It never settled back down after 40 rounds. It kept at ~2700FPS.
Here's some background leading me to my 'suspicion' that IOSSO, even in limited quantities, can hurt a barrel. I'm also not trying to make any profound statements here; merely sharing observations & my own speculation.
A couple of key things to get out of the way.
- I use IOSSO fairly conservatively; usually one patch worth and ~10-15 back and forth strokes per ~250ish rounds (on average). I never put it on a brush (of any kind), and I always run a ton of butches soaked patches afterwards to ensure I remove it. I'll even pull the boreguide and mop the chamber area.
- I own a borescope. The reason I used IOSSO is because it removes carbon better than anything out there.
- All of the components in my loads are the same lot, across both of these barrels. Same lot of powder, same lot of bullets, all the barrels are cut from the same reamer. N150 powder/200.20x bullets.
So.... lets begin.
Barrel 1: 30" Kreiger on my FTR gun. Barrel is the most accurate I've ever owned. When I was finished load deving it was holding 1/4 MOA at 300 for 20 rounds. Crazy accurate.
This was probably the first barrel I'd started using IOSSO in. I had previously been using JB, and found IOSSO to be significantly more effective on the borescope. That said, the barrel abruptly died on me at ~800-900 rounds, and I couldn't tune it back in. It went from shooting insanely well, to struggling to hold the 9 ring at 1k in calm conditions.
The last match I shot, I recall after the last string letting an observer take several shots with my rifle. Probably 10-15 after I'd just finished shooting my 20 for record. I do remember him doing quite well with the rifle. I think he only dropped a point from the shots he fired? Basically...it was still shooting well.
I couldn't really make heads or tails of this barrel abruptly dying. I didn't think putting ~45 rounds on the barrel in relatively quick succession would kill a tube (because I do shoot long strings regularly...I shoot a lot of sighters).
I chalked it up to "I guess Krieger had a bad batch of steel or something." or "maybe I should be more careful with cleaning". Regardless, a new barrel fixed it.
Barrel 2: 30" Brux on my FTR gun. Barrel isn't the most accurate in load dev, but it's the most consistent by far. I think it shot at least one clean at every 1k match I entered it in (with exception to the last), it got me an honest LR HM card shooting an FTR gun. The barrel was good. It was tuned in at 2640FPS 44.4gr of N150.
It had shot really well for the duration of the gun. I didn't log using any abrasives until about the 1200 round mark.
That said, for the last ~3 matches I'd been shooting V2 qualifiers, and as a result had been shooting ~120-140 rounds per match. Because of this increased round count, and the extended barrel life, I started using IOSSO every time I was cleaning the gun (lets just call it from round 1500-2000 it was getting IOSSO).
For the first V2 match it hammered; shot a personal best 597-something x. Second V2 match, 592-something x, third match I could absolutely tell accuracy was falling off; it was still competitive, but X counts were lower than most others. Shot a 589 low 20s X.
At the end of this last match, there were also two observers/new guys who I offered to let shoot after we'd concluded our pair firing v2 strings. They each shot ~7-10 rounds, and they cleaned the target lol.
I take the gun home, clean it like normal, and take it out to see how it looks at 300 yards, and to run it across a chronograph.
To my surprise it's running 2700-2710, and continues to do so for like 40 more rounds. It's putting up .8 MOA of vertical at 300. Yikes.
That day I also brought with me my secondary FTR rifle (it's identical to my primary), and it's got a Krieger screwed onto it (same chamber). The Krieger is running 44.6gr (so .2gr higher) and it's running 2660 across the same chronograph, in the same temps.
I decide to just replace the Brux because it's really not worth dumping another ~$150 worth of components trying to retune a barrel with 2000 rounds on it.
Summary:
Those two experiences lead me to believe IOSSO might be damaging my barrels. It could also be me letting new shooters put rounds on my gun immediately following strings. I'm not real sure. What I am sure of is I'm not going to be using IOSSO in my TR guns for a bit, just to see if the behavior is any different.
While thinking through this, I've also never observed a TR barrel lose accuracy (at least accuracy that matters in F-Class) due to carbon. I'm planning to continue with aggressively brushing/butches (and maybe some BoreTech Cu for copper), but I'm going to give the abrasives a rest; I'm not sure they're needed for what I'm doing.
And now you know, the rest of the story...
Edit: Also not trying to scare anyone here. [obama voice] If you like your IOSSO, you can keep your IOSSO[/obama voice]. I'm also not advocating anyone change their routine. I'm confident there are better shooters than me who love the stuff.
That said, I've done quite a bit of reading on this topic, and I believe I saw Alex Wheeler mention he stopped using it due accuracy concerns. After reading that, along with my own observations listed above, I'm just trying something new.
Some say use abrasive cleaners--some say not. Some say use abrasive cleaners on a bronze brush--a top barrel maker and gunsmith say it will ruin barrels. Some say not to use brushes at all. Then I bought a borescope. Now I'm scared on top of being confused. Rant over. Carry on
