is .312 and that was on a Ross.

Hope this helps,

Phil

[NVcurmudgeon]

Cast Bullet Association members can send slugs to a gentleman who is frequently mentioned in The Fouling shot. He has all the special mikes, knows what he is doing, and is a very literate, courteous gentleman. He does ask that "customers"
send a stamped, self-addressed envelope for his reply. I have sent him a number of five groove, and even one seven groove slug. Slugs are not returned.

[Ricochet]

I think wrapping something around it, measuring and subtracting twice the thickness is much easier than setting up that V-block contraption.

[BudRow]

If you have access to a set of Small Hole Gauges which is a "Clam Shell" arrangement that is opened by a wedge as you screw the adjustment knob, then try this. Take a cleaned inside neck of 30-06 or 308 case and expand it in very small increments using a very gradual tapered expander mandrel. I use a Case Spinner mandrel I bought from Midway many years ago. Now keep trying the slug in the neck till it just passes through. At this point adjust the Small Hole Gauge till it just passes through and then mic the gauge. This will give you an accurate read of the GROOVE dia.
Best Wishes, Bud

[texas tenring]

I tried the wrap around meathod using a .006 brass feeler gauge and pinched good and tight with needlenose pliers. The slug measured .322 and then subtract .012 that gives .310. Of course the tightest spot is at the muzzle.

This does seem like a tight groove diameter from everything I've heard about these rifles. This rifle is a 1943 No. 4 Mk I made at the Maltby plant with a near perfect bore. Also I inserted a 312-185 Lee cast boolit into the muzzle and the .302 nose of that boolit went in with just a little resistance.

So I would say that this rifle slugs .310X.302 unless I goofed somehow?

[Ricochet]

Sounds right to me.

[Phil]

Ok, I just slugged a five groove barrel for grins. Checked it with a 120 degree anvil micrometer. Groove diameter is .312. Then I checked it in a machinists X block. Measured .312. Next I wrapped the slug half way round with some .004 shim stock. Measured .315, so I subtracted .008 for two thicknesses of shim stock and I get .307. Two things are happening, the shim stock will not follow the major diameter of the slug, it wants to flatten at the lands (you can see it if the light is right) and/or the micrometer spindle is collapsing the shim stock slightly. At any rate, you WILL get a false reading with the shim stock. Then I slugged a DCRA six groove barrel (303 Brit cal) and it measured .316. Checked a Parker Hale prototype Envoy barrel (five groove) and it was .314. I'll stick with my methods.

Cheers all, finally getting some warmer weather and the snow is melting!

Phil

[montana_charlie]

I'm no mathematician, so I don't know (without thinking it over) how you would handle the numbers, but...

Measure the slug (from land to groove) and record it, then run the slug through a sizing die that you know well.
Measure again and compare the results.

There must be a way to make the two measurements tell you something useful...
CM

[Scrounger]

I'm no mathematician, so I don't know (without thinking it over) how you would handle the numbers, but...

Measure the slug (from land to groove) and record it, then run the slug through a sizing die that you know well.
Measure again and compare the results.

There must be a way to make the two measurements tell you something useful...
CM

CarpetMan tells me he just wraps a string around the bullet and measures the string agains the free ruler the paint store gave him.

[fourarmed]

Phil, would you take a look at your description of the X block (is that like a V block?) measurement again. I don't understand. Do you mean that the difference in the measurements is the DIFFERENCE in diameters of the two bullets?

[Larry Gibson]

Phil is correct that you want the bullet to fit or be larger than the throat. Fitting to the throat is better for accuracy than fitting to groove depth. I agree with Phil that if you pinch the shim stock too tightly you can get a false reading. I use .003" steel shim stock between 3/8 and 1/2" wide. I do not pinch it tightly and get pretty reliable reading when compared with a 120 degree two anvil micrometer.

As I don't have access to the micrometer anymore I also would like Phil to describe the "machinist's X block" if he'd be so kind.

Larry Gibson

[wills]

CarpetMan tells me he just wraps a string around the bullet and measures the string agains the free ruler the paint store gave him.
Seems like that would give the circumnavigation distance. Shouldn't there be Pie involved there somewhere?

[mozark]

The 5/16" gauge hole in a standard Fractional Drill Gauge, while marked a nominal .312, almost always measures .315, which is perfect for measuring 5 groove .303 Brit. bore slugs. Measure the hole, and try the slug in it. IME most .303 barrels measure .314/.315 Groove diameter. The specifications, if memory serves, are .303 bore and .005 to .0055 lands, which translates to .313/.314, but they seem to run a bit larger. I have a couple at .316.

MM

[Scrounger]

Seems like that would give the circumnavigation distance. Shouldn't there be Pie involved there somewhere?

Pi if you're using it in geometry. Only add the 'e' if you're going to eat it...

[IcerUSA]

Could try it with the calipers, measure across the slug at the center and then measure the land higth with the depth gage end of the caliper and subtract it from the center diameter. Just a thought.


Keith

[Phil]

Crap, I had this all typed and hit heaven only knows what key, and it all went away. I hate it when that happens.

Anyhow, good evening Gentlemen. Sorry to be so long in answering but I'm building up a rifle and have been spending lots of evenings getting that finished. Also drew up a blueprint and am having the shop wire me a tool to convert 32 Long cases to 7.65 French Long in one shot.

So, to end the confusion, I must apologize for using incorrect terminology. It is, of course, a machinists V block. To be exact, a Starrett #268 V block. This block sits on a shelf above my work bench end on, and over the years I guess I have been looking at that X form and gradually began thinking of it as an X block. Here is how I do it.

Find the side of the V that will allow you to put two grooves of the slug in question against the sides of the V and give the greatest contact area. Remember what side you used.

Next, mike a jacketed bullet. I use a thirty caliber bullet for checking 30/31 caliber slugs. Place the jacketed bullet in the chosen V and measure from the top of the V to the top of the bullet with a depth micrometer. Record the reading on the micrometer.

Then place your slug in the V and measure it with the depth micrometer. Record that reading.

Calculate the difference between the readings and add that difference to the diameter of your jacketed bullet reading and you have the groove diameter of the barrel you slugged. For instance, the jacketed bullet I use for reference gives me a reading of .127 from the top of the bullet to the top of the V. Then I put my slug in the V and measure it. I get a reading of .124. The difference between the readings is then .003. Thus, .308+.003=.311, which is the groove diameter of that particular barrel. In this case a brand new Win M1917 barrel in my barrel rack. Remember to subtract if dealing with bullets smaller than your reference bullet.

All this took much longer to write than it takes to measure a half dozen slugs. It really is simple.

I hope this makes sense to you. If anyone has more questions just give me a shout.

Cheers,

Phil

[AkMike]

So after all this work with the proper tooling is your measurement radically different that measuring the slug by laying the calipers on the table and twirling it to get the largest measurement? Not trying to be a smart azzz just wondering.
Thanks

[Phil]

YES!

Cheers,

Phil

[AkMike]

Ok, How much difference?

[fourarmed]

OK, I worked this out last night. If the diameter of the jacketed bullet is d, and that of the bullet to be measured is D, the angle of the V-block is A, and the difference in depth measurements is X, then

D = [2/{1+1/sin(A/2)}]*X + d.

If the angle of the V-block is 90 degrees, this becomes

D = [2/(1+root 2)]*X + d,

or approximately

D = .828*X + d.

This assumes D>d. Otherwise, subtract the .828*X.

Obviously, the closer X is to zero, the less the effect of the correction.