Barrel Cutting - Gas Block Screw Torque

[my1911s]

My barrel cutting project is moving into the final stages. Having completed the barrel and flash hider and worked through some small issues that were affecting group size, I am down to the gas block screw torque. I gathered information on this subject from searches and questions I posted here as well as searches on the net. In the end, I just needed to find the answer on my own, so I setup a controlled test for screw torque.

Beginning with a clean barrel, I removed each gas block screw and cleaned off all the thread locker. I then set the gas block gap at .032” @ 5 in.lbs. and proceeded to torque the screws to 20 in. lbs. in an X pattern. At the range I setup an 8” target and four 4” targets at 100 yards. I fired four rounds at the 8” target to foul the bore and check the scope alignment. I then Bore Snaked the barrel one time and checked the screw torque and fired a five shot string at the first 4” target. Again the barrel was Bore Snaked and the screw torque increased to 25 in. lbs. I repeated this process for 30 and 35 in. lbs. with the following results:

Test 1 / 20 Inch Pounds - Max. Horz. Deviation 1 ¼” – Max. Vert. Deviation 2 ½” – Extreme Spread 2 7/8”

Test 2 / 25 Inch Pounds - Max. Horz. Deviation 3 ½” – Max. Vert. Deviation 1” – Extreme Spread 3 ½”

Test 3 / 30 Inch Pounds - Max. Horz. Deviation 2 ¾” – Max. Vert. Deviation 2 1/8” – Extreme Spread 2 3/4”

Test 4 / 35 Inch Pounds - Max. Horz. Deviation 1 3/4” – Max. Vert. Deviation 2 1/8” – Extreme Spread 2 1/8”

I response to an earlier post, “pbrktrt” said “gundoc” recommended 36 inch pounds and he is right. I setup another 8” target, Bore Snaked the barrel, increased the torque to 36 in. lbs. and fired two five shot strings as follows”

Test 5 (Red Center) / 36 Inch Pounds – Max Horz. Deviation 1 1/8” – Max. Vert. Deviation 1 ¼” - Extreme Spread 1 5/8”

Test 6 / 36 Inch Pounds – Max Horz. Deviation 1 7/8” – Max. Vert. Deviation 1 ¼” - Extreme Spread 1 3/4”

Not only did each five shot group shrink, nine of the 10 shots grouped 1 5/8". At this point, I’m satisfied with the rifle modifications and I am ready for load tuning.

[rutro]

Excellent report my1911s!!! That's some great info too. You just convinced me to invest in a proper torque type screwdriver. I've been trying to get by with an old 3/8ths drive longhandled inch pound wrench. It's getting me in the general area of torque but it ends up being all feel at the end. What are you useing if we may ask?

[my1911s]

I'm using a KD 1/4" drive beam wrench. About a year ago I heard Wheeler was comming out with a 1/4" torque driver but when I contacted them, they said it would be about six months. I couldn't wait so I bought the KD. It works just fine but I'd rather have the driver.

[tri70]

This is excellent info! Thanks for all your hard work on this project. Have you cryoed your barrel?

[tri70]

Here is a link on a torque wrench 1/4" drive and 20-200 in/lbs from Harbor Freight. http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=2696

[my1911s]

No on cryo, the wrench you mentioned does not have the range needed for most gun work. Zero to 60 inch pounds is most useful. Here is a link to a beam wrench that works well.

Manufacturer: KD Tools
Manufacturer #: 2955
ToolSource #: 71321


http://www.toolsource.com


Another source would be Midway for the Wheeler torque driver.

[texastom]

Just received an update from Andean and they show the Wheeler torque screwdriver (but not in stock currently).

They are on our vendor link page and I am not affiliated with them, but did buy my camo lamo stock there and was pleased with service.

http://www.andean-inc.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=TAOS&Product_Code=WH553-556