300w (7.62x40) - 20" is now cycling

[txjm]

I opened up my kinda 7.62x40 barrel with the port in the rifle location barrel to .108" and tried it with 1680. I am functioning now. Happy days. Stock A2 lower. I am at about 2300 fps. I am cycling but not locking back, I'm happy for the moment. I hope it shoots as good as it looked like it would the first time I took it out.
Thanks Kurtz.

Chip

[kurtz]

Originally Posted by txjm

I opened up my kinda 7.62x40 barrel with the port in the rifle location barrel to .108" and tried it with 1680. I am functioning now. Happy days. Stock A2 lower. I am at about 2300 fps. I am cycling but not locking back, I'm happy for the moment. I hope it shoots as good as it looked like it would the first time I took it out.
Thanks Kurtz.

Chip

sounds like a good news.....I had the lock problem also, the quick fix on the rifle I built a week or so was to open the port another .002 - .003.....if the port size is too close to the edge as it carbons up it will only get smaller and compound any cycling problems.....I've seen .223 guns with the port in the rifle position sized .125 so I don't think .110 to .115 with a .30 cal bore is too outa line....

does your last name start with a 'N'.....think I may know ya.....

[nwcid]

I have one that I may need to open the port on. How do you measure one and how do you properly open it if needed?



.

[txjm]

does your last name start with a 'N'.....think I may know ya.....
M - Live west of fort worth a little ways.


How do you measure one and how do you properly open it if needed?

I would think a pin gage would be the best way to measure. You could probably get by with back side of different drill bits. You could get close with multiple reading with a caliper. I opened mine up by clamping the flat section of barrel in a v-block and squaring off of the lower surface of the upper. I used a center finder to center on the hole. Be carefule a drill bit likes to drill oversize, work you way up slowly. Don't go to deep. I used a mill, if you are careful you could get by with a small drill press. You would get in trouble with a hand drill.