Bullets tumbling in flight

I recently bought a box of Nosler 155g HPBT projectiles to use with my Enfield M1917. Previously, I had been using 150g Speer HotCor RN projectiles. In each case, I loaded with 49.0 grains of ADI's AR2208 powder. The rifle barrel is not the best but I have managed to shoot some tight groups with the 150g Speer bullets. As most M17 owners will realise, lateral sight correction has to be made by adjusting the foresight on the rifle. This operation is performed by grouping on the target and adjusting the sight accordingly. I found that I needed to reload more ammo for the job and the only projectiles I could buy at the time were the 155g Nosler HPBT bullets. When I got to the range, I fixed a bullseye target at 100 metres. I fired my first shot and peered through my spotting scope. The bullet had entered in the 4 circle at 1530. My intention was to fire 5 rounds in order to verify the grouping prior to adjusting the foresight. However, the second shot did not hit the target, neither did the third, forth or the fifth! Something was dreadfully wrong! I knew I wasn't that bad a shooter. When the range all clear signal was given, I brought the target to the fifty metre mark. How could I miss here? Well, you guessed it; three shots later and I could not see one extra hole on the target. There were 2 rounds left in the magazine, I took extra care aiming and fired. Again I looked through my spotting scope; nothing! But wait! what was that at the bottom of the target? It was a hole the exact profile of the bullets I had been firing. And, there was another hole, half on the target paper just to the right of the one I had noticed; again it was in the profile of a bullet. No wonder I hadn't been hitting the target! each round I had fired it seems had tumbled in flight and ended up who knows where. I gave up then and there, packed up my gear and went home. Now, I'm not sure what to do. I know it would be nice to have a new barrel but they really cost where I am . What I would like to know is whether the fact that using the 155g HPBT ammo would have had anything to do with what happened. I personally feel that it does, but what? And why was the first shot a good one but all the others apparently lost their stability. Has anyone encountered this before? I sure would like your thoughts and opinions.

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Originally Posted by orez

Has anyone encountered this before?

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Yes I have, more than once. The answer is usually that the throat is either cut very deep or is worn, thus effectively lengthening the distance from the case mouth to the start of the lands. The round-nose bullet has a longer cylindrical section than the boat-tail. The guidance is better.
A boat-tail loses contact with the case mouth (and thus the guidance) as soon as the tail starts to appear. There is a free-flight distance before the start of the lands. During this time the bullet tips, gets rammed into the throat with a skew, and that causes the keyholing.

It would be a good idea to make a simple check on the throat depth - it only takes a couple of minutes.

Get a 1 meter/3 ft length of brass (not steel - that might scratch the barrel) threaded rod. 1/4" or 6mm will do nicely. Close the bolt on an empty chamber. The bolt must be cocked (or the firing pin must be removed), as you do not want the firing pin to be sticking out!

Establishing the effective barrel length
1) Stand the rifle upright. Lower the threaded rod into the barrel until it is resting on the bolt face.
2) Run 2 nuts down the rod. set the first one so that it is just touching the muzzle. With a bit of practice you will be able to sense when the nut is touching just firmly enough that the rod is just starting to lift. Not micron-accurate, but quite accurate enough for the present purpose.
Use a felt tip pen to make a position mark on the rod and nut, just in case you disturb it.
3) Run the second nut down until it is just touching the first nut. Again make a position mark as a precautionary measure.

Establishing the absolute maximum OAL for the cartridge
4) Now remove the rod from the rifle, and holding it slightly tilted, place a bullet in the chamber and tip the rifle so that the bullet slides into the chamber and rests on the transition (start of rifling). Do not drop the bullet into the chamber, as it will go in somewhat deeper, until it jams hard, thus falsifying the result.
5) Keeping the bullet in position by using a piece of rod (I have small fingers, and just use a pencil), but not jamming it into the throat, insert the threaded rod gain until it just touches the bullet. You can sense this very well, as you will feel when the bullet is pushed back against the pencil (or whatever you are using).
6) The nuts are now well out of the muzzle. Without disturbing the outer nut, run the inner nut up until it is just touching the muzzle again. Again, you will feel the push when the rd touches the bullet. This is the most delicate part of the operation, and you may need to repeat a coupl of times to develop your touch.
7) Without disturbing their position, measure the distance between the inner faces of the 2 nuts. Best is to use a slide gauge, and fix the slider when you have made the measurement, as you then have a gauge for the following steps.
8) You now have the overall cartridge length that you would need to get the bullet to touch the lands. This is the absolute maximum OAL that you could theoretically use safely, and you are probably now going to discover that such a cartridge is impossible.

Finding a suitable bullet
9) Lay the slide gauge (with the slider clamped) on the bench. Take one of the cartridges you used previously (or take an empty case and seat a bullet to the same depth) and lay it between the jaws of the slide gauge. I predict that there will be quite a gap between the tip of the bullet in the case and the jaw face that represents the contact point on the throat using that bullet.
Your BT bullet is probably losing neck contact long before it reaches the start of the lands.
10) If that is indeed so, then my long-range diagnosis is confirmed. You need a bullet with a much longer cylindrical section

In such a case, flat-base bullets are better than boat-tails (the good old 174 FB bullet is still frequently the best for 303 Enfield!). FMJ types with an open base are good, because the open base allows a tiny amount of upset to seat the bullet better in a worn barrel.

But for deep throats, long round-nose bullets are best of all. Hornady 180gn RN (even the 220gn if the throat is really bad), Lapua Mega 185 gn (or 200gn) - that is the kind of bullet you will need. You may still find that you need to seat the bullet as far out as you dare, to get it closer to the lands. A practical value is about 0.5mm / 20 thou off the lands - if you can achieve that with an acceptable amount of the bullet still in the case neck.

Give it a try. If that doesn't work, you probably have a wallhanger. But I don't think so - you already had satisfactory results with a different bullet. And please let me know how it turns out. All this has been AFAICTWAHTOIMH.
(As Far As I Can Tell Without Actually Having The Object In My Hands)

Patrick

Another possible drama- the boat tailed configuration of the bullet. If the bore's a bit oversized, this type of projectile tends to allow gases to blow by the base. A flat based or, as originally used, an open core flat based bullet is more likely to "bump up" to fill the rifling.

Measuring bore diameters on these rifles isn't as easy as some due to the odd nimber of lands and grooves, but there's ways of doing it. (some cost more than others)

I would beg, borrow, or steal a few flat base bullets to see how they perform.

you didnt say who the maker is,...a group of Winchester made 1917,s had over sized chambers, and throated bores....all the failed 17,s iv seen were Wichesters with over sized chambers, owners also said they had issues with accuracy as well.