Blown Accuracy in less than 1 mag...? Heat treat?

[pointblank4445]

Here ya fellas go JBS target (White is 1", Gray 2", Black 3") shot prone, pack supported at 100y:

The step-by-step of how it goes EVERY TIME
1) Solid group with at least 10+ shots in a 1" square
2) Group slowly opens 2-3x bigger
3) Group now more than 3x
4) No longer able to keep rounds in a 4" circle



3 hours later after the gun has cooled:
5) Aggregate back to roughly 1" though with slight POI deviation
6) Group back to not being able to hold 3" before the mag is done




Inherently, I/we/the system has proven over, and over, and over that WE are indeed capable. Meanwhile its identical sister build can easily show me this with after dumping 3x 30-round mags and produce the same baseline accuracy as when its cold, warm or scalding.

Granted only 5-round group (2x in lower left) but enough to note POA/POI is GTG

[pointblank4445]

I've never done the accuracy test,
.

Then you have not ACTUAL bearing/reference in this matter of your own.

Bold move to rest on the words of others.

With respect to physics/metalurgy, agreed how things SHOULD be, but as I mentioned before, every barrel has its own thing.

[bryan1211]

OP, have you checked that your gas block isn't making contact with anything inside the rail? Also, is the gas block taper pinned by any chance?

[pointblank4445]

OP, have you checked that your gas block isn't making contact with anything inside the rail? Also, is the gas block taper pinned by any chance?

In regards to this, yes it has been checked for alignment and contact with the FF rail...nothing to note there. The upper has been disassembled and re-assembled now per OEM torque specs. Roll-pinned GB not taper pinned. There was also concern that the barrel nut was bottomed out on the upper affecting torque (seen previously on a friends large-frame build) our out of torque spec. but does not appear to be the case.
The muzzle device and question of bore concentricity has been brought up and is being looked into. Again, the culprit DOES appear to down to the barreled upper assembly at this point.

[markm]

Bold move to rest on the words of others.

It's really not THAT bold. Like I said we probably experience this with 300 WSM but didn't realize the problem a the time. I don't see why you're so combative about this subject.

[pointblank4445]

It's really not THAT bold. Like I said we probably experience this with 300 WSM but didn't realize the problem a the time. I don't see why you're so combative about this subject.

It's mostly just been an illustration of the baseline level of ignorance and arrogance of the/our shooting community.

Personally, Mark... while I don't agree with some of the conclusions you and papa come to out there in the desert, but despite my feelings toward some of your assertions here, I actually do respect the work you put in to develop your own conclusions. I can say with certainty, your values/context/perspective and mine are not in alignment...which is fine.

I guess I had hopped for better from this place in regard for the inherent knowledge of what the AR15 is indeed capable of and not parroting generalizations.
...though no one has yet to come at me with "da M4 only need so hold 4MOA...so stop complainin" yet or questioned if I know which end the lung-blower-outers come out so at least y'all are still better than Snipershide.

[georgeib]

I'm going to go ahead and throw these two ideas out. First, if a barrel has an excessive extension to upper clearance, or a very poorly trued upper face, I can see this happening as things heat up. Second, if a barrel is hammer forged, and the steel not properly stress relieved, I can see this being a result.

Thoughts?

[ndmiller]

Feels like things are expanding at different rates with heat moving something else out of alignment, and I know a duh.

Using a straight edge, is the top rail straight after the dozen or so round heating up? Maybe it's torquing slightly? A small amount could be a lot at 100Y.

[pointblank4445]

Second, if a barrel is hammer forged, and the steel not properly stress relieved, I can see this being a result.

Thoughts?

It's been a while since I've had a barrel this apparently responsive to heat and that was a Remington bolt action and even then barrel mirage would require you to let off for a bit and let the gun cool if we were say in a school and allowed to go "free" on the 800y pop-up range. That said, the groups with increased use (whether heat or fouling) would wander up and slightly right.

With CHF and heat treat, would the gun just blow groups shotgun pattern (shots deviating in all directions) or would we see more "walking" in a direction....at the very least gravitating toward one half or the other...up or down? left or right?

[pointblank4445]

Feels like things are expanding at different rates with heat moving something else out of alignment, and I know a duh.

Using a straight edge, is the top rail straight after the dozen or so round heating up? Maybe it's torquing slightly? A small amount could be a lot at 100Y.

Rail is indexed to the upper and can't rotate.