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So a friend and I were talking about groups today.

My friend and I were talking about groups and use of different powders. I had shot some different loads today and noticed that the groups were all over the place. So I went back and researched some range notes and came up with this conclusion. Here is an example. I have a Remington 700 SPS in 223. 1/8 twist 26 inch barrel. I have shot a lot of sub MOA groups with it using both Hornady 75gr BTHP and Sierra 77 grain Match Kings. So my thought today was why the spread in groups. Then I looked at my notes and pictures and it dawned on me. With the above two mentioned bullets I got nice groups at around 2600 fps at the muzzle shooting at 100 yards. So I was thinking well I will just look for loads with different powders that obtain a 2600 fps at the muzzle and see how the groups are? I feel the groups should be about the same size since everything else is. The only thing that will change is the powder. What do you guys think? Am I on the right track? I am trying to duplicate a load that I got with Varget at 23.3 grains on the 77 gr bullet. I noticed that I might be able to get the same group using AA 2520 at around 22.5 grains. I know I need to load some up and go to the range. Trial and error, right? But the range is kind of far from my home, and finding a load quickly would help. I might mention that I also got great groups using AA2230 at 22.6 grains. Just experimenting and trying to find loads that perfom almost like each other. My thought is that if the bullet leaves the barrel at the same speed or near the same speed, it should fly the same? And the groups should be very similiar.
 
There are many members here with far, far more experience and knowledge than I have.
From my experience, there are no 'magic' velocities across bullets/powders.
Just for example, if you use the same bullet with different powders, tune one of the bullets to an accuracy node, then find a powder charge for the second bullet so it has the same muzzle velocity, the pressure curve and time in the barrel will be different.

Since H75's and S77's are fairly close in weight and the H75 has a slightly longer bearing surface, an accuracy node for each would probably be fairly close in velocities.
 
First- unlikely the wind effects are the same for each shot- without wind flags you're just plinking. Best to clean the bore after a powder change. Forget velocity and base results on what the target tells you. Loading at the range will allow you to test closer to "everything is the same" (i.e. conditions). We all have shot small on occasion, but the fact is the wind can blow a shot "into" a group as well as pushing one out.
 
I shoot one caliber. Been using the same barrel brand and Smith for over 15 barrels. Same components. I have been lucky I guess. I find a powder charge that gives me around 2800 fps and it has always shot .3 to .4

I will have to adjust the charge as I change powder lots. The other components haven't been affected by lot number changes
 
Your loads are not exactly the same in my opinion. With two different bullets and then a powder change, even if used in each cartridge, you rifle is telling you what it likes or does not like.
Find a load for each bullet that works best, for what you want in groups, etc. and use it in it's given rifle.
Another factor that will enter is also the seating depth of each bullet in each rifle.
 
In my experience, trying to extrapolate data from one load to another is a guess at best. Here are few things I learned over many years of shooting, albeit, at the varmint hunting precision level:

With a few exceptions, I found that it is the bullet more than any other component that affects accuracy rather than powder assuming you select a suitable powder for that cartridge.

Environment affects are greatly underestimated by most shooters. Wind, mirage, and temperature (air density) can have a significant effect on dispersion.

Shooting consistency, even off the bench can have a major effect. This means the type of rests used, the consistency of rifle placement on the rests, the shooter's ability to apply consistent shoulder pressure, trigger squeeze, follow-through, eye alignment with the reticle, and shot sequence, etc.

Equipment issues such as the bore condition when testing, the bedding of the rifle, quality of the equipment, etc.

Bottom Line: there are so many variables affecting accuracy that trying to duplicate performance by extrapolating a parameter such as velocity, is futile in my experience. There is no substitute for concentrated load testing if one's goal is obtaining the best accuracy possible.

I would also add that a consistent POI is more important to me than group size within my needed area of impact. In other words, I will accept a 3/4 moa that places shots consistently in same area POI as opposed to a 1/4 moa that varies outside my desire POI. Ryan Cleckner did an excellent video on this issue, "Acceptable Accuracy." For hunters is should be a must watch.
 
I was testing different bullets in a well worn XTC back up upper Shillen 7.5R I did a little change up to a AR Tactical rifle for fun. (NRA/CMP) seems to be a popular thing now for those not shooting course or sling. Took the tried and true SMK77 , Midway 77 seconds, RMS 69's and a bulk lot of H75's.
The SMK 77 (firsts) shot just like it always did, the seconds 77s were bit a garbage and the H75 bulk ( which I am wondering if are seconds) were not great.
The RMR 69's started to shoot close after a brief shotgun pattern .
First some more of the SMK77 and they do what they always have in my Service Rifle uppers.
Mind you this barrel was moved from a primary upper to back up. Its has at least 5k rounds on it. But it still shoots. testing was only at 100 yds may be able to stretch to 500 this weekend.

The brass was all the same. 450 SRP, 22.8 gr Pull Down 8208, (the good lot) My new 8208 is all gone.
The RMR 69 was new production 8208.

I rolled up more SMK77 to try this weekend again. For fun.
SMK 77 2.25 COAL
H75 2.240 COAL (kind of what has been the sweet spot for me and H75)
RMR 69 were 24.0 8208 and about 2.235 COAL.
I dont mess with Base to Ogive with short line ammo for The Turd.

The SD were reasonable around 14 but I was getting some wild ES readings.
I let the barrel cool but did not do any cleaning, same powder for the most part other than pulldown old 8208 (black volcanic sand looking stuff) vs the RMR with new 8208.

If you are changing up multiple components I would do as has been suggested and clean maybe between tests and try to keep environmental the same as possible.
 
One time, a friend and I were doing some experimenting with different cartridges (his money, my time). In this particular instance we started with a Winchester model 70 in 270 Winchester. We used H4831 powder and 150 Hornady bullets. The factory chamber gave us 2920 fps with the 150 but shot best at about 2870. We rechambered to 270AI. Top velocity was 2980. Best accuracy occurred when we backed down to 2870. Rechambered to 270 Gibbs. Velocity was 3040. Accuracy was, again, at 2870. Set back a 1/4 inch and rechambered to 270 WBY. Top velocity was 3160 and accuracy was pretty good but still slightly better at 2870. The velocity figures were interesting but we were even more interested by the preference shown by this particular rifle for velocity in a pretty narrow range. It seemed like the Wby velocity was getting close to hitting another sweet spot but any increase loosened the primer pockets so that was that. WH
 
I have been fooling with a 223, Savage action and Savage barrel that has been cut to 17 inches. I found Varget to be best with 70 Speer (flat base) and 75 Hornady. Tried 2520 and 4895 at about the save velocity and the groups opened up. Have tried the same experiment with RL15 and found it to shoot better than similar powders. My conclusion is that Varget and RL15 burn more uniformly, hence better accuracy. Have not compared Varget and RL15 head to head. I only have a pound of $75 RL15 left!
 

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