Following loading recommendations in the Nosler #6, why do I get less velocity with a 180 Accubond as compared to the 180 Nosler Partition ? All things being equal.
Please educate me !
Thanks,
Jim

Partition probably has a longer bearing surface. This would increase increase pressures, and increase velocities.

Other way around (right, AS?)

The energy of the powder is divided by three.

Driving the bullet.

Overcoming the fiction force.

The escaped energy in the exhausted gas.
If the friction force is different from one bullet to another of equal mass this will change the available energy transmitted to the bullet and the energy residue in the gas. roger

BN, I'd have to measure to be sure. BT has a bit of a boat tail, I'm not sure how differnt the nose profiles are.

Jim, you said you got a difference in velocity.

How big was your sample, and how big was your differnece?

The sample was not much. I have loaded the partition enough for one barrels life span, approx. 2200 rounds. The accubond approximately 150 rounds. The same rifle ( new barrel ), same powder, case, primer, same range session the velocity of the Partition is 3086 fps., the Accubond runs 3028 fps.
The caliber is .300 Win. mag., 25.3" Hart barrel, 81 grs. H-1000, Fed. 215 m primer. Nosler brass, the same weight. Everything as identical as possible. So, about a 60 fps. spread.

The two bullets are of a totally different jacket design, whereas the partition has a thinner and softer jacket with no solid mass and obturates into the rifling easier than the Accubond, which does have a solid mass towards the rear and a tougher jacket making it more difficult to obturate into the rifling, needing more energy and most likely has more gas blow-by in this process...equaling less velocity. Just my take on it.

My Nosler #5 shows velocities for both BT's & PT's that are about 100 fps slower than does my #6 for Accubond's and PT's.

Recent firsthand experience with .358 225 gr BT's & Accubonds in a Rem. 700 CDL 35 Whelen (chrono'd velocities) showed this to be pretty close to the mark.

The Accubond's were absolutely faster - same gun, same case, same prep, same primer, same powder, same powder, same load. Why? Dunno, but there you have it. I honestly expected almost identical performance across the chrono and on paper but I was wrong.

I don't kn ow if they are also faster than PT's because I haven't loaded it with them for this rifle.
-WSJ

I have found flat base bullets get a little more velocity, but not enough to concern me...
...tj3006

tjroberts,
That is probably the correct reason. I have never loaded boat tails before, so no experience.

Sir,
"New barrel" = different rifle. Not to say all what the fellas said above doesn't matter, it does. Just saying no way to compare in your stated case.
Best regards
Dmw

Fury01,
The same barrel.

quote:

Originally posted by Jim Hundley:
The sample was not much. I have loaded the partition enough for one barrels life span, approx. 2200 rounds. The accubond approximately 150 rounds. The same rifle ( new barrel ), same powder, case, primer, same range session the velocity of the Partition is 3086 fps., the Accubond runs 3028 fps.
The caliber is .300 Win. mag., 25.3" Hart barrel, 81 grs. H-1000, Fed. 215 m primer. Nosler brass, the same weight. Everything as identical as possible. So, about a 60 fps. spread.

Are the bullets the same length? Does one intrude more into the case? You'll change the interior ballistics if the case capacity is reduced. Did you alternate shots or fire one string with one bullet and then the other? Barrel fouling and temperature could be variables. I alternate shots and fire a fouler first when comparing loads.

Why would you think you would get the same velocity? Different bullet.

Basicaly what Roger said.

Monolithics have more pressure than lead core slugs. The partition is a solid copper unit at the point in the middle of the slug where the partition resides. I think that would be the most likley explanation with your particular situation. That "could" be what is causing slightly more pressure as opposed to a softer lead core. Mileage will certialny vary, garanteed. No two guns are the same.

Read "why ballisticians go gray" in the old Speer manual..

Havng tested all three, the Accubond, Partition and VLD, to a "T", in the order I've stated, pressure reduces and velocity increases.'

Alan

Is 58 fps of any real consequence. Lots of good loads will vary that much in a 5 or 10 shot string.
Your target will never know the difference.
Leo

so your talking about approximatly 2% difference in two bullets?
take two steps forward, then shoot, your impact velocity will be the same.
unless you are shootng 1,000 yds then take 10.
seriously now.
you have a new bbl and new bullet i'm more surprised they are that close.
i have seen 2 rifles shootng the same loads from the same box have that much [50-75 fps] difference.

60 fps might not sound like alot, but if you are getting different velocities, it may indicate different pressures. QL predicts a difference of 60 fps may represent a differnece of 1.5gr of H1000 and 5k PSI. Jims loads appear to be safely under max, but as a person approaches maximum pressure, they need to be aware of how variables such as bullet shape can effect these pressures.

First off the two bullets are of different OAL lengths so the accubond, being longer takes up a bit more room inside the case assuming your OAL seated length is the same. This changes the load density factor which typically creates higher pressure. In other workds... for an equal load for both bullets the powder has more wiggle room behind the partition.

Secondly, I agree that the differences in the jacket and core materials must equate to some lower resistance and pressure factors. This is the moste likely culprit.

Thirdly, the accuonds higher BC will offset any shortage at the muzzle down range and the difference your seeing is insignificant. Not worth the headache of figuring it out IMHO.