6mm

casterpollox

casterpollox

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Just for conversation sake... What makes the 6mm so accurate? Its used in so many standard cals and then in wildcats as well. But what seperates it from the rest of the choices?

I have a .243 and love it.
 
Can you

elaborate a bit more by what you mean more accurate.

The little that I think I know is in a case like the 6BR or 6PPC is they appear to have a very good powder to bore ratio for the bullet and case size. The BR has slightly more case capacity over the PPC which would aide in pushing the 105/107 bullets slightly better. I have heard of the PPC being thrown together to shoot the same heavy bullets as well with VERY GOOD results.

The bullets also seem to have very good ballistics. Recoil is less making it a lot easier to shoot.

I hope this is a start.
 
While I do mean accurate for competitions... I guess I also mean popular in the same breath. It appears, IMHO, that a lot of people are using the 6mm.

I just got bored the other night and was wondering why the 6mm has such a following? Nothing sinister here, no trolling, just for conversation.
 
Years of experimentation by the benchrest guys. Without them, there'd be no factory match grade bullets. Trust me. When I first bought a .243, long ago, there weren't any. There were varmint bullets or deer/bear bullets and nothing else.
"...why the 6mm..." Without doing any research, I think it has to do with the calibre to case capacity ratio. Fat cases with wee bullets tend to be more inherently accurate. Mind you, the other 6mm's give long range accuracy with little felt recoil. It's just more fun to shoot all day when it doesn't hurt. It's a versatile calibre too. One load for light varmints, one for larger varmints and one for deer sized game out of one rifle. Mind you, one heavy bullet load for everything works too.
I've always thought that a 6mm cartridge would make a good military cartridge too.
 
The right combination af a high ballistic coefficient for their size, and two cases that have proven to be some of the most accurate cartridges made: 6PPC and 6BR. This has also - as Sunray points out - driven R&D on match bullets in 6mm. (It's why you probably won't find a 25BR or a 270BR very easily)

Not all 6mm's are inherently accurate. 6Rem's and 243's are good, but will not match the absolute accuracy of the BR and PPC variants
 
From an F class perspective, recoil and barrel heat are its two strongest points. You are not going to win anything if your shoulder is black and blue no matter what the ballistic advantage. Big reason the 7mm are not taking over.

Not alot of shooters can handle the beating.

Also, the smaller lighter bullet requires less powder to push to desired velocities. That heats up barrels less making them more stable over long relays in the summer. Barrel wear is creeping up though so there is a point of diminishing returns here.

Where it looses some is in wind drift and calibre size. The 6.5 bullets are equally accurate and as developed. They offer a tangible reduction in wind drift with tolerable recoil. Sooner or later, that bigger bullet hole is going to gain you a point.

I don't see it dominating LR F class in the near future. With new bullets, I may change my tune....

Jerry

PS Obtunded, just read a very interesting post on brass prep. In that post, it was discussed the success that Henry Childs has had with a slightly modified 243 case at 1000yds. When given the opportunity at a 'free' 6BR, he declined citing comfort in his set up.

So the 243 case volume isn't that bad....for that application.
 
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casterpollox said:
While I do mean accurate for competitions... I guess I also mean popular in the same breath. It appears, IMHO, that a lot of people are using the 6mm.

I just got bored the other night and was wondering why the 6mm has such a following? Nothing sinister here, no trolling, just for conversation.
Click to expand...

I think the point about "popular" is important and would add the related idea that the bullets that are favoured have something to do with the application, e.g. score vs group, 100 meters vs 1000 vs 2000 and so on. As a friend often points out to me, the 30 cal finds favour with many more when shooting for score. The term "inherent accuracy" has to have a precise meaning to have any value and I find it much easier to use when it is applied to measuring instruments or processes. There is always some form of standard to compare to for one thing and some statement of variability. To compare inherent accuracy of bullets I would expect to see tables of comparative averages and variances for various bullets impelled by standard propellants (air, gas?) of some kind, with standard, specifiable forces acting on them, etc. Maybe such exists and I haven't seen it. This might have been one thought behind using machine rests. Interesting thing is that old benchresters (I am genuflecting to 4 points of the compass, while using the br word.:D) talked about being able to beat machine rests, probably because conditions would cause variation in results from the machine rests that the machines couldn't adjust for... The fact speaks to an idea of having some objective standard to compare to while showing that we, as shooters, were supposed to add something to the bullets flight. But, this is shooting, not inherent accuracy. (I'm tempted to reflect on some previous conversations here, but...;)). At any rate, being lazy, I have accepted that competitive shooting, as it exists today, is empirically derived with incomplete standardization and fads that change as the rules change, e.g. 222 then 6 PPC then...?). Sometimes I would very much like someone to put all this stuff in perspective, but maybe the fun would go out of it for some us. I don't know, but I think 6mm popularity has at least something to do with the rules followed by people who are most influential in the sport. respectfully, fred
 
Fred,

Good points and valid ones. Very interesting discussion.....

There is no doubt that fads have influenced the paradigms in competitive shooting. Look no further than Tom Fripp for that example... He was about the first shooting in Kamloops to use 6BR in F-class around those parts and now everybody has it. I'll be the first to admit I am a bit of a follower rather than an innovator when it comes to trying new things, because I get angry at the money spent on a project that doesn't work as well as I hoped. I want to spend my money on a "sure thing" and from what i could see, 6mm generally, and 6BR in particular had everything I wanted in an F-class cartridge.

With theoretical accuracy being equal, I think in the absence of a ballistic "Factor" that encompasses powder burned, velocities and general cartridge efficiency, the salient numbers are BC, SD,s and practical velocity.

I think a 210 grain 30 cal Berger driven at practical velocities is a more inherently accurate bullet than a 6mm, but you are into the realm of magnum cartridges.

There may be a yet-to-be discovered way of practically driving a 210 grain berger at 2900 fps with 30 grains of powder, but in the interim, within the limits of the chemistry and physics available to the shooter, 6 and 6.5's are cartridges that offer the optimal ratio of "best for least".

There are of course going to be exceptions to the rule and I bet that guys like Bill Leeper can chime in here with their vast experience and refute what I have said here, but 6mm does everything I want it to very well.

When we go to Bisley, I may have to go to the dark side and shoot 6.5 to stay competitive though, however, I would dealy love to do well with a 6BR just to say I did.

Jerry,

I know a fellow that has an improved 243 and is driving 115's in a 1:7.5 with it and having spectacular results! I agree that from a physiological point of view, having the crap beaten out of me by a canon is not fun... I think you are bang on in that 6.5's are really probably the best balance between light recoil, accuracy, velocity and ballistic efficiency for long range shooting.
 
Obtunded, Bisley goes to 1200yds????? At least 900yds??????

My 6.5 Mystic mimics the common 6.5-284 loads so there is little point in going that big if all you want is 2900fps (got it all dialed in so if you want to build one/two, just ask). However, I hear that winds there can be brutal with many teams going to the 7mm, enduring the pain to get a wind cheating edge.

180gr Bergers at 2900+fps will give a tangible edge in wind drift but OUCH!!!!

Personally, if I were building a rig, I would use the 6.5-284 and try and find the faster node. There is still tons of case capacity and everyone seems to be using fast powders.

I think 55 to 60grs of slow powder might just get more speed without stressing out the bullets too much. 3100fps would be my goal. However, anything over 3050fps would be fine.

Barrel life would suck but so what, I would enter to win and that is a small cost vs the trip. Yep, more R&D.

The 6BR is more then capable in the accuracy department. The problem is being trashed by the winds. Against all the other F(O) choices, I would want every advantage I could take.

A large cased 6mm with the 115/111/117gr type bullets at 3000+fps would be pretty close to the 6.5 Mystic with lower recoil. Again, barrel wear will be right up there with the 6.5-284.

If you want to steer hard all day long, why not F(F)? At least, everyone is using the same cartridge - well, kind of. I believe the 308/223 bullet weight rules are still intact.
Jerry
 
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sorry i know not alot about this subject, just saw someone said something about military use.
the japanese in WW2 used a 6mm or 6.5mm in their type 38 Arisaka rifles, they then brought out a larger calibre as the rounds didnt have the stopping power

correct me if im wrong
 
Yes, they used the 6.5 as it was based on the Carcano. They also used the 7.7 as well which is basically a jap 303.

there are may experts (NOT me) on Japanese military arms lurking about that may help clarify.

...so at end of the day, 70 years later NATO uses a 22 caliber gopher cartridge as its small-arms cartridge of choice. Makes ya think, dun'it?
 
cycbb486 said:
elaborate a bit more by what you mean more accurate.

The little that I think I know is in a case like the 6BR or 6PPC is they appear to have a very good powder to bore ratio for the bullet and case size. The BR has slightly more case capacity over the PPC which would aide in pushing the 105/107 bullets slightly better. I have heard of the PPC being thrown together to shoot the same heavy bullets as well with VERY GOOD results.

The bullets also seem to have very good ballistics. Recoil is less making it a lot easier to shoot.

I hope this is a start.
Click to expand...

there is also the 22/250 case necked up for a 6mm bullet or what some might be calling the 6/250. Then there's Tubbs 6XC case or something similar... both are very accurate. I shot a 6mm 22/250 for a couple of seasons using 105's in bullet weight. It was a move upwards from the 6BR which I always thought was a little over pressured for long range i.e. 1000 yards in f-class. I just didn't like running on the edge of envelop with the 6BR case at 1000 distances. Some still have loads for the 6BR which they use or work with all the time and they love them. I just got tired of giving up v's to 1/3 more bullet weight as in the 6.5 x. 284s...

...on cetain days where the conditions are right both the 6BR and 6/250 or variations thereof can win. It's been seen and proven many, many times and doesn't come as a surprise to competitive shooters. You just have to be a better wind reader and make less mistakes... course that's pretty much what we're all trying to do, isn't it?
 
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I am currently playing with a 6X47 Lapua which in terms of case capacity and performance is not too dissimilar to the XC (22-250 based) or the 6-22-250. The jury is still out on this one as I would like to see it perform better at higher speeds if possible, but you're right. The 6.5's make it slightly easier to shoot better than a 6mm under less than ideal conditions.
 
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