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Reloading using Optimum Bullet Time (OBT) – often referred to as Exit Time

12 FV .223 with a 1:9 twist, when I bought it ($320 Cabela's special version), had a hidden mag and a stock without the aluminum strut to give it rigidity. On the same day I also bought its brother, a 6.5mm CM, also with a hidden mag and the same cheap stock.
The .223 version was OK, but the 6.5mm CM version would twist under recoil so I looked for a sturdier stock and chose the MDT Oryx chassis with a detachable AICS mag.
When I started loading heavier bullets in the .223, I found my old fingers had a hard time loading the longer rounds into the hidden mag.
So I also bought an Oryx chassis with an AICS detachable mag for the .223. The AICS mag allowed loading rounds out to 2.515 OAL so I could pretty much use it for all the bullets including 77 grs that the 1:9 would stabilize.
I kept that Oryx set up for the .223 when I changed the barrel to a 416R Shilen Select Match barrel with a 1:7 twist. So, with the new barrel chamber with no appreciable wear, the AICS mag will handle the 90 gr SMKs and even the longer newer designed 80 gr ELD-Ms and Bergers.
 
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I have not noticed that that relatively small changes in velocity from changing seating depth or jump are even visible when using average group size as the measuring goal.
Of course, like many of us, my shooting skills mask many of the nuances in reloading that we spend so much time trying to investigate and discuss.
As I get older and older, I tend to depend what I can measure and let all the other nuances be.
That doesn't mean that the nuances aren't causing an impact, only that I can't measure their effect.
I agree that if the node is wide enough then smaller changes in vel won't make as much of a difference, which is the whole idea between finding a good node.

A while back I shot the .223 and had consistent 1/2MOA groups at 300yd. Back then I had a chronograph with screens. I set it up one day and measured es/sd to be in the 50/25 range! I was kinda shocked as I thought my reloading skills were better than that (and they were with the .308). I think I just ended up on one of those really wide nodes. Even more interesting is I ended up with that load by chance. I picked a load out of the Sierra manual based on being 1/2gn below max and same seat depth as the manual. No load development at all.

FWIW, that rifle is what drew me down the rabbit hole. If I could shoot 1/2MOA then why can't I shoot 1/4MOA? :) And so here I am :)
 
I like the single shots better for overall stiffness and why I stick with the
3 screw Savage PTA's. I love my Oryx chassis stocks. I install an aluminum
block in the stocks mag well, then transfer the center screw to it......One of
the guys at the club uses a Sinclair bipod. For testing, he clamps down on
the bench a Delrin sheet with tracks milled in it, and a positive stop front.
 
A while back I shot the .223 and had consistent 1/2MOA groups at 300yd. Back then I had a chronograph with screens. I set it up one day and measured es/sd to be in the 50/25 range!
from what i have read, and found, high es on .223 is not at all unusual. since .223 is not an elr round anyway, i started ignoring the high es more while also enjoying the shooting more. it has still taken plenty of pdogs out to the 400+ range for me.
 
As usual, charlie b and Fug are voices of reason and always have information that helps with improvement.

charlie b, you, as usual, put things in context that I can understand.

Fuj,
I never thought of using a Delrin sheet under the bipod with tracks milled into it.
My set up routine allows the bipod to move back but the bipod doesn't move much with a .223.
Then I always reset the position to ensure I have to lean forward just a bit. That, and then moving my head back to see that the black ring around the edge of the scope image is concentric and then moving forward just far enough for the ring to remain concentric as it just goes away guarantees, a best I can tell, that I am in the optical center of the scope and the eye relief if exactly the same for each shot.
I found out years ago that about 1/8 inch variation in eye relief makes the POI move about 1/4 of an inch.

You are right that the single shot Savage rifles are stiffer.
But they cost a lot more than the $320 Cabela's specials.

I bought both 12 FVs because a range buddy got an even better sale and really liked his 12 FV rifle. At those prices, I figured that I could see if they were as good as he claimed.
Cabela's had the two calibers in stock and I bought them both.
I am thrilled with their accuracy.
After the great results with the change to the new Shilen barrel in the .223, I am considering replacing the barrel with a Shilen in the 6.5mm CM also. Almost ready to place the order on a 28-in barrel version for the 6.5mm CM which is in stock.
 
FWIW, in 223, I've found the difference between being on a node to being not on a node to be over a MOA.
That said, I test from prone with a sling and, with 2 MOA ten rings and 1 MOA X rings, my requirement for accuracy is 1/2 to 3/4 MOA.
My process for load development used to be to shoot a 5 step 'ladder' of .2 grain per step and 3 shot at each step. Currently, I use + and - .2gr around the GRT predicted mode - after inputting fired case capacity, bullet length, COAL and velocities of 8 shots. In both approaches I confirm the selected load with a 5 shot group.

Clearly, both of these approaches have relatively few shots and, more importantly, are shot from a platform that is relatively unstable vs good bench technique. But, I have confidence in the range of groups over the steps of powder charge because there has always been a range.

When doing the 5 step 'ladder' I've seen groups go from well over 1 MOA [as best I can recall in the 1 1/4 - 1 1/2 MOA range] down to .5 to .6 MOA. Sometimes the largest group would be in the 1 MOA range.

In any case, in my experience, the difference between being in/out of a node is more than 1/2 MOA.
 
from what i have read, and found, high es on .223 is not at all unusual. since .223 is not an elr round anyway, i started ignoring the high es more while also enjoying the shooting more. it has still taken plenty of pdogs out to the 400+ range for me.
I have heard that, but, I have gotten better. I think part of it is no one expects any better from it. Most FTR folks don't use it since the little bullets have 'issues' at 1000yd. Benchrest guys tend to go to 22PPC, 6PPC, etc. A few might go for the 222. There seem to be some who can work with it. I REALLY like mine at 600yd with heavier bullets. It is a challenge in the wind, but, I used to shoot cast bullets at that range so this is 'easy' :)
FWIW, in 223, I've found the difference between being on a node to being not on a node to be over a MOA.
That said, I test from prone with a sling and, with 2 MOA ten rings and 1 MOA X rings, my requirement for accuracy is 1/2 to 3/4 MOA....

My experience is close to that. If I am off of a node the groups will be a bit over 1MOA. Makes me cry :)

If I am on a good node I can be a bit sloppy with my reloading and still get 1/2MOA. When I am more careful that shrinks a bit more, which is what makes me feel good :)
 
The barrel reflection frequency depends upon the type of steel.
The factory barrel was 0.3% carbon steel with a reflection speed of 19,107 fps. For a 26-in barrel, that results in a reflection time along the barrel of 0.11340 msec. yielding 1.134 for 10 reflections or 1.361 for 12 reflections.
The Shilen barrel was 416R stainless steel with a reflection speed of 20,014 fps.
How are you obtaining this info and where are you inputting it in GRT?
 
Speed of sound in various alloys you can look up. As stated by someone earlier it isn't exact since any steel alloy can be 'off' a bit in content.

GRT's OBT calculator is based on Long's work and he only used the constant for carbon steel barrels (4140?). I wish I knew where it was in the program so I could change it for stainless. It is enough that the numbers come out significantly different. Long had a spreadsheet at one time that could be downloaded to calculate OBT, but, I don't remember where it went.
 
4140 and 4150 steels are generally known as chrome or vanadium steel with reflection velocity is 19969 fps.
Carbon steel, usually called 0.3% carbon steel, has a reflection velocity of 19107 fps.

charlie b, you're in luck. Most Savage steel barrels are 0.3% carbon steel unless they are specified as Stainless. So GRT's calculator will be right in your wheelhouse, unless your Axis barrel is stainless.
Savage stainless is probably 20000 fps.
416R stainless is 20014.
 
LOL Yep.

CFJ, at one time I had a spreadsheet with all the barrel time calculations for different steels at different barrel lengths. Not a difficult calculation to make. I just like the automated part of OBT that GRT uses. It would be nice to adjust it for the proper barrel material. The Axis is not stainless but my 6BR is.
 

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