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Squib slugging a barrel - pros and cons

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So I recently got some 125 blue bullets. Id heard that they were a bit undersized at .355 and accuracy reports were varied. I've slugged rifle barrels before, but not slugged my CZ barrel. So... I decided to try something new and hopefully easier. I've never heard of anyone else doing this and looking for opinions on why or why not to do it this way.

 

With no powder on the bench, and only this single bullet, I sized and primed a case and seated the bullet, intentionally creating a squib. Took this squib round directly to the gun and then fired it outside in safe direction and got the expected puff, removed the barrel and pounded it out. There was my slug - it had definite markings for the rifling - ready to measure. It was dark and not well lit so I had a tough time getting calipers in the right spots on the lands and grooves but from what I could tell it was swaged down by the barrel a bit on both the lands and grooves.

 

cons - The only con I can see with this method is that the throat or leade may be shot out and a little bigger than the muzzle of the barrel.

 

pro - much easier than slugging the entire barrel. you slug the barrel with the actual bullet you will be using, not some super soft lead that may have some spring back and not give proper measurements.

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Soft lead does not 'spring back' at all after being pushed through the barrel.  In fact, the soft round balls usually used for slugging a barrel will provide much more precise results than using a coated bullet.

 

As for slugging only the rear of the barrel, that won't tell you anything about the rest of the barrel.  Most of the work is done once you have the slug engraved.  Forcing it down the rest of the barrel requires little effort.

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I've done it that way years ago with an oversized home cast pure lead bullet.  Clean bore out, load bullet with no crimp, and .3gr powder.  Shot into a laundry basket full of towels.  

 

Worked great.

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23 minutes ago, d_striker said:

I've done it that way years ago with an oversized home cast pure lead bullet.  Clean bore out, load bullet with no crimp, and .3gr powder.  Shot into a laundry basket full of towels.  

 

Worked great.

 

Does it need to be "pure lead"?  I have some oversized commercial cast bullets that I would like to try but they are not "pure lead".

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1 hour ago, Flatland Shooter said:

 

Does it need to be "pure lead"?  I have some oversized commercial cast bullets that I would like to try but they are not "pure lead".

It works best. Pure does not have spring back. Alloys will measure slightly larger than actual. Not usually terribly important as long as it starts oversized. Hard alloy undersized will not obturate to the bore with no/little pressure behind it.

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FS, as Beef said, pure lead works the best.  If you use hard cast, just remember your actual bore diameter will be a tad less than measured.  The reason is because the barrel bulges when hard projectiles are fired.  When you shoot a .356 hollow point through a .355 bore, the bore is still .355 afterward, and the bullet is still .356"  The barrel bulges as the bullet pass and returns when it has passed.  

 

Your problem with hard cast will come if you have a big bore.  There are 9mm barrels out there with .357/.358 bores.  A hard cast slug won't help you if that is the case.  I order my slugs from Dardas Bullets.  The are pure lead round oversize balls.  If memory serves they are 3 for a buck.  Drop one in and tap through using a bore sized dowel and a small hammer.  No matter how large your bore, these ball will measure it.  If you are not sure of your measurements, you can send them back to Dardas.  He will accurately measure them for you.

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2 hours ago, zzt said:

FS, as Beef said, pure lead works the best.  If you use hard cast, just remember your actual bore diameter will be a tad less than measured.  The reason is because the barrel bulges when hard projectiles are fired.  When you shoot a .356 hollow point through a .355 bore, the bore is still .355 afterward, and the bullet is still .356"  The barrel bulges as the bullet pass and returns when it has passed.  

 

Your problem with hard cast will come if you have a big bore.  There are 9mm barrels out there with .357/.358 bores.  A hard cast slug won't help you if that is the case.  I order my slugs from Dardas Bullets.  The are pure lead round oversize balls.  If memory serves they are 3 for a buck.  Drop one in and tap through using a bore sized dowel and a small hammer.  No matter how large your bore, these ball will measure it.  If you are not sure of your measurements, you can send them back to Dardas.  He will accurately measure them for you.

that's very interesting. thanks for sharing the bulge.

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This is what I did not saying this the best but I took a clean fired 9mm case and put some split shot sinkers in it and melted it with a propane torch let it cool and tapped it thur the clean lubed barrel with a brass rod worked good for me.

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Lead alloys "spring back" when released from the barrel.  Gives a false measurement.  That process is worthless. You want pure lead. 

 

OR you can just test bullets of different diameters and let the gun tell you what it likes. Which makes more sense. 

 

Would you shoot what slugging told you was correct if the gun told you different? Of course not.  Just buy bullets of different diameters and let the gun speak to you. 

 

 

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For slugging, use lead with a hardness of no more than BHN 6. Anything harder may spring back.

 

Firing bullets through as a slugging shortcut is not recommended as the base may obdurate and the ogive may deform from bullet expansion on striking the target. Any bullet hard enough not to do this is too hard for accurate measuring.

 

Pounding bullets through is a really bad idea. Had to re-crown a barrel for a follow who did this. To pound out the bullet, he braced the muzzle end against something and pounded hard enough to screw the pooch. Another fellow used a cleaning rod instead of a dowel to pound the bullet through and the rod went through the side of the bullet and scratched the the bore up pretty good. The gouges caused severe leading issues and I had to lap the barrel to make it quit.

 

Also remember that unless you're using calipers that were recently and professionally calibrated, they are not as accurate as you think. Micrometers are usually pretty accurate but $25 calipers, not so much. Even some very good ones I've checked were off by .004 so either get expensive tools, pay a pro to do it or as noted above, let your gun tell you what it likes.

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On 12/11/2018 at 6:54 PM, Dwbsig said:

This is what I did not saying this the best but I took a clean fired 9mm case and put some split shot sinkers in it and melted it with a propane torch let it cool and tapped it thur the clean lubed barrel with a brass rod worked good for me.

 

Very creative!

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