Odin
.375 Atomic
Posts: 1,068
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Post by Odin on Nov 25, 2020 17:48:14 GMT -5
With all else being equal, will a gun with minimum spec (aka, tight) chambers give lower ES numbers for a given load than one with more generous dimensions?
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Post by z1r on Nov 25, 2020 18:47:07 GMT -5
Assuming similar brass, I've not found that. But, what I have found to be "generally true" for a given load, is that the larger the chamber, the lower the velocity & pressure tends to be.
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Post by bradshaw on Nov 25, 2020 18:47:53 GMT -5
With all else being equal, will a gun with minimum spec (aka, tight) chambers give lower ES numbers for a given load than one with more generous dimensions? ***** odin.... smart question which theoretically should answer itself in the affirmative. Top .44 Mag silhouette and hunting loads fired in the Ruger Super Blackhawk, S&W M-29, Interterms Virginian Silhouette Dragoon, Dan Wesson Arms M-44, and Freedom Arms Casull M-83 indicate the load is much more important than the orchestra of dimensions each of these revolvers represent. In general, disparities in bore & groove, forcing cone, chamber exit hole, and cylinder gap contribute notable differences in average velocity, with far smaller differences in extreme spread. All of my info was gathered on Oehler chronographs, mostly the Model 33 and later Model 35P, spanned quite a range of hot & cold weather, Mostly 5-shot strings, but quite a few 10-shot strings. The term “tight chamber” usually refers to the THROAT (CHAMBER EXIT HOLE). For whatever reason, chamber walls were amazingly consistent across the guns, with shells extracted from one gun often fitting another. I have shot Ruger and S&W .44s with .432", even chamber exits which group 5x5 under 3 inches @ 100 yards, shooting Sierra and Hornady jacketed bullets. A DWA M-44 with .426-inch chamber exits twice toppled 7x10 quarter-size turkeys and rams @ 220 and 225 yards, shooting under 4-inches @ 200 yards, Creedmoor with iron sights; thoroughly witnessed, thus mentionable. The first FA M-83 .44 Mag----with .429-inch throats----shoots no better than a like gun with .430” throats, with no difference in velocity. A pair of M-29 8-3/8” .44s----.004” gap on one. the other with .010” gap----each record 5x5 into 2-inches @ 100 yards. Tighter gap gives one higher velocity, but differences in extreme spread are minor. Velocity advantage1) FA M-83 2) Ruger SBH 3) S&W M-29 4) DWA M-44 5) Interarms Silhouette Dragoon Velocity observation* Given firm chambers, minimal gap, and minimal forcing cone, a “loose" groove diameter may enhance velocity. Read that again! A loose groove diameter NEVER increases accuracy. Oversize exit holes, oversize forcing cone, wide cylinder gap----each bleeds velocity. * Oversize groove diameter may increase velocity. * Tight cylinder gap favors velocity. * Wide cylinder gap bleeds velocity. These observations were made with .44 Mag revolvers of silhouette accuracy. Powders include Hercules 2400, Winchester 296, Hodgdon 110, IMR 4227, Hodgdon 4227. David Bradshaw |
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Post by taffin on Nov 25, 2020 20:14:14 GMT -5
SOME OF the most accurate loads have high ES while some of the loads with low ES have mediocre accuracy. Every sixgun has its own personality.
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Post by boolitdesigner on Nov 25, 2020 20:41:55 GMT -5
^^^^^^^^^^^^^^ One day back in the late 80's I was working with a 624 in the 6.5" barrel length with the Lyman 429383 for group and velocity over a Pact chrono. A really nice surprise happened..... I got a chronograph string for 5 shots being the same exact number with the six 1 fps higher. That wasn't the surprise though, it was the group.... being it was a 0.431" diameter bullet, that wonderful revolver put them all in one slightly over caliber hole you could cover with your thumbnail at 25 yards. As you said sixguns have their own personality and you can't judge one by another.
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Post by z1r on Nov 25, 2020 20:45:30 GMT -5
SOME OF the most accurate loads have high ES while some of the loads with low ES have mediocre accuracy. Every sixgun has its own personality. Yeah, I was shocked when I got my first chronograph and found that some of my most accurate loads, has some unimpressive ES's. |
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Post by bradshaw on Nov 25, 2020 22:32:11 GMT -5
SOME OF the most accurate loads have high ES while some of the loads with low ES have mediocre accuracy. Every sixgun has its own personality. Yeah, I was shocked when I got my first chronograph and found that some of my most accurate loads, has some unimpressive ES's. ***** z1r.... all of which is true. It is a mistake to equate low ES with accuracy. Clear example: while a particular powder & charge may produce tight Extreme Spread, it cannot make an unbalanced bullet fly straight. And then there are powders which are not at their best in a particular case, even with an accurate bullet. For example, take the .357 Maximum: Winchester 296/H110 produces reasonable ES with the Bradshaw-Martin cast, powder coat 194 SWC GC, yet cannot approach accuracy of H4227 or IMR 4227. Whereas, 296/H110 produces top accuracy in .357 Magnum over a range of bullets. It his quite evident COMBUSTION DYNAMICS influence accuracy. Two places ES directly affects accuracy 1) Vertical stringing with heavy bullets a) low V impacts high (longer barrel time). b) high V impacts low (shorter barrel time). 2) Long range, where time of flight spells trajectory. David Bradshaw |
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Post by messybear on Dec 3, 2020 9:11:18 GMT -5
Interesting thread. Thanks Dave for observations.
I hate wide ES but as mentioned usually doesn’t equate to accuracy except as Dave pointed out vertically long range ect. So I have been on a quest to lower ES and maintain accuracy for years now. I agree that it’s all about the load.
In interchanging cylinders of different dimension in the same guns, I have found an increase in velocity with tighter chambers but no meaningful change in ES.
The only other things I have found that influences the ES is light hammer strikes or excessive headspace and light bullet pull.
As I mentioned I hate wide ES because cold conditions make it that much worse and I don’t want a load that’s on the edge of good ignition in cold weather.
Messy
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Post by bushog on Dec 3, 2020 10:15:32 GMT -5
I agree with everybody but you are assuming your chrono is absolutely accurate and precise.
The instrument itself may be the biggest source of variation.
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Post by 45MAN on Dec 3, 2020 15:09:09 GMT -5
EXTREMELY INTERESTING AND INFORMATIVE TOPIC
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Post by zeus on Dec 3, 2020 15:11:46 GMT -5
SOME OF the most accurate loads have high ES while some of the loads with low ES have mediocre accuracy. Every sixgun has its own personality. Absolutely true and at sixgun distances, it doesn’t really matter. |
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Post by boolitdesigner on Dec 3, 2020 18:00:32 GMT -5
SOME OF the most accurate loads have high ES while some of the loads with low ES have mediocre accuracy. Every sixgun has its own personality. Absolutely true and at sixgun distances, it doesn’t really matter. It all depends what your're shooting for. High extreme spread (or a little ES) does matter when you get beyond what most people do. |
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dhd
.327 Meteor
Posts: 941 
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Post by dhd on Dec 4, 2020 1:59:09 GMT -5
Yes, it's an interesting topic. Coming from 600 yard benchrest (a medium distance only) ES was important as were other picky OCDish tricks. As I've played with these blankedy blank revolvers I've found what matters and what doesn't matter as much. A rifle case wouldn't be fed into one of my chambers that hadn't had all of the tricks done to it (regardless if the case head had Lapua stamped into it). With revolvers, folks take a case from the bag/box and expand them, then load. It still makes me shake my head but the target doesn't lie to much. I'll admit some things are so ingrained in me that I still do what I do.
Good quality revolvers can shoot some fine groups but it's not luck getting the last bit of accuracy out of them. Powders that work best can be a study unto itself. I've tried to use what I learned from the rifle with the revolver and It's just enough different to keep my interest up.
At least with revolvers I don't have to count bullets going down the barrel and mourn the barrel before last that I had on an action...
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Post by flyingzebra on Dec 4, 2020 7:30:17 GMT -5
I agree with everybody but you are assuming your chrono is absolutely accurate and precise. The instrument itself may be the biggest source of variation. This |
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Post by zeus on Dec 4, 2020 10:47:41 GMT -5
Most Chronos are pretty consistent these days. We run all kinds side by side and it’s extremely consistent across the brands.
Looking at pure drop from a wide ES, my point earlier was that in handgun distances it’s sort of moot. I ran numbers on a standard 44 270 grain Gold dot just to compare drop. At 200 yards, there is 3” of difference in drop between a 1300 FPS and a 1200 FPS load. Not many of us can hold a 3” difference at 200 yards with a sixgun. I’d much rather know all my bullets are dropping in the same spot at typical differences than worry about a 3” drop at 200 yards.
Now, in a long range rifle that we are shooting 1-2 miles, yes it makes a BIG difference. At those distances, a 10 FPS variation can take us off the plate. So in that case, we chase the tightest group possible with the lowest ES. Completely different animals needing different things.
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