Technical question

[rost495]

So lets toss this out for consideration of bullets "going to sleep-or not"

Shooting VLD bullets for the prone slow fire stages of matches I see in almost all of my barrels accuracy that hovers around the .5 to .8 moa mark at 100-300 yards. Yet once we pass the 300 yard mark that ammo will, most times, get accuracy from .4 to .5 moa.

Transferred to inches I'm not at all worried when I see 3 inch groups at 300 yards with VLDS because when I take that ammo to 600(double the distance) I'm often seeing groups in the 2 to 4 inch range.

One normally assumes that the accuracy would be equal to or worse than the distance. IE 3 inches at 300 would be 6 at 600.....

Any thoughts on this one?

Jeff

 

[Guest]

rost495, looks like your bullets get tired after about 300 yards. I have seen some of my bullet loads seem to have a lower moa after 300 yards.

 

[chris matthews]

GonHuntin,
No I don't think the longer barrel stabilizes the bullet more. The twist rate determines stabilization, not barrel length. A 1 in 10 twist is still 1 in 10 in a 10 in where the bullet make 1 turn before exiting or a 20 inch where the bullet makes 2 turns before exiting. Do the math, it all comes out the same.
If a bullet started crooked but would straighten out more in a longer barrel then we all use 40" barrels like DC

, however due to the drag DC mentioned and the fact a short barrel is stiffer (less whip) long barrels are not practical with some calibers.
The only reason for 30" barrels on guns like Palma rifles is for a longer sight radius using iron(aperture) sights. Since most of us use optics now that long sight radius is not needed.
There's just no reason to believe a longer barrel stabilizes a bullet better.
As a general rule of thumb, I would use the shortest barrel I could to obtain the desired velocities in the caliber of choice.

Rost,
I mentioned the answer to your question in my first post as to why you are seeing your groups tighten up at longer ranges. I truly believe it has to do more with sight resolution than anything else. Try experimenting with different shapes and sizes of targets, even at 100 yards. It will make a difference in groups. That why the 100 yard, 200, and 1000 yard benchrest targets are not the same. Look at a couple of good target companies, Sinclair carries one brand in particular that I am thinking of but can't remember the name, they have different targets for the same distance but different magnification levels of scopes.
Play around with it, you might be suprised by the differences.

 

[Agunner012]

Happy New Year,

Question: For some of these Ultra Mags, etc. Isn't the longer barrel used to burn the powder more efficiently?

Even the 26" tube is too short for a .300 RUM. If you were to shoot thru a sheet a few feet away you would see all the wasted unburned powder from the shorter barrel splattered on the sheet.

Is there some accurate way to calculate barrel length for maximum powder efficiency?

Thanks

 

[Michael Eichele]

Just another thought to chew on. I have used loads in a given rifle that had a fair but semi low BC (168 SMK) and more twist than needed. This one load would shoot 3/4" at 300 yards. This would = .25 MOA. The same load would open up to .4 MOA at 400 yards. By 600 yards it was 1.000 MOA. This is clearly a bullet that has not gone to sleep.

On the other hand, that same rifle with a heavier bullet (175 SMK) would shoot .25 MOA from 100-1000 yards. This is clearly a bullet that has gone to sleep. Or as some agree, being stabilized properly.

Regards

 

[Michael Eichele]

Agunner012,

I personally am not aware of the calculations for your question. Usually you have to experiment with different bullets and powders and charges while shooting through cardboard 10' away. I had the same problem in my old 30-378 w/a 26" barrel. I tried the 180 XBT and 107 grains of RL-25. It stopped shooting unburned powder out the barrel and the velocity got a lot more conscistent. The easiest is just experiment with a few powders. Faster powders generally burn all the powder, but ya have to be carefull not to use to much in a case that big.

[ 01-01-2004: Message edited by: meichele ]

 

[Brown Dog]

Gonhuntin,

As far as I can see, if each bullet leaves the muzzle at the same velocity (and therefore same spin rate) the only difference will be that the bullet from the 18inch barrel will start 'free-flight' 4 inches closer to the target than that from the 14 inch barrel.

 

[rost495]

Hi Chris

Its very seldom, in my opinion, that I can see better at 600 than I can at 300 yards while testing. But I'll keep that in mind. I've experimented for years on my 600 yard bench here in the backyard with target clarity and have come to the conclusion that for my vision a white diamond of 2.5 inch dia encased by a black edge thats 1 inch thick is what I can see clearest. But I still feel that its rare if ever that I can see better the further out you go. Why there are orange and red targets is beyond me. The glare allows you to never see a sharp edge.

BTW the reason for the 30 inch tubes on palma rifles is NOT for sight radius. We have bloop tubes for that. It is the fact that it almost always takes 30 inches of tube to get a 155 up to a high enough speed to consistently be supersonic at the 1000 yard line. A 30 inch tube is used not for stability or accuracy, but simply due to the regulations of the match and the fact that it takes that barrel length in the required cartridge and projectile combination to stay supersonic.

 

[Guest]

Darryl
******************************************
You wrote;
Then, let's say you built loads for each barrel identical in every way except one......

DC---The loads are the "same" in "BOTH/each" barrels.
******************************************

You cut the quote off before you got the whole idea....

What I said was: "Then, let's say you built loads for each barrel identical in every way except one......the load for each barrel produced the same velocity in it's respective barrel......in other words, both pistols shot the same bullet at the same velocity....."

Notice the part about being " identical in every way except one"? That one difference is that the the loads vary so that they each produce the same velocity from their respective barrels.....in other words, load A produces XXX velocity in the short barrel and load B produces the same XXX velocity in the long barrel......both loads use the same case, powder, primer and bullet, but the amount of powder in each load is different so that both barrels produce the identical velocity.....

Clear as mud? OK, let's say the short barrel requires 50 grains to produce 3000 fps and the longer barrel requires 45 grains to produce 3000 fps....everything about the loads are the same except the amount of powder used......is that better?


I appreciate the input from everyone.....I know this may just be mental gymnastics, but I find it interesting!

 

[chris matthews]

Rost, kinda used the palma thing as a general example... anyway, I shoot 155 Lapua which do have a higher BC than the 155 MK out of a 22" and have no trouble keeping them supersonic at 1000.
But you can argue with irons benefitting from a longer sight radius, which most get by using a little longer than "normal" barrel. Whatever in the hell normal is...

As for the sight thing, didn't mean you can see better farther out... just the opposite. The target gets smaller farther out so you have a smaller aiming point. Sometimes we use to big of a target up close. Make sense?

 

[Brent]

GoneHuntin,
Even with the same charge weight used, PSI at the muzzle on the shorter tube would be higher, add more powder to equal the MV's out just makes that worse, as you probably have already figured.

Enter/return key posted before I was done.

Switching to a faster powder might be a better choice than simply adjusting charge weight.

I've seen bullets do better at long range than they do at shorter, but it could be that one concentrates harder and does better at farther distance, maybe unconsciencely. Could be low sample size makes it appear they tighten up.

I'm not sure, but I have seen it. I've got a way to determine if the "same" group at 100 yards gets tighter at much farther distance and still plan to run some tests to end this question in my mind. If it does prove to be true, you'll still be hard pressed to nail down the cause for it.

I think the heavier the muzzle is, the less it may climb upon recoil, and probably is more consistant from shot to shot.

If a bullet yaws back and forth steadily until it slowely dampens out from disruptions at the muzzle, I don't see why it couldn't change direction each time it yaws the other way from the decreased drag on one side, isn't this exactly what happens when they start to keyhole at LR, groups open up wildly?

[ 01-01-2004: Message edited by: Brent ]

 

[rost495]

Hi Chris

Its a really new ticket that Palma shooters can finally use any 155 bullet instead of only the sierra 155. It was with that bullet that you needed the extra tube length.

I'd bet that since the rules have changed just recently the shooters will opt for a shorter tube with a bloop tube on for the sight radius. Personally I'm amazed that in a standard 308 Win chamber that you can stay supersonic with a 155 vld bullet in a 22 inch tube. Thats gotta be on the edge. When you practice all year and then travel all day in a jet to get to a country you've never been in before to shoot a world championship, well that 30 inch tube is just more insurance to stay supersonic. Especially in the years you had to shoot the issue 155 sierras provided by the host country.

I hear you now on the target issue vs distance. Problem is that it won't answer my question. Maybe some other folks do that , but I always size my target to be for the distance that I test at which is normally 300 and 600 yards. So while that may be an issue with some, its not with me. In fact I dont' have a clue how my rifle shoots at 100 or 200 yards off a bench as I have never accuracy tested that close.

It may just be that there is no real answer to this question. Suffice it to say I still see other folks with VLD bullets that can tear up the X ring at 600, yet have serious trouble holding the 10 ring at 300. Switch to a non VLD design and they'll shoot just as good at 300 as they do at 600 with VLDS. Of course the 300 yard target is tougher than the 600 as far as pure accuracy requirements, IMHO, but the wind can kill you at 600 and beyond.

As to barrel length, if veolcity is not an issue, I'd prefer a short tube all the time.

Jeff