CZ Threaded Barrel out of Spec? Extreme POI shift on CZ75 w Silencer Suppressor

[mountainmanSTI]

Hey all-   I've been tooling around with CZ's for a number of years now and I've upgraded and ripped apart every aspect of my CZ75b Omega "suppressor ready" and a few P07/P09s. 

I love the feel and function of the 75.  It's pinpoint accurate and has a great trigger feel with the CGW pack.  I can only imagine what a pre-b feels like because I can't picture this getting any better.  My only gripe is that for some reason this CZ75 experiences horrid POI shift when I screw on a silencer. 

I've resorted to keeping my 75 as a Safe Queen because I love shooting suppressed and my P07/P09s are 10x more accurate when suppressed.  I only shoot my 75 without the suppressor and it seems kinda pointless having a "supressor ready" gun that I only shoot loud. 

My question is--- Is the P-series lockup mechanism superior to the 75 design as a suppressor host?  What could be causing 3" POI shifts on my 75?

Here are a few observations I've made:

1. at lockup, I can wiggle around my barrel in the 75.  In fact, the entire slide moves and rattles within the body of the firearm.    I actually threw a CGW barrel bushing on there to try and tighten it up.  It didn't help POI at all, or have any affect at all for that matter.  It only made it impossible to cleanly remove the barrel from the slide for cleaning.

2. Despite the sloppy, rattling slide---The 75 shoots better groups than all my guns when i'm not using the can.  But, when I hang 10oz of aluminum on the end of the barrel-  it creates a nasty downward POI. (3-5" at 15'). This makes me think that I've got something other than lockup/slide slop issues.

3. All my P- series guns all seem to have a very tight lockup both to barrel and slide to body.   No movement, rattle, or slop at all.

4. Lastly, I just recently noticed that that threading is a different depth on both of my threaded CZ barrels.  The difference is enough to affect where the silencer indexes-  IE on the 75, the threads are LONG and the suppressor indexes on the muzzle.  The threads on the P-series are shorter and the silencer indexes on the SHOULDER. 

Attached pic has the 75 threads on the right AND a P-07 barrel on the left.  Notice there is a good 1/8" difference when stacked  against each other. 

Am I dealing with slide slop, poor barrel lockup, or am I dealing with some sort of thread alignment issue?  I can't seem to figure this out and any help or knowledge is appreciated!  I might just knock off my high sights and get a regular barrel for this 75 at this point! 

[mountainmanSTI]

Picture comparing CZ75B omega threads to P-07 Threads.  Both are CZ factory barrels

https://drive.google.com/file/d/1e3ksw6xWRYzLW9_LDfTtPEbovQOQhfkf/view?usp=sharing

[mountainmanSTI]

Barrels are pictured to show the difference in length and how it affects where the suppressor indexes.  The CZ75 indexes off the muzzle and I suspect this might be an issue due to the fact my P07 indexes on the shoulder and shoots laser beams all day.

My 75 shoots better than any gun I’ve got until the can is on it.  Then is completely falls apart-  indexing off the muzzle due to the longer threads

I’m using a CGS mod9 with a booster/Neilsen.  I actually honed it out beyond the factory specs to try and address this no to avail.  No noticeable baffle strikes even on freshly machined baffles and end caps

Now you’ve got me thinking about machining down the CZ 75 barrel to match the P series threadin depth..... 

[mountainmanSTI]

JOHN A -  your member level describes how I feel about you right now (HERO).  Thanks kindly.

The cz75 threads are absolutely too long to get to the shoulder.  (on three of my boosters) It's seating right against the muzzle.  And, to your point my "groups" are shotgun-like, randomized mostly downwards from my point of aim.

This booster is the perfect length for the P-series threads however.  Those threads run just slightly shorter, and allows enough clearance to index on the SHOULDER. 

I can't believe I never thought of using shims, what a great suggestion.  That will certainly preserve the integrity of my muzzle, crown and WALLET!  Thanks for the tip, I'll let you know if this is the solution.