Lessons Learned on the Final Stage of the Journey to Subsonic Sub-MOA Accuracy with the 300BLK

[dellet]

PLEASE DO NOT LOCK THIS THREAD

He should have the chance to clear up the questions as to whether

a) He has a faulty barrel
b) He does not have the tools to measure headspace and throat depth.
c) Has the tools but does not know how to use them.
d) Has the tools, knows how to use them, but can't read a technical drawing.
e) Has the tools, knows how to use them, can read a technical drawing, but can not do the simple math required to come to the conclusion that his barrel is out of spec.

[smustian]

From an earlier post from sundevil he wrote:
smustian wrote:
So let me get this straight. I like to have .250 bearing surface of the bullet inside the case neck. Determine CBTO from that length. Then I randomly choose a powder charge from the min/max data provided by the manufacturer to be used in all subsequent testing. 5 round groups are a minimum for me if testing for group, so I would then have to load 90 rounds (5 shots per .001 change in CBTO) and then go shoot to find the most accurate/repeatable load for my rifle. Then repeat the same process with EACH bullet I choose to load? Way too much work, time and expense for me to consider trying it.

I usually use the CBTO as described above then load 5 rounds each of 5 loads which are in .5 grain increments, starting with max and working down. In those 25 rounds, I generally find a sub moa load. 25 rounds can easily be shot without your eyes getting tired and throwing off your focus. If two adjoining groups are the same, then I split the difference for the powder charge as they more than likely represent each side of a node. Maybe I am just getting old but it has worked for me for a long time and I am all for doing so something the easy way. "Work smarter, not harder" has a lot of merit.


I would have "started at max" and worked down, too. Anyone who has read my post knows I didn't do that. I didn't do that because I wanted to be able to report objective findings so I started from the other end. But when pushed, I suggested to Smustian that if he wanted to save time he could start at max COL and work down and do only (16) .001" intervals because he was bound to find at least (3) minimums in an interval like that. The best or lowest minimum would be the one closest to maximum COL. How is that wrong. That's exactly what he says he does only he looks at the (5) intervals closest to maximum COL instead.

Reread what I wrote. I stated that I picked a CBTO and left it there. I adjusted powder charges only in .5g increments starting at max and working down. My COAL and therefore my CBTO are almost always above what published data state. That provides extra case capacity thus reducing pressure. Published data is conservative due to lawyer stuff so starting at max powder charge I do not feel that I am in any danger zone. Your suggesting that I move the CBTO was not within the testing parameters I was using for my ladder.

[rebel]

This leads me to Rebel's comments. Actually, Rebel did a post on the CBTO curve, which predates mine and is actually the original definitive work on the subject for this forum:

CBTO- How it effects precision, rebel, Tue Jan 03, 2017 1:23 am
viewtopic.php?f=141&t=99968

This method is not original and is used by precision shooters everywhere. I just described as one of the processes I use.

A few things need to be said in comparing my work to Rebel's work, though. I was using a subsonic load with very low chamber pressures compared to the high power rifle with a supersonic load that Rebel was loading for. Also, I was staying within maximum COL, and not trying to get the last best minimum harmonic that exists within less than .020" from the lands.

Rebel admitted he had a lot more experience with that powder and that cartridge, though. That counts for something, but still loading beyond SAAMI spec for maximum COL is not recommended by the manufacturers.

The thing is that with the 300BLK round, you can't do it. The cartridge just doesn't have enough neck length to even let you try. That makes those pictures of the 300BLK cartridge in a bullet comparator pushed out to maximum freebore distance awfully silly.
....

Here you show your complete ignorance on this, and I suspect many, subjects.
I'm not wasting my time pointing out where and why, in this statement. I don't feel the need to prove that I am smarter, better, vastly more experienced, than you. You are doing a fine job of that. I am beginning to feel punked - like maybe you are really a 12 year old kid with a decent IQ and to much time on their hands. If this isn't the case and you are an adult - just shut up.

[bangbangping]

I looked through all the "other powder subsonic loads," and not a single one mentions or claims to be sub-MOA. Could that possibly mean that my load is the first?

Ummmm....no.

I'm guessing most folks didn't wade through the pages of batman's facebook post. Here is the (copyrighted...sue me) image of the much ballyhooed "sub MOA" load that took six months to achieve. I know I'm old and my eyes aren't what they used to be, but I see:
1. Two five round groups have only four holes.
2. One group nearly 1.5 MOA
3. One group just over MOA
4. One group just under MOA

By some sort of mathematic wizardry I don't understand, this is a consistent sub MOA load?

[bangbangping]

PLEASE DO NOT LOCK THIS THREAD

He should have the chance to clear up the questions as to whether

a) He has a faulty barrel
b) He does not have the tools to measure headspace and throat depth.
c) Has the tools but does not know how to use them.
d) Has the tools, knows how to use them, but can't read a technical drawing.
e) Has the tools, knows how to use them, can read a technical drawing, but can not do the simple math required to come to the conclusion that his barrel is out of spec.

Since batman seems unwilling (or unable) to answer, I'll throw out my speculation. He has destroyed the rifling ahead of the throat with his brush-on-a-Makita cleaning technique, doesn't realize it, and is unable to read the SAMMI drawing to understand that 2.993" is insane.

I use two rods. I use a copper wire brush on one rod. That's the rod I connect to my Makita. I use a jag with a cotton patch on the other. I use Hoppe's No. 9 Cleaning Solvent. I go through about (9) or (10) patches in a cleaning session before I feel that the residual copper trace on the patch is insignificant... I wet patch the barrel after every run with the Makita driven rod. When I'm done with all that I dry patch the barrel tell I get nothing...Then I spray the barrel abundantly with a generic, off-the-shelf Teflon lubricating spray.

Question about 300 BLK Bullet Drop on First Few Rounds