Velocity flucuations with compressed loads

[jtoews80]

Just went out and tried my chronograph that I got for Christmas for the first time. Seems to work very well. I tested my 44 Henry rifle, loaded with 23.o grns H10 & a 240 JHP Nosler velocity was 1585fps with maybe +/- 10 fps. Tried some loaded with 23.5grns(slightly compressed) and didn't get any velocity increase. OK, no big deal.

WEnt to my 308 CZ550 w/26inch heavy barrel. Load is 180 NBT, 44.0 grns IMR 4064(serious compressed load). The velocities were very uniform +/- 5 fps @ 2665fpsavg for the first 4 rounds, then suddenly one 80fps lower, 3 more @ 2665 then one at 2718. I believe I've got a few with some crushed powder. The primers o the hotter velocities were quite flat, more than I would accept as a usable load.

I really like this load, it's seriously accurate some of the time. I had initailly attributed the variations to seating depth problems as more compressed loads are more difficult to seat uniformly. Problem is, I've got 100 180 AB's loaded the same way.

I haven't finished the seating yet, I was waiting to test the seating depths since I thought that was the problem. I've got the Accubonds sitting @ 2.865(where the bullet will push itself back to usually)" and the other load is seated @ 2.83". Is there some way to avoid ruining the powder in these rounds, perhaps putting a orbital sander against the seating die to vibrate the powder tighter when seating?? I had found that tapping it with my finger does help settle the powder a bit, but it can also do too much and seat them too deep.

 

[rick smith]

Use a drop tube when loading the powder in the cases will help, I have tried vibrating the case while loading powder and spilled a lot of powder. Have you tried the loads with the NAB? You are switching bullets so the load with the NAB should have been tried before loading 100 of them. I haven't looked in a manual for load data I-4064/180gr bullet so won't comment on the load itself but you have reached/passed the usefullness of that size case. I have found I-4064 to be useful with lighter weight bullets but on the fast side for heavier bullets in 308 and 30/06. If you want to shoot 180s in the 308, I would look at some ball or short cut powders.
I have a couple loads that are compressed and haven't had the velocity variations as you have. If the powder in your loads is so compressed that the bullet is being pushed forward after seating then you either need to change a component or work back up using more neck pressure on the bullet or start crimping. Another consideration is seating depth vs magazine box length vs lands. Most 308s that I have loaded the mag box controls the seating depth not the location of the lands. If your bullets are moving forward from powder pressure, a little recoil on the same loads could cause the bullet to move against the magazine box and cause feeding problems.
Seating depth can have a dramatic effect on group size so you have to be able to keep that in control.Rick.

 

[Ol` Joe]

The more you play with your new toy the more you`ll find velocity isn`t always as consistant as we believe. The factory stuff often is really terrible in my limited experiance. There are a number of ways you can get bad readings from your unit,
Different/poor lighting.
Reflected light from ice or water under the screens can make it hard for the sensors to detect the bullet properly
Heat from the barrel or, as I`ve been told, the bolt face on the primer alters the burn rate
Screens improperly set-up
Muzzle blast

Sometimes there just seems to be nothing you can do to improve the load. Try changing primers to see if it helps. Seating can change things if it alters the tension or pull on the bullet. Seating into the lands, or a bit back if you are at the leade can sometimes cause different results. Color the bullet with majic marker. This makes it easier for the sensor to pick up then a shiny new copper jacket and sometimes helps, especially with reflected light.
Praying to the gods of reloading and offering the proper sacrifices is often the only thing that appears to help. On these days I pack up, give myself a good talkin` to, and head for the books or inter-net with a couple fingers of Glenfedich and a asprin or 2 in search of a cure. I never seem to find a inclusive fix but, often the next time I go out, shooting the ammo ammo from the same box I see some improvment.....Why? Wish I knew. :?

 

[Antelope_Sniper]

JT, an 80 fps variation is nothing.
It's not unusual for factory and military loads to vary 200+ fps on a 5 shot string. The +/- 5 fps is usually the exception, not the rule. Here the real question, IF IT'S AN ACCURATE LOAD, WHO CARES WHAT THE CHRONOGRAPH SAYS? The accuracy was good enought to load up 100 before you chronographed them. That hasn't changed. It's the same load, you just know a little bit more about it. Besides you have 100 loaded up, chronograph a few more strings. It might be interesting to see what the load does on a different day under different conditions.

 

[jtoews80]

The load is "somewhat" accurate. After working up I shot it some at the range in single shot landed .015" off lands, 1st 3 shot string 1.41" edge to edge or 1.08" minus bullet diameter @ 300M or 333yds. 2nd string 4.5", which is nowhere acceptable for target use, but will hunt on deer size game. The velocity differences are showing up at the target.

I've tried W748 42-45 grains, groups started opening up @ 44grns and seen serious pressure signs @ 45.0, flat primers and 4 thou bulge at case head. Discard test cases, save the 748 for 150's.

I may just use the rifle in singe shot, it works well. I've noticed alot of compressed loads in Nosler #6, so I probably will have to make a long drop tube.

CC

 

[coyotetrapper]

I see that most times those with a lower SD no matter the speed have the best accuracy, but as others have said sometimes I can get an 8 FPS SD and other times it is 30 something SD. I like those extreme powders of hodgdon as I do see less SD more foten than not with those powders over others that I have tested through a crono.

My best .243 load is 37.5 varget at 3080 avg, I could go faster but this load is very accurate less than 1" at 200 yards more often than not. The more speed the more SD/bigger groups I see in this rifle. So I quit messing around with 4 different bullets, 3 different powders and seating depths and just come to the conclusion this load is darn good and I don't see it getting better, on paper or a crono. Plus I'm off max by quite a bit and will give me longer barrel life and great accuracy to me that is a win/win. Speed doesn't kill accuracy does the killing on game.

A guy could pull his hair out over this reloading stuff LOL!

 

[Big Squeeze]

Just went out and tried my chronograph that I got for Christmas for the first time. Seems to work very well. I tested my 44 Henry rifle, loaded with 23.o grns H10 & a 240 JHP Nosler velocity was 1585fps with maybe +/- 10 fps. Tried some loaded with 23.5grns(slightly compressed) and didn't get any velocity increase. OK, no big deal.

WEnt to my 308 CZ550 w/26inch heavy barrel. Load is 180 NBT, 44.0 grns IMR 4064(serious compressed load). The velocities were very uniform +/- 5 fps @ 2665fpsavg for the first 4 rounds, then suddenly one 80fps lower, 3 more @ 2665 then one at 2718. I believe I've got a few with some crushed powder. The primers o the hotter velocities were quite flat, more than I would accept as a usable load.

I really like this load, it's seriously accurate some of the time. I had initailly attributed the variations to seating depth problems as more compressed loads are more difficult to seat uniformly. Problem is, I've got 100 180 AB's loaded the same way.

I haven't finished the seating yet, I was waiting to test the seating depths since I thought that was the problem. I've got the Accubonds sitting @ 2.865(where the bullet will push itself back to usually)" and the other load is seated @ 2.83". Is there some way to avoid ruining the powder in these rounds, perhaps putting a orbital sander against the seating die to vibrate the powder tighter when seating?? I had found that tapping it with my finger does help settle the powder a bit, but it can also do too much and seat them too deep.

......................Very interesting!.............. The max. load in my Sierra manual for the 180 gr. shows 42.8 grains of IMR 4064. As you say, it is easy to have a very compressed load with that charge!............In some cases, depending on the rifle, one can have the best accuracy in a given powder when loaded over the book maximum........... As an example, last month my best 3 shot group ever was 0.544" (outer hole to outer hole; not center to center) using .8 of a gr. over the maximum. I deliberately loaded over the max. to see what pressure my rifle would accept with a particular powder I was experimenting with!....Even though the most accurate, with extremely little to no pressure signs, I will not continue to use that charge. I will go down in small increments until I get the same results. Even over the max., the powder I was using was not a compressed charge.........I am not a big fan of overly compressed charges for the very reasons you state above. You may want to try another powder that is a slightly faster burner or slower with a better density in the .308. Less charge, same velocity! Or stay with the 4064 and reduce your charges by 2/10ths of a grain increments and see what happens ...........Like another said, if you get great accuracy, don`t worry too much about the velocity variations..........However, your COL or seating depth must be as uniform as possible. That may have played a role in your velocity variations and fluctuation in pressure........If you are not comfortable in shooting what you have left, then use a bullet puller and start fresh.................Change your powder for a better density and watch your unifomity in case trimmed lengths, carefully weigh each individual charge (I use a digital scale w/ a powder trickler), and you should be fine!.....In your case, your problem I believe is two fold; lack of unifomity in seating depth and too much of a compressed charge with the powder you were using!