Slugging a bore

[IditarodJoe]

I'm thinking about slugging the bore on my No4 Mk1 rifle (keyholing badly). I've never slugged a bore before. Would the .315 diameter pure lead round balls sold by Brownell's be an appropriate size for this? Thanks. -IJ

[Hecklerusp45]

You want to start with something close to .311 and I don't know of anything sold that is closer than that, so I would give it a try.

[Sunray]

Those will do nicely. Lead being soft stuff the ball will squeeze readily to size. A .308" cast bullet or suitable diameter lead fishing sinker works as well. The thing doesn't have to be close or above nominal diameter. Obviously doesn't need to be an actual bullet either.
Bash it through, preferable from the chamber end, with a 1/4" brass rod and a plastic mallet. Rifle in padded vise.
Montana Bullets sells gas checked 180 and 200 grainers that are .311" to .315" diameter. If you need to go that way. Not stupid expensive either. Roughly $25 per 100.

[Parashooter]

303barrelDims.jpg

Since groove diameter on some No.4's can easily reach .318+", you'll probably want a bigger slug. Size 00 or 000 buckshot do the job nicely and are easily found in 5-packs of loaded shells at reasonable cost. Be sure to use a sturdy steel rod for all but the first few inches. A wooden rod fractured deep in the barrel can be very hard to remove.



If yours is a 5-groove barrel, measuring the slug with a conventional micrometer can be a challenge.

[John Sukey]

Keyholing can be traced to muzzlewear caused by the "pullthrough" causing cord wear at that point.

[IditarodJoe]

Thanks for all the tips! For the price, the idea of using "0" (0.32 in) or "00" (0.33 in.) buckshot is tempting, but I've read that most of it is made of a lead alloy that makes it harder than pure lead. I suspect pure lead would be easier on the barrel. I have to place an order with Brownell's soon anyway so I think I'll start with the .315 lead balls and see what happens. If they don't fill the grooves, I suspect I can try deforming (flattening) one a bit before putting it into the bore. I hadn't thought about it being a five-groove barrel . . . this could be interesting.

John, I'll pull the rifle out take a really hard look at the muzzle and bore tomorrow. It was shooting fine when I last shot it a few years back. Then a few months ago I took it to the range again and it was keyholing every shot using three different types of ammo. Probably could be a number of things.

[Parashooter]

Some buckshot aren't quite pure lead, but they're close enough that it doesn't take more than a couple-three whacks of my light plastic mallet to drive a .360" 000 into a .30 caliber muzzle. Considering that we often fire jacketed steel-core bullets through military rifle barrels with no harm done, it seems a bit over-cautious to fret about tapping in a buckshot. After you've slugged a few, you'll understand.

Using an undersized ball isn't ideal since the impression taken is pretty narrow and tricky to measure.

[IditarodJoe]

Well, I pulled the old girl out and gave her a good look. The bore is fairly dark, and with my aging eyes it's hard to see the lands and grooves clearly but there is a little fine pitting visible. The muzzle crown still looks pretty good and I can't detect any nicks or burrs. In the "bullet test", the bullet of a Hornady Match .303 cartridge leaves about 1/16 inch of the jacket showing. The cartridge wobbles roughly 1/4 inch in one direction at the case head, so I'd say John is right about cleaning wear.

This is a 1943 (Fazakerly) No.4 Mk.I with all the wartime expedients - flip sight, pot metal buttplate, etc. It's still a handsome rifle but it certainly saw its share of use. It probably isn't worth sinking a lot of money into but I'll slug the barrel and see what that looks like. Worst case, I'll either sell it off or just keep it as-is.

At least I'll have learned how to slug a bore! Thanks to all of you for all of your help!

[Nate]

I have had two #4s keyholing because of boat tail bullets . They shoot flat tails just fine. Don't know if may be your problem.

[Johnny P]

As parashooter noted, 00 buckshot works great for slugging bores near the diameter mentioned. 00 is .330 in diameter and is no problem at all to run through a bore.

The Germans used the same method to quick check bore uniformity on military rifles. The bore was oiled, and a led pellet was seated in the bore. The technician then pushed the lead pellet though in one push and this gave him a feel for tight or loose spots in the bore.