View Full Version : Barrel Slugging
08-21-2008, 12:45 PM
How does one go about slugging a barrel, and how do you measure the resultant slug?
Also, is the optimal cast bullet diameter .oo2" over groove diameter, or should it be more?
08-22-2008, 07:39 PM
A better way is to slug the chamber throat.
it is not so much that a bullet must fit the bbl, as it must fit the throat.
Fill an empty case with lead. load it into the gun.
Make a chunk of pure lead that will fit down yur bbl, and drive it down the bbl with a rod.
Pound on it till yu feel it go dead.
You will know what that means when you do it.
Take the mess out of yur gun, and measure the throat, and fit yur cast bullet to that.
By slugging a bore all the way thru you get a slug measurement of land and groove diameter that is the smallest of any part of the bore. By obturating a slug AT the throat you get a "slug" or "casting" of only the throat area. Theoretically this is the critical first area of the bore that tha bullet encounters when it is fired thus the most critical for best fit and minimum leading/blow by potential. For those rifles with throats that are larger than groove diameter the best bullet diameter is theoretically the throat diameter.
You can take an empty case and fill with lead to the mouth. Or use a metal rod that is about a snug fit into the case. Cut the rod to length of the case (even with case mouth). Put plugged case into chamber. Push a soft lead slug down from the muzzle until it stops at the plugged case.... which is the throat area. Use a slug about 1/2-3/4 inch long. Gently tap, tap, tap this slug with the rod used to push it down from the muzzle. It will obturate to fill the throat area. As ra_balke posted- you can feel it quit obturating (goes dead). Remove plugged case from chamber. Gently tap the throat slug on thru. You should end up with a casting of just the throat area and a small part of the bore. Sounds harder to do than it really is.
08-23-2008, 07:53 AM
Could you please clarify how you fit the bullet to the throat?
Piet , I've done as 405 described with a fired casing and it works well . I did however resize the case first before filling it with lead . Leaving the fired primer in is a good thing and putting a light coating of lubricant on everything so it would be easier to remove .
Either way will help you get the throat measurements . I've found that bullets sized up to about .0005" over work without problems , the groups you make will tell you what's best .
11-22-2008, 11:45 PM
I have used a hardwood dowel to do the driving to good effect. I am too scared to use a metal rod.
11-23-2008, 01:25 AM
Good morning The Chamber area is very important.. this must be sealed off at the time of firing. Now that you know the real throat diameter You can decide how much over that diameter will you begin sizing your boolits.
Augois... did not mention a caliber ? Rifle ? When you ask a question it will help to give as much information with the question about the firearm and caliber as you know.
In my caliber .30 rifles I usually start with a cast boolit at least .001 OVER throat size. Larger calibers you can do the same. I have one particular 45.70 trapdoor that gets a boolit (40-1) .0035-.004 oversize and shoots this one the best..rough throat area. Smaller calibers .001 may be all the EXTRA room you have.
If you have a MATCH chamber (small diameter) you might have diffulculty so it pays to make a dummy cartridge( no powder, no primer) and test how things fit. Semi auto loaders may be more work intense as they have to chamber under spring power and a TOO FAT boolit may get hung up half way into the throat... so there are veriables involved.
Then there is the question of how far to seat, and lead mix, and.... BUT in the end you have a load that will probably be THE most accurate load that rifle will shoot... and YOU made it and can repeat the results.
11-23-2008, 06:48 AM
take an empty case and fill with lead to the mouth. Or use a metal rod that is about a snug fit into the case. Cut the rod to length of the case (even with case mouth). Put plugged case into chamber. Push a soft lead slug down from the muzzle until it stops at the plugged case.... which is the throat area. Use a slug about 1/2-3/4 inch long. Gently tap, tap, tap this slug with the rod used to push it down from the muzzle. It will obturate to fill the throat area. As ra_balke posted- you can feel it quit obturating (goes dead). Remove plugged case from chamber. Gently tap the throat slug on thru. You should end up with a casting of just the throat area and a small part of the bore. Sounds harder to do than it really is.
It sounds simple enough but if you only want to measure the throat, wouldn't it be simpler to breech seat the slug? If the barrel is removed or the weapon is a single shot, you could tap the slug in from the chamber end using your filled case. Or would it not obdurate as well if you did it that way?
11-30-2008, 07:32 PM
I make a funnel from an index card and pour the heated Cerrosafe alloy into a lubed (30 wt oil is fine) and plugged barrel (plug it with a tight patch) about two inches down from the end of the receiver. You will be pouring into the breech end and don't get it up into the bolt recess or whatever because you will have a problem getting it out.
Give it 10 mins to cool and tap it out from the end of barrel with a cleaning rod or dowel. The whole shooting match tumbles into your action and you remove the slug and measure it. Make sure to wait an hour or so before you measure it as the design of the alloy shrinks the plug about .001 or so to allow removal. Once it hits max size measure your throat and get the diam of the lands and grooves.
My .303 has a .316 throat. The deepest grooves measure 315 just past the throat and down to 311 at the crown. Lands measure from 311 down to 309. I plan to use a .316 base boolit.
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