Originally Posted by ozo

" Uniform flash holes can help make powder ignite more uniformly"--iowegan

IF it can improve ignition ANY percentage......why wouldn't you ???

Originally Posted by ozo

" it really has nothing to do with sizing brass"--iowegan

Didn't say it did.

" Uniform flash holes can help make powder ignite more uniformly"--iowegan

IF it can improve ignition ANY percentage......why wouldn't you ???

Originally Posted by ozo

Maybe I am missing something.....I am old
I only uniform the flashhole ONCE, on new brass.....
it has never slowed down any production rates on my Dillon....
Hmmmm.....

Originally Posted by JerryLP

Why should I resize GP-100 reloads? The rounds are going to be fired (no max loads) in the same revolver, so why exercise the brass unnecessarily?

Originally Posted by Iowegan

tglazie, No problem ... it's all related to the OPs question in one way or another.

The 50 fps max velocity spread assumes a muzzle velocity of 1000 fps ... so 5% would be a better way to express it. The "50 fps rule" originated from quality factory ammo, which is loaded to this standard. Some of the cheap crap ammo has a hard time getting under 100 fps spreads. Here's the breakdown .... match grade ammo should have a max spread of 2.5% or less and should be capable of sub-inch groups @ 25 yards. Field grade or self defense ammo should be 5% or better on max spreads and capable of 2.5" groups @ 25 yds, whereas "plinker grade" ammo can be as high as 10% spreads and group size would be 5" or better.

Max velocity spreads are a good indicator of accuracy potential in handguns but do not always ring true, meaning ..... just because the loads chronograph really tight, it doesn't always mean the load will be accurate. On the other hand, I've never seen match grade ammo shoot mouse ear groups when velocity spreads were much over 2.5%. As we all know, reloaders have different accuracy standards. Some are very happy to hear a bang and see a hole appear somewhere in a man-sized silhouette. Bullseye shooters are the most picky where ammo and the gun must be capable of sub-inch groups at 25 yards, in fact most bullseye guys demand 1/2" or better @ 25 yds. It takes a good gun and very good ammo to do this, not to mention shooting skills.

Rifles are expected to be way more accurate than handguns so generally "MOA" is used to judge accuracy. If you were to chronograph a rifle and ammo capable of 1 MOA groups, you would find max velocity spreads will be quite tight ... typically 2~3% max spreads. It is not unusual to see match grade bench rest rifles shoot groups under .5" at 200 yards (1/4 MOA) but to do this, you need a really good rifle and match grade ammo.

So what determines how well ammo will group in a handgun? Obviously it starts with the gun itself ... and not all guns are created equally. As for the ammo, the single most important issue for consistent results is neck tension. See, I told you it was all related! Consistent neck tension depends on a properly sized case plus the the brass at the case mouth must be uniform thickness and hardness. As a case is fired and reloaded multiple times, irregularities in the brass will cause the neck to develop thin areas and will get harder with each reload, eventually resulting in splits. To get consistent bullet-to-case neck tension capable of match grade standards, about 3 to 4 times loaded is max, plus the cases need to be from the same batch. After 3-4 times loaded, max velocity spreads will increase because the thinner areas in the mouth do not apply uniform neck tension and crimp from cartridge to cartridge. This will have a dramatic affect on how the powder is ignited and in turn, a change in muzzle velocity. Many people will load cases until they split ... which is fine for plinker loads. If you want to achieve "match grade" with any ammo, your loading techniques must be as perfect as possible. This includes weighing each charge of powder to the precise weight, +or- 1%. Same goes for bullet weight +or- 1%. So for a 5 gr load of powder under a 158 gr bullet, the powder drop should be accurate to 1/2 of a tenth grain (.05 gr) and the bullet should weigh between 156.4 and159.5, which is pretty easy to achieve. Most reloading scales are not capable of accuracy better than .1 grain so it may be very difficult to achieve match grade powder drop standards. The good news is .... bullets usually weigh pretty darn close to advertised weight so the accumulated error rate between the powder and bullet is not mission impossible.

Last but not least is bullet seating depth. The faster the powder's burn rate, the more critical seating depth becomes. With fast burning Bullseye, just a few thousandths variation in seating depth can change chamber pressure by 1000 psi, which in turn changes velocity considerably. Slow burning magnum powders, such as H-110/W-296, are much more forgiving because the bulk of the burn takes place after the bullet exits the case. Besides, in handgun length barrels, H-110 / W-296 never gets a complete burn so it is almost "self regulating". That also means the powder charge weight is not critical. It is not unusual for 357 or 44 Mags loaded with these powders to produce max velocity spreads under 20 fp and astounding accuracy, even with less than stellar reloading techniques.