Extreme Case of 1st Round Flyer

[B-P-UU]

Some background... I checked velocity on my dasher since it had 1800 rounds on it last week and it's slowed down about 30 fps and groups have opened up a bit. So I decide to increase powder charge to try and get back up to the 2950 fps range. Went up in 0.1 grain increments from 32.6-33.0 grains of varget and one lower at 32.2 grains (5 each). Did not adjust seating depth. I also went ahead and loaded 75 rounds at 32.8 to work on positional shooting since I was out.

Ok, decided to warm up with a 6x of the 32.8 since I had a bunch of them.. about half MOA.. good deal. All of this shooting was at 100 yds.
Moved on to shoot the 32.6 without letting things cool off. Not great results-no big deal. Pulled my can cover off and let things cool off. Resume shooting 32.7 and couldn't even tell where the first round hit it was so low. Went on to shoot remaining 4 and they grouped. Repeated results for 32.9, 33.0 and 32.2 loads.. let things cool between and got crazy fliers the 1st round, then things would settle in. I re-shot 5x 32.8 to confirm my initial results and it did the same thing.. 1st round flyer.

What is really strange is how dirty the first round would come out of the chamber.. as dirty as a .223 out of an AR running a can. Next 4 would be normal in terms of cleanliness.

Barrel has between 200 and 250 rounds since last cleaning.. nothing unusual there. Suppressor was and is tight.

Never experienced anything like this before.

Here is the target.. bit of an eye chart, but shows how far the flyers deviate from the groups. First 6x group is lower left.

Brass

 

[B-P-UU]

Shot at distance a few hours later.. at 500, first impact was low and then shot a nice 3x group.

Moved to 660 with little cool down and still had a 1st round flyer, but not as severe. 8 rounds on this target.. 1st is low/right. Target is about 16 square for reference.

Let things cool down and shot again at 660. First round splashed in the dirt.. like 1-2 MIL low and 0.5-1 MIL left... didn't touch a thing and re-engaged 3 more. Here are shots 2-4 on a 10" plate at 660. You can cover that group with a spray can cap.

Very strange.. thoughts appreciated.

 

[Alaskashooter]

Not sure what barrel life is on these but it sounds a lot like that first round is warming things up to make the steel swell and tighten back up somewhere.

 

[Precision Underground]

It’s like it’s not sealing and losing energy spitting gas into the chamber on the case. Why the hell that happens on round one only, hmmm.

 

[spife7980]

How cold was it? Cold enough for that hot combustion air and water vapor to condense on the chamber walls when given a chance? If you leave the spent case in while it cools down or leave the bolt closed, does it do it?
If you wipe it out with a paper towel or dry bore mop does it do it?

Does it do it without the can cover off?

 

[Ruby]

I am new to the site and just caught this thread. I have the same problem with a .224 Valkyrie. 450 rounds through the Criterion barrel.
The can is a Mack Brothers Varminter 3.0 .30 caliber can. I have checked the can with an alignment rod and it looks very centered. The rifle groups consistently .75 moa or better. and I have had some 3 shot groups as small as .35. with the can and can cover on. The issue seems to be the short cool-down between strings. I can get anywhere from 1-4 inch change of impact (or more) on the first round after a 5-10 minute cool-down. Point of impact of the flier is not consistent either. During a long rang class we were doing a consistency check of our position. One shot, then break position then reestablish position and fire a single shot at another aiming point. The attached picture is at 100 yards. First round impact way off. I can't say it does this all the time either. The last range session I was intentionally trying to get a flier. I shot 8 groups with a cool-down between and had no issues.