Fitting gas block to barrel
 

My AR project rifle is starting to come along, although it's going much more slowly than I'd like.

I just received my low profile adjustable gas block. I measured the bore diameter of the gas block and the diameter of my Oly barrel at the gas port. I either have to open the bore of the gas block .010" or turn down the barrel at the gas port .010" (hmmmm, I just thought of measuring the bore diameter of the old gas block :bangin: ).

Anyway, what did you guys do to ensure a proper fit of gas block to barrel?

Thanks for your help.

I had to turn my barrel down to 0.750. The JP gas block has a nice snug fit.


320pf

Like 320pf I also turn the barrel down. Great care must be excercised when turning the barrel because a loose fit will haunt you. Most would probably turn to within a couple of thousandths and then hand fit the block.

Thanks for the replies and information.

Would it be easier to open up the bore of the block a little at a time & test for fit?

No, not really. You will have to have it machined. .010 is too much to try and polish and would take a long time to try to hone it with a wheel cylinder hone.
Much easier to turn the barrel in a lathe.

You did not mention what size your barrel or gas block is.Go with the standard sizes like .750" ,.875" or .937". for your barrel. Gas blocks can be replaced a lot easier then your barrel. I would machine the gas block for that reason.I also make gas blocks for the ar in stainless. Sometimes they are undersized like .935"
or something.What ever the customer wants.regards.

tp555,

My Oly barell measures about .762" at the gas port, the old gas block measures .760", and the new JP gas block measures .750".

I thought it might be easier to hone out the new gas block, but if not, I'll have to find someone to machine my Oly barrel down to .750".

Thanks to everyone for advice.

closing off a gas port
 

On a somewhat related subject.

Does anyone have an idea on how to go about closing off a gas port?

thanks in advance

320pf

Your barrel is off standard.Oly is a pita about this. I would recommend machining the barrel to .750" which is standard. Then you can use anyone's .750 gas block.You do need the equipment to do it right and the experience.If you can't find someone locally I do this .I do make ar barrels for a living.The shipping back and forth would cost more then the job.Plan B machine the gas block to fit or send the gas block out for machining.Not as expensive for shipping as the barrel.
Plan C get a custom gas block made .I also do this.

For blocking a gas port you have to drill and tap for a set screw without going
through to the bore.A set screw with an allen hex in it.This was one way of testing out gas port holes. By drilling through the set screw different sizes of holes can be tested.You don't want a large hole going into the bore.The smaller the better.This does require equipment a good mill or so.

tp555

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