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Discussion Starter #1
Im looking for anyone that may know the thread pitch for the UMP .45 acp barrel, had a gunsmith make me a match grade barrel with a 1-16 thread pitch, the gun is having problems with 230 grn ball ammo, as far as keeping all rounds on target, he advised to go with a 185 grn round, that may cure the problem.
 

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That's not true 'thread pitch' it's barrel twist rate.

The stock USC barrel does have a 1 turn in 16" barrel but with polygonal rifling, so that is the correct barrel twist rate to be used with pretty much all .45ACP loadings. I get very good accuracy out of my 8" USC barrel (SBR Form 1) with all loadings from 185gr to 230gr, and can't complain. They are accurate out to several hundred yards with 'Kentucky windage' (holdover guessing) and print good groups up close.

I would say you should try a few different loads and see what kind of accuracy you're getting. What range are you trying to group this rifle to?
 

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Discussion Starter #3
UMP barrel twist

You are corect, sorry, just got off the phone with a gunsmith talking about thread pitch, when i posted, anyway, Im trying to zero at 50 yards, with 230 grain CCI gold dot, and it is all over the paper, im locking the gun in a rest, using the aimpoint, and it will not zero for me, i will try some 185 grain to see if it will group for me.
 

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Merchant of Death (Admin)
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There are so many variables that come into play here. My USC holds pretty darn tight with the factory barrel. And I have just ordered another one. I pretty much use only 230gr hard ball and it seems to eat just about anything that I throw down its throat. Since you mention that it is a newly made barrel, I would ask about how it is crowned. Any immediately noticeable areas that are rough; or is it crowned?

Of course, you may just have to spend a bunch of time at the range (darn) and get that barrel lapped...
 
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