[cevgunner]

Ok ,
I just finished getting my CAI FrankenInch back together - and I took about 2-2 1/2 inches off the barrel.

Prior to the rework , it would put most shots into a paper plate at 100 yards. 8 -10" groups , no matter who pressed the trigger , or what ammo.

Having put a new crown on the shorter barrel , as well as a US flash hider , and an Inch pattern gas block , I find myself wondering if I need to open the gas port up , as I don`t have enough pressure to cycle the action.

The gas plug is installed correctly , I`m finding carbon on the gas piston , gas piston moves freely , the ports are lined up , and I`m getting pressure signs on my brass/primers.

The regulator is presently set at "0" , which cycles the bolt far enough to reset the hammer, but not extract the spent case.

I know there`s a time/pressure/port size/barrel length relationship , just can`t recall what the port diameter should be on the 18" barrel .

Anyone have any thoughts ? It ran before , just wouldn`t group. Now, it puts everything into 2" with 47 year old eyes behind the sights , just won`t cycle enough.

Help ? Please

 

[ken k]

if memory serves, .090 on or about is standard, you start at .100, most go .109

 

[shortround]

Metric barrel gas ports are drilled at a 90 degree angle to the bore through the hole behind the front sight threads. The inch barrel gas port is drilled at an angle through the hole underneath the gas regulator. If you replaced a metric gas block with an inch and the hole location/angle is different metric to inch, you may have some misalignment/ blockage of the gas into the system.

 

[ammolab]

I would think that with all the gas going to the piston (none vented) your gun should work.

You only took a few inches off the barrel.

Check out that alignment on the gas block/port. Let us know.

 

[cevgunner]

Thanks to everyone responding !
Ken; I had opened the port to a #39 (.099" ) , looks like I may have to go larger...

Ammolab , Shortround; gents , you`re onto something - looks like I need to recheck the alignment of the barrel port and gas block. I`d thought to have aligned the ports when I cut the barrel shoulder back to allow the ports to line up.

With what everyone has shared with me , I`m thinking I missed the port , by just a wee bit.

It may be that the barrel port is partially occluded by the gas block , which would explain the gas piston getting dirty , but not enough pressure to fully cycle the bolt , and having some pressure signs on the primers.

Time to break out the coffee , punch set , and bench block... I`ll have a look , let you know what I find.

Thanks to all,
cevgunner

 

[cevgunner]

OK,
One pot of coffee , one drill bit , and I found:

Mis-aligned gas ports.

I ran a slightly undersized bit into the gas block , in towards the barrel , and it marked the top of the barrel where the gas block sat. Took off the gas block , lo , and behold : 20% of the hole from the barrel was uncovered , AND the hole in the gas block was offset from the barrel centerline.

Damn.

I`m looking at opening the barrel port to .109" at least , and try to redrill the gas block to either open it up enough to align the holes , or at a minimum pas more gas.

This is what happens when you go cheap... but then again it`s a CAI metric/Inch hybrid, so maybe I should have laid out $200-300 for the correct barrel , and paid even more money to have it fixed by a professional. Not!

Knowing for certain now , I`ll try my fix , and get some rounds downrange on Tuesday after work.

Thanks to all for the guidance , I`ll be back soon with better news

cevgunner

 

[ken k]

also check the o.d. of your gas piston, .428 to .430 is normal

 

[cevgunner]

Thanks Ken - Tapco`s Inch pattern , it miked out at .430" , slides freely when rifle isn`t left in the car all day ( 18 deg. F. Wisconsin day )...

Shortround ;
Thank you - I believe I`m going to have to redrill the gas port. Apparently , having to flow up , and turn abruptly , just isn`t going to work. Likely have to plug original port , weld or just thread a plug in.

Six rounds fired , 1st w/regulator set at 4 , next 2 at 2 , last at zero, no change - no function.

The Winchester commercial .308 fired , no cycling , and the Radway Green Ball , fired - no cycling. Cases hung a bit in the cold chamber , but following shot extracted easily.

Sights are dead on , now. woo hoo.

I`m stumped .

 

[shortround]

Unless you need the inch gas block for sight height reasons, the simplest fix may be to replace it with a metric gas block. You can also look for a metric "open ear" gas block if you want nearer the inch look.

 

[cevgunner]

An update on the fix for lack of gas :

Shortround is correct - the gas port for an Inch pattern has to go into the barrel on an angle , drilled into the barrel towards the muzzle. The gas block was installed for sight correction , as well as having cut and recrowned the barrel. Wish I`d done it before the Appleseed shoot !

Once drilled in that fashion, the gas system operated fine. It`s set at 4 now , and runs the gun without excessive recoil being felt. At 18 degrees outside air temp, with the rifle stored in the trunk for 9 hours , it had to be set at 2 to run at all. Very much like the 1950`s cold weather test against the M14 in Alaska.

Recoil was noticeable , ejection was "brisk" , and I stopped firing after 12 rounds. The hammer and back of the bolt carrier had some fresh shiny places where none were before.

That would be the battering the 1950`s tests mentioned , I`d think.

Anyway , a large thanks to all - for the thoughts and direction. Here`s a pic of the finished project.

Thanks,
cevgunner