Thread: Lower than expected velocities

Originally Posted by Longrun

Garbage. All of the data can't be incorrect. I expect to achieve an accurate 100gr load with no pressure signs at around 3200fps. There's shit loads of data and real world experience to support this. Some of which is kindly posted in this thread.
Whether I achieve that with stabal 6.5 is yet to be decided.

Fark me....if you can't do that with 25/06 you might as well just use a 270 and do it.... Just chuck the chronograph away and be happy lol

Greetings,
The biggest variable is often the powder. I have found large shifts of powder speed in my own comparative chronographing for both AR2209 and BM8208. As most of you know these powders are sold in the US as H4350 and IMR8208XBR. With AR2209 I was able to chronograph the same load in my T3 6.5 at 2,720 fps for the older powder and 2,805 fps for the newer. The older powder still chronographed the same as it did in the 1990's. The Hodgdons max load of BM8208 for the 60 grain Vmax claimed 3,057 fps in a 24 inch barrel only chronographed 2,940 fps in a 26 inch barrel. The figures for AR2206H were spot on. Previous tests of an early lot of BM8208, packed by IMR, in the .308 were also spot on. That's why I work up using a chrono.
GPM.

Cases could be a factor?
A bigger volume case could suck up a couple of grains of powder compared to another case.
GPmac have you and others suggested though that in the absence of sometimes erroneous pressure signs it more to do with the velocity as yiu can't have the velocity without pressure?
Stand corrected if I've got that wrong as I don't do bugger all reloading and have only just bought a chronagraph

Originally Posted by No.3

Nailed it there - for whatever reason that batch of components are not achieving the listed speeds. 'Max' is what the factory lists for the rifle using factory ammo , within a few percent should be achievable or to put another way you should be able to duplicate the factory specs with handloading. If you can't - why? That's the issue I have with my .308 - 20" barrel which is fairly standard for a .308 yet seems to be almost 300fps slow whatever I feed it.

Greetings @No.3,
I would be interested to know what velocities you are getting in your .308. I did some comparative chronographing with 5 different powders and 3 different projectile weights in my 20 inch .308 and found the Hodgdons data was mostly pretty accurate once barrel length had been factored in.
Regards Grandpamac.

GPM that's only 85 fps difference. That's an es lots of folks will be used to anyway.

Originally Posted by csmiffy

Cases could be a factor?
A bigger volume case could suck up a couple of grains of powder compared to another case.
GPmac have you and others suggested though that in the absence of sometimes erroneous pressure signs it more to do with the velocity as yiu can't have the velocity without pressure?
Stand corrected if I've got that wrong as I don't do bugger all reloading and have only just bought a chronagraph

Greetings @csmiffy,
You are quite right in that a lighter case, with more capacity will result in lower pressure but how much is another question. I have a test loaded for my .308 with light and heavy cases but have yet to chronograph them. I suspect the difference is less than some think. The BM8208 loads I mentioned in my previous post were loaded in heavy cases but were still well short of the Hodgdon velocities and more in line with later data from Handloader and Hornady. The problem with "pressure signs" is that when they appear, assuming that they do, you are well over the specified max pressure and have used up most of the safety margins. I have found that max loads may vary between data sources but the velocities are more constant. The data still needs to be for the same or similar projectile especially for the new whizzo ones around today.
Regards Grandpamac.

Originally Posted by Micky Duck

GPM that's only 85 fps difference. That's an es lots of folks will be used to anyway.

Two inch longer barrel was 85fps slower though - that's significant and if that barrel was the shorter length I would be thinking it would be more like 150fps slower. All barrels have personalities they say, I think with that .308 it has what they call a 'fast' barrel (which is to say it spits the pill out quickly and doesn't let the pressure get up enough to make the expected fps).

Originally Posted by grandpamac

Greetings @csmiffy,
You are quite right in that a lighter case, with more capacity will result in lower pressure but how much is another question. I have a test loaded for my .308 with light and heavy cases but have yet to chronograph them. I suspect the difference is less than some think. The BM8208 loads I mentioned in my previous post were loaded in heavy cases but were still well short of the Hodgdon velocities and more in line with later data from Handloader and Hornady. The problem with "pressure signs" is that when they appear, assuming that they do, you are well over the specified max pressure and have used up most of the safety margins. I have found that max loads may vary between data sources but the velocities are more constant. The data still needs to be for the same or similar projectile especially for the new whizzo ones around today.
Regards Grandpamac.

Which is where it can get tricky with these 'different' barrels that don't generate the speed you'd expect - you can keep jamming powder in until you get to the point where something lets go and you still haven't hit the speed the book says if you aren't careful and looking for weirdities...

I will need to go back and redo the speeds off that .308 - last time I ran the magnetospeed with the silencer fitted and it didn't generate completely reliable figures. Not reliable enough for me to want to rely on anyway!

Originally Posted by Micky Duck

GPM that's only 85 fps difference. That's an es lots of folks will be used to anyway.

Greetings @Micky Duck and all,
The quoted speeds were averages and the ES were all very low so the difference was real. To get some context the extra speed was equivalent to adding almost 2 grains more powder. I have found reference of this change in powder speed for AR2209 (H4350) on the internet but nothing from Hodgdons.
@No.3,
The 2inch longer barrel was on the .223. The chronographed data was 117 fps slower than the Hodgdons data to which you should add another 50 fps for the longer barrel. total close to 170 fps all up. Handloader listed 2,910 fps for the same 23.6 grain load with the 60 grain SP v 3,057 from Hodgdons so there is that 150 fps difference again.
Regards Grandpamac.

Umm..speaking out of relative ignorance, is there a point in the discussion to think about relative neck tensions? Like, would more neck tension, or less, make that big a diff to velocity all other things being equal? Lee FCD anyone?

Originally Posted by Jhon

Umm..speaking out of relative ignorance, is there a point in the discussion to think about relative neck tensions? Like, would more neck tension, or less, make that big a diff to velocity all other things being equal? Lee FCD anyone?

Greetings @Jhon,
I just keep cases in batches. The whole batch of the same lot get sized, trimmed, annealed and loaded at the same time. I don't crimp necks as I don't have any really big boomers.
GPM.

Originally Posted by grandpamac

Greetings @Jhon,
I just keep cases in batches. The whole batch of the same lot get sized, trimmed, annealed and loaded at the same time. I don't crimp necks as I don't have any really big boomers.
GPM.

Greetings @grandpamac,
I understand that most of us loading for BA rifle stick with the tension delivered by standard resizing techniques. Also that most of the focus on neck tension is around group size from consistency. Tension must vary some according to brass thickness and hardness so variations in case manufacture as well as hardness come into play. All that aside my thought is that, other things being equal, increasing neck tension increases pressure = more velocity. Using a crimp may not deliver a lot, and may have other consequences (brass life), but if OP is looking for even modest velocity increases would using a crimp from the Lee FCD not only increase pressure/velocity but also consistency?

I don't think increasing neck tension increases velocity/pressure much.
Consistent neck tension affects ES of load.
The load in question has a ES of 30 which is not too bad.

I suspect the load is slightly down on pressure despite the data and I'll be doing a ladder test while looking for pressure signs and velocity/pressure spikes.

Greetings,
Over the years I have noticed significant differences in load data for 6.5mm cartridges in particular the 6.5-06. This has become worse since Americans "discovered" the 6.5mm bore. The Continentals had been working with 6.5mm cartridges since the 1890's and had worked out how to deal with the long projectiles and fast powders. Most of these rifles had slightly or sometimes more loose groove dia. When A2 introduced the 6.5-06 as a factory cartridge they seem to have used much tighter groove barrel specs which push up both pressure and velocity. The data put out by Hodgdon for the 6.5x55 agrees pretty well with my results but the 6.5-06 I have been working with (put together in the 1990's) produces significantly less velocity than the data would suggest, much closer to vintage chronographed data from the 1980's. To me this seems likely to be the barrels.
Regards Grandpamac.

Originally Posted by Tech

Thanks, there is also a 257 Roberts and a 250 Savage AI hiding in the safe.

All you need now is a 257 weatherby mag to round out the Stable


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