AIAT barrel change issue

[verdugo60]

Have had it since 2014, really love the rifle. I have a Europtic 6.5 CM barrel that I have never gotten to shoot quiet as well as my Gradous 243 barrel but it's still usually 3/4 moa. I have about 500 rds on it and decided to check my distance to lands with an ELD-M 140 grain. Thought it might have grown since my initial load development. My current load with that bullet is 2.828" coal.

I use the Hornady coal gauge with a Hornady modified piece of brass. Screwed on the 6.5 barrel hand tight, torqued the set screw to 50 in lbs with a borqa torque wrench(the variable one, not the set one) and checked the distance to the lands. Got 2.72" with two different 140 ELD-Ms.

Questioned my sanity and ability to read a micrometer, then unscrewed barrel and screwed hand tight, torqued to same spec again...2.82" with same bullet. Tried again, 2.83". Screwed on hand tight but twisting a bit harder and then torqued, back to 2.72".

Now I don't have a comparator to measure to ogive, but with polymer tipped bullets you don't see the variance you do with an smk tip, etc. Plus I used the same exact bullet each time. I have not tested my other barrels yet but this is concerning because I'm assuming if the lands are changing depth, so is my headspace. This affects accuracy and brass life, I'm only bumping the shoulder .003" but apparently my headspace changes more than that just by how much I flex when hand tightening. Anyone else measured this? I'm wondering if it's an issue with this specific barrel or what. I'm not cranking super hard to get the difference, just going until I feel the shoulder is flush and it's a solid lockup against the receiver.

Curious what you guys think.

Thanks.

 

[Supersubes]

Its your oal measuring, and has nothing to do with the barrel install. There is no way you’re changing chamber dimension by adding a little more hand torque. If you added 100ft/lbs barrel torque you’d hardly shorten things .001” let alone .1”

How’d you come up with/choose the 2.82 figure in the beginning? Curious your current measurements(except for the erroneous 2.7”) match your established load seating depth. We’re you intentionally seating them to touching, or jamming. The throat probably hasn’t moved much, but it has moved.

 

[verdugo60]

I normally load .02" off the lands with eld-m's. My original coal touching the lands was 2.85 so 2.828 was .022 ish off. Another clue that the barrel isn't locking up the same each time because I'm getting 2.83 currently and that's close to jammed with my original coal. My lands shouldn't be getting closer unless I got a magic barrel, lol.

I know it takes practice with the coal gauge but I checked and measured half a dozen times and kept getting the 2.72 number for coal. Verified it with 2 bullets. Wasn't until I loosened the quickloc, backed the barrel out, hand tightened and re-torqued to 50 in lbs that it changed back to 2.83.

 

[verdugo60]

I'm going to borrow some go/no go gauges to check headspace next.

 

[Supersubes]

I normally load .02" off the lands with eld-m's. My original coal touching the lands was 2.85 so 2.828 was .022 ish off. Another clue that the barrel isn't locking up the same each time because I'm getting 2.83 currently and that's close to jammed with my original coal. My lands shouldn't be getting closer unless I got a magic barrel, lol.

I know it takes practice with the coal gauge but I checked and measured half a dozen times and kept getting the 2.72 number for coal. Verified it with 2 bullets. Wasn't until I loosened the quickloc, backed the barrel out, hand tightened and re-torqued to 50 in lbs that it changed back to 2.83.

You’re having issues holding a full tenth of an inch tolerance with your seating depth checker now, do you really think the .020 variance you had between new barrel(then) and now is significant?


Your barrel has a 2 mm thread pitch. When you screw the barrel into the receiver, it advances .0787” per revolution(.0021” per degree). So you’d need to screw the barrel on an additional 1.27 turns to shorten the chamber .1”. The opposite situation would be a .1” air gap between the receiver face and barrel shoulder, which would be obvious. Now that’s not happening since the barrel shoulders on the receiver face, and the barrel nose shoulders on the breech ring. You’re barking up the wrong tree here.

If your rounds were .1” too long(2.82 in a chamber that’s 2.72), you wouldn’t be able to close the bolt. Even if you were able to, it would take some serious effort.

 

[Badfinger]

Have you tried factory ammo? I found that my AIAT .308 doesn't like long bullets and does it's best at 2.80 to 2.810.