Approaching max. velocity - discoloration in muzzle-area?

)Stephan

)Stephan

Member
Dear all,

with my newly acquired 6BR I am currently working on a load with 105grs Scenar bullets.
I finally found a load that will give me a v0 of roughly 2.850fps and now I would like to search a sweet spot between 2.800fps and 2.850fps.

What I noticed is that a discoloration (black, more than usual in this area) is visible with a borecam when approaching the muzzle.

I think I have never seen this before (with lower fps) and I am wondering if this should tell me something?

TY and best regards,
Stephan
 
It‘s a 24“ Walther (germany) barrel and I use N140.
I always clean with Iosso etc (not until it is perfect, but 97%).

Below are some pictures:
Chamber area:
IMG_5045.jpeg

Middle of the barrel:
IMG_5044.jpeg

Near muzzle, notice intense black stripes:
IMG_5043.jpeg

P.S. This is how the barrel looks like after 35 rounds, uncleaned
 
hmmmm how much n140..i see high pressure for 2850 in software
and advertised high velocity form a 6br is normally a 28" bbl
 
30.8grs of N140, maybe too much?
Primer still seems fine and bolt opens ok as well
 
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- Sure your gesture / movements at cleaning are the very same or as "intense" at chamber and muzzle side ?

- Barrel lapping choke/cone fitted the wrong way on action with small dia fitted on receiver side and large dia on muzzle side ?


Here, stainless Lothar-Walther barrels have the reputation of being hard on reamers. Not our usual 416. It may not be stress relieved, meaning that cutting the barrel profile with quite a cone therefore a tiny muzzle dia will naturally "unchoke" the barrel muzzle area and lower the accuracy potential, maybe also tending to gas leakage around a bullet which also has less acceleration in that area, therefore less expansion.

That was particularly true for Walther 22 LR match rifles, with reduced dia between chamber and muzzle for gun weight / rules reason, BUT full dia on the last 4 inches on muzzle side for balance reason (official) and muzzle choke (secret reason).

There have been a bunch of articles in PS about a 22BR guy slugging 22LR barrel blanks to seek on which side place muzzle and chamber and where to cut the crown.

You are maybe encountering something similar.
 
fwiw, I think the newer powders with bismuth might explain all or a lot of what you are seeing. Not smart enough to say it as fact but can say that the bismuth powders do this much more now than the same powders previously, of different lots(many). Of course that assumes we are talking about the same thing and I think we are. It also changes burn characteristics and I'm told it actually speeds them up a bit, for whatever reason. This would explain some changes I've seen from lot to lot, both faster and slower, before they seemingly got it pretty much right. Third time's a charm, I guess. It could be other things I suppose, too so take it with a grain of salt but I wouldn't completely dismiss it either. At least, that's how I've approached it and I see no reason to doubt what I was told. I've seen some of the newer powders make a lot, I mean a lot, of black goo that the same powders did NOT do and has improved since. There's a correlation but I'll let the chemists be chemists and just read the results. Lol! The powder that I'm referring to specifically was possibly the cleanest burning powder I had ever seen when pressures were even close to top end, but the newer stuff, ya couldn't put enough in the case to clean that up. Didn't seem very pressure related, really. Maybe some but not like I was used to anyway. Same powder is better/close in all regards but not quite like it used to be. Just fwiw
 
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