What happens to your groups when you switch bullet brands mid-session

[Donnie]

I switched from one 147-grain load to a different 147-grain load mid-session just to compare and my groups shifted noticeably at 50 yards even at the same advertised velocity. Anyone with similar experieces?

 

[Tom L]

When I go to the range I start by using the ammo already loaded. It's my edc ammo. Then I use target loads for the rest of my time. Could be I get tired or sloppy or both as the session goes on, but my groupings with the hollow points always result in a tighter grouping. Could be the ammo or could be me????? I am disabled and use supplemental oxygen and shoot sitting. As aside, my edc ammo is Sig hollow points, practice is generally Federal target loads.

 

[CZMark]

In my experience, there can be a significant difference, but not always. Some rifles seem more "picky" about particular bullets than others, and bullets of the same weight can have very different aerodynamics from others.

 

[Tom L]

In my experience, there can be a significant difference, but not always. Some rifles seem more "picky" about particular bullets than others, and bullets of the same weight can have very different aerodynamics from others.

Knowing which ammo is best is a science all of its own. And to throw in a ringer depends on your specific barrel rifling. Part of what makes the hobby enjoyable. And very expensive.

 

[white eagle]

Started handloading many years ago and one of the very first thing's I noticed and was taught as well was "IF" you change any one of your components you need to recheck and adjust if need be your load.
Now you did not mention that you were handloading so I can assume your using factory ammo, that rule would apply to that as well and it makes sense that your groups and poi changed.
Best.

 

[Crash87]

It can be more the rule than the exception. Ive been doing a lot of load development lately with rifles. 7mm Rem Mag, 9.3X62, and the 338 Win Mag. 7mm Rem mag in particular, 1 grain in powder change will shift the P.O.I. easily 1"+ @ 100yds.

 

[Tom L]

That is amazing @Crash87 . As I noted earlier, the science of ammo is something that keeps this hobby so fascinating. As I have begun research on my guns and best ammo it really is a balance between cost and best ammo. After seeing info from @Tabby and discussions here I need to make some changes. As a rule I use Sig hollow points for edc and a mix of Fiocochi, Speer Lawman and Federal for target loads. Mostly been using Federal. But it is curious that I end up with a better group with the edc ammo than the others. While the hollow point may be part of it, wondering if I am not using the right target loads. FYI, I know part of the problem is the operator, and I am working on that too.

 

[Crash87]

Tom L, heres another for you. My 2nd 9 auto was a Springfield XD-9 bought a good many years ago now. Im a bullet caster, but decide to buy bullets from a supplier as cast unsized, no lube. I did this because I didnt want to shoot up my lifetime supply of wheel weights. Working up a load I was curious, are individually weighed charges more consistent than thrown, from My Redding 3br powder thrower. Not just 5 or 10 rounds but 50 each. The thrown charges in this case were more consistent in extreme spreads and standard deviations than the weighed charges. I never took this as being the absolute rule but found it an interesting case study.

 

[Tabby]

Just for giggles and something to do I did some experimenting with both factory and hand loaded ammunition to test both velocity spreads and accuracy.

After receiving a Garmin Chrono as a gift from a friend I have been able to pay close attention to the velocity spread of both factory and hand loaded ammo. This has unfortunately led to the realization that factory ammo, even match grade pretty much junk when it comes to maintaining a constant velocity. So far I have tried 4 different brands of 308 168gr match ammo and found that the difference in velocity between the rounds in a standard 20 round box of ammo varied up to 125 fps. The groups shot with this ammo never came close to 1 MOA.

I then tried hand loads using just a powder thrower set to a given powder charge then 20 rounds loaded with 168 gr Nosler RDF bullets. The difference in velocity was up to 90 fps when using extruded powders such as IMR 4350 but only 70 fps when using ball or flake powders such as Winchester 760 Ball.

The final testing was done again with 168 gr Nosler RDF bullets this time weighing each powder charge individually, throwing a short charge with the powder measure then trickling powder slowly using an approach to weight method where I trickled the powder slowly until the desired charge weight just barely tripped. This was the most consistent way I could devise to ensure accurate shot to shot powder charges.

Again on the range checking each round for shot to shot velocity difference and accuracy, using the approach to weight method mentioned above the shot to shot variation over a 10 shot group with a tubular powder resulted in a velocity variation of 40 fps. Using a flake powder the 10 shot groups varied between 20 and 30 fps with group sizes sub moa between 0.6 and 0.8 moa.

Again, just for giggles I followed up loading 20 308 cartridges in exactly the same manner using 165 gr Nosler Partitions. The velocity variance was identical to the Nosler RDF bullets, the groups were still sub moa but at 0.85 moa.

All rifle shooting was accomplished using an out of the box but well used Winchester Model 70 chambered in 308 Winchester. The rifle has a 20 inch sporter barrel with approximately 1500 to 1800 rounds fired through it. I have a new stainless Bartlein match grade barrel with a varmint taper which will be chambered for 7.62 x 51 (308) with the barrel length increased to 24 inches. And for you nit pickers, yes I do realize there is a difference between 7.62 x 51 and 308.

While I have not done such an extensive study on handgun ammo I have noticed that when loading 357 magnum reduced charge target loads that the cartridges that where the powder charges were simply thrown using the powder charge were not as accurate as the cartridges where the approach to weight method for the individual cartridges was used. The comparison was informally made bench rest shooting off of a bag with a S&W Model 66 at 50 feet. The difference in group sizes vary slightly but with careful shot placement are around 1 inch with the approach to weight cartridges and around 1 1/4 to 1 1/2 inches with the cartridges using just the powder throw method. Both Bullseye and Power Pistol powders were used during the pistol comparison.