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Angle for Perazzi MX8 locking block?

5999 Views 14 Replies 10 Participants Last post by  BL350
What is the correct angle for the engagement surfaces of the locking block and the locking surfaces of the rear lugs on the barrels? I would assume they are equal and the block moves forward with wear as the top lever gets closer to the center. Next question, how many thousands of an inch of wear does it take to get to the center requiring a rebuild? If the gun locks tight does it really matter where the top lever stops? Thanks in advance for the Perazzi pro's advice on here.


Duane Nicholson
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· Sky Buster
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According to Pat Laib (Laib's Gunsmithing) you can discount
the position of the top lever in determining if it's time
for replacement. He advised me to hold the receiver in one
hand and the barrel in the other. If you can detect any movement
between the two parts, it's time for replacing the locking block.
If the gun jumps open upon firing, it's another matter.
 

· Vendor
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caution. YOu need a pro. Doug braker. 218-947-3600. Doug does not "guess". He uses a michine to measuer the lug angle andthen he has another machine to cut the block angle to match
 

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Dear MIA,.....Well said! Doug's skills & performance on locking blocks, ranks right up there with the skill levels of A NASCAR Engine builder!!! Sincerely........ "from the guy that bought a virgin TM-1 34 inch barrel from you!!!)
 

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#1 Perazzi's angle is 7º.<BR>
#2 Kerry Allor likes to cut them at 8º.<BR>
#4 No, if it locks up tightly, it really doesn't matter where the lever sits. However, the lever will wear and in doing so, it approaches 6:00.<BR>
#3 If the barrel flies open upon shooting it if DEFINITELY TIME FOR A NEW ACTION BLOCK. A top lever return spring by itself won't keep it shut. You can sure give it a try, but if the lever sits at 6:00, it's time for a new #103. And, if you have it apart to install the lever spring, you are at the same point where the action block can be installed, anyway.

Give or take a couple of degrees, the 103 simply need proper fitting, and at the same time, and because the action is all apart, a new 121 top lever return spring should be installed. It's cheap and appropriate to do at that time. A close inspection of the guide #111 is also pretty critical at this time.

And for God's sake, don't weld up the worn action block unless you are a metals engineer. You are introducing different metals' properties, and the last thing you want to do is wear the notches in the barrel's monobloc.

WW
 

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The early MX8 and MX3 bbls and locking bolts floated all over the place for the angle. Rarely have I ever saw one less than 9 degrees with some over 12 degrees. These are untouched angles by anyone other than the factory.

Most all TM-1s are around 10 degrees. I recut them to 8 degrees to ensure the top lever never jumps in the future.

Other than a gun just a few years old, I never trust any angle. At least half that I see have had the bbl lugs filed on. Some almost square with no angle to the worst one I've ever seen..pushing 25 degrees. Those I need to weld up and recut. This small angle cannot be measured accurately with a protractor.

To know if the bbl lugs have been messed with, with out using a an optical comparer, look at the angle of the bbl lug from the side. The angled "line" should run up toward the mono-block and be even with the bottom of the ejector head cut. If it is not even...don't worry, you can loose about .015"-.020" and still have a new or rebuilt locking bolt installed. You will not know if the angle got changed though.

As for how much material is needed to move a top lever from dead-center (6:00) to the approx 5:00 position....About .006"-.007". Not a whole lot.

Proper angles and a proper fit are essential for keeping the top lever from jumping. If everything is correct, you can shoot the gun without the top lever spring...I've done it several times. The 8 degree angle is one degree away from the start of a locking taper...7 degrees.

If your top lever is jumping now, get it repaired NOW! You will break the tip off the bottom of the top lever...a $450 fix. Here's a simple little test you can do to see if the top lever moves while you're shooting...

Load you gun as you would normally do. Take a small chunk of the non-drying modeling clay and place it along the right side of the top lever, nearer the thumb area. Shoot the gun. If you see a gap has formed, that is because the top lever pushed on the clay. 8-10 shots should give you an answer.

Doug
 

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Discussion Starter · #11 ·
Thanks guys for the expert answers to my questions. Only one remains if you will. How many thousands of an inch of wear does it take from the new gun lever position to the 6 O'clock position? This seems to be where people suggest a new locking block before experiencing a safety concern. I see almost every gun for sale on here, that the location of the top lever, when the gun is closed, is key to selling it.


Thanks again, and I appreciate the information provided by all. Duane
 

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How is it that Lucio and Giacomo manage to do such exacting fitting with nothing more than files?

And I have to admit, having watched both of them work on my guns, that I never had a questions about their abilities or the results. Fact is, I was pretty down when Giacomo retired and I'm not sure just what I'm gonna do when Lucio gets around to doing that.

Guess I'll have to just load up all the guns whether they need any attention or not, and hit out to L.A. one last time - and hope me and the guns last about the same time.
 

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Lucio and old Giacomo never measured it when they worked on my guns, they only know how to do it by hand with a file.

As a matter of fact, I asked Lucio about this 7 & 8 degree question years ago, he answered: "What 7 degree?" with a smile.

The only person who actually told me 7 (or maybe 8) degree was Daniele Perazzi almost 15 years aog.
 

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Performance testing of the firearm (after the locking block work is done) is very, very important. One of my experiences was shooting in the rain (after such a repair). The top lever started moving again during the shot and throwing water on my shooting glasses. It went BACK to have the block redone. Then the top lever would stick closed after the shot. More block work performed..... and more!!! Enter Doug Braker!!! After his block repairs, THE gun performed better then it was when NEW! and no jamming closed in all kinds of weather and low temperatures. Excellent precision repairs that WORK put Mr Braker at the head of the list. Not faulting the skills of the old master's with files, but performance after the repair is my ONLY requirement!!!
 
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