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Acceptable Bullet diameter for 38 Super barrel


benos

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I got this in email...

 

I purchased a new witness gold custom in .38 Super. Well, naturally I want to reload this caliber for practice shooting. After I did my research and realized .355 and .356 diameter bullets are both used with no issue for this caliber. That's great.... except my factory barrel measures .353 after I slugged it... 3 times, to ensure accuracy. My question is, is this normal and/or safe to reload .355/.356 diameter bullets it? Obviously I'm worried about exceeding pressures from shooting a bullet that's .002/.003" larger than the diameter of the inside of my barrel. .353 Barrel diameter for .38 super which shoots .355" diameter bullets seems off to me. 

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Interesting. We're used to seeing oversized bores, but not too many undersized bores.  

 

Schuemann recommends a jacketed bullet of .001 to .002 inches larger than the bore, and lead bullets .002 to .003 inches larger for the best accuracy. Nowlin also suggests slightly oversize bullets.

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Load a few rounds with some  . 355" bullets and a mild load. I suggest a 125gn Jhp over 4.7 gns of 231 or HP38 with a oal of 1.220".

That should shoot Ok and is not going to get anywhere near over- pressure. 

You should have a good shooter that will make bullet speed towards the lower end of the Reloading scale.

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It sounds like the slugs were not measured properly.  Dardas Bullets sell slugs specifically for slugging barrels, and offers to measure them correctly for you.  He says many people do not get an accurate reading, and that's why he offers the service.  If the barrel is truly 2-3 thou undersized, it is defective and should be sent back.

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The Hammerli P240 in .38 Special is known for its super accuracy in Bullseye circles. The barrel is slender, lightweight, has a twist rate close to 1:20" and a bore of .352" to .354". Bullets are sized .357" to .358". 

You will be safe so long as you don't start with the biggest bullets and the biggest charges of powder at the same time. 

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Tanfoglio Elite pistols utilize polygonal rifling rather than traditional lan and groove rifling so the same rules of thumb don't apply when measuring the diameter of a slug because you're measuring from a point to an opposing flat.

 

My suggestion is to work up a load with 0.355" bullets, then switch to 0.356", drop the charge back 0.4gr, work back to the same PF and compare accuracy.

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