Keyholing question?

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.
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I concur with your statement concerning grossly unstable bullets, or near unstable something I'll have to keep in mind. I hope these Kindler Golds are not that close to a tumbling threshold that just buffeting wind will undo what stability I've gained by increasing the load. I will be doing a little more experimenting with these bullets before I give them a full pass, other wise its off to try another 30 gr. of some sort. I really liked the Berger flat base 30 grainer and if you ever seen a 25 grain vs a 30 on a coyote you can definitely see the difference.
I've been gathering the 17 Rem is good for about 1000 rounds. Everybody knows shooting hot loads all the time would invite premature wear and with my limited budget that would be a shame especially if the barrel is a keeper. It seems like the attraction to the 17 Rem is making it scream 4000+ fps, but that's not how I approach the 17 there is a lot of good loads well under the max that are very accurate, that one might be better off with if they want to extend the barrels life.
 
The only rifle I have that ever had a tumbling bullet problem is my 220 Swift. It was all about bullet length, and I couldn't 'fix' it with muzzle velocity. If there was something interesting about going through loading and testing with various bullets, it was that minor changes in atmospheric conditions made a bullet I thought was stable change to unstable. Surprising. Educational. So I'd go with the flat base bullets in your case.

Also, I'm on the second barrel on that rifle and I don't remember having any increase in bullet stability problems as the first barrel wore out (throat). But, that could be because I was using a bullet that was very stable and not marginally so.
 
603 Country said: So I'd go with the flat base bullets in your case.

I'll have to agree with you on the sticking with flat base bullets... in fact I favor them in the sense that they are what my rifle likes. My father told me that a flat base will most of the time shoot more accurate than a boat tail and for the most part he was right. I wont make a blanket statement about that because there are boat tail bullets out there that are built with incredible precision and may print groups like a dream come true, and I'm still looking for that bullet in a boat tail design. I noticed that the 30gr Kindler Gold bullets in question are a rebated boat tail design. Its my understanding that the rebated design is supposed to have the accuracy of a flat base and the aerodynamic benefit of the boat tail because of the way it disperses the gas as the bullet exits the barrel. I'm not so sure I gained any benefit from that. The BC is attractive because by the inherent nature of bullet flight it should be the way every bullet be designed. There just isn't a free lunch when it comes to boat tails, but I love giving them a try once in awhile. In my 300 mag I use Nosler Accubonds almost exclusively and they shoot great but still don't group as tight as Sierra Pro Hunter 180 FB. I looked at the Genco bullets and it looks like they have a 29 gr FB in their line. might have to give them a try as well...
 
"...seated the bullets 5 thousandths off..." Forget fiddling with the OAL until you have a load. Seat 30 grainers to 2.150". 5 thou is very likely too close anyway.
You need to work up the load from the start load, not just pick one and hope too.
Key holing is caused by undersized bullets, an over sized barrel and sometimes excessively low velocity. You're loads are mid-range loads, so velocity isn't the issue. Hodgdon's data was complied for a 1 in 9 twist, but that really only applies to velocities being close.
77gr match bullets through a 1-9 twist AR-15 Varmint has nothing whatever to do with a .17 Rem.
It's hard to get pertinent information about anything unless someone asks the right question.
 
Certainly keyholing can be caused by the above mentioned factors (undersized bullet, etc), but the OP hasn't led us to think that's the cause of the problem. I'm more inclined to think, unless I just missed something, that he just has a bullet that won't stabilize in that twist.

In my 220, the flat based 63 gr Sierra SMP shoots fine, and is a rather stumpy little bullet. Neither the 64 gr Nosler BSB or the Sierra 65 gr GK will stabilize. Nor will the FB Nosler 60 gr Partition. All are just a teensy bit longer, but that's all it takes to not work.
 
Indeed. 10% increase in bullet length requires 10% tighter in twist rate to compensate. But 10% decrease in caliber requires 20% tighter twist.

-TL
 
Certainly keyholing can be caused by the above mentioned factors (undersized bullet, etc), but the OP hasn't led us to think that's the cause of the problem. I'm more inclined to think, unless I just missed something, that he just has a bullet that won't stabilize in that twist.
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603Country Your right about the normal factors that cause keyholing certainly shouldn't be ignored...I was mostly wondering how I could remedy the problem like seating depth, velocity increase etcetera if any. I guess I should of clarified that a bit. My seating the bullet close to the lands was my attempt to reward myself with tight groups (wishfull), but I'm convinced that the bullet instability was due to low velocity if you want to call 3800 fps low.... only when I made an increased of .2 of a grain was when it stopped keyholing. I've since increased another .3 bringing it to a 26.5 charge and still no keyholing even at 200yrds with a varying right to left wind 5- 10 mph my latest loads for this bullet chronograph @ 3900 to 3950 and grouped 7 out of 10 in about a 2x2 inch cluster just left of the bull the other three were out side of the cluster but still on the 8 inch target and those were caused by me getting in a hurry. I would love to really ring this bullet out, but its prime time for coyotes and these loads right now will work if I keep shots under 300 yrds.
 
About 2 weeks ago I was shooting 600 yds with my fairly new AR-15 match srevice rifle , and was shooting Nosler 77gr CC's with 23.9 gr of Varget. This load was typically an awesome performer. During a shoot I was about 4 shots into my string and I take a shot, and my target was staying down for quite a long time. I then hear over our RSO's radio that target #8 (me) experienced a bullet tumble on the last shot. I was shocked as I loaded 50 rounds of this load and shot this same batch the week prior with no issues. The only difference was the ambient temps, it was much colder and windy on this day, but I didn't think this could cause a tumble. The RSO commented "take a few more shots and see if it keeps occuring" I did , and the next 18 rounds fired perfectly ,so in hindsight I must have unknowingly loaded a blem undersized or malformed bullet.
 
Road_Clam,


Yeah Right I hear ya, it probably doesn't happen too often and probably one component we all rule out just because of that. I agree its possible to get a bad batch of bullets. Matter of fact I'm going to weigh mic a few more out of what I have left to see if there are any bad apples.

I was doing a search and found these Bullets called Alco bullets have you had any experience with them, they look like their a well built bullet. Its funny I say that considering I've shot some pretty good groups with much cheaper bullets, Impressive looking bullets though.
 
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They are heavy and long, so you will need a fast twist. The secant ogive will be more sensitive to bullet jump. The reabated boattail was developed by Lapua between the World Wars, IIRC. If you can't keep your bullet production symmetrical, then it helps. If you can keep them symmetrical, then it doesn't, except that the a less-than-perfect muzzle crown may prefer the rebated type, despite the small BC loss associated with it.
 
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