I have a Criterion 6.5 Creedmoor barrel with just over 1200 rounds through it. It has shot right at and just under .5 moa up to approximately 900 rounds with 140 Berger VLD's jammed .010". I have chased the lands .020" so far and it has been able to maintain .5 moa. As it neared the 1000 round mark, even with the bullets jammed .010", it started shooting closer to 1 moa. I played around with jamming the bullets more and have got it to shoot better, but still not .5 moa with the bullets JAMMED .070"! This seems to be an excessive amount of jam to me, and not something that is very common from what I have found in the past. What would cause my barrel to suddenly need the bullet jammed so much to shoot half way decent?
Excessive VLD Jam
- Thread starter Tom Smith
- Start date
When was the last time it had a really good scrubbing? Not trying to be a smart-ass, Tom, but a thorough scrubbing frequently helps.
You need to measure your cartridge base to ogive before and after checking in the gun. I bet the bullets are being pushed back. I never saw a gun that would allow a .070 jam. About the most I ever saw without moving the bullet was around. 030. Also maybe you have carbon in the throat. A good cleaning and check with a borescope sure wouldn't hurt it. Matt
yep
losso and a parker hale jag with a patch wrapped around it dampened with your bore cleaner of choice. short stroke with the losso and damp patch the throat and first 10 or so inches of the bore until truly clean. lyman borescope is the best way to ensure you have it clean.
after clean then redo your overall length with your favorite bullet again.
soft seating works well for me with some bullets. sort of what you are doing with your .070 jam depending on neck tension.
losso and a parker hale jag with a patch wrapped around it dampened with your bore cleaner of choice. short stroke with the losso and damp patch the throat and first 10 or so inches of the bore until truly clean. lyman borescope is the best way to ensure you have it clean.
after clean then redo your overall length with your favorite bullet again.
soft seating works well for me with some bullets. sort of what you are doing with your .070 jam depending on neck tension.
There is a 22-250 thread with a "shot out" barrel on this forum a few or so pages back that the owner ended up seating the bullets way out there to the point of absurdity when looking at the loaded round and he did groups throughout an experimenting process. He also cleaned the barrel very extensively and by the means recommended on the thread. I only mention it because I though it was very interesting and wondered if I'd ever see something like that myself. I asked him to chamber a round without closing the bolt and shove the round in tight with his finger and tip the gun barrel up to see if the round would stick or fall out, he said it fell out. If the OP here does that then that would tell us if the bullet is indeed shoving back into the case I'd imagine. Plenty of creative and/or proper ways to tell the bullets relation to lands...
I measured the COAL with a hornady tool and a frankford arsenal tool and they both gave me the same thing, 2.215" measured off the ogive.
I came up with the .070 jam by partially neck sizing a case and chambering it with a bullet started in the neck. After closing the bolt on it several times I measured the the COAL and got 2.285". According to the measurements I got from the COAL tools that puts me at .070" jam. I have repeated the process several times because I didn't think it was possible, but I get the same results every time.
Only other explanation is that both tools are wrong and my actual COAL is 2.285"
COAL always confuses me, don't even know why it's used outside of AR or "MSR" purposes... To me it seems that closing the bolt when using your method isn't sensitive enough. I've been pretty close in the past doing that with my fingers. Take your brass you use now and seat the bullet by hand and shove the round into chamber with your fingers and measure each time, I shove it in and tip gun barrel up, if it sticks then I measure and seat bullet deeper, repeat until it falls out of chamber, I do that process twice and come up with a CBTO for my round very close to when I use the proper tools, with only a couple exceptions.
Dusty Stevens
Shiner
You can go .070 on standard leade angles and vld bullets. Youre right at what short range br shooters call jam which is seating long then pushing it back. It takes .100 sometimes to stop getting land marks which is what other shooters call touch
Ahhhhhh …. I've wondered about that. Probably helps with concentricity seating a known concentric bullet into the lands "manually". I've seen their loaded rounds and have always been surprised at how much further out they were then I thought logical. Also give me some thinking/questions regarind playing with leade angles.
Dusty Stevens
Shiner
Let the reamer maker decide on leade angles. No need in wasting time trying to reinvent the wheel- most times you get a square wheel.
gme
Site $$ Sponsor
so is 2.215" the CBTO (cartridge base to ogive) measurement of a cartridge when the rifle was new?
I always measure base to ogive
gme
Site $$ Sponsor
I see, so what does the 2.215 dimension represent? Was it taken at some point in time between the 2.205 and the 2.285?
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