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Sanity check on coated bullet diameter vs bore diameter


thormx538
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I slugged my regular X5 and Legion barrels, and got 0.35525" max on the X5 and 0.35585" max on the Legion, using a +/- 0.00005" micrometer at work. I've shot Blue Bullets and Brazos (sized to 0.356") through the X5 without issue, and haven't shot the Legion yet. I need to order more bullets soon, but I'll be able to run a handful of what I have loaded through the Legion first in a couple weeks to test first hand. Before I get to the range; guys that have done this experiment before, -- would you expect any issues in the Legion with the 0.356" sized bullets? Is there any downside or advantage to running 0.357" sized bullets in my X5, given that bore diameter?  I've always just ordered the standard option with bullets (I've never slugged a barrel before) but I was reading the rule of thumb is to have the lead bullet be 0.001-0.002 over the bore diameter. I assume I'll be fine running both .356 or .357 in either gun, just wanted to hear opinions from others that have similar data points.

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A well regarded bullet maker, now retired, once told me you never can tell.  He said that with lead bullets, generally .001" over bore diameter was the most accurate.  He also said that sometimes bore diameter was the best.  You don't know until you try.

 

Some coated bullet makers size first then coat.  So there nominally .356" bullets are actually larger than that.  Most size after coating.  I don't expect you will see any problems with .356" in the Legion.  An overly large diameter coated bullet can cause leading if some of the coating is scraped off when it is squashed to bore diameter.

 

My suggestion is to order .356" and .357 bullets and test.  Then decide.  BTW, you have to measure the slug at various points around the diameter.  Many barrels are not perfectly round.

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Per this forum I have tried .355, .356, .357 and .358 in my Tanfoglio S2 and without a doubt, scientifically checked and verified the .355 FMJ RN from Precision Delta are the most accurate. But the same sizes tested in coated found the ACME .356 147 FP were the most accurate and more accurate than Precision Bullets(same profile) .358 in 147 and 125 (all tested at 25 yards).

 

One thing though, it is true the .358 Precision Bullet coating is tougher than ACME (I trapped the bullets and inspected them post Chrono), they were slightly faster, about 10fps, and the SDs were almost the same. The observable smoke of all my tests were similar.

 

Moral of the story; find the bullet/powder combo at the price point one would support, load them and shoot away. Bigger may not be better. 

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I have an X5 and legion. I got major leading with .356” bullets. 3 different manufacturers. 
I went to a .357” and all my problems went away. Accuracy was not better or worse. Just got zero leading. No real downsides to running a .357”

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