Yaw and oval bullet holes.

[JeffinNZ]

Team.

In December I bought a 91/41 Carcano in 6.5x52mm. I am shooting the Lee 6.5mm Swede "cruise missile" bullet sized to throat diameter (0.269). It has a standard, static twist of 1-8 and not the gain twist.

My best load to date is 25gr H4350 (AR2209) with 8gr BPI original buffer producing 1750fps. Alloy is 21 BHN. Accuracy is between 2-3 MOA at 100m so pretty good for open sights.

Thing is almost all my bullet holes are oval suggesting yaw. I have disgarded any idea of instability as if the 1.26 inch (4.65 calibre) long bullet was not stable it would side on at 25m let alone 100m. I have seen a slow twist AR15 put M855 ammo broadside at 25m and a .303 with a worn throat and oversize groove do the same. I am open to hypothesis on the cause of my yaw. My theory is the bullet is canting in the throat on start up. Only the first two(ish) driving bands are supported and there is generous neck clearance. I believe that when the case neck 'gives' on firing the rear end of the bullet is without support and is skewing. Maybe the lube grooves are displacing unevenly etc. I have tried bumping the nose to throat diameter to generate more contact up front however the results were erractic and I don't like asking my 4500 to do this to bullets.

[runfiverun]

here comes the rpm issue again.

[jimb16]

Not enough speed to stabilize the long bullet design. It ain't spinnin' fast 'nuf!.

[mpmarty]

I think I'd vary the powder charge up and down. If it gets worse with a lower velocity than I'd agree with "under stabilization". If it gets better with more powder I'd have the same conclusion. But, with a Turin Twister (Manlicher Carcano made in Turin Italy) CAUTION should be your main concern.

[mooman76]

Try the same load out to 150 or 200y. If it is starting to destablize it will be worse there.

[JeffinNZ]

Have tried velocities from 1300 - 1900fps and same results. It can't be a factor of rate of twist. As I have said already, if the bullets weren't stable they would be side ways long before 100m.

[garandsrus]

Jeff,

Do you have any relatively non-destructive way to capture one of the fired boolits to take a look at it?

John

[JeffinNZ]

Jeff,

Do you have any relatively non-destructive way to capture one of the fired boolits to take a look at it?

John

I wish I did. Our range uses ground tyres in steel bunkers so I can't recover my lead. Trust me, I would love all my lead back. :bigsmyl2: I might have to go out and find a soft, sandy bank somewhere.

[303Guy]

If there is insufficient spin to stabilize a boolit, increasing MV will not increase the stability. The higher the MV the higher the required spin to stabilize it. That's why a 22LR will stabilize the same boolit in it's 1-in-16 twist barrel as a hornet will. Actually, subsonic requires a bit more spin than does supersonic but trans-sonic requires even more.

JeffinNZ, might I suggest that your alloy is a tad too hard? I think you need boolit obturation to prevent gas cutting (not to say that's the problem). Can you load up some sub-sonic loads with that boolit to a pressure that would obturate at least the boolit rear section? Maybe it's time I made a mold for you! In fact, I could do just that. (Umm... send me the rifle and I will make a mold to suite the chamber. Don't worry about your return address! :bigsmyl2: ) You could give me the dimensions to make a mold to and I could give it a try.

Just a thought, a boolit that srips in the bore will tumble at very close range - closer than 25yds! An unstable boolit might just yaw badly a long way down range before settling down to nose first orientation. High muzze blast pressure might be the cause (if that boolit is just on the edge - how else can a 1-in-16 twist hornet stabilise a 60gr bullet when a 1-in-14 223 will not?) Just a thought.

One question - is the bore at the chamber end larger that at the muzzle end? (It's a good thing if it is but certain allowances need to be made).

[wistlepig1]

Jeff, I used gallon mike jugs filled with water with 1/2 pine boards to catch 30/30 bullits. At 25 yards i would find the bullits in the second set of jug/board setup. 150gr HP @ 1800 fps. hope it works for you as it did for me. jug,board-jug,board inline, one round did go through a 3 setup and is still going as far as I know.:kidding:

[303Guy]

Our range uses ground tyres in steel bunkers so I can't recover my lead. Hang on! There are some very clever ideas out there! Like the wooden encased boolit trap filled with ground rubber and transported (and mounted) on a hand truck!

[JeffinNZ]

303Guy - Nup, soft alloy makes patterns. The 21 BHN might yaw a little but it does group.

I reckon Carcanos need a Loverin bullet with as much bearing surface as is phyically possible.

I will do another chamber cast and photography it. Immediately in front of the case neck is a taper down to the throat. That is the problem area in my opinion.

[shaune509]

double check the bore size. this 6.5 is known to be larger than the norm. hornada even sells a larger j-word bullet just for it.
check the carcano web site under ammo and hand loads for more on this.

[303Guy]

Nup, soft alloy makes patterns.Now that you mention it, I have found evidence of a boolit upsetting between the case mouth and throat entry taper. That's with a faster powder (AS30). The evidence was preserved by virtue of the paper patch.

[405]

I may have missed it but what is the chamber neck dimension (or in other words how much slop is there between the case neck and chamber)? Also, is the "bore rider" section of the bullet in firm contact with the lands when chambered?

Seems like unless you go super hard with the alloy those bullets are so long (large sectional density number) that the relatively large amount of inertial obturation may be putting a small amount of bend in the bullet or otherwise messing up the integrity of the base/shank section. Just a big theory or WA guess if the bullets are indeed getting enough rotation for stability.

So as that theory goes, with a messed up base/shank section, while the bullet is getting enough rpm to stabilize, the center of mass is not aligned with the center of form on a dead center axis. Additionally, the base might end up slightly canted as it leaves the muzzle. A slightly messed up bullet that begins flight askew, particularly a long one, may maintain that perturbation of rotation/spin for most or all of its flight.... yielding the decent accuracy but showing the yaw print on target. Just another WAG

[JeffinNZ]

405: Bore riding nose into the lands!? HAHA. You've never owned a Carcano then. The throat is nearly an inch long before the rifling starts. Good thinking though.

I think you hit the nail on the head with the rest of your theory however.

[405]

Never owned a Carcano. Closest I have is 6.5 Swede and a Krag both with liberal throats, but nothing like that! No wonder so many original Jbullet loads for those things have the extremely long, round nose sticking out of the case. May call for a bullet that is sized to slip-fit the throat (throat riding design) :) then seated WAY out. You're right, a Loverin style seated out with the front GGs well into the throat might work. Getting the last potential out of that may require a custom mold based on the specs of a chamber/throat cast. :( $$$

[303Guy]

.... You're right, a Loverin style seated out with the front GGs well into the throat might work. Getting the last potential out of that may require a custom mold based on the specs of a chamber/throat cast. :( $$$That's where I come in. I can attempt to make something up as part of my learning curve! And since we're only an island apart, postage is not so horrendous! (I might even attempt a Loverin).

405, I was thinking almost exactly as you have said. I was aware of the long throating. I think that is an advantage if one gets the boolit proportions right. (Perhaps it's time to start suggesting paper patching? [smilie=1: )

Oh yes, on the bent boolit thing, I have had my boolits coming out the mold bent. Its to do with dropping them from the mold too soon I think - unless there is some stress release during the freezing of the alloy. I did notice mold sliding marks on some boolits corresponding to the bend. :?: