Primers and cases

[Wolfdog91]

So getting to where I'm thinking about trying to test more when it comes to primers and cases after noticing like a 1/2" difference in group sizes with my .22 creed between cases i converted from 6.5 creed vs factory.22 creed brass . Anyhow got me curious and was just wanting to know what's the biggest difference y'all have seen in group sizes when you just changed brass or primers ?

 

[CF Junkie]

With a 6.5mm CM, comparing CCI BR-4 and Remington 7 1/2 SRPs, with multiple 5-round groups (minimum sample was over 30 groups for each) with the same match bullet and powder, I measured 0.010 difference in average group size at 100 yards (0.326 to 0.316 respectively).
Good primers aren't going to make a 0.5 difference (50 times larger) in group size.

In winter temperatures, with my .223 with a Shilen barrel at 100 yards with match ammo and the same powder:
I measured 64 5-round groups with Starline brass at an average of 0.222.
I measured 64 5-round groups with Lapua brass at an average of 0.218. (Average temps were slightly colder.)
The choice of brass made a difference of 0.004 in average group size.
Good brass isn't going to make a 0.5 difference (125 times larger) in group size.

All of my rounds are loaded to the Optimum Bullet Time for each barrel within +/- 0.001 msec., so the load conditions were just about the same for each load, and the cartridge base to bullet ogives were seated to +/- 0.001 inches.

Even if you happened to get really crappy brass or it wasn't sized and trimmed the same, I suspect you may have done something different in loading or even in your shooting position set up or even with your concentration. My set up and concentration cause the biggest variation in my results.
I always start by looking at the "nut behind the trigger" first and then shoot a lot of samples and measure everything before I make any decisions.

 

[ebb]

^^^^^ what he said! 6.5 Creed brass necked down to 22 would certainly have thicker necks, did you neck turn the brass? A tight chamber and thick brass might have ill effects.

 

[jelenko]

With a 6.5mm CM, comparing CCI BR-4 and Remington 7 1/2 SRPs, with multiple 5-round groups (minimum sample was over 30 groups for each) with the same match bullet and powder, I measured 0.010 difference in average group size at 100 yards (0.326 to 0.316 respectively).
Good primers aren't going to make a 0.5 difference (50 times larger) in group size.

In winter temperatures, with my .223 with a Shilen barrel at 100 yards with match ammo and the same powder:
I measured 64 5-round groups with Starline brass at an average of 0.222.
I measured 64 5-round groups with Lapua brass at an average of 0.218. (Average temps were slightly colder.)
The choice of brass made a difference of 0.004 in average group size.
Good brass isn't going to make a 0.5 difference (125 times larger) in group size.

All of my rounds are loaded to the Optimum Bullet Time for each barrel within +/- 0.001 msec., so the load conditions were just about the same for each load, and the cartridge base to bullet ogives were seated to +/- 0.001 inches.

Even if you happened to get really crappy brass or it wasn't sized and trimmed the same, I suspect you may have done something different in loading or even in your shooting position set up or even with your concentration. My set up and concentration cause the biggest variation in my results.
I always start by looking at the "nut behind the trigger" first and then shoot a lot of samples and measure everything before I make any decisions.

Any chance you've tested the impact on group size if the capacity of the brass differed in the order of a 1/2 grain of water? 1 grain of water?

 

[CF Junkie]

No, I haven't.

I generally use Lapua brass and check each lot for base to tip length variation.
In loading more than 5 calibers with Lapua brass for at least 15 years, l find that the base to to length variation out of the box is minimal.
Most are within 0.001 different.
I have always doubted my ability to keep my caliper readings exactly the same because my squeeze pressure changes the readings by 0.001 pretty easily.

Because Lapua .223 was unobtainable for a while, I tried Starline.
I measured the base to tip length of 400 Starline cases and was amazed that the longest was 0.003 short of 1.750 and the bulk of the brass was between 1.746 and 1.744.
Even then, the difference in group averages shot with Starline was only 0.004 worse than the group averages shot with Lapua.
But I did adjust my seating depths to compensate for the differences in Starline trim length.

I think trying to measure the capacity of brass with water capacity assumes that the brass are all the exact same length base to tip and are all exactly on the SAAMI brass trim length. When they aren't, I'm not sure how to interpret the results.

 

[Wolfdog91]

With a 6.5mm CM, comparing CCI BR-4 and Remington 7 1/2 SRPs, with multiple 5-round groups (minimum sample was over 30 groups for each) with the same match bullet and powder, I measured 0.010 difference in average group size at 100 yards (0.326 to 0.316 respectively).
Good primers aren't going to make a 0.5 difference (50 times larger) in group size.

In winter temperatures, with my .223 with a Shilen barrel at 100 yards with match ammo and the same powder:
I measured 64 5-round groups with Starline brass at an average of 0.222.
I measured 64 5-round groups with Lapua brass at an average of 0.218. (Average temps were slightly colder.)
The choice of brass made a difference of 0.004 in average group size.
Good brass isn't going to make a 0.5 difference (125 times larger) in group size.

All of my rounds are loaded to the Optimum Bullet Time for each barrel within +/- 0.001 msec., so the load conditions were just about the same for each load, and the cartridge base to bullet ogives were seated to +/- 0.001 inches.

Even if you happened to get really crappy brass or it wasn't sized and trimmed the same, I suspect you may have done something different in loading or even in your shooting position set up or even with your concentration. My set up and concentration cause the biggest variation in my results.
I always start by looking at the "nut behind the trigger" first and then shoot a lot of samples and measure everything before I make any decisions.

Ok very interesting and extensive testing ! Thank you !

 

[Straightshooter1]

So getting to where I'm thinking about trying to test more when it comes to primers and cases after noticing like a 1/2" difference in group sizes with my .22 creed between cases i converted from 6.5 creed vs factory.22 creed brass . Anyhow got me curious and was just wanting to know what's the biggest difference y'all have seen in group sizes when you just changed brass or primers ?

There's a lot of variables involved when looking at brass and when comparing primers.

For brass, if you prep them to the same dimensions where you're able to get the same case volume, you're not going to see much (if any) difference in performance. Some brands take a lot more prep than others. Like some Federal .308 cases I tested against some Lapua cases after making sure things like flash hole burrs, neck thickness (after turning) and trim lengths (after fire forming) were the same between the two brands. I found little difference, if any, in the results. Without such processing, I did get noticeable difference in performance since the Federal brass didn't have as consistent dimensions as the Lapua brass. Likewise, I also tested some PPU and Peterson brass against Lapua and found I could get just as good performance.

Without any special prep on brass I've seen a difference at around 30% better (sometimes more) with good brass like Lapua than with PPU brass that had no special preparation.

For primers, there can be a significant difference, a lot of which depends on the powder and temperature you're shooting in. Some brands tend to be less consistent than others where you can get one lot that works really well and another that's very inconsistent (this is where sort weighing primers can really help ).