Bullet base below the neck. Accuracy?

[joeb33050]

My savage striker has been fired, by me, more than 1219 shots with lead bullets. In all that time, the base of the bullet has been below the neck of the cartridge case.
This pistol, 308 Win with 2-6 Simmons scope, was fired at 100- yards, in 5 shot groups.
6/24/09, 3 groups averaged 1.558"
6/24/09, 3 groups averaged 1.783
6/24/09, 8 groups averaged 1.91"
6/17/09, 5 groups averaged 1.879"
6/17/09, 5 groups averaged 2.121"
and so on........
This past summer I brought the pistol to Massachusetts to shoot and get sight settings for 200 yards.
At 100 yards;
5 shots in 1.75"
5 shots in 1.75"
At 200 yards, 12 shots in 6 1/8", 11 of them in 4 1/2", 10 of them in 3 1/2"
and
7 shots in 5 3/4", then 10 shots in 6 1/8" 9 of them in 4 1/2"

This gun will shoot lead bulllets into less than 2" 5 shot group averages at 100 yards.
And, I believe that it would average around 4" 5 shot groups at 200 yards.
Much of the group size is me.

I have read many times here that the bullet base, gas check, below the case neck = less accuracy. Not in my Striker.

Does anyone out there have any data showing the loss of accuracy with base or GC below the neck?

Thanks;
joe b.

[leftiye]

IMO, so long as your lube doesn't interaact with your powder, there's no issue . Lots of calibers have been marketed (they don't use cast when designing new calibers, so you could say Jword calibers) where there's no possibility of the bullet base not extending below the neck when the bullet is seated as designed. Until you long throat them at least.

I do suspect that the ideal situation, cast or jacketed, is a minimum chamber neck diameter, with concentric case necks, where the whole straight (groove diameter - bearing area) portion of the boolit/bullet is supported in either the case or the freebore in a coaxial, straight manner, and the ogive either rests on the leade or within 1/32" of it. If you can avoid canting at the start of launch, this should be satisfied, and no ill consequences.

[StarMetal]

I think he's referring more to the cast bullet being damaged by the hot gases rather then the relation of where the bullet meets the rifling. Also he may be talking about the gas check coming off inside the case.

I have a 7mm-08 with a very short throat and I've fired the Lyman 150 Loverin from it with excellent accuracy and it seats way below the neck base.

Joe

[9.3X62AL]

Joe--

This is not a scientifically-collated observation, so it might not be up to the standards of many who crave exactness. Sorry about that.

I cannot make a definitive statement that having the boolit base or its gas check section protruding into the "powder space"--for this purpose, below the case mouth/shoulder junction--is consistently detrimental to accuracy. I just haven't seen that with my several bottle-necked calibers that I shoot extensively with the castings. One in particular--a Rem 788 in 243--shoots WONDERFULLY at 100 yards with the RCBS 95 SP's base below the junction, as does the 250 Savage with NEI 100 spire point in a 1930 Savage 99--which protudes not quite so deeply. Both are sporter-weight factory barrels on field-grade rifles, and both can reliably shoot 1.5 MOA--sometimes better.

One boolit I designed via the Mountain Molds software to specifically keep the boolit base out of the powder space has also performed wonderfully for me. This is the 270 grain tangent ogive flatpoint 9.3mm boolit. Its drive shank with gas check was drawn to have the boolit base even with the shoulder junction as the ogive kissed the rifling leade. Also a sporter (CZ-550 Lux), it is a consistent 1.5 MOA shooter to 200 yards.

The 30-06 has been less impressive in 2 rifles, so far. Boolits seated out of the powder space (#311041) or into that space (#311291 and #311284) all seem to "max out" at 2.0-2.5 MOA, 50/100/200 yards. Go figure--I can make the smallbores behave, but the 30-06 wants to act the fool. There's obviously something I'm missing or doing improperly, and it is not related to the matter under discussion here.

Summed up.......I don't believe a boolit base in the powder space is the first/most likely cause of fliers or overall inaccuracy. The condition might be taking the rap for misdeeds committed by other flaws in the equation.

[Larry Gibson]

Joe

It depends. I believe there is an article/post in the NRA Cast Bullet supplement(s) that describes some damage done when the basw of the bulle t extends into the case. I also have had similar results. Not always but enough to warrent not doing so if I can help it. The reason being is you never know when the bullet will be damaged or not. I believe the damage is influenced by the alloy hardness, MAP, the time pressure curve and if a filler is used. Again, it doesn't alway happen and I've not found rhym nor reason to it. That is why I avoid it if possible.

"This gun will shoot lead bulllets into less than 2" 5 shot group averages at 100 yards.
And, I believe that it would average around 4" 5 shot groups at 200 yards.
Much of the group size is me."

Are you sure it is you? Or could it be that the base of the bullets re being slightly damaged and that the inaccuracy from such is not telling until 200 yards is shot? If your bullets are not damaged and you shoot them well at 100 yards then there is no reason you shouldn't shoot them equally well at 200 yards. You may only be thinking it is you and hoping it is not the damage d bullet. Just some food for thought.

Larry Gibson

[joeb33050]

Joe


"This gun will shoot lead bulllets into less than 2" 5 shot group averages at 100 yards.
And, I believe that it would average around 4" 5 shot groups at 200 yards.
Much of the group size is me."

Are you sure it is you? Or could it be that the base of the bullets re being slightly damaged and that the inaccuracy from such is not telling until 200 yards is shot? If your bullets are not damaged and you shoot them well at 100 yards then there is no reason you shouldn't shoot them equally well at 200 yards. You may only be thinking it is you and hoping it is not the damage d bullet. Just some food for thought.

Larry Gibson
I shot twice at 200 yards. The first time I found that my 16/IMR4227 2" 100 yard loads were shooting into 6 ' = feet at 200 yards. I reloaded with 18 and 20 grains of powder, then went back and shot the second time.
I find shooting a pistol with a scope to be difficult, and find that practice and paying attention to technique is important. I can see that much of the group size is my fault. And, I think I'd be better off with a larger power scope.
So my answer is, yes, it's me. Or, much of it is me.
Now, I've got an M10 Savage that needs bullet bases below the neck. And I CAN shoot a rifle from the bench fairly well. If only the range were open.
Thanks;
joe b.

[BABore]

My shooting buddy ran into below the neck problems on his '03. He was using my 311041's and the "Load", 13 grains of Red Dot. The boolits were water dropped 50/50 at 22 bhn. I also shot the same load from my model 700. I have a well worn throat and seat into the neck. His '03 had to have the GC well below to chamber. I would guestimate that the middle of the next driving band was about at the junction. He had good accuracy of just over an inch at 100 yds, for 5 rounds. Scoped bubba. Anyway, he'd get an occasional flyer, nothing too serious nor worth worrying about. Maybe 3/8" or so out. What did cause some concern was that he would occasionally split the case, right at the neck/shoulder junction. It would start there and run towards the mouth, but never all the way. The only thing we could figure out was that the speed of RD, and the hard wack it was giving the boolit's base, was obturating it in the case. Brass age was ruled out of this. I had him switch to Unique and the problem disappeared.

So, IMO it's not a good thing to have the base below the neck. Yes you can work around it, but you are never quite sure if your getting just a little bump that's throwing the base slightly out of wack. I had a 450 Marlin that had a chamber that was pretty much to spec. The throat on the other hand was almost 0.004" bigger than the largest diameter boolit I could use. I had terrible fits with consistency with what I feel was an uncontrolled base. It could cant whichever way it wanted upon ignition. I think the same thing applies above.

[44man]

I hated WW calibers because of short necks when I was varmint hunting. I preferred Remington calibers. I think it was a question of support, not a bullet down below the shoulder.
Now we have everyone worrying about cast below the shoulder but I think it is still a support and tension Question.
With the proper powder the boolit will move ahead before hot gas can affect the base and a slow powder will cushion the base, not only from the slower start but from the powder granules.
But for some reason with all the great choices of powders, why does one choose Red Dot or some such in a large rifle case??????
Why not a hefty load of Bullseye so you can form the boolit base to the inside shoulder shape???
What is it that makes a cast boolit need a much faster powder?
I am surprised nobody said your boolit is too hard, you need to OBTURATE it!!!! :bigsmyl2:
Babore is right there again with harder boolits even though the alloy is sort of soft until hardened. It is OK, good hunting alloy. But slow the powder thump. Give that boolit a nice gentle push and build velocity in the barrel after the thing has left straight, taken the rifling and is moving along.
Why do you need to slam a cast boolit?
Instead of blaming a lot of silly things, work the powders to find accuracy.
Come watch me shoot Red Dot in a 30-06 or .308---Yeah, sure, in your wildest dreams.

[leftiye]

Ba, Sounds to me like yer right about what caused the split cases. I once had a hot load for .45 Colt that split 2 or three cases out of every 50 clear up one side. My take was that it wasn't just the higher pressures as much as the rapid expansion of the brass. In your example, Red dot might be said to be a fairly fast powder? And, yes, if one doesn't tailor their load correctly, there just possibly might be some damage to the exposed boolit. Probably can be made to happen (ya think?).

[303Guy]

Just a question.
If the base protrudes below the shoulder/neck junction, does the powder not get rammed around the base on ignition which would then engrave it some? Or even peen the heel? Not to mension wedging between the boolit and tapered neck entry?

[carpetman]

Someone in chat said that the base of the bullet touching the powder made enough difference that he weighs his powder charge out to 3 decimal points to avoid it. But by doing this he shoots an 8 inch group at 1000 yards with a .300 mag.

[StarMetal]

Just a question.
If the base protrudes below the shoulder/neck junction, does the powder not get rammed around the base on ignition which would then engrave it some? Or even peen the heel? Not to mension wedging between the boolit and tapered neck entry?

Same as in jacketed factory ammo in which many calibers the bases are loaded below the neck, huh 303Guy?

Joe

[44man]

Just a question.
If the base protrudes below the shoulder/neck junction, does the powder not get rammed around the base on ignition which would then engrave it some? Or even peen the heel? Not to mension wedging between the boolit and tapered neck entry?
Maybe, but I feel powder can also act as a cushion. It seems better then peaking pressure way below the boolit and slamming it from all sides. Since powder is laying in the case, who says pressure hits each side of the boolit nice and even?
I think I would rather have a nice, even load with minimum airspace, being pushed around and behind a boolit as it moves forward, starting the boolit out before getting slammed.
I know we are talking time that is hard to measure but a lot can happen with very little change.
I don't have the answer but it is worth thinking about. What is wrong with moving the boolit into the throat or at least the brass with a steadily increasing pressure, before a sharp increase?

[303Guy]

Same as in jacketed factory ammo in which many calibers the bases are loaded below the neck, huh 303Guy?Not really as the J-words would pe plenty strong enough to resist any deformation. We do know that a cast boat tails won't work because the tail gets deformed. However, they will work if the base and tail is encapsulated in a waxy cup. Maybe a protuding cast boolit base gets deformed the same way?

[rhead]

To really tell you would have to try a set with the base below the neck and then a set with the same bullet but the base inside the neck without changing the overall length. I can't get a handle on hoe to change only that one thing. I have loads with the base below the neck that shoot very well but I have no idea if they would shoot better if I increased the raised the base out of the chamber area because I would be changing too many other things. It would be nice to know but IMHO it is one of those things that may be unknowable.

Like the question "What does unexposed, undeveloped photographic film look like?" My intuition and knowledge of physics say the flattest of flat blacks, but there is no way to KNOW.

If the load shoots well keep it until you tweek it into something better. If it stinks try something else. The real problem may be bullet length or something else. Interesting question though.

[StarMetal]

Not really as the J-words would pe plenty strong enough to resist any deformation. We do know that a cast boat tails won't work because the tail gets deformed. However, they will work if the base and tail is encapsulated in a waxy cup. Maybe a protuding cast boolit base gets deformed the same way?


If unburnt powder kernels "sand blast" erode the throat what do you think they do to the base and sides of a jacketed bullet. You think that a max load in a 300 Win Mag doesn't swell that base any?

Joe

[Ricochet]

With many of the boolit, throat and case neck combinations I load for, it would be impossible to load with the gas check in the neck and get the round to chamber without excessive force to engrave the boolit in the rifling. With others it is possible as long as the cartridges are single loaded, but not using an OAL that will work through the magazine.

[felix]

Everything expands with pressure. It's all a function of what item expands the most, WHEN and WHERE specifically. Ever stick a case in the chamber? Reason: case, projectile and chamber expanded to the extent that the case went beyond its elastic limit, and the chamber contracted more than the case. Heaven knows if the projectile was expanded excessively to cause the havoc, but not likely for a standard chamber design. ... felix

[qajaq59]

I wonder if the bullet can move far enough forward before the burning powder gets to engrave it?

[StarMetal]

I wonder if the bullet can move far enough forward before the burning powder gets to engrave it?

I was going to mention that, but what the hey. We know a primer can push a bullet out the case. Now that has been brought up and I myself use a filler, how many think the base is getting damaged now? I don't use fast pistol powders by the way, like RD.

Joe

[Larry Gibson]

It's not a matter of "thinking" they get damaged. There is proof, look at the photo in the NRA cast Bullet handbook. I'm also not sure having the same AOL in the test is necessary. Numerous times I have I have found accuracy to be better, especially with soft alloy cast bullets, in rifles with longer throats by just ensuring the GC was at least started into the base of the case neck. This was with very long throated milsurp chambers with the driving band still no where near the leade.

I believe this is why many "newer" designs that keep all of the GC and lube grooves in the shorter case necks such as the 168 silhouette bullet in the .308W are generally more accurate. The strength of the alloy has much to do with it in relation to the burning rate of the powder. Using a filler also protects the base/shank of the bullet. This was mentioned previously. Another situation of part of a cast bullet outside the neck but not yet inside the throat is particularly noticeable with most 30-30 chambers. For some unknown reason the chamber neck length is almost always quite a bit longer than the case neck length. This allows quite a space ahead of the case mouth for the bullt to expand, obturate or rivet into as it transcends from case to barrel. The softer the alloy and higher the accelleration the greater the expansion into this area. Then swaging the bullet back down or shearing off some of the expanded part can do nothing good for accuracy. I have run into this numerous times also over the last 40+ years with numerous 30-30s. The easiest solution is to use the longer .32 Special cases or 38-55 cases to form and get case neck lengths that fit the chamber neck. This just provves that cast bullets can obturate/expand before the leave the case neck.

If the base of the bullet is below the case neck then unwanted obturation and a subsequent unessasary swaging down may happen depending on alloy and the time pressure curve. That is not conducive to the best accuracy. You may very well get "okay" or "good" accuracy (depending on you definition) if the GC and base of the bullet is below the case neck with your load. But is it the best accuracy or is your load one that just does not have an adverse effect? You don't know. Not knowing is why I prefer to negate that potential problem whenever I can by not seating the GC below the case neck. I concur with BaBore.

Larry Gibson

[StarMetal]

It's not a matter of "thinking" they get damaged. There is proof, look at the photo in the NRA cast Bullet handbook. I'm also not sure having the same AOL in the test is necessary. Numerous times I have I have found accuracy to be better, especially with soft alloy cast bullets, in rifles with longer throats by just ensuring the GC was at least started into the base of the case neck. This was with very long throated milsurp chambers with the driving band still no where near the leade.

I believe this is why many "newer" designs that keep all of the GC and lube grooves in the shorter case necks such as the 168 silhouette bullet in the .308W are generally more accurate. The strength of the alloy has much to do with it in relation to the burning rate of the powder. Using a filler also protects the base/shank of the bullet. This was mentioned previously. Another situation of part of a cast bullet outside the neck but not yet inside the throat is particularly noticeable with most 30-30 chambers. For some unknown reason the chamber neck length is almost always quite a bit longer than the case neck length. This allows quite a space ahead of the case mouth for the bullt to expand, obturate or rivet into as it transcends from case to barrel. The softer the alloy and higher the accelleration the greater the expansion into this area. Then swaging the bullet back down or shearing off some of the expanded part can do nothing good for accuracy. I have run into this numerous times also over the last 40+ years with numerous 30-30s. The easiest solution is to use the longer .32 Special cases or 38-55 cases to form and get case neck lengths that fit the chamber neck. This just provves that cast bullets can obturate/expand before the leave the case neck.

If the base of the bullet is below the case neck then unwanted obturation and a subsequent unessasary swaging down may happen depending on alloy and the time pressure curve. That is not conducive to the best accuracy. You may very well get "okay" or "good" accuracy (depending on you definition) if the GC and base of the bullet is below the case neck with your load. But is it the best accuracy or is your load one that just does not have an adverse effect? You don't know. Not knowing is why I prefer to negate that potential problem whenever I can by not seating the GC below the case neck. I concur with BaBore.

Larry Gibson

Doesn't sound like a bad explanation Larry. My Finn 39 has quite a cavern for a throat and I have to just seat a little of the bullet in the case to get close to it. That's with either the 314299 or 311284. It prefers the 314299.

Like I've said I got good results out of my very short throated Sako 7mm-08 with the 150 grain Lyman Loverin, but I used a filler too. I'm talking on the order of 1/2 inch groups. I've since switch the shorter 135 grain Lee 7mm with even better results.

Joe

[405]

Agree with the idea that it may not be best to seat the base below the junction. I try to avoid more than the slightest base encroachment even with jbullets. Can't cite the source but I know I've looked at pressure data from a set of pressure experiments where the bullet base was set back into the case body farther and farther. The data clearly showed that as the bullet encroached farther into the case the pressure went up higher and higher. In at least one test the combination started causing very erratic and higher and sharper than expected pressure curves. This increase in pressure along with the erratic data could not be explained away by the small decrease in case volume as the bullet encroached. If for no other reason I will continue to avoid it.

[Ricochet]

It shouldn't be news to anyone that seating bullets deeper into the case runs up pressure. It decreases the internal volume of the case.

I don't see how an exposed boolit base can obturate before it enters the case neck. The sides of the base have the same external gas pressure on them as the base does.

Obturation into a long, loose chamber throat is a big problem with most old military rifles. Actually they're the ones I don't have to seat boolit bases below the neck for.

[Larry Gibson]

Ricochet

I don't see how an exposed boolit base can obturate before it enters the case neck. The sides of the base have the same external gas pressure on them as the base does.

Here's "how" from the NRA Cast Bullet Supplement #1. That means it is "published" so perhaps it is more "believeable".

Larry Gibson

[405]

Don't know at all. I don't think evidence one way or another was part of it or a way to test for it was included in the pressure data I read. It simply reported the data. Conjecture is up to whomever wishes to.

A thought???? could it be that since the bullet is a "plastic entity" that by pressurizing the portion of the base and shank below the neck juncture that the rest of of the bullet could swell??? Like.... take a long skinny balloon..... squeeze the bottom part..... does the top get fatter???? Goofy theory I know but sounds as good as most :)

No matter, I'll still avoid doing it. I haven't found a single person yet who has forced me to shoot a 160 grain .264 telephone pole bullet out of my short-throated 260 Remington :mrgreen:

[joeb33050]

Ricochet

I don't see how an exposed boolit base can obturate before it enters the case neck. The sides of the base have the same external gas pressure on them as the base does.
Here's "how" from the NRA Cast Bullet Supplement #1. That means it is "published" so perhaps it is more "believeable".

Larry Gibson
This published answer makes no sense. I don't know what happens when in the cartridge case, and Ed doesn't know either. Certainly there's no way that the bullet base INSIDE the ctg. case will get BIGGER; unless I'm missing something. It could get smaller, and longer, but not bigger. 1/10" on my bullets is from the bottom of the gas check to the groove above the gas check, so the bottom band, supposedly gas cut in the picture, was in the neck when the ctg. was fired. Ed had an opinion. No data.
joe b.

[jandbn]

What about powder or even filler being trapped in the exposed grease grove(s) inside the case? If tolerance between the boolit's shank and case neck is small enough after the cartridge is fired, I would assume that any powder/filler in the exposed grease groove(s) could damage the shank of the boolit as it is "swagged" moving into and through the case's neck-shoulder junction? Maybe not all the time, but sometimes which could explain a cracked case neck or a flier here and there.

[Larry Gibson]

This published answer makes no sense. I don't know what happens when in the cartridge case, and Ed doesn't know either. Certainly there's no way that the bullet base INSIDE the ctg. case will get BIGGER; unless I'm missing something. It could get smaller, and longer, but not bigger. 1/10" on my bullets is from the bottom of the gas check to the groove above the gas check, so the bottom band, supposedly gas cut in the picture, was in the neck when the ctg. was fired. Ed had an opinion. No data.
joe b.

I have put in bold and italics the problem. That is your assumption Joe, not fact. You are indeed "missing something" and that is in some instances the hot gas errodes the bullet, probably does nasty things to any exposed lube, rivets the base of the bullet, causes the GC to enter the throat not square with the bore or may even cause the GC to be pulled off the shank. None of those are condusive to best accuracy even if they happen to a minute degree.

Remember I said, along with a couple others here, that seating the GC below the case neck doesn't always cause inaccuracy. There are numerous other influences to be considered. In another thread you are seeking an empiracle answer to this question and there isn't a "yes" or "no" answer. Simply throating your Striker to seat 314299 longer will only answer that question as it pertains to that cartridge, in that barrel with that alloy, etc. Rethroating and retesting will not answer "the question" as it pertains to all cast bullets in all cartridges in all rifles. Like many of us are trying to tell you and you are "missing something", it depends is the answer. Thus rethroating may or may not improve accuracy. It may improve accuracy because your bullets are sustaining some damage from being seated deep. It may not improve accuracy simply because your bullets are not sustaining any damage from being seated deep. In either case I doubt a rethroating would case any decrease in accuracy.

However I would suggest a much simplar way would be an attempt to recover several (probably 10-20) of the bullets and see if the bases show any evidence of damage (as perhaps illustrated in the article's phot) were damaged in the area where they were seated below the case neck. If they were damaged then a rethroating would be in order or perhaps trying another better fitting bullet as Starmetal suggested. If the bullets are showing signs of damge from being seated too deeply then you are doing as well as probably possible with that particular bullet.

Larry Gibson

[Ricochet]

I don't disagree that a boolit base could be damaged by hot gases or impact of powder grains. I do assert that it is impossible for gas pressure in the cartridge case to cause the exposed base of the boolit inside the case to "rivet" or "obturate," as the pressure on the exposed sides of the boolit is the same as on the base. Also, the gas check can't be pulled off as it enters the neck, as the boolit is being forced into the neck by the pressure on the base (which is being applied through the gas check.)

The only scenario I can imagine causing expansion of the base would be if powder grains settled at the rear of the case were driven forward by the primer to strike the flat base of the boolit en mass. Suppose that could occur, but it'd be a special situation.

[StarMetal]

I don't disagree that a boolit base could be damaged by hot gases or impact of powder grains. I do assert that it is impossible for gas pressure in the cartridge case to cause the exposed base of the boolit inside the case to "rivet" or "obturate," as the pressure on the exposed sides of the boolit is the same as on the base. Also, the gas check can't be pulled off as it enters the neck, as the boolit is being forced into the neck by the pressure on the base (which is being applied through the gas check.)

The only scenario I can imagine causing expansion of the base would be if powder grains settled at the rear of the case were driven forward by the primer to strike the flat base of the boolit en mass. Suppose that could occur, but it'd be a special situation.

Excellent thinking John.

Joe

[Larry Gibson]

Starmetal, John

Don't let you what you "imagine" limit you as the proof is sometimes found. In this case it has been. Not always as I and others mention but enough so that we try not to seat a GC below the case neck.

Wow, what a reversal folks! Me telling Starmetal not to "limit" himself;-)

Larry Gibson

[Ricochet]

Don't let you what you "imagine" limit you as the proof is sometimes found.
Where's the proof? Not in the above posts.