As mentioned in my other thread about VV N320, I loaded up some test rounds and my velocity was very low compared to the stated velocities, about 150-200 fps less than printed velocities. One member suggested the BC gap, which I measured at .006" on all six holes. Is .006" enough to reduce the fps that much? I have another round of test ammo loaded up with Titegroup and hope that I have better luck.
BC gap and velocity loss??
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STORMINORMAN
Member
No info as to the firearm used, barrel length, etc.
What "stated" velocities were you expecting? What was the length of the test barrel used in the load data?
Cheers!
What "stated" velocities were you expecting? What was the length of the test barrel used in the load data?
Cheers!
OP
5" model 625 in 45 Colt.
DWalt
Member
I don't know, but I wouldn't expect .006 is excessive. All I can say is you can't do much about it anyway except to use your chronograph to adjust your load little by little to produce whatever MV level you expect. I give very little to no credence to any published MV numbers given in reloading manuals, etc. as it will very nearly always be incorrect for your specific revolver.
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A LOT of the data out there is with barrels that are 4.5" or longer than a
"Standard" revolver or pistol barrel or worse yet, a "Universal receiver"
that has no cylinder gap that has higher fps than a gun.
Some guns are "Tight", some "Loose", and both can have a 100fps difference or more.
Just because a load is 75-110fps slower than the factory load, does not mean that, it will not work.
Relax and smell the roses.
"Standard" revolver or pistol barrel or worse yet, a "Universal receiver"
that has no cylinder gap that has higher fps than a gun.
Some guns are "Tight", some "Loose", and both can have a 100fps difference or more.
Just because a load is 75-110fps slower than the factory load, does not mean that, it will not work.
Relax and smell the roses.
OP
VV's website said that 6.9 grains was max at 915fps. My test loads were up to 6.6 grains with an average fps of 704, with a spread of 112 fps. Thought that I should have been closer to the fps, but the spread has me wondering also. Going to try TG next.
I checked the VV website. For 45 Colt, they indicate velocities were measured from a "Test barrel: 150 mm (6"), 1 in 16" twist". I'd say they were likely using a universal receiver and possibly a non-vented barrel, which will give higher velocities than a revolver.
smoothshooter
Member
A .006" B/C gap will not cause nearly that much velocity loss.
There are other variables.
There are other variables.
STORMINORMAN
Member
What device are you using to weigh the powder: is it possible your scale is off...?
Cheers!
Cheers!
Barrel length, crimp, primer, and COAL,even brass can all factor in on pressure and pressure is what pushes the bullet down the barrel (MV). not to mention every gun is different.
The temp outside and the temp. of the barrel will effect MV.
Good luck finding the sweet spot for YOUR gun.
The temp outside and the temp. of the barrel will effect MV.
Good luck finding the sweet spot for YOUR gun.
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IMHO the "perfect B/C Gap is .004-.005 but .006" is still acceptable even to a fussy OCD'er like me. Wouldn't want anything bigger but .006" will work just fine.
FYI: very tight B/C Gaps such as .002"-.003" can sometimes get fowled up with lead and carbon while shooting.
As far as velocity loss is concerned, I believe the difference between .003" and .006" would be negligible and pretty much meaningless in real world scenarios. Yes, it might be measurable on a good Chronograph but won't change over all performance.
From what I have read here, the "new S&W spec's" on B/C Gap are up to a whopping .012" and that is a deal breaker for me! I'd not buy a Revolver past .006" personally.
FYI: very tight B/C Gaps such as .002"-.003" can sometimes get fowled up with lead and carbon while shooting.
As far as velocity loss is concerned, I believe the difference between .003" and .006" would be negligible and pretty much meaningless in real world scenarios. Yes, it might be measurable on a good Chronograph but won't change over all performance.
From what I have read here, the "new S&W spec's" on B/C Gap are up to a whopping .012" and that is a deal breaker for me! I'd not buy a Revolver past .006" personally.
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.012?....guess I'll be getting out the gauge and check my collection of 686's which are all less than 5 years.
For a little study on the effects of barrel-cylinder gap and velocity, I will point to this link.
BBTI - Ballistics by the Inch :: Cylinder Gap
BBTI - Ballistics by the Inch :: Cylinder Gap
Ivan the Butcher
Member
FYI, just for a field measurement, a post-it is .004" at the non sticky end.
Ivan
Ivan
bmcgilvray
Member
I once cooked up a warmish 185 grain load for the .45 ACP using Unique. Clocked 950 fps from a 5-inch 1911 in chronograph tests. A test in a 5 1/2-inch Colt New Service Model 1917 revolver showed the load gen'd up 1050 fps.
Did the extra half inch of barrel boost the load? Did the barrel/cylinder gap of the revolver rob the load of additional potential performance?
At the time of the tests I simply shrugged my shoulders over this discovery.
Did the extra half inch of barrel boost the load? Did the barrel/cylinder gap of the revolver rob the load of additional potential performance?
At the time of the tests I simply shrugged my shoulders over this discovery.
OP
Using the scale on my RCBS electronic powder dispenser. It was 5 degrees outside though, that might have had some effect on it, but I wouldn't think that much.
STORMINORMAN
Member
This may sound silly, but do you ever cross-check/calibrate your RCBS against any other scale?
I have a digital scale, an auto Hornady L-n-L & an old Ohaus 1010 and I occasionally do a comparison (even using the LEE dippers as well) just to insure I'm really dealing with accurate weights.
Not all the time, but just occasionally for my peace of mind.
Cheers!
OP
I do occasionally check it. Here is my crimp, which I think is good. 1.595" COAL.This may sound silly, but do you ever cross-check/calibrate your RCBS against any other scale?
I have a digital scale, an auto Hornady L-n-L & an old Ohaus 1010 and I occasionally do a comparison (even using the LEE dippers as well) just to insure I'm really dealing with accurate weights.
Not all the time, but just occasionally for my peace of mind.
Cheers!
Attachments
I have two "identical" model 66 revolvers, one of which has the dreaded .012" BC while the other has the "Perfect" .005" BC. Difference of avg MV with identical competition "Minor" loads using HP38, 30 fps. Big whoop.
Shooter uses factory load data taken with test barrel and goes blissfully along assuming he is shooting xxx fps, then FREAKS when chrono data for HIS GUN does not match. After running chrono for matches for 20+ years, it is a familiar story, happens more often than not.
Shooter uses factory load data taken with test barrel and goes blissfully along assuming he is shooting xxx fps, then FREAKS when chrono data for HIS GUN does not match. After running chrono for matches for 20+ years, it is a familiar story, happens more often than not.
bmcgilvray
Member
I have a certain 158 grain .357 Magnum load using 2400 that makes a little over 1300 fps from the 6-inch Smith & Wesson Model 27 here, yet that same load barely musters 1100 fps from a 6-inch Colt Python on hand and the Python has the tighter gap.
Go figure.
Go figure.
