Slugging a 5 Groove barrel??

[MikeSSS]

Today I got some bullet shaped fish sinkers made for worms. They had various lengths I went with the short ones. The base is almost made to fit a 1/4" steel rod.

I slugged the .303 No4 MK1. Agghhh, 5 grooves and lands. So when the dial caliper is on the land on one side of the slug it is on the groove on the other side. Great. I tried caliper sideways and length ways on the slug and got the same maximum reading both ways.

The biggest measurement is .311 or .3115, there are lots of measurements smaller than that. The smallest measurement is .308, I get that a lot.

The rifling looks deep when looking down the barrel but not nearly as deep on the slug.

I'm guessing that the groove diameter is more like .314 and the bore diameter about .305.

Any ideas on how to read a 5 groove slug?

Thanks,

Mike S

[NVcurmudgeon]

If you have a selection of lube-sizer dies remove the bottom punches and find out which die will barely accept your slug. Caution: the dies are not always exactly as marked.

Drill a hole in soft steel, iron, or soft metal one drill bit smaller than 5/16." Lap the hole out with emery clothuntil it will just pass your slug, I've come pretty close this way.


Join the Cast bullet Association and send the slug to the man who has all the good measuring tools and is listed in the magazine. It's worth it just for the polite, old school reply you will receive.

[Larry Gibson]

Today I got some bullet shaped fish sinkers made for worms. They had various lengths I went with the short ones. The base is almost made to fit a 1/4" steel rod.

I slugged the .303 No4 MK1. Agghhh, 5 grooves and lands. So when the dial caliper is on the land on one side of the slug it is on the groove on the other side. Great. I tried caliper sideways and length ways on the slug and got the same maximum reading both ways.

The biggest measurement is .311 or .3115, there are lots of measurements smaller than that. The smallest measurement is .308, I get that a lot.

The rifling looks deep when looking down the barrel but not nearly as deep on the slug.

I'm guessing that the groove diameter is more like .314 and the bore diameter about .305.

Any ideas on how to read a 5 groove slug?

Thanks,

Mike S

This was posted on another board regarding measuring slugs from 3 groove trapdoor barrels. It works the same for 5 groove barrels.


Sorry for the late resonse, just saw the question. Take a strip of shim stock (I use .003" thick) about 1/2" wide by 2" long. Wrap it around the "slug" and pinch the two ends together holding it tight around the slug. Mic the new diameter over the shim stock. Subtract twice the thickness of the shim stock (in my case that would be .006") and that will give you the actual groove depth of the barrel.

Larry Gibson

[44man]

One point worries me, Mike says the grooves look deeper in the rifle. I would slug again and upset the slug in the bore before making a way to measure them. Save a lot of work ---just in case!

[Bad Flynch]

You can find a local machine shop and have them use a "Vee-block" micrometer on it. They are rare, however.

Some SMLEs had Metford-style rifling, which is also difficult to measure properly.

[cropcirclewalker]

I took a beer can, scissors and cut out a strip about an inch wide and 2" long. Dimensions not important.

Wrap it around as stated above a boolit and mike. then mike the boolit. subtract.

That tells you how much to subtract off the reading you get from wrapping the same piece of beer can around your slug.

Make sure the beer can strip is long enough to like, bridge the rifling and don't squeeze too hard or you could mash the aluminum into a groove.

Beer cans were easier for me to locate than shim stock. That's all.

[MikeSSS]

OK! I'll have to get some beer. Somebody has to do it, guess it'l have to be me.

Excellent ideas.

Thanks guys.

And, lots of "why didn't I think of that"s too.

[The Double D]

Gent's this is so easy to do. No special strips, no v blocks nothing no sending it off to a far land and waiting a couple of weeks.

I was taught this by an old Milwright Gunsmith.

Hold the slug between he jaws of your dial caliper with the slide jaw slack and roll the slug. Do it three or four times and read the measurement each time. You will see the measurement repeat. The repeating measurement is the measurement you want.

[KCSO]

Double D has it thats the way we do it in the shop, havent used V block for a long time now. Tested against the v block this is so close the difference won't matter.

[StarMetal]

If you have a V block mike why not use it. It's just as easy and the same to use as a regular flat anvil mike.

Joe

[The Double D]

How many people have v-block mic's anyway. Dial Caliper close is all you need for a cast bullet measurement. You still have to roll the slug in the V-block mic if you have one, and the difference is usually in the fourth digit and doesn't really matter in a cast bullet.

Oh yeah, and I almost forgot, the V-block mike will only measure some odd size slugs. They won't measure things like Slugs from a 7 or 9 groove Henry rifle barrel.

Mitutoyo quoted $1300 for a mic to measure just the 7 groove Henry.

So that why I use a caliper.