Bryan, one comment and one question: one of the arguements for 6mmBR is that the amount of powder and size of chamber allows for more consistent velocities and therefore more precision since the SD for velocity is tighter hence greater accuracy with repeated shots. While this maybe more of a factor for 338 and 375 magnums, this may not be as important in the comparison with 30 based cases. Hence the importance of hand loading consistency - any comment?
With your military background, how does the ballistic performance of large shell such as 105mm etc or even larger rounds compare with 30 cal and since the research is possibly more advanced, how do the exteme calibers inform our understanding? Do the large military rounds follow the exact same ballistic laws as our 30 cal rounds, since this may add to our understanding of the differences between the calibers.
I'm not sure what you're asking re: 6mm br and larger cases, but I'll comment anyway!
What you may have been getting at is how much vertical dispersion a small caliber will have from a given muzzle velocity variation compared to a larger caliber.
Consider the 6mmBR shooting 105VLD's at 2800 fps. At 1000 yards, a 20 fps variation in muzzle velocity will cause the vertical impact to shift by 5.5".
A .300 Win Mag shooting 210's at 2800 fps will have 5.0" shift in vertical POI from a 20 fps variation in muzzle velocity.
The comparison favors the higher BC round, but only slightly. In order to achieve the 5.0" of vertical spread, the 6mmBR would have to cut the muzzle velocity variation from 20 fps to 18.7 fps. In real life the 6mmBR would probably be capable of much lower velocity ES than a larger magnum, so the actual results would probably favor the 6mmBR.
In general, higher BC bullets will be less sensitive to all variables (including muzzle velocity variation) than lower BC bullets. This isn't a caliber specific statement, but is a general trend.
As for military munitions, they certainly obey the same physics as our small arms stuff, but they push against different corners of the envelope. An artillery shell is mechanised with moving parts, fuses, threads, etc. It's a nightmare to make something like that balanced. One of the biggest challenges in artillery shell design is making sure the round will trace when fired at high angles of elevation. Depending on the stability characteristics, the round may not be able to trace. If it doesn't, it will fall short of the target and fail to fuse (probably a good thing for the friendlies that sometimes occupy the ground short of the target)
Modern systems are being outfitted with GPS guidance which changes everything.
It may be a surprise that many large scale cannons (20-30mm) have a certain level of dispersion built in to them intentionally to give a shotgun effect. If you're trying to gun someone down in an air-to-air engagement, you don't necessarily want to be shooting small groups. The dispersion is controlled with the bore diameter. The rounds are generally steel body with bronze or plastic rotating bands. The rotating bands are quite narrow, and they engage the riflings while the body of the round augers down the tube. The specific clearance between the projectile body and the bore controls the dispersion quite predictably.
Small cal MG's also have that dispersion built either into the rifle or ammo.
Read an article on Mr. Browning back in the day. His MG's were too accurate for area surpression so they built in some wiggle to disperse the rds.
I tried some surplus powder a few years back and it shot really well at 100yds. I was getting 1/2 min accuracy in my hunting rifles.
However, at 500yds, 3 rds wouldn't all hit a piece of paper. Stunned, I switched powders (H4350) and voila, 1/2 min accuracy retained at LR.
I later found out that this surplus powder was a pull down for 308 machine gun ammo. Maybe the powder was designed to give very irratic SD's which would lead to a whole lot of dispersion the further you got.
When is Berger going to make GPS bullets? Or at least fly by wire?
Not to intrude on Bryan's thread here, but I'll hazard a guess that there was some other issue (perhaps improper storage at some point, etc.) with that powder that lead to the inaccuracy problems you noted or more likely, that it just wasn't a suitable propellant. You didn't mention the cartridge, but the surplus powder would have been something in the burning range of 4895, WC846, etc.. Considering that 4350 is significantly slower, it was probably just an issue of one powder being better suited to this application than the other. There's never been a powder designed to give large SDs, at least that I've ever heard about. The military does deliberately increase dispersion for some types of weapon systems, but there are other (better) ways of doing this as he so aptly described. Seems counter intuitive for a bunch of guys on a long range precision forum, but picture using a "Turkey Extra Full" choke tube on a covey of fast-rising quail at close range, and you'll get the picture.
Excellent thread, terrific article and some very good questions!
Kevin Thomas (the new guy)
Last edited by Kevin Thomas; 02-16-2009 at 03:04 PM.
ww2 surplus military powder is what started the hodgden company in business.
purchased in huge quanities, stored in rail cars in dry locations, then packaged and sold to consumers.
i have been using h 570 powder for decades. im of the opinion this was a machine gun powder.
remember there were very few suitable powders for the large wildcat cartridges some were using. surplus machine gun powder was and still is in use.
ive found none of the problems mentioned here.
just a suggestion here on my part based on limited info. The suitability issue stands, though. Bruce Hodgdon did indeed play a significant role in launching the handloading industry we enjoy today, but powders still need to be selected carefully and matched to the task at hand.
As far as the storage issue goes, I've known several guys who were still using huge drums of powder in the early '80s, that they'd purchased from Bruce shortly after the war. I believe Jim Huill still had some of this on hand when he retired and it was still perfectly good. I've seen powders stored under all sorts of conditions with nary a problem, but I've also seen some deteriorate. Always worth mentioning and checking.
certainly would agree on the proper suitability of powder for a given cartridge. fact is though the powder i referred to was and still is suitable for the 30x378 i use it in.
25 or 30 years ago there were only 2 powders that were suitable to my knowledge. those being h570 and h870.
it goes without saying all powder should be properly stored, and even then its possible for it to go bad.
my point was however that myself or no one i know has experienced the accuracy problem cited as existing with machine gun powder.