Accuracy, velocity and extreem spread

08 April 2002, 01:50

I finally went out and bought myself a chronograph to check velocities of some of the loads Iï¿½ve been using for the past 15 years, and low and behold, the velocities were not quite what I expected. For example;

55 grains of IMR 4350 in my 30-06 behind a 180 Hornady produced a meager 2486 fps. Factory Remington cor-lokts in the same weight clocked 2614 out of a 22ï¿½ barrel. The Speer #11 and Nosler #2 manuals predicted around 2700 fps for the handload. Thereï¿½s also an extreme spread of over 100 fps, though the load is accurate enough for my use (1.75ï¿½ @ 100 yards).

Even more interesting are the results in my 308. I get an average of 2493 fps from the Remington factory 180s, 2557 with a handload using 47 grains of w-w 748 and the same Hornady 180 grain bullets with an extreme spread of only 24 fps, and 2490 from my hunting load, using 50 grains of IMR 4350 and the Hornady bullet (20ï¿½ barrel). The kicker is that the hunting load is accurate at 1.5ï¿½ with an extreme spread of 118 fps and the load using the w-w 748 sucks, spraying bullets into 6ï¿½ patterns.

Has anyone else had this kind of experience? Can you guys recommend a powder that I can try in the 308 that is accurate, and produce velocities over 2500 fps in that short tube with 180 grain bullets? For now Iï¿½m going to stick with what works (4350), being more careful with checking the weight of loads, cases etc. Iï¿½ve tried IMR 4064, but velocities are low at max pressure.

08 April 2002, 02:47

<stans>

Chronographs are great devices, but they can quickly disappoint the reloader. I thought I had a hot load in 357 Magnum that would equally match or exceed factory ammo. The chronograph says that I am still slightly under the factory load that I attempted to beat. I have had similar experiences with loads that had huge extreme velocity spreads, but printed great groups.

08 April 2002, 04:04

<Abe Normal>

I also have found this to be true, to a point. Wherein the ES was up in the 75 to 130 range and the SD was 15 to 24 but the load printed quite well i.e. .75 to 1.3 inches. It has happened to me more than a few times, that loads chronographed with elevated numbers out shot the loads with numbers that said they should be the better shooters!

However, once I started seeing loads that had a ES in the low teens to mid 30's and SD in the 4 to 8 range it all seemed to change. Group size dropped down, .25 to .75 inch range was the rule. Water began tasting like a fine wine, life became good and the vision of one-hole groups became clear again!

In short, it seems there is indeed a spot where accuracy improves even though the numbers would say otherwise! Why? I don't know, but I've seen it happen quite some number of times with several different caliberï¿½s, handgun and rifle!

------------------
Abe

If everyone thought like me, I'd be a damn fool to think any differently!

08 April 2002, 04:17

Robert D. Lyons

All of my reloading manuals list the maximum load for the .308 Win with a 180 grain bullet using W748 as either 45.0 or 45.5 grains.

08 April 2002, 04:44

beemanbeme

How old is your 30-06 and .308? You may have some throat erosion or perhaps have a couple of long throated rifles. Within the limits of your magazine, try setting your bullets out further and adjusting your powder charge up a bit. When you see your velocity gains start to flatten out, you are at the functional top end of your rifle. We are discussing bolt guns, right?

08 April 2002, 06:28

dogtagger

Robert D. Lyons wrote: "All of my reloading manuals list the maximum load for the .308 Win with a 180 grain bullet using W748 as either 45.0 or 45.5 grains."
Speer manual #11 lists 47 gr. as max, Nosler #2 make no mention of ww-748. The load is on the hot side. I was shooting in the early morning with a temperature of 28 degrees.

The rifles are a Remington 660 in 308 and the OAL is limited to the magazine length, the '06 is a Remington Mountain Rifle, I got in 1991. I would be able to seat bullets out further. I'm also pretty sure that I can get more of the 4350 into that case. The 308 is a max load with 4350, being compressed as much as I care to squeeze into it...

Any suggestions for other powders to try?

08 April 2002, 17:29

Pecos41

What about H-380? Wasn't this developed specially for the .308?

09 April 2002, 02:28

<6.5 Guy>

Use Reloader 15 for the .308 Win. The non-canister version of Re 15 is now the standard powder for government military .308 rounds. It is far and away the best powder I've tried in this caliber.

If you have Viht N140, you can try that too. It's burn rate is almost identical to Re15. It's the standard powder that Lapua uses for their commercial .308 cartridges.

09 April 2002, 04:06

<eldeguello>

I have often found that reloads give less velocity than predicted in loading manuals. I have also found that in some cases, loads CAN safely be increased beyond what some manual says is max. The proof of this is the often great disparity between maximum loads in different manuals. A chronograph will help you keep your loads at safe levels, while SOMETIMES pointing the way to improved ballistic performance.

09 April 2002, 15:14

<El Viejo>

That last post raised a question for me. Given that different lots of the same powder may burn at slightly different speeds, does it follow that by loading to a specific velocity, we get the same chamber pressure with the same powder, regardless of slightly different charge weights.
If one lot of the same kind of powder burns slightly slower, and I increase the charge to get the same velocity as another batch of ammo, would the pressure be the same in both loads?

Lacking a lab, I can't test this theory. I hope one of you knows the answer.

------------------
Never teach a pig to sing.
It wastes your time and annoys the pig

09 April 2002, 16:52

Nitro Express

Some famous gun writer once said, "Never chronograph your favorite load," the point being it will only serve to disappoint you and ruin what otherwise was perfection, or close to it.

09 April 2002, 17:12

<dsverdrup>

quote:
Originally posted by eldeguello:
A chronograph will help you keep your loads at safe levels, while SOMETIMES pointing the way to improved ballistic performance.

Is there any correlation between the chronogaph velocity and chamber pressure? This seems more tenuous than CUP vs PSI. Or has history shown/demonstrated that if you stay within published maximum velocity for a given powder and bullet that anything goes?

10 April 2002, 04:22

beemanbeme

I think El Viejo may be onto something here. Ammo companies load to pressure not velocity nor volume. The theory being the same pressure, regardless of the powder, will give you the same velocity. So why can't you work in the other direction. I use the books to get me started but I kinda let the chrony and the cases tell me when I'm approaching the top end FOR THAT PARTICULAR RIFLE.

10 April 2002, 15:16

<6.5 Guy>

There isn't necessarily a direct correlation between peak pressure and velocity. Remember, peak pressure is achieved within the first few inches of bullet travel. From then on, the pressure steadily drops, but the bullet is still accelerating due to the fact that pressure behind it is still higher than pressure in front of it.

If you look through a powder manufacturer's reloading info, you might see from time to time different powders used for the same bullet, and the one that has a lower peak pressure may indeed achieve higher projectile velocity (usually the slower burning powder of the two). That is because there is a slower drop off of pressure once peak pressure is reached, therefore more push for a longer period of time on the bullet as it travels down the barrel.

In a nutshell, velocity is a fairly good indicator of where you're at pressure wise, but two loads that achieve the same velocity may not necessarily have the same peak pressure. One laod may have a lower pressure peak, but longer and flatter curve. You'll still have to pay attention to the usual signs, i.e flattened/cratered primer, sticky bolt lift, etc...

11 April 2002, 12:46

<Dasmoofler>

Pecos,
From Hodgen's manual "H380 was an unnamed spherical rifle propellant when the late Bruce Hodgen first used it. When a 38.0 grain charge behind a 52 grain bullet gave one hole groups from his 22 caliber wildcat (now called the 22-250), he appropriately named the powder H380.

11 April 2002, 14:25

Pecos41

Thanks Dasmoof for the H-380 history. I had not read or heard that. What I was told years ago was simply that the military had the powder cooked up for the Nato round and indeed at the time at least, it seemed to produce about the best for the .308.

6.5, I believe you are dead on about there NOT being much of a correlation between chamber pressure and velocity. In fact, any reloading manual will list loads with LESS pressure outrunning loads with MORE pressure. I think assuming anything about pressure from velocity readings is a dangerous sport.

Whoever said never chrony your favorite loads has a good point. I got a chrono years ago and was so excited I about wet myself, but soon became very disenchanted with it. It seldom gave me the answers I expected and sometimes the answers were disappointing and/or even alarming! The best thing is showed me was when I was working up some "duplex loads" that my velocities were TOTALLY erratic and thus so was my pressure, powder burn etc. In other words, I was rushing into an area where angels feared to tread.

I will get blasted for this, but sometimes I think we can get TOO technical about our shooting and reloading. Over the years I can recall a lot of targets I missed because I was so busy calculating the angle of the dangle and mass of the ass in my head that I didn't have time to simply put the crosshairs on the damn thing and squeeze.

All this has lead me to the belief that the secret to good results hunting is to cook up a load that shoots well in your gun, get familiar with your gun and that load, and then just concentrate on doing YOUR part and trusting to the gun/ammo/etc to do their part. It's not as complicated as some of us make it sometimes. Otherwise our pilgram fathers would still be fighting for a beach head at Plymouth Rock.

11 April 2002, 15:26

Ku-dude

DT,
First thing you must do when comparing your load to the book's is check to see how long their barrel was. Many of the reloading manuals use 26" barrels. If you have a 22" barrel, you will be not less than 100fps behind from the get go, and more like 150fps. If you add 150fps to your results that isn't all that bad.

Second, you will find that when you find the right powder for your rifle, and work up to a max load, your Std Deviations should drop and then as you get thru the sweet spot, expand again. This is not an absolute, but frequently observed. Some loads with poor SD's have good groups, but it is a poor sign at the upper pressure limit.

Third, without encouraging you to sin, your loads are at the SAMMI limit for 30-06, and has been pointed out on this forum and others, the 270 limits are somewhat higher. If you are serious about the 30-06, get OKShooters book on the 30-06. It has some interesting data regarding pressures for this cartridge.

My 30-06 180 gr load is to the higher pressure spec, and absolute max is 2750 from a 23 inch barrel with IMR 4350. My SD's were horrible. I came off this load a half grain. It will reach out and kill anything you can hit. If you want more than 2700fps with 180 in 30 Cal, go to a magnum or longer barrel! Ku-dude

12 April 2002, 05:43

beemanbeme

6.5 Guy, you need to tell that to the ammo manufacturers. Soon, Winchester and Remington will have little elves under hollow logs working away with Lee ladles and Ohaus 10/10 scales making ammo the old fashion way: one at a time. Oh, look out for that acorn, it may be the sky is falling.

13 April 2002, 00:16

dogtagger

Thanks guys,

I'm going to try (carefully) to work that 30-06 load up to 57 grains (max in the Speer #11) and see what happens. Seems That I settled on that 55 grain load years ago because it shot so well... I WOULD like to get at least 2600 fps with it though. The barrel lengths in the test rifles (both of my manuals) are 22", so the velocity shouldn't be that far off. We shall see. Maybe I'll try some 4831 if the 4350 won't work.

I'm not displeased with the 308's performance, in fact just about what I expected for average velocity out of the 20" barrel. That's my close-in-open sight gun, that I use when it's snowing (or raining), and I expect to get close. 2500 fps is perfect with that blunt 180 Hornady. I was surprised by the accuracy/velocity spread thing.

The deer that Iï¿½ve shot with the loads never seemed to notice the ï¿½lowï¿½ velocity much, mostly they just keeled over...