Well first problem is if your shooting 180 grain and less bullets you only need a 1-9 twist. This can cause accuracy issues with the wrong twist rate. You’ll have to jump up in bullet weight. 190 grain and heavier.
One of my 28 Noslers is in a 7.5” Lilja Barrel. No accuracy issues whatsoever. Shooting 180 Bergers as main bullet. Does not like ELDx’s and will cause nullet failures. More spin drift but that is deterministic. .5 MOA gun all day long on 5 shot strings.
. From your description of the things you tried it sounds like you have been meticulous at removing potential sources of error. Have you ever annealed the brass? I’ve read about neck tension causing flyers and annealing is the only thing you didn’t mention. I don’t know many people who trim the inside and outside of necks. Do you have a tight neck chamber or are you just trying to make the brass as concentric as possible?
Reasoning through it with logic here:
With a stock bedding pressure point, would this consistently affect just 1st shots?
I had a lens bedding issue in a NF NXS once(unknown for quite a while). Caused random double groupings 3/2, or 4/1. However, It was never consistent to a particular shot. NF tore the scope apart, found it, and actually fixed it,, on my suspicion alone!
Ammo issues are not gonna land on 1st shots only.
To me, a change between 1st/2nd shots, at least, is barrel temperature.
So the most logical culprit is a barrel affected by this.
I have heard of this problem but this is the first time with a Proof Research barrel.
I have seen it with factory Rems, Weatherbys, Howas, once with a Winchester that was rebarreled, a certain vintage of Savage.. but a Proof Research.. not until now.
as I remember the two guns that I saw with this problem; one was a buggy whip, the other was a magnum profile. the buggy whip was just tempered wrong (cold places and hot places) it showed some unusual metallurgy that made it dangerous to shoot.. the magnum was hard in one place and when it cooled the barrel bent, as it was shot the hard place heated up and straightened out.
all I can say for sure is I have questions.. lots of them.
the first is if it is consistently 2" to the right then it starts shooting.. that lends itself to a barrel that has either a hard spot or soft spot on one side of the barrel. soft spot left side, hard spot right side.
next question is have you called Proof and told them? they might have some insight on this problem.
next, well the next set of questions to be asked; first we must have an answers to the first two before going on.
As I stated, it sounds like a poorly heat treated barrel to me.
I have seen my fair share of these over the years. Tang safety Rugers had this problem, as did a few other manufacturers around the same time frame.
It’s not a proof trate like some have stated or suggested, I have 4 carbon proofs on my hunting rifles, all different cals, all shoot Cold boar and I can’t tell difference from my rock creeks which are also shoooters.
If they had been unsuitable for hunting applications the likes of Gunwerks and other manufacturers wouldn’t be using them on their hunting orientated rifles either.
it’s possible it may be a bad egg but it’s the last place you should be looking IMO.
I have contacted proof about a barrel. They are very helpful and nice. Hard to prove a target and or show a smith your problems with out being there shooting for them.
I put up a thread on SnipersHide trying to get some input or if anyone else experienced what I am with this 22” proof sendero. I really don’t want a rifle to sit at a smith again for another 5 months just to say it shot fine for them. LOL