A definition of OCW might help understanding.
A definition of OCW might help understanding.
AKA "Old Vic"
"I am a great believer in powder-burning".
--Theodore Roosevelt, Hunting Trips of a Ranchman
I have found that incremental charge weight testing does lead to finding an 'accuracy node' with most rifles. Using charges that are 0.2 grains apart, at 200 yards there will be a vertical string of the testing, BUT there will be several different powder charges that group together and do not string vertically. I consider that group to be the 'accuracy node' for that powder and bullet combination. I usually pick the middle powder weight of the group as my 'standard' load, the 'OCW'. I sometimes fuss and do additional testing at .01 grain increments with more shots per increment but it is a good way to find an accurate load for a bullet/powder combination without burning huge amounts of powder. The testing can be time consuming, I usually shoot two rounds at each weight, walking back and forth on my 200 yard range marking the bullet holes, calling the walk exercise. This grouping can be noticed with most rifles that shoot 1.5 MOA or better. It is at the longer ranges that the incremental/ladder load development shows the differences with differences hard to determine at 100 yards. Using the middle powder charge of such an 'accuracy node' also reduces/eliminates the need for trying to weigh/measure powder charges to less than a 0.1 grain tolerance.
This method has worked for me using cast bullets in the .308, 32 Special, 300 Savage, .35 Rem using 5744, RL7, 4198, 4227 and others for 'mild' loads. I have also used this method in the .308, .300 Savage, .300 Win Mag, .358 Win, others for full power 'hunting' loads with RL15, H1000, 2015 others.
My results are the results of rounds fired down range, not engineering calculations. Along with vibration nodes from bore expansion there is large vertical 'vibration' or nodes based upon recoil and the barrels' normally vertical displacement due to recoil. It is this vertical node, top or bottom, when the barrel is stopped and about to change direction that I am trying to find.
Last edited by MostlyLeverGuns; 03-16-2021 at 01:11 PM.
Felix Robins was an early member of this site who has since passed on. He was an engineer and a bench rest shooter whose knowledge far exceeded most of ours here. He wasn't shy about sharing what he knew if you asked. He believed that most barrels did their best at accuracy multiples of 800 fps and IIRC called this accuracy nodes.
He also said the half nodes were close, so best theoretical accuracy should be looked for at 800, 1600, 2400 and 3200 fps with close accuracy coming in at 1200, 2000, and 2800 fps. i have found this to be accurate in my limited testing.
[The Montana Gianni] Front sight and squeeze
Here is some more on OCW. http://www.ocwreloading.com/
AKA "Old Vic"
"I am a great believer in powder-burning".
--Theodore Roosevelt, Hunting Trips of a Ranchman
In engineering calculations, it would be necessary to find the moment of each individual barrel. Barrel taper, barrel diameter, caliber, barrel length, attachment to the receiver, type of bedding - free floating versus contact of any sort any and any attachments - gas ports and such with hardware. In my testing I have found that the lighter and longer a barrel is, the more significant the 'accuracy node' becomes in shooting smaller groups. Heavier barrels are less affected by changes due to the heavy barrel vibrations being smaller with less 'whip'. Shorter barrels also show less vibration due to less 'muzzle whip'. The longer, thinner, lighter barrel is not necessarily less accurate, it just requires more careful development to attain accuracy that is easily found in barrel that is not carried longer distances in rough terrain(too heavy). The various tuners, mostly at the muzzle, are based on adjusting the barrel moment to the load being fired, rather than adjusting the load to the barrel. Browning did sell hunting rifles with such a tuner, the .22 Rimfire benchrest folks commonly use such devices. SOME vertical stringing at closer ranges can be eliminated with load tweaking to find the 'sweet' spot or OCD. It is there for most load levels, but might take more room (distance) to be noticed with low to moderate 'close range' shooting.
If I understand this concept, the bullet has no affect on OCW. OCW is determined by the time it takes for the bullet to exit the barrel at the node point.
So, if testing 55 gr bullets in a .223, if the node occurs at an OCW of 24 gr of powder X, every make and style of bullet that is tested will be most accurate at that charge. If one bullet shoots 1/2 MOA, and another shoots 1 MOA, trying different loads with the 1 MOA bullet is a waste of time....it will never shoot better.
Don Verna
I do not think you have to give up on a different bullet without a little testing.
The exit velocity and time of exit is a function of the powder charge, primer and case capacity after the bullet is seated. I created a fictional 223 Rem load for a QuickLoad analysis. Load is 25.4 grains BL-C2, Nosler Bal Tip 39525 (55 grains), seated 0.309" and COL of 2.260". If fired in a 24" barrel, the exit velocity is 3,053 fps and an exit time of 1.099 mS.
A 24" barrel has a theoretical node at 1.100 mS. This fictional load was designed to match that node (1.099 mS vs 1.100 mS). I selected 9 bullet styles from three manufacturers (Nosler, Hornady and Sierra) and created loads identical to the Nosler Bal Tip load. In each case, the seating depth was maintained at 0.309". However, this did result in changes of the COLs for the other eight loads. As expected, the barrel exit times were constant since all the load parameters were the same with a constant seating depth. This was a comparison of nine different style bullets.
I select four different Nosler bullets; one being the Nosler Bal Tip 39525 (55 grains). The four bullets were modeled at 25.4 grains BL-C2, Nosler Bal Tip 39525 (55 grains) and a COL of 2.260". This changes the seating depth of three loads. The exit times ranged from 1.062 mS to 1.14 mS. The desired load had an exit time of 1.099 mS. In this example, the 1.062 mS load is a half node off a desired node. Theoretically, an accuracy node occurs when the wave is at the rifle breech; when there is the least disturbance of the muzzle. The 1.062 mS exit time would put the wave at the muzzle at the time of bullet exit. This would be the time of most disturbance and least accuracy(?).
I think this shows that the seating depths of the bullets can affect the timing and accuracy. So, that comparison weight bullet that is not performing well may tighten up with a little adjustment in the seating depth to get back on an accuracy node.
Just my thoughts.
I have for many years used a load of IMR 4350 54.5-55.5 grs with 168 SMK's,and Nosler 165 gr ballistic tips in the 30-06. However I do use a magnum primer. 3 model 70 Winchester match rifles, one standard model 70 and my Sako 75 Hunter with detachable magazine. The match M70's all had aftermarket heavy barrels, both the standard M70 and Sako have sporter style barrels. I have used both Remington and Federal cases. That load will chronograph at 2800 plus or minus 15 feet per second out of the Sako. Never had a chronograph for the other rifles. But when the same basic load that will shoot 1moa @100 yds in 5 different rifles and give an honest 1moa @ 100 yds then I'm a believer. Frank
2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
"Before you argue with someone, ask yourself, is that person even mentally mature enough to grasp the concept of different perspectives? Because if not, there’s absolutely no point."
– Amber Veal
"The Highest form of ignorance is when you reject something you don't know anything about".
- Wayne Dyer
Please pardon me if I seem out of step with the discussion concerning nodes, which I am enjoying following tremendously. I am truly a neophyte regarding the search for nodes. However, I am not seeing this composite "group" as some sort of failure, as you are.
Each 5-shot group is very good. However, I do not see the composite group as truly indicative of anything more than an inconsistent (minor at that) technique at the shooting bench, or some other external influence as discussed earlier in this thread. I don't see the composite group as having much concern with your search for the node, at least in this case. Of course, this is truly just my opinion. The groups are wandering a little group to group, but not each individual shot as such. The cumulative circular error in each group is small, and can hardly be improved upon. In fact, given the vagaries of circular error involved in any discussion of group size, can it totally dismissed? In fact, does the inability to refine the group farther mean the node is found and circular error cannot be improved upon? Or, are you just chasing circular error around at some finite point?
I also have a thought as to shooting at 50 yards while trying to find your node. I would think shooting at 100 yards would give you the opportunity to see your results in a more dramatic manner, as how do you know you are improving the situation as you change your load when you are already all but shooting one-hole groups?
Please forgive any ignorance on my part in this discussion about nodes. I mean no intrusive conjectures that are not in step with current discussion and knowledge(s).
Thanks,
Bob
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