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Mk IV Block Cracked
I went to the range yesterday and shot 4 rounds through my MkIV. Got home yesterday evening and removed the block to clean it. Cleaned and oiled it and while looking closely noticed a hairline crack on the left side, midway between the face and the rear of the block at the top. The wing area to the left of the dish where you slide round down into the chamber. I didn't notice this before so have no idea how long the crack has been there. When I get home tonight I will see if I can take pictures so others will know what to look for. It bothers me enough that I just ordered a replacement from IMA, along with another trigger spring. I made a replacement trigger spring for one of my Francottes but it was labor intensive and I had to do it twice because I didn't temper the first one correctly and it broke right off the bat. My trigger spring is definately the culprit in the heavy, 10#+ trigger pull I have.
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I'm surprised if this was caused by firing, the block is in compression.
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I don't know what caused the crack but it appeared to start between the stamps on the left side.
https://www.milsurps.com/images/impo...lock0031-1.jpg
Actually the crack starts at the tip of the wing of the "W" and runs upward. I think it is the stamping of the WD caused a stress riser.
The "W" on one side and the "4" on the other side. Also the block does not have much meat there. I got my replacement block and it looks good.
https://www.milsurps.com/images/impo...ment0041-1.jpg
https://www.milsurps.com/images/impo...ment0031-1.jpg
I ended up swapping strikers and striker retaining nuts between the MkIV and MkII blocks. Also swapped tumblers between the MkIV and the MkII. Cleaned up the trigger assembly and loosened the trigger spring screw a bit. A really good trigger now.
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It looks like a fatigue crack.
Have you tried cleaning it up on the side with emery paper? It will not solve the crack but you may see the crack is in fact longer.
In any case it looks like a goner.
