"Match" Chamber?

[Susquatch]

I speced their 260 match reamer. I think it gets refered to as the tac reamer because (at least my reamer) was throated exactly for 139/140/142 "tactical" type match bullets....... Both love Berger 140 target hybrids.

I see. That makes sense to me. So we both have the same reamer then. Dunno if I'll call mine a Tac though.... LOL!

I built my deer rifle with a 9" twist for lighter 120/130 gr bullets so I can't use "tactical" 140's anyway.

Thanks for the info.

BTW, some time ago I wondered why the average 6.5 twist was so fast compared to other calibers. (picking just two examples smaller and larger, the avg 243 rifle is 10, avg 308 is 10, but the average 260 is 8). So I did some research. It turns out that the avg 6.5 bullet is quite a bit longer than other bullets for its caliber. If you make a statistical bar chart of all available bullets of all calibers by caliber you will end up with a fairly linear distribution for everything EXCEPT the 6.5/264. For some reason, they are different and have a scatter bar more like the 7mm but down two calibers - a significant "bump" or anomoly in the curve. This doesn't need to be so, but it is! I do not know for sure, but I think this is probably an artifact of the original long range intent of the 6.5s and also explains their relatively high ballistic coefficients, pencil bullets, and therefore higher twist rates. The bottom line is that the average 6.5/264 bullet is longer than other calibers for its caliber or better said, the average 6.5 bullet has a higher sectional density than the average bullet in other calibers.

 

[J E Custom]

J E CUSTOM,
I really don't have a problem with having to turn the neck because I would like to get the accuracy out of the rig.

I have never turned a neck before...looks like i will be looking into it on youtube...

Good. I think you will see the improvement in your ammo. Many of us old timers grew up loading using only crude tools. My first set of dies were the type you used a hammer strike to size (No Press) and they were very slow and not very precision. (I still have them as a reminder of how far re-loading has progressed).

I went many years without turning the necks and never new the benefits of it. Later when I started match shooting , i found that some of my loaded cartridges would not always chamber as easy as needed for rapid fire matches. So I tried neck turning and the problem went away. The interesting thing was that accuracy also improved.

With that revelation, I started turning all of my necks (Other than just my match loads). At the time I would just clean up the necks by taking how ever much was needed. When All of the other rifles began shooting better, this became my routine.

As more tools for turning became available and I better understood the advantage of truly concentric brass in truly concentric chambers,
It almost became an obsession to load great ammo.

Now I buy new cases for each rifle, and before I fire it in that rifle, I turn the necks all to a uniform/same thickness. This way when it is fired in the chamber for the first time, It comes out absolutely concentric inside and out. Using a concentricity gauge, I check each piece of brass before I load it so I can evaluate my loading quality
when I check the loaded rounds for concentricity.

I realize that this seams like a lot of trouble and not worth the effort, but when you are trying to shoot groups below 1/10th MOA, it is essential.

with great barrels, great chambers, great rifles you need great ammo to reach the full potential of the rifle. Now most, if not all of my rifles will out shoot me making me the weak link. This process has eliminated any possibility of a bad shot due to poor loading, and has eliminated any excuses of why I made less than a good/great shot.

In MY Opinion everyone that is interested in extreme accuracy should be, or learn how to properly neck turn there cases.

Just my opinion for what it's worth.

J E CUSTOM

 

[Gcan]

I see. That makes sense to me. So we both have the same reamer then. Dunno if I'll call mine a Tac though.... LOL!

I built my deer rifle with a 9" twist for lighter 120/130 gr bullets so I can't use "tactical" 140's anyway.

Thanks for the info.

BTW, some time ago I wondered why the average 6.5 twist was so fast compared to other calibers. (picking just two examples smaller and larger, the avg 243 rifle is 10, avg 308 is 10, but the average 260 is 8). So I did some research. It turns out that the avg 6.5 bullet is quite a bit longer than other bullets for its caliber. If you make a statistical bar chart of all available bullets of all calibers by caliber you will end up with a fairly linear distribution for everything EXCEPT the 6.5/264. For some reason, they are different and have a scatter bar more like the 7mm but down two calibers - a significant "bump" or anomoly in the curve. This doesn't need to be so, but it is! I do not know for sure, but I think this is probably an artifact of the original long range intent of the 6.5s and also explains their relatively high ballistic coefficients, pencil bullets, and therefore higher twist rates. The bottom line is that the average 6.5/264 bullet is longer than other calibers for its caliber or better said, the average 6.5 bullet has a higher sectional density than the average bullet in other calibers.

I believe you are on to it. I suspect if you did the same study for only long for caliber bullets (140-150 .264 and say 95 SMKs for 224 Valkyrie) you will find that velocity/diameter/rpm determine twist and there is a mathematical predictable relationship. I don't want to use a number without reading my notes but I believe 225,000 to 250,000 rpm is where I start. With the 224 everyone said 7 twist at first. Then 6.5 then 6.5 below 2600 and 7 above 2600 fps. We think in fps but its really rpms that determines stability and twist. I'm so sick of the 224 and flyers from bad non-concentric-necks and bad tempered brass from "—————" that I'm building a 22-250AI to shoot 95-100s. I should get 3100+ So by using rpm I get back to a 1:8 to shoot the same bullets a 224 needs a 6.5 to shoot at 2600-2700.

I think this is why some 264s need fast for caliber twists. Ex: a 6.5-284 is going to stabilize a 140 with a 1:9 or 1:10 twist where a 6.5CM or 260 Rem might need 1:9 to 1:8 or faster for same bullet. Put that same 140 in a 300UM case at near 4000fps and you might be at 1:12-1:14 (240,000 rpm) like a 22-250/50 grain.

I suspect that most of the 6.5s or rounds with hi twists that are anomalies will be slow fps for caliber with heavy bullets.

If that makes sense to anyone.
I'm not even sure I'm addressing your point.

 

[misterc01]

From what I read on my Savage, the chamber is sized and then a go-gauge used to set the barrel at minimum SAMMI specs. Chambers factory match ammo just fine, and then I use the once-fired brass from that for reloading.

 

[Susquatch]

... .. If you did the same study for only long for caliber bullets (140-150 .264 and say 95 SMKs for 224 Valkyrie) you will find that velocity/diameter/rpm determine twist and there is a mathematical predictable relationship... .
...........
I'm not even sure I'm addressing your point.

There are also many formulas and even on-line tools that determine stability and many manufacturers also provide recommendations for their bullets

Actually, no - that does not address my point. As usual, I didn't make my point very well. I seem to do this too often.

Of course, if you did the study using only long bullets in other calibers you would get this same result. In effect by limiting the study to long bullets, you would get a long bullet result! There is no point in doing that.

My point as succinctly expressed as possible is this: The AVERAGE 6.5/264 bullet (averaging all bullets from all manufacturers) has a higher sectional density than the average bullet in other calibers. In less succinct words, but more meaningful to a shooter, is that this means that the average 6.5/264 bullet has a higher ballistic coefficient and also that the average 6.5/264 rifle has a faster twist.

Since this there is no scientific or geometric reason for this result, and because this result did not NEED to be so, it is apparent that the 6.5/264 caliber has somehow managed to specialize in the long range market to a much greater degree than other calibers have.

Does that help?

 

[wjarrell]

wjarrel,
Good to know I won't have someone flip out just because I might question what I hearing!

As much as I don't want to turn a neck I may have too...3" groups at 600yds...I could live with that!

I've never had to turn necks with mine. Size em load em shoot em repeat.

 

[Gcan]

There are also many formulas and even on-line tools that determine stability and many manufacturers also provide recommendations for their bullets

Actually, no - that does not address my point. As usual, I didn't make my point very well. I seem to do this too often.

Of course, if you did the study using only long bullets in other calibers you would get this same result. In effect by limiting the study to long bullets, you would get a long bullet result! There is no point in doing that.

My point as succinctly expressed as possible is this: The AVERAGE 6.5/264 bullet (averaging all bullets from all manufacturers) has a higher sectional density than the average bullet in other calibers. In less succinct words, but more meaningful to a shooter, is that this means that the average 6.5/264 bullet has a higher ballistic coefficient and also that the average 6.5/264 rifle has a faster twist.

Since this there is no scientific or geometric reason for this result, and because this result did not NEED to be so, it is apparent that the 6.5/264 caliber has somehow managed to specialize in the long range market to a much greater degree than other calibers have.

Does that help?

Yep. And that is all true.