Weird grouping issue

[Blowout]

What if you tried waiting longer between the first, second and third shots. If read correctly you tried a 2 minute wait between shots, but perhaps 15 min or longer would better replicate the same temp conditions as the first round.

Wondering if the receiver isn't trued to the barrel extension and it's enough to throw off a cold bore shot. Doubt Palmetto would true the receiver. Just a thought...
Should be able to rule this out with a long wait between shots.

[Whole Bunches]

I said two minutes. Actually I had two fans blowing on the bbl and suppressor. I would shoot when the bbl and suppressor felt cool to the touch. It took about two minutes for that to happen. Other than a couple of groups fired as fast as I could aim with no fans blowing to see if a hot setup changed anything...it did not...the setup never got hot to my touch, as I wanted to duplicate cold bbl hunting conditions. Inbetween groups I would also have a Caldwell AR bbl cooler attached blowing inside the bbl to make extra sure all was cool, so it is possible that the bore could have been a touch cooler on the first shot. I ran the inside bbl cooler when I would walk to the target, so it was more like a few minutes than two minutes. I “measured” the temp with my hand, not a thermometer.

I used to have one rifle which if shot with a hot suppressor and a cold bbl would open up the groups, so to avoid that possibility, I made every effort to keep the bbl and suppressor cool to the touch for each shot. That rifle was a Blackout Remington M700.

I have never had a Blackout bbl do like this. The upper receiver is a Bear Creek side charger and only with the Barnes 110 gr black tips. Even tried Barnes 130 gr copper Hog Hammer bullets (not available to the general public for reloading) and while not a small group as I would prefer, the first shot was not out. Tried 123 gr 7.62x39 bullets...first shot not out. Nosler 125 gr BT...first shot not out and small groups, so that is what I will use, although they are not my first choice for hunting like the Barnes is.

Edited to add: will be taking it out to sight in with a thermal prior to a hunting trip. Will fire first shot and leave the subsequent shot chambered and give it a long time to cool with double fans blowing and see where the subsequent shots go. Thanks for the suggestion. Will keep gun in the shade too.

[bangbangping]

Curious...did you ever eject a middle-of-the-mag round instead of firing and then place that round as the first in a mag? Seems like the only things not completely ruled out are a change in the way the cartridge lies in the chamber or a change in the cartridge itself when auto loading. If it's the latter, an ejected auto-loaded round might work as a first shot round. Just a thought.

[dellet]

It’s possible that the barrel either does not like copper, or flat base. I can’t remember what the Hog Hammer bullet was.

Do you possibly have any of the 120 Barnes?

[bangbangping]

It’s possible that the barrel either does not like copper, or flat base. I can’t remember what the Hog Hammer bullet was.

Do you possibly have any of the 120 Barnes?

That still wouldn't be definitive. Maybe the barrel doesn't like black tips or has a beef against Barnes.

[Whole Bunches]

I have maybe 5-6 of the 120 Barnes. Never ejected a middle of the group round...may try that, but at some point I get tired of trying different things. Have not put the bbl on another upper either.

[bangbangping]

at some point I get tired of trying different things.

Understood, but you must keep your audience in mind.

[dellet]

It’s possible that the barrel either does not like copper, or flat base. I can’t remember what the Hog Hammer bullet was.

Do you possibly have any of the 120 Barnes?

That still wouldn't be definitive. Maybe the barrel doesn't like black tips or has a beef against Barnes.

Copper bullets need more pressure to expand and seal the gasses behind the bullet.

The only thing he has had trouble with is copper and flat base.

I don’t remember the the Hog Hammer bullet being solid copper, it might be.

This is also why I suggested slugging the barrel.

If the bore is a bit loose, it’s possible that what is happening is gas cutting the base of the bullet, that would effect a flatbase more than a boat tail and could change with temp if the bore tightens even slightly. I don’t think that would give repeatable results tho.

I would be looking hard at barrel nut torque, and possibly the mating surfaces of the barrel extension and upper.

[Grouse870]

I think I may have figured it out i tried a spikes st2 buffer. I was able to shoot the below group (assuming the pics work) with hornady 125 hp (any idea how these work on deer? Max range 200 or so yards) still need to try some 110 blacktips to fully trust this. But these groups are encouraging

https://imgur.com/gallery/wqZkv5T

[dellet]

I think I may have figured it out i tried a spikes st2 buffer. I was able to shoot the below group (assuming the pics work) with hornady 125 hp (any idea how these work on deer? Max range 200 or so yards) still need to try some 110 blacktips to fully trust this. But these groups are encouraging

https://imgur.com/gallery/wqZkv5T

Looks like a good start, will be interesting to see the barnes.

I right clicked the photo on your link and chose "copy address" used the IMG button at the top of the page and pasted the code . There should be an easier way.



Nice target anyway