Lane

That's fine for this purpose of course. It was the stated "better than 0.1% error" that I saw in the specs, and wondered just how much better it really was. I spent a bit of time looking over discussions about QuickLoad. It appears the powder I have on hand (CFE BLK) isn't even in their latest database update. That's actually not the worst thing though; it means I will have to do my initial load testing by hand, and then try to hit OBT numbers from empirical data. The charge weights in most 300 Blackout loads are near 1.0 grain between start and max loads. Ladder loading shouldn't take very long... In a technical sense, it seems more appropriate to gather data first; and then see if the calculations match up. This is a good case for a shoot first and ask questions later approach. Of course I will still use QuickLoad later on to work up loads with other powders when I get to that point. Did some more reading about the failures of Long's theory; and there is some dissent in regards to totality and accuracy. Some people didn't get matching data with an explicit barrel length, and others found correlation; but also intermediate nodes that the theory doesn't address. Someone explicitly mentioned having to add exactly 1.5" to the barrel length to make it return the correct values. Seems like a great theory with plenty of room to grow. This thing showed up in the mail today; doesn't look like much, but it's a 10 GHz doppler radar module. I don't think it will help me inspect bullet speeds, but it's worth looking at in my spare time. Initial investigation indicated it could probably be improved dramatically with a horn antenna; but those are well over $100. I noticed one reviewer of the labradar indicated it didn't work at all where his targets were near trees. I wonder if I would be in that same position here; I shoot off into the edge of a wooded area myself.

You got me; I was tired. It was about 4 am here, and I had numbers on the brain. I should have absolutely written 0.010 MOA at 100 yards.

I tried to go to sleep; but this thing kept kicking me in the brain. Turns out that the Houston Warehouse is the key here. If those superior firearms were shooting at 0.010" MOA at 100 yards; that's 0.1" MOA at 1,000 yards. At 4,000 yards it is still shooting less than half an inch groups; assuming everything else is working in your favor of course... I guess that's the high water mark on the wall here.

That's harsh. Does anyone know anything that compares to this? I mean; a .45 ACP to the throat is cool at 200 yards... But this makes me question everything about making rifles. Is he shooting sub-atomic particles?

I'm all about recreational and games; but 3,520 yards is serious business.

All of this...

That is the truth sir. I haven't settled on a chrono solution; can't hurt much to use more than one. I would be curious to know how tight you think the measurement data is. Does it meaningfully measure 0.1 fps? The specifications on the Labradar are a bit loose in terms of accuracy; just states "better than"... Everything in the optical chrono department is laughable in terms of accuracy.

In case anyone cares; this guy attached a strain gauge to measure chamber pressure for less than $10. Clearly my kind of solution... http://www.ktgunsmith.com/straingauge.htm

Looks like he was testing bolt guns. These 300 AAC Blackout builds have no gas ports drilled, for this reason; among others. Also; couldn't find a gas block to match barrel diameter, didn't want to interrupt the barrel profile, and the gas system makes a mess where I don't want it. In general; I assumed making these semi-automatic would reduce achievable accuracy. I do not have Quick Load (yet); but he provides the formula to return each of those nodes at the bottom of the paper; under the heading Master Model. A, B, C, and D are all constants; L is barrel length in inches, and N the node number: OBT in ms= (A*N + B)*L + C*N + D. I think 98Z5V just stated that I will need the software to get the data for my specific loads though. This is still a huge step forward in terms of exploring resonance theory with authority. I can do all the calculations necessary to meet these specifications; then try to search for any missing nodes in the gap experimentally. At the very least it will be interesting to see how the groups evolve across that resonance profile. Looks like he swears by hardware called PressureTrace, which is little more than a strain gauge attached to the barrel; and an oscilloscope. That type of sensor hardware was already on my shopping list for this project; and I have an oscilloscope behind the wall I shoot next to here at home. The PressureTrace site has some interesting graphs about what a good load looks like; and those secondary peaks on BAD loads are pretty scary. I suspect the tiny necked 300 Blackout factory ammo I have here might be able to do just that; but I don't want to see it happen in these builds if I can help it. QuickLOAD software is only $150; clearly it's going to save me a lot more than $150 in aggravation trying to reinvent the wheel in this case. Adding it to the list right now...

I've got some other things I really need to work on; but I just want to leave this here in the mean time... I'm aware my colored annotations might actually be off by some vertical shift; this is still a general observation. No longer totally convinced this is the final word on the resonance issue. I think this basic graph ignores a second dimension (actually both X and Y); it appears to only look at Z (or girth). Regardless of how that was devised; there is clear support for this idea based on observed stringing when load testing. Once you cross a node at one of these points bullets will go either vertical or horizontal. Chris's empirical data actually shows the possibility of another node where he couldn't tune the load near 1.188 ms. It is my belief that there are a number of other points to test; one of which might be, at the very least; similarly accurate in terms of group size. His research very much makes a case for 1 FPS load tuning in my opinion. To hit these minimum jump points; a bullet needs to exit the barrel in a very precise window of time.

This Chris Long character is a real powerhouse. It appears he pissed all over the 21.750" doctrine more than 15 years ago. That assertion of resonance in the Houston Warehouse tome appears to be true; but not at all related to the 21.750" barrel length. He has done some further research and circles back to say this: "OBT theory clearly supports the prediction of the best time to leave the barrel so that the Jump (incidental yaw from barrel muzzle change in shape and rotational angle due to the shock wave strains) is minimized. The POI is still determined by the main vibration modes of the barrel, but the dispersion is all Jump. Minimize Jump, and the Swerve component is also minimized (assuming that the bullets are of high quality)." From what I can tell, he never did go back and measure the vibrations with strain gauges and acoustic pickups. His formula appears to be so airtight it might not even matter; but it's not much of an investment to collect the physical data myself. This appears to be a home run; and something I can easily test with any of my other builds right now (minus the 21.750" comparison).

Holy crap, I finally got a chance to read this carefully; twice... That was technical; and may well save me a lot of time. It appears most all of the data came from simulation, but proved the best groups in practice too. Apparently, there is an idea exit time based on vibrations in the barrel. If you miss one; you can probably still hit a different one with a different bullet weight/charge combo. But; you are also correct in that this supposes the barrel length will not matter... An ideal exit time can be hit for any barrel length by matching to a vibration peak. I would like to replicate some of these simulations with real vibration sensing. Seems like it would be trivial to determine an accurate load for a barrel with that data in hand. The only question in my mind is whether I hand tune loads first, and compare; or calculate first and try to hand tune it afterward.

Cheaper than a surface plate, and does the job I need; check. Now that 6-8 weeks for fabrication business is a problem. Found a Wheeler at Midway, and Brownell's sells something for a few dollars more. Not really fond of the look (quality?) of the Wheeler; and the Brownell's products looks like the Pacific Tool product. Seems like an easy decision considering I have a few uppers for this project. Same deal here; the Boot_Scraper thread sold me on that for sure, there will be 609 on each build (after I get done swapping barrels around once).

That was a good read. Sure enough; there is a thick walled, side charging upper in the pictures. They also recommend Loctite on the barrel as a substitute for real bedding in the upper receiver; something I've been contemplating as well. Everything else checks out except for truing the receiver... That is something I don't feel I have accurate enough tools for at home. I may have to find a machine shop that wants to do that if becomes a real concern. I suppose that won't be possible to determine without a surface plate, so add that to the list of tools outstanding for this project. The cheap stuff is flatter than 0.0001" which should be ok, but I'll see what I can afford. It doesn't need to be huge for this application.

I'll take this as a vote for "heavier may be better". My Bear Creek side charging upper is a totally different profile, and noticeably thicker in some places. I'll see what other options I can find in terms of weight difference. This was my initial thought on the barrel length discussion as well. But I won't be totally convinced until I see the data side by side; chopping a 24" barrel next to the 21.750" reference build. As has been earlier discussed; I don't expect my small sample size will amount to proven fact, but it will help me form an opinion for myself. And; I stopped at the store while I was out taking care of other business today... I might not be able to save them all for these builds; if it weren't snowing I might be outside right now trying to break rocks.

I want to believe this; I really want to drink that Kool Aid... But there is a point in this experiment that needs to be proven otherwise. My efforts may never make that dent; but I still wish to know. In a free floating barrel design; the upper is the only other variable (given appropriate lower constraints).

Which forge marks are on your AR-15 uppers? I would like some input here. I need another upper or two; and I think that is a worthwhile investigation. Houston Warehouse article talks about resonance; and that matters. If barrel nuts are mated with upper receivers, I should be able to fool around with barrels a bit in this way. I'm a firm believer in always having; but never using the forward assist. Might need to try a few other options though; to see if that make a difference.

Lol. Yes. I will be shooting explosives when I KNOW I have 2001 FPS down range. I'm going to have to invite my neighbor when I do; not because he would be scared, but he'll want a few targets too. When the 21.750" fires straight and fast; that will be my first task. This was really a comparison to the 7.62x39 gun with a 21.500" barrel. I should be able to shoot the 21.750" 300 AAC side by side, and get some good reference data. And I wanted that gun to be purposeful. I think I could hut the 21.750" if 150 grains are the one... Empirical data is the only way I'll be convinced on that front. This will be fun. And I can't see past my forth barrel in this project yet. The third will be ordered with the .260 barrel to save on shipping again. Armalite uppers should be available quite soon... I'm so excited.

Ordered the tube micrometer, and case length gauges for most everything I am reloading now. The trimming die should be here tomorrow for 300 AAC Blackout; I'll cut everything I have (a bit long) when I see it. I have a bunch of other cartridges to trim when I do; might as well collect all the brass shavings in the same sitting. I picked up some crude tools to cut brass down for 300 Blackout (and more once fired 5.56 brass). I was at harbor freight a few times recently, but didn't buy much; certainly not that chop saw at $35+tax. I wanted to, really; but it seems like I have better options around here already. Never going to use a tubing cutter on cases again, but it does work fine with a well adjusted tool. I just don't see the point when I'm going to trim it in the die anyway. That end can be raw and nasty. If I do it right I might get an ok anneal when cutting cases en masse.

I THINK I finally have my head wrapped around this; but feel free to add any correction. While the 1:7 twist is considered the standard that covers the whole range of 300 Blackout; if I'm trying to key in on the supersonic range, I may want something different. I did some more shopping around for future barrels in the process. Green Mountain sells this particular 1:7 blank specifically for 300 Blackout, but I should have considered their other blank options in .308 caliber. Those are available in 1:8, 1:10 and 1:12 twists. Fabrication won't know the difference or care; they are all .308 barrels... These initial 1:7 barrels can still give me an idea roughly what twist I'm going to want in a light projectile / supersonic optimized barrel (which may not even work for the heavy projectiles if taken to the extreme). The basic Greenhill formula I found doesn't account for bullet speed (very well); but can give me some estimates none the less. T=150(d/r): T=150(.308/(1.150/.308))= a twist of 1:12.3735 for a 165 grain Speer Hot-Core. Now; that 150 in the formula is apparently a constant related to bullet speed (I just don't know how to adjust it accurately). With some bracket testing I suspect the reality for the 300 Blackout may be closer to 1:10 or even 1:8 with the roughly 2000 FPS expected in a long barrel. I had a box of 155 grain match grade projectiles in my hand earlier; but nobody in the shop could find load data for 300 Blackout in 155. Turns out Lee had it, but not with CFE-BLK. Sierra actually provides the same load data for their 150 and 155 grain projectiles; I never thought to look at the projectile manufacturer's site before. Not sure I totally understand why lighter is going to be more accurate, but that's a problem with my incomplete knowledge on the subject. I'll try to work that out in my head as I do some load testing.

I walked outside today and heard someone shooting full auto; dumping 10 round mag, after 10 round mag. What a tease... Picked up some test projectiles for this project at the local shop. I know we discussed match vs. game projectiles last night; but I don't see a problem tuning my loads with game projectiles; and buying match grade when I find a good weight. Also got a micrometer today so I can measure necks; and about to order a tube micrometer to check wall thickness. I ran all the numbers I have through a ballistic calculator, and checked against barrel twist calculators. I didn't see anything to be overly concerned about with this 1:7, but I may be missing something important. I realized that I can start collecting empirical data with my .308 Win which has a 1:10 twist, and supports the same range of projectile weights (about 1000 FPS faster of course). Heard the weather should be reasonably nice this weekend... Sure enough; I saw a bunch of 1 pound exploding targets at the gun shop today. There wasn't a price on the shelf, but when I got home I looked it up. They aren't very expensive, I should have grabbed a handful. Next time for sure...

So far as I can tell, that's still totally legal. These builds should all land above that 2,000 fps threshold. Might find some nice fossils if planted correctly.

Tight butt holes; and nobody looks you in the eye. Everyone checks out your belt region though. They'll call the cops if the see a bulge. Welcome to NY state.

I want to; my local gun shop offered to take if for free (usually a $35 fee). Only now; the last few times I've visited, it wasn't a friendly environment. New people, and it's not going well in the back of the store. Again in NY, we can't quite buy online; has to be shipped to an FFL. I wish anyone would try to fix this garbage; but I just reload as a result. I really wanted to buy that 21.5" 1:8 twist GM barrel. I just couldn't justify the shipping when dealing with the rest of this. Is that a necessary accessory in this mix?

Or am I wrong again in my calculations?