Following results of a ladder method load:

308 Norma Mag., IMR 4350, Win. LR primer, 165 gr. Nos. Part.

72 gr. = 3268 fps
73 gr. = 3212 "
73.5 = 3217
74 gr = 3212
74.5 = 3197
75 = 3172
75.3 = 3163
75.6 = 3126
75.9 = 3131
76.2 = 3114
76.5 = 3058

First time I ever had the velocity drop with each increase in powder charge.

What am I missing here?

Regards,
hm

First thing I'd be suspect of is the chronograph. Might try the same loads over another one. There's no way (at least that I know of) that a 4.5gr increase in powder will result in a velocity loss of over 200 fps.

If it were me, I'd suspect the row of loads got put in backwards (mis label). JMO, Dutch.

just a guess here....ok?
Ifyou';re using a Chrony (like most of us) and it's a fold up box and the box is not totally unfolded upon commencement of shooting and the shock of shooting causes it to open slightly as you shoot (effectively increasing the distance between sessors) the velocity readings will decline as you shoot!....possibly enough to offset increases of charge!

Just curious if you had worked up to 72 or started there??? My nosler manual lists 70 as max. Loadtech stops at 69.3 at 62350. I've had one rifle that had two loads drop. I was trying to determine the head expansion point and the loads were right at that point.

I believe this was explained /talked about in Richard Lee's book on reloading,I read it but it was a while back and forget the reason's why they say this occurs.
Hank

Craigster: I have used this chrono quite a long time (Pact Professional model) and (until today) had no reason to doubt it, but who knows.

Dutch: That was my first question! These rounds were actaully loaded by a friend of mine and he swears that he "could not have mixed them up; (he)was very careful". Funny thing was, that as he shot the string, he swore he could feel the increase in recoil w/each "increase" in powder. (I suspect this was a cumulative effect on his shoulder ).

Vapodog: Can see where this could be a good explanation, but the Pact screens are in a rigid base and screen distance cannot change shot to shot.

quote:

Just curious if you had worked up to 72 or started there??? My nosler manual lists 70 as max. Loadtech stops at 69.3 at 62350. I've had one rifle that had two loads drop. I was trying to determine the head expansion point and the loads were right at that point.

Ramrod340: He had been using the 72 gr. load previously and decided to see if he could improve on it. I don't know where he got his data, but indicated that 77 gr. was shown as max.

My Nosler book doesn't even list the 308 NM but my Hodgdon book shows 72 gr. of H 4350 as max??

He shot the ladder string which started at 73 gr. and then shot the old 72 gr. load last just to compare velocities. This would seem to rule out the chrono or reversed loads. I sure don't understand everything I know about this.



Dutch: Just an afterthought, but note above paragraph. The 72 gr. load was taken from an old box of shells and produced a higher velocity than any of the ladder string, all of which had more powder.

Darned if I know???

Regards,
hm

The range shown in the A-Square manual is 69.0 gr to 73 gr with a 165 from a 24" barrel. I am surprised at your result, but also surprised that you were able to get to that high a charge weight with no pressure problems.

I have seen this sort of thing a few times.

In some experiments some years ago with coatings and piezo pressure sensors read by computer every 20 microseconds, we noted that if the bullet moves further down the bore at a given time, the pressure in the bore is lowered ... resulting in lower velocities.


Just a SWAG ...



I suspect that to a point, additional powder is burned in the bore and results in additional velocity.

Beyond the point that the extra powder is being burned in the bore, it is burned in the free air after the projectile leaves the barrel.

If more powder is present than will be burned in the bore the initial acceleration could push the bullet faster earler in its travel in the bore resulting in the volume into which powder is burning being larger at any time X ... thus the pressure can actually drop.

I think I'd load one round @ 72gr and one @ 76.5gr. Fire each over the chrono and see what you get.

quote:

Beyond the point that the extra powder is being burned in the bore, it is burned in the free air after the projectile leaves the barrel.

Mike: We talked about that possibility at the range today. Have never experienced this condition before, however. Always a first time for everyting, I guess and this seems to be most plausible explanation.

We were watching for pressure signs and there were none. No marks on head of case, bolt lifted easily, and primers still nicely rounded.

Since my buddy is an experienced reloader, I didn't question his data, but just checked several of my books and highest load I could find was 71 gr. in an old Sierra book. So just called him and asked him to check his data again.


Aha! My buddy just called back and we get to the bottom of this....sort of, that is. Here's the straight poop.

He recalled that he was using N 205 powder, not 4350 and 77gr is the max. listed for that powder. Soooo, the chrono data should read:

72 gr. IMR 4350 = 3268 fps

Following were loaded w/ Norma 205 powder:
73 gr. = 3212 "
73.5 = 3217
74 gr = 3212
74.5 = 3197
75 = 3172
75.3 = 3163
75.6 = 3126
75.9 = 3131
76.2 = 3114
76.5 = 3058

He still maintains the rounds could not have been reversed in the box.

Thanks for all the input.

Regards,
hm

quote:

I think I'd load one round @ 72gr and one @ 76.5gr. Fire each over the chrono and see what you get.

Craigster: Please see my post above. Since my friend remembered that his ladder test used N205, not 4350, we solved the difference between the 72 gr. charge and ladder charges.

Regards,
hm

quote:

Craigster: Please see my post above. Since my friend remembered that his ladder test used N205, not 4350, we solved the difference between the 72 gr. charge and ladder charges

Just looked at Loadtech for RL22 & MRP(it doesn't list 205) The program calculates 100-130fps range for a 3.5gr spread. Lower to higher of course. Sure sounds like loads in reverse order.

Sure glad I've never done that.

His 72gr load puts him at or above 300Wby listings in my Nosler manual. I sure can't get there in my 308N

quote:

Sure glad I've never done that.

ramrod340: Yep, me too! LOL. I told my bud that I now use a sharpie to number the primers on my ladder loads to be absolutely sure they do not get reversed and he just growled at me.

quote:

Just looked at Loadtech for RL22 & MRP(it doesn't list 205) The program calculates 100-130fps range for a 3.5gr spread.

That's real close! Chrono showed 154 fps. By the way, according to my bud, MRP is supposed to use the same data as 205.

Regards,
hm

Ahhh ... this now better squares with my experience ... I've usually seen this kinda thing in situations where I am working up loads with what turned out to be too slow a powder. N205 has a burn rate between IMR 4831 and H4831. Way slower than IMR 4350. Pretty slow stuff.

I think my swag is probably what is at least a plausible explanation for what is happening.

quote:

I think my swag is probably what is at least a plausible explanation for what is happening.
Mike

I tend to agree. Thanks for the input.

Regards,
hm

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No Way Jose

quote:

Originally posted by hm1996:
Following results of a ladder method load:

308 Norma Mag., IMR 4350, Win. LR primer, 165 gr. Nos. Part.

72 gr. = 3268 fps
73 gr. = 3212 "
73.5 = 3217
74 gr = 3212
74.5 = 3197
75 = 3172
75.3 = 3163
75.6 = 3126
75.9 = 3131
76.2 = 3114
76.5 = 3058

First time I ever had the velocity drop with each increase in powder charge.

What am I missing here?

Regards,
hm

.

quote:

Originally posted by doctorxring: No way Jose
Originally posted by hm1996:
Following results of a ladder method load:

308 Norma Mag., IMR 4350, Win. LR primer, 165 gr. Nos. Part.

72 gr. = 3268 fps
73 gr. = 3212 "
73.5 = 3217
74 gr = 3212
74.5 = 3197
75 = 3172
75.3 = 3163
75.6 = 3126
75.9 = 3131
76.2 = 3114
76.5 = 3058

First time I ever had the velocity drop with each increase in powder charge.

What am I missing here?

Regards,
hm

[/QUOTE]


doctorxring: Read on..........

quote:

Posted 29 June 2007 07:13 Hide Post
quote:
Beyond the point that the extra powder is being burned in the bore, it is burned in the free air after the projectile leaves the barrel.


Mike: We talked about that possibility at the range today. Have never experienced this condition before, however. Always a first time for everyting, I guess and this seems to be most plausible explanation.

We were watching for pressure signs and there were none. No marks on head of case, bolt lifted easily, and primers still nicely rounded.

Since my buddy is an experienced reloader, I didn't question his data, but just checked several of my books and highest load I could find was 71 gr. in an old Sierra book. So just called him and asked him to check his data again.


Aha! My buddy just called back and we get to the bottom of this....sort of, that is. Here's the straight poop.

He recalled that he was using N 205 powder, not 4350 and 77gr is the max. listed for that powder. Soooo, the chrono data should read:

72 gr. IMR 4350 = 3268 fps

Following were loaded w/ Norma 205 powder:
73 gr. = 3212 "
73.5 = 3217
74 gr = 3212
74.5 = 3197
75 = 3172
75.3 = 3163
75.6 = 3126
75.9 = 3131
76.2 = 3114
76.5 = 3058

He still maintains the rounds could not have been reversed in the box.

Regards,
hm