Modern powders and barrel harmonics in 303's

[Cdn303]

Russians AND the Yugoslavs make a .311", 174gn FLAT-BASED ball projectile

Do you have a name?

[CINDERS]

Rightoh last Q where can one procure a 174 FB spire point I have some 170gn Taipans FBSP's .312" but they are in a 100 packet and a collectible about one of the last batches Malcolm Bone made and Woodleighs are too expensive to cut paper, I may try driving 174 SMK's a bit slower will consult Load data and look at 2,350 - 2,400 fps thanks chaps

[ssj]

I think Varget is equal to ADi2208 not 2209. You will have to trial what flies best in your gun, I found start loads of ADi 2208 fine. You can go higher but the gun whips about as I found out when my electronic scale read 7gr low, ikky.

---------- Post added at 08:48 AM ---------- Previous post was at 08:45 AM ----------

Barnaul.

I use their 0.3105dia 174gr flat based FMJs. We get under 2inch MOA (actually 48mm) in a std P14 with a fairly worn barrel at 100yds, very happy with it.

[Patrick Chadwick]

I will explain it this way; say Ball ammo exits the muzzle in 2 mili seconds after ignition and the reloads even though going at the same terminal velocity due to the faster burn rate get to the muzzle in say 1.5 mili seconds will this alter the barrel harmonics and groups ?

I can clarify this (I hope) with an analogy, that also concerns vibration in steel.
It is easily demonstrated (and you can hear it, even if you cannot measure it) that the tone quality of a note struck on a piano varies with the "attack", i.e. the speed and duration of the hammer strike, bound up with subtle variables such as the hardness of the hammer felt, stiffness of the pegs holding the strings etc.

The harmonics, being harmonics of a fundamental note determined by the string length, not random frequencies, are not altered, but their relative intensities will vary, and this varied mix is perceived as a difference in tone quality.

In a rifle barrel, the strike is the burning of the propellant, and the attack is the rate at which it burns and how the rate varies during combustion. So the harmonics generated in the barrel will also vary in amplitude, depending on the "strike", and thus with the type of powder that is used. If different primers have an effect, it is also through their influence on the "strike".
All those harmonics make the barrel whip around in a complex manner, and one may imagine that harmonics that hit the muzzle at the same time as the bullet exits are going to do most to throw the bullet of course. So yes, it is to be expected that the time taken for the bullet to reach the muzzle will have a noticeable effect on grouping.

This barrel time aspect is not a novel consideration, although I hope that the analogy with a piano string is perhaps a useful aid to understanding. Look on the internet for "Optimum Barrel Time" and load development.

[Patrick Chadwick]

Do you have a name?

PRVI. The S&B SPCE hunting bullets are also very good, and come in various calibers - the best I have found for my 7x57 Mauser - as they have the flat base, providing a long cylindrical section up to the step at the junction with the nose, which makes a very clean hole in the target, rather like a wadcutter.

[CINDERS]

Thanks Patrick I did some Physics at TAFE and sorta look at barrel harmonics as wave motion though the barrel harmonics would be considered a pulse as there is no rebound as the pulse travels from breech to muzzle I really appreciate the input perhaps the theory lies in not driving them at the Mk VII Ball speeds but perhaps backing off to duplicate the harmonics which the lower projie speed giving it more barrel time will be compensated by the better BC of the projectile.

Anyway that to me sounds plausible perhaps the Mythe Busters can have a crack at it and save us, hhhhmmmmm that may not work as it will then mean I cannot use load testing as an excuse to wrack off to the range!!!

[the old gringo]

I agree with Bruse_in_oz
the 303 barrels differ in barrel dia so much each should be slugged I have a plethora of the old war horses and each differs slightly . I finally settled with 40 grains of Varget with a 174 grain Sierra bullet I have one rifle that gets .72" groups at 100 yards to 1.80" in my oldest rifle the bore slugs .315 on it so !!!

[Patrick Chadwick]

but perhaps backing off to duplicate the harmonics which the lower projie speed giving it more barrel time

Not quite right. The answer is not more or less barrel time, but the optimum barrel time. A couple of years ago I did a write up of my M1917. I took some trouble to try loads over the maximum plausible range, and plotted the grouping results on a simple graph, which I posted.

This graph showed two bad "peaks" of group size, which were about twice as large as the best value, in the middle of a shallow "valley" between the peaks. It was easy to determine the bad values, but the flat floor of the valley means that the optimum value has some tolerance (+/- several tenths of a grain) over which any difference is swamped by day-to-day variations of wind, weather, light, personal constitution etc.

So the secret is OPTIMUM barrel time, not simply longer or shorter. That is why I suggested that you search the forum, to save me having to write it all up again.

[CINDERS]

Appreciate the answer Patrick I feel sometimes the variations above all across all the processes to build a rifle for combat even though the tolerances are quite stringent will still give you a cross section of same rifles that would vary in groupings considerably, given some of the fought at ranges in WW I - II you could have used a stick (Not a boomerang as they come back) a stick won't.
Then again the enemy could throw it back at you.

I am trying one more thing with the T and that is to medium crimp the rounds not as hard as they did the stabs on the Mk VII round but just a trial to see if it improves anything going to use my bog standard loads of 39 to 40.5 grains Varget + 174SMK ladder test and go from there.
If things are still awry then perhaps a look at a few other things and the last resort will be the scope to Peter L but it will all take time and I am not to fussed that much at this point just processes of elimination it is all fun though and I never aspire to win anything just range time and helping others.

Life does not get much better than that, though my wife has decided she likes to shoot the 303's now along with my son both who also shoot full bore and F class I am slaved to the reloading press such is my lot in life sigh!