Keyholing question?

R

Rogerbeep

Inactive
I'm shooting a cz527 in .17 Remington with a 9 twist. Not to start 'a use of moly debate I've been using moly in the bore, on the bullets, and in the case necks. I've heard all the pro's and con's and when my loads show potential to shoot tight groups I use the moly, but I, since bought some Woodchuck Den 30 gr BTs and opted to go naked using Nosler brass instead of the regular rem brass and 26 grs H414 and CCI 450 primers as well as tried 7 1/2s Remington's with same results.

First off I seated the bullets 5 thousandths off the rifling shot ten rounds @100yrds and the results were a peppering of the target in about a 3" group with one keyhole print in the mix. The next load I used the same charge 26 gr H414 but this time I seated the bullets deeper about as much as would just fit in the neck sized area of the case about triple what I seated before and got the groups to shrink however I had another 2 keyholes from those ten fired. So far a total of 21 firings. Next I bumped up the load to 26.2 and changed the primers from 7-1/2 Rem's to CCI 450 and viola a satisfactory tight consistent group of say 3/8 inch. A total of 41 bullets down the bore. I'm hoping I'm in the sweet spot. I don't think the bore is worn out, since it shoots 25 Hornady's and 30 gr Berger's without a hitch.....What's your take.

Now bare in mind I started with a bore cleaned to bare metal, so I know I had to build some fouling in the bore to settle the rifle, so the question is could the keholing been caused by being seated to far out or barrel needing to be re-fouled or both?
 
Any idea what velocity might be? I know squat about .17 caliber, but if the bullet is not stabilizing, that could be an issue. Longer bullets require faster twists to stabilize. You can use an online stability predictor to see if that might be the cause. JBM Ballistics is a good one. You need to know velocity, twist, and length of the projectile.

Other than that, how many rounds down the tube? Is it possible that throat erosion is getting significant? If the throat is getting rough that can make bullets go unstable,, and result in occasional (or consistent) key holing.
 
Your post indicates you are a very experienced reloader and shooter. I am a little surprised that you changed both the powder charge and the primers at the same time. In my opinion, changing both prevents a determination of which change eliminated the key hole problem. It has been many years since I had to deal with a key hole problem, but if I recall my experience correctly the problem was the rifling twist rate and the length of the bullet. I could not solve it with bullet seating depth, but using a shorter bullet solved it. My experience is consistent with CR's statement that longer bullets require faster twist rates.
 
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@Colorado: First run averaged 3815 fps for the 26 gr. charge and 3857 for the 26.2 gr. charge. I used to shoot 30 Bergers until they stop making them so I though I'd try these Woodchuck Den 30s in boat tail its BC being attractive and performance is supposed to be great on coyotes from what I gather. I bought the rifle new in 2005 I'm going to guess its probably only had about 500 - 600 through it. I'm going to rule out throat erosion based off the fact that it doesn't keyhole with other bullets I've tried and I've practically babied this rifle it has only had a few hot loads through it. If its has potential I quickly switched to medium charge weight using moly as a to reduce friction and vibration...this is really the only time I have shot naked bullets through it. Cleaned rifle with JB prior to testing these 30 Golds.

@Lefteye: I learned on my dads bench when I was a teen on a Hornady single stage O frame and still remember his old 50s Herters press as well. I had an intense desire for it, so I learned quickly how to assemble cartridges. Awe fond memories of dad showing me how not to blow myself up... I later bought a RCSB Rock chucker II and been using it since with Hornady lock -n- load conversion done to it. I'm impressed this set up cranks out good ammo for being an older RCBS press but by no means vintage. You can say I done my share of loading and know a few tricks, but I'm not a high roller.

The reason I bumped the load is because I've had experience with the 30 gr Bergers and that load was a 26.5 load and had no problems with that flavor of bullet. Your right about the dual switch of load increase and primer I usually follow the same rule, but I figured .2 grain increase might help with spooling them up a bit quicker but not enough to be concerned and a change in primer is something I already lean towards as not a significant change/or disturbance. Especially shooting in cooler winter temps.

I guess in short is it possible to cant the bullet during firing if your seated out too far because possibly theres not enough neck tension?....Yeah I agree with about twist rates, but I have the right 1 in 9 twist recommended to stabilize it, or its possible to that I have a bad batch hum don't know, but not ruling it out either. thanks your for replies guys.
 
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I learned on an uncle's press about 60 years ago (more or less) and don't remember the brand. I've had the original Rock Chucker for about 40 years. I was never a high volume reloader. I have reloaded only for hunting and have always used my own loads for rifle hunting. In short, my experience is spread over many years and is somewhat limited, e.g., only once with key holes.
 
Yeah this is my first keyhole I've experienced, and being I've also never seated that close to the lands with this particular rifle, however I did seat the bullets back and still had two more keyholes and only when I increased the load and change primer did the groups tighten and no keyholes (cross my fingers) so far.

I also wonder if the bearing surface of the 30 gold is more than say other brands of 30 grain bullets such as the Bergers... Just looking at them the only difference I can tell is the boat tail otherwise the bearing surface length appears the same or so close I cant tell without measure. Oh well It seem that the bump in powder and switching primer solved the keyholing, but this kind of thing still makes me scratch my head.
 
I've only experienced keyholing once. I have a BFR 460. When I first got it, I played around with 45 Colt, 454 Casull, and 460. If I loaded up 45 Colt Brass with a 255 gr cast bullet and used Unique powder, the bullets tumbled. At 25 yds, one might hit the target, the next might be 5 feet high, the next 5 feet to the left, then to the right, etc.

I tried the full range of Unique, from ultra wimpy to hot Ruger only loads. They all did it.

Every other powder I tried(231, Universal, Power Pistol, Trail Boss) were fine. So there's some sort of weird interaction between my gun, that bullet, and Unique.

So you are doing the right things, you just have to experiment to figure out what makes it go away.
 
Try seating them shorter. Go to max length that will load in the magazine, and drop another thousandth or two. In my experiences with smaller caliber rifles is that they do better with a running start.

I tried the loading longer thing in several rifles. The end results were the same in all of them. The pain in the butt to gain in accuracy ratio was not worth it for me. If the load won't shoot great at the specs length, making longer is not going to improve it. If it shoots great at specs length why screw it up trying to make it better. Shooting more with good ammo will improve groups better than shooting less because you are still fiddling with trying to make the perfect load.
 
I have herd that up to 200 Yds. a flat base bullet will stabilize quicker than a boat tail bullet. My most accurate bullet in my 222 is a flat base bullet at 100 Yds.
 
Rogerbeep,

The calculator at Berger is suggesting a minimum 8.25" twist to properly stabilize their old 30 grain bullet, for which I have 0.637" as the length. I don't know the length of your new bullets. The Berger calculator suggests your 9" twist is marginally stable for the old bullet, a condition in which they will fly, but it doesn't take much perturbance to throw them off.

An understabilized bullet, unless grossly unstable and unbalanced, does not tumble immediately upon exiting the muzzle of the rifle. Its nose describes a gradually increasing radius spiral until finally the spiral loop is wide enough that the lateral drag component on it starts the bullet tumbling. The distance at which this happens can vary from bullet-to-bullet, depending on how perfectly formed they are and on how perfectly straight they started into the bore. Take the keyholing load out to 200 yards and you might find that by then all the bullets were all keyholing.

Due the declining slope in the drag coefficient curve with velocity past Mach 1, stability will tend to improve a little with velocity. With a marginally stable bullet, that improvement can make the difference. It just isn't a huge difference, so buffeting by irregular wind or other adverse conditions could possibly undo it.
 
Increasing velocity increases the RPMs, and bullets lose forward velocity faster than they lose RPMs, so increasing velocity may give you the performance you want inside the range envelope you are looking at.

Or it might not. Until you load 'em up and pull the trigger it's all academic.

Jimro
 
For a fixed velocity bullet, increase in spin increases the gyroscopic stability factor about as the square of the spin rate. With variable velocity, Newtonian drag, including that which seeks to overturn the bullet, also increases as the square of velocity. So, when you increase spin using a fixed rifling pitch and increase velocity, the extra stability from the faster spin and the extra overturning drag just cancel each other out. This is true right up to the bottom of the transonic velocity range.

But once inside the transonic range, up to about Mach 5, the drag coefficient, which is the term you multiply Newtonian drag by to account for the aerodynamics of your projectile's shape, has a velocity dependence of its own, jumping up starting somewhere around Mach 0.9 to peak at Mach 1. It then gradually drops down as the Mach number increases until, at about Mach 5, it is essentially 1.0. So when you fire a supersonic bullet faster, say at Mach 3 instead of Mach 2.5 in the same rifling pitch, though it develops stability that is proportional to the square of the increase in velocity, it does not develop quite as much drag as the square of the increase in velocity between 2500 and 3000 predicts. This is because that drag coefficient is lower at the higher of those two velocities. Thus you have a net increase in real stability.

It's true that a stable bullet will become more stable as it coasts down range. This increases the yaw of repose, causing spin drift to hook more sharply when the bullet's are getting way far down range. However, even if an unstable bullet slowed quickly enough for this increase in stability factor to stabilize it before it tumbled, the drift radially from the trajectory path to the target would already be established in some measure, so that while it would group much better than bullets that remained unstable, it wouldn't group as well as a bullet that was stable from the git-go.
 
As Jimro said, upping the velocity, if possible, may solve the problem. My only experience with keyholing was with my very first loads which were very conservative. Increasing the velocity solved the problem. An increase in velocity increases rotation and stability.

Looks like Uncle Nick stepped in in the meantime and gave a much better explanation.
 
1 in 9 twist seems slow. Greenhill's equation requires bullet length of shorter than 0.48" for stabilization.

At the same weight, a boat tail bullet is longer than a flat based bullet. It might have caused the tumbling.

-TL
 
I'm getting 0.671 length for the Kindler Gold and 0.633 for the Bergers. My Berger load I settled on was like I said earlier 26.5 using H414 powder its probably on the medium hot side right there and I could probably go a bit more because of the slipperiness i.e pressure drop from the moly , but not necessary to do so, since they shoot great right there. Again its sad Berger done away with them.

Now since I'm committed to getting the Gold 30s to be coyote accurate I'm excited to whack one to see they go bang flop, DRT, or do the spin and run routine like I've seen some of the Hornady's do. Hoping for a nice big adult coyote in its prime to volunteer to be test medium broad side @100, but they're smart this time of year.

Thanks for all your responses.... I have this hypothetical hunch that an increase in powder charge is what the doctor ordered and too I feel that much more validated about this keyhole anomaly with the info you provided... all of you. Again Thanks.

Unclenick, I will have to take you up on the going to 200yrds but I don't think I want to drop my loads back down to tumbling velocity, but instead I want to see if at the load I have them set at now of 26.2 H414 and maybe bump them up to 26.5 to see too if I can get them to go 3900fps without pressure problems and print satisfactory. I have my back strap sinew handy for pelt damage, if I need it.
 
@m&p45acp10+1 Absolutely your spot on. I don't know what possessed me to seat them long in the first place as it only invited problems being a boat tail design as well. I guess what made me want to try it was because they were functioning in the magazine good at that c.o.l. and concentricity looked good too, and of course I'm a bit of an accuracy nut. I figured if I got good so, so accuracy I could live with it till I shot them up considering my batch was only 21 rounds a pop I could quickly back out of this endeavor, but I wasn't anticipating a keyhole problem. I'm seated good now and the load is giving me tight groups, but I think I want to go back to the range to confirm its zero and if I determine its still eligible to go up in charge I'll try that route till I get it to do 3900 if it will let me, as I'm willing to sacrifice a bit of accuracy for more performance.
 
Unclenick, I go ahead and give the "clif notes" version and you had to go and explain the mechanics :)

I appreciate that, it explains why increasing the velocity of an unstable subsonic bullet won't give the same increase in stability as increasing the velocity of a supersonic bullet. For folks loading for a wide range of velocity from the same rifle (300 Blackout for example) that is very useful information.

Jimro
 
ROAD_CLAM<----- Is taking notes on this thread ! GOOD info in this one. I love a solid data based cause and effect post !
Click to expand...

ROAD_CLAM if you ever owned 17 center fire of any type you quickly find out its hard to get pertinent information about them unless someone asks the right question. I have scoured the internet for various information regarding the 17 Rem and I'm still learning about this little screamer. At some point I will wear this factory barrel out and then its going to be time to throw a Lija barrel on it and that's a whole new ball game for me as I haven't ever re- barreled a rifle before.

I like it when I can go to a forum and find that little piece of info to whatever I'm looking for and ask a question and get the information I'm after, but that's not the case especially the 17 Rem. Its gotten better over the past, but when I first got this rifle It was tough to find answers on what and how this rifle likes to perform. I give credit to those guys who do a lot more shooting and experimenting than me. I would say the moral of the story here is don't seat too far out if your gun shoots fine at normal seating depth and don't be afraid to approach max load, since sometimes its how the rifle and components want to operate.
 
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