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Discussion Starter · #1 ·
The fit of the top and bottom parts of the gas block to the barrel is not great.

It seems that the diameter of the gas block hole is smaller that that of the barrel - or may be the hole is not curcular. That causes a tiny gap on top and on the bottom of the barrel. It is clearly seen by the fouling being blown off from the gap or cleaning liquid seeping through. Quite possibly it causes pinching of the barrel on the sides and less secure fit - requiring higher torque on the screws. Also the increase of the gap between the halves of the gas block.
Also, due to smaller contact area between the barrel and the gas block, the block must not be warming up as fast as the it could, causing more of the uneven expansion and pinching of the barrel.

Does it make sense to wrap some fine sandpaper around the dowel and sand off the gas block - using the marker to see where it rubs against the barrel, to make sure the whole area is in contact with the barrel, not just parts on the sides?

Maybe even sanding and then lapping it to the barrel with valve-lapping compound to ensure the best fit and heat transfer?

V.
 

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Voruzon, mine fits tight, no leaks. If you go slow, and careful you should be able to work it tighter as you described.

I wouldn't lap it on the barrel, as you would remove barrel material, and it would become even a smaller diameter. Just the blocks.

If you want there is a product to measure this gap, called Plastiguage. Available at better autoparts stores, You put a piece of the guage in the gap on top or bottom of the gass block, then torque blocks down. Remove the plastiguage, and measure the width, this tells you how many thousanths, thick the gap is. So you will know when you get it worked out. Consistant Torque is critical, as it will change the gap.
 

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Discussion Starter · #3 ·
OK, I've disassembled the gas block - with the main intent to switch to the smallest Mike's bushing to try on Friday.

I was wrong that the hole diameter is smaller that the barrel. It seems a little bit larger. The permanent maker rubbed off around teh top, not on the sides - though not evenly. There is a tiny sidewise wobble even. The appearance of gaps on the ends and crud blons throug probably owns to the hole not being precise cylinder.
So I will think before I do anyting. Probably check the prices on replacement gas block halfs on Numrich and if decide anything, experiment on "spares".

As for measuring the gap and torquing, I do not believe that the method you've mentioned makes sense, Cajungeo.

The gap is what you make it which depends on how you tighten the bolts, not a constant value.
It takes me about 20 munutes to torque the bolts - very slowly, returning to each many times.

I set the gap and the torque on one side, them I do the same on the other side. That changes the torque and the gap on the first side. So I go bact to the first side, losen then retighten the bolts, and so on. If I overdo it, I may have to just loosen the bolts/widen the gap on one side and compensate by tightening the other side.
All four bolts work together, considering any one of them separately when it comes to torque or gap would not work. Precise value of torque is meaningless for one bolt if turning the one on the other side may change it.

So I increase the torque on the bolts grarually - by 2-3 inch/lbs at a time to 30 inch/lbs. I use a feeler gauge from an automotive store to measure the gap and make sure it is the same on both sides - 0.022 in my case, after some sanding done.

Oh, I also put a thin sliver of spring steel - almost like foil, into the lower part of the gas block around the bushing. It made the bushing stop wobbling inside the lower gas block half. The fit of the bushing to the barrel is better than the fit of the bushing to the lower gas block half.
It made for much less wobble of the gass block on the barell before the bolts were tightened. I hope it will not cause any adverse effects.
If you think of any, please tell me before I shoot tomorrow night.

V.
 

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voruzon, the gaping I described is not the gap between the halves, as it was the gap between your gas block halves, and your barrel. You said it leaked between the gas block, and barrel.

You are more miticulas than I. I spend only 3 min gaping the gasblock halves, and torquing the screws. I guess the years in aircraft give me a certain feel for things.

I had to use the largest of mikes bushings, as the smallest made my mini a bolt gun. The middle one jamed. The largest is just right. As my slide assembley spring softens with use I will be able to use the middle size bushing.
 

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I also used the larger of Mike's gas ports on my rifle since the middle one caused jams. Since I didn't have a torque wrench, I evenly gaped the gas block using feeler gauge. I just made sure that the screws wer not gorilla tight. I also used breakable lock tite (blue) to make sure the screws stayed put. Rifle shoots fine.

Chris M :usa:

Semper Fi
 

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Discussion Starter · #6 ·
cajungeo: voruzon, the gaping I described is not the gap between the halves, as it was the gap between your gas block halves, and your barrel.

Oh, I see. In that case I would certainly be interested in trying it the next time I open the gas block.

You are more miticulas than I. I spend only 3 min gaping the gasblock halves, and torquing the screws. I guess the years in aircraft give me a certain feel for things.

Right. Experience makes an amazing difference.

I had to use the largest of mikes bushings, as the smallest made my mini a bolt gun. The middle one jamed.

Could it be such a great difference between the rifles? I've shot 80rounds with the medium bushing without a glitch. Is that too few rounds? Mike recommends starting with the smallest one and I am going to try it today.
I am shooting Wolf ammo which is allegedely not too powerfull compared to the average US-made stuff. It should have made things worse.
It would be interesting to compare the stiffness of our springs. Maybe by pulling back on a slide with a trigger gauge and measuring the distance it takes to achieve 4 lbs?

V.
 
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