Can bore riding CB's that don't ride the bore be accurate?

[Maven]

I several bore riding CB molds, e.g., Ly. #311291 & #314299 and Lee C324-175-1R (8mm. Mau.) with undersized nose portions (#311291 and the 8mm. Lee), which drop into the muzzle of their own weight and/or aren't engraved by the rifling of certain of my rifles. Some perform poorly, as expected. Yet others defy expectations and theory*, and are quite accurate (examples to follow). In all instances, velocity is rarely greater than 1,800fps (with WC 820, XMP 5744, WC 860, IMR 5010 + filler) and CB's are seated so that the driving bands are sized to fit the bore and seated long enough so that the bands are marked by the rifling. Can anyone explain why bore riders that don't ride the bore are sometimes accurate?

Example 1, Mod. 70 Win. in .30-06 (circa 1982): None of the Lyman bore riders, #311291, #31141, nor #311284 had noses large enough to be marked by the rifling and gave no more than 2moa -3moa accuracy with my best loads. However, CB's with their expanded to .302" or those that are at least .301" (Saeco RG-4, for ex.) on the nose -> 1 moa accuracy (sometimes better) with the same loads.

Example 2, Sako, M 28/30, 7.62 x 54R, "as issued" (CB's sized to .311"): This rifle will shoot #314299 (nose is .3030" - .3035") and a CBE #313-185 (looks like a flat-nosed RG-4; nose is .3040" - .3045") like a house afire: 2 moa when I pay attention, sometimes a bit better. However, it will shoot 311291 with a measurably smaller nose (~.300") almost as well and occasionally even better (5 in 1" @ 100 yds., witnessed).

Example 3, Mod 1909, 7.65 x 53mm Arg. Mau., "as issued": The only CB that I had that would fit its bore was #314299 (sized to .314" and .313"). Yet, when I slugged the bore with -299, not one portion of the bore riding nose was engraved by the rifling. Accuracy was typically 2 - 3 moa, but sometimes half that (The barleycorn sight, since replaced, was a real problem.). Moreover, if I fired 10 shot strings, I would almost always get a flyer or two every 50 shots (5 strings), but with the others clustering into 3" or less.

Example 4, re-bbl'd (Shaw 1" x 26" bbl.) 8mm. Mau. milsurp. rifle purchased new in 1964: I kept this one 8mm. (have to size to .324"). It is pillar bedded into a Bell & Carlson synthetic stock and wears a 3x- 9x 'scope. It will put 10 j------d bullets into better than 1 moa when I position it correctly on my bags. CB's will do almost as well, but not at the same velocity. I recently purchased a Lee C324-175-1R mold (generic design) for it and am both pleased and baffled by it. To wit, it is the ONLY Lee mold I own whose sprue plate hasn't galled the mold's top surface (after deburring, filing, polishing, etc.) and it casts beautifully as well. But...the CB's noses are too small (don't have one at hand to measure) since they fall into the muzzle of their own weight. Yet, when seated so that the front band is engraved by the rifling, they'll shoot into <2 moa: I put 5 into a nickel-sized hole again the other day @ 50yds. (not boasting, just describing what occurred).

Obviously something other than a "perfect" CB-to-bore fit is operating to produce, at the very least, acceptable+ accuracy from imperfectly fitting bullets. Is it velocity (no more than 1,800fps typically)? Does seating into the lands sometimes compensate for non-engraving noses? Is it the alloy, whcih is a trifle softer than WW + 1% Sn, but not heat-treated (I get only an occasional, but easily removed smear of Pb near the muzzle of the above rifles.). This is a puzzlement!

*I'm referring to Robert N. Sears' comment, "A most revealing check of a bullets's fit can be made by simply placing it nose first into the rifle's muzzle. If it drops in of its own weight up to the driving bands, no more than mediocre accuracy can be expected." (p. 134) in "Cast Bullets Must Fit The Bore" in E. H. Harrsion's "Cast Bullets" (1982).

[felix]

Maven, as always: If the boolit is centered by whatever means during loading, remains centered during ignition, and leaves the tube centered, then the accuracy is left up to the boolit external dynamics only. Really, there is nothing else to it. ... felix

[NVcurmudgeon]

Maven, no light to shed here, either. But I would love to see anybody's explanation of the accuracy my Ideal 311413 delivers from my NRA Sporter Springfield. My best bet the ranch loads with Lyman 314299 are 1.5 to 2 MOA, yet the widely sneered-at 311413 will stay in 2 to 3 MOA at the same 100 yd. distance. Velocity of my pet 2400 load with 299 is 1550 fps, and so far the 413 has been held to 1150-1250 fps with 8.0 to 9.0 gr. Green Dot. Length of the "bore riding nose" of the 413? About 1/8" of the nose is .302" to .300, then rapidly dwindles to a point.

My .303 No. 4 rifle also sometimes ignores the "bore riders must engrave at the muzzle" rule. I have an old Ideal 308291 or 311291 that casts .299" X .314", while the rifle is .302" X .3138". I think it was two groups, anyway this strangely dimensioned 291 delivered some 2 1/2 MOA groups at over 1700 fps with 18.0 gr. 2400. Of course, this latter accomplishment may be in the 100 monkeys with 100 typewriters eventually typing Hamlet category! Again, 2 1/2 MOA matches what the old No. 4 will do on a good day with its favorite 314299 load, or jacketed, for that matter.

The more I learn, the less I am certain of, but is gratifying to see a rifle pretending to be a fine target revolver shooting full wadcutters.

[Pat I.]

Maven,

First realize that Bob Sears shoots BR so his idea of mediocre accuracy and someone else's idea of mediocre accuracy might be two different things.

I have a Shilen barrel chambered in 30 BR that has a big bore, .301, and I used to use a RCBS 165 sil. in it that cast with a .300 bore ride out of WW. The bullet was tapered using a die I made with the same reamer I throated the rifle with, .310x1 1/2 degrees, and it shot very well even with the undersized bore ride section.

Like Felix said I think if you have a straight chamber and throat and can get the bullet going down the barrel straight they'll stay straight up to a point. Plus most of the moulds you mentioned have a pretty long body to bore ride relationship if I remeber right and I'm sure that helps too.

[Maven]

Felix, NV Curmudgeon, & Pat I., If I understand you correctly, concentricity and bearing surface may overcome a too-small bullet nose? Do you think limiting velocity to 1,700fps - 1,800fps helps? As for definitions of accuracy, I realize they can be measured objectively to the nearest 0.01" if necessary and they certainly have a different connotation for BR shooters, but none of my rifles even remotely approaches a bench gun. I'm happy with moa or smaller groups (sometimes a rarity!), but what I mean by "accuracy" is repeatably small groups that increase the odds that I'll use a particular loading technique, powder & powder charge and CB of a given design & dimension again and maybe even try to improve upon it. As I wrote earlier, this has puzzled me for quite some time and I'm most appreciative of your answers.

[Buckshot]

............Maven, it's very possible that there is a combination that helps a 'Non-Riding' bore rider shoot well. As has been mentioned, being loaded and chambered with the boolit concentric would appear to me as the most likely #1 thing.

Possibly then boolit design is next? I would more likely expect a balanced design, ie: 50/50 drive band/bore rider to be a better shooter then the Saeco RG4 (to use an extreme) everything else being equal. Number 3 might be the throat and leade design. To be simplistic, it would seem to me that a long throat just provides a longer area for the unsupported nose to wiggle waggle around.

Now if a 50/50 design, or one even more biased to drive bands (and especially if sized to the throat OD were used, the drive bands would have a tendancey to help keep the boolit 'on axis' to the barrel.

My own experience has been pretty universal in needing the nose to al least touch, if not engrave to get any kind of accuracy. Which brings back up the rather desperate attempt to get a M1909 Argentine Cav Carb by sizing down a .325" 8mm slug to .314". Nothing else was working, to be sure.

...................Buckshot

[Pat I.]

Maven,

Why I mentioned BR is that if you're used to looking at pretty small groups an inch and a half group would look pretty mediocre even if it was shot out of a Moisin Nagant using round balls. So even though Bob wrote that the accuracy was mediocre with what we're taking about it might not be mediocre to everyone else. Shooting HVY class 5 shot aggregates in the mid 6s in BR shooting is pretty mediocre performance nowadays but other guys might think it's great.

Getting things started straight helps any bullet but for certain I have to believe that a long bearing surface would definitely help a bullet with an undersized bore ride section. Seating the bullet so the lands are engraving the first band has to be a great help too and I'd be willing to be that if you set them a little deeper you might be agreeing with Bob Sears.

When I was shooting the barrel and RCBS bullet I mentioned if I remember right I was using 29.5 grs of 2495. It's been a while and I don't remember if I chronographed it but in a 14 twist barrel it had to be going over 2100 fps and maybe closer to 2200.

[leftiye]

Maven,
Not trying to be a smart @$$, but maybe NVC got it right with the 1000 monkeys analogy, it could happen. Probably works better than they say it does.

Maybe cut off some of the bore riding portions, and lap the front of the mold out bigger with them and some diamond lap? I'm just coming from my personal approach here, anything might work, but if you start out right, then it has more of a probability of sucess.

[Bass Ackward]

Well, this was the reason for the rise of the infamous DD band was it not? I am kinda surprised that this isn't a bigger request for Buckshot. I would have thought it was as big as hollow pointing. Must be dieing out.

[Bret4207]

Well, this was the reason for the rise of the infamous DD band was it not? I am kinda surprised that this isn't a bigger request for Buckshot. I would have thought it was as big as hollow pointing. Must be dieing out.

True enough, though I never heard tell of anyone claiming it made a huge difference. I always liked the idea.

My best guess is with the well prepared/concentric ammo crowd. That seems to be Bobs theory over in the 6.5 thread too. Seems like it would make sense.

[Pat I.]

Since we're not talking about tight or fitted necks like on the 6.5 thread I think band to bore ride ratio and jamming the bullet into the rifling has a much bigger effect on Mavens outcome than perfect loaded round concentricity. I have nothing to base this on except gut feeling but I think if he loaded his rounds with zero run out but used a bullet with a short body and long bore ride or took the bullets he's using now and set them so they had to jump before they took the rifling his results would be a lot different.

[Maven]

Bass, DD bands? Were these the same as the Wilke bands? If so, wasn't their purpose to reinforce the CB's driving bands, thus allowing higher velocity rahter than enhanced accuracy per se (don't recall any claims about the latter)?

Pat I, You're right: Although Sears' article is aimed at CB shooters in general, 3 of the 4 photos it contains directly pertain to BR shooting (a 10-shot group on a CBA target; Ly. #311335 in the muzzle of a Rem. 40X rifle; specially bored top punch to expand the nose of #-335 for that rifle). However, his advice, which I obviously follow, is well-taken. The subtitle of the article is "size is more important than shape."

Leftiye, I suppose I could modify the molds, but that's risky without expertise and a lathe. What I prefer to do is either substitute a properly fitted CB, e.g., a CBE 195gr. Loverin in the Arg. Mau. or a wide[r] nosed CB, e.g., the RG-4 or Ly. #311644 in the '06; or expand the nose of Ly. #311291 or Lee C309-180-1R to .302"via a Hanned die made for that purpose. For my 2 Finn. Nagants (one is a Mod. 39), I'll leave #314299 alone since it performs quite nicely in either. 1,000 simians...etc., i.e., chance may play a role here, but these results are repeatable and have been for 10+ years.

[Pat I.]

Pat I, You're right: Although Sears' article is aimed at CB shooters in general, 3 of the 4 photos it contains directly pertain to BR shooting (a 10-shot group on a CBA target; Ly. #311335 in the muzzle of a Rem. 40X rifle; specially bored top punch to expand the nose of #-335 for that rifle). However, his advice, which I obviously follow, is well-taken. The subtitle of the article is "size is more important than shape."

But I wonder what his results would have been if he'd picked the 284 or something like the RCBS 180 FN with an undersized bore ride instead. The 335 does have a pretty short body for the bullet's length and was probably chosen more for it's BC.

[felix]

Maven, a DD band is typically a ring around the boolit nose, convex in nature rather than concave like for a lube groove, up towards the tip of the boolit, and just before the final ogive starts. Used to help center the boolit while being chambered. Perhaps not heavy duty enough, as first intended by Walt of NEI just to keep the round centered, to hold a boolit straight during hard acelleration. A heavier ring (longer, like with a true band) would prolly work to satisfaction. Buckshot surely could gouge out the band areas in the mold. Worth a try when the boolits are destined for a good shooting gun. ... felix

[Buckshot]

............I have the report from "Handloader" magazine where Al Miller tested one of NEI's new DD band boolits. NEI will also cut the DD band in your mould. Anyway IIRC it was a 180gr 30 cal bore rider similar to the RCBS 180 grainer.

Part of the idea was less friction, and with the DD band the nose OD could be reduced to NOT ride or engrave. The DD band doing that instead. I think it's main utility is NEI's ability to cut the DD band on an otherwise usless bore rider mould you have, that doesn't :-)

In the test it was a good shooter, but no better then a correctly sized bore rider. Since I'm a real afficiando of Saint Loverin's designs, his are just bore riders with 4-5 DD bands out there on the nose, HA! HArd to go wrong with a Loverin IMHO.

..............Buckshot

[Maven]

Felix & Rick, Now I remember that concept! Did that mold, or a variant of it, cast a "Coke-bottle" shaped bullet that Al Miller described as being like the fuselage of the F-16 (only more accurate, I'm sure!)? Apparently it was an idea that never really arrived, a fad, if you will, which may explain its relative scarcity in 2007.

[Buckshot]

Felix & Rick, Now I remember that concept! Did that mold, or a variant of it, cast a "Coke-bottle" shaped bullet that Al Miller described as being like the fuselage of the F-16 (only more accurate, I'm sure!)? Apparently it was an idea that never really arrived, a fad, if you will, which may explain its relative scarcity in 2007.

.............Nope, that's not the DD band, but I remember THAT test too :-) The DD band is merely like a drive band way out there on the nose just aft of the ogive.

..............Buckshot

[joeb33050]

Yes.
It's mostly a matter of measurements and geometry.
A 1" bullet with a .1" band at groove size +.001" and a nose of bore-.002" will tip, draw the picture.
A 1" bullet with .5" bands at groove size +.001" and a nose of bore - anything won't tip, again, draw the picture.
The short base band long bore rider nose bullets work fine if the dimensions are correct or over the minimum.
The base band/s at groove size + at least .001", if long enough, will keep the bullet straight.
311291 with undersize nose and long bands will shoot, often.
311299/314299 will sometimes NOT shoot, with undersize nose, because the bands are short.
311284 with undersize nose will most often shoot because the bands are long.
joe b.

[Wayne Smith]

Felix & Rick, Now I remember that concept! Did that mold, or a variant of it, cast a "Coke-bottle" shaped bullet that Al Miller described as being like the fuselage of the F-16 (only more accurate, I'm sure!)? Apparently it was an idea that never really arrived, a fad, if you will, which may explain its relative scarcity in 2007.

NEI still lists that mold style in several calibers. I've wondered what it was for. Looked quite slick. I wondered if it would stabilize in the bore.

[Buckshot]

NEI still lists that mold style in several calibers. I've wondered what it was for. Looked quite slick. I wondered if it would stabilize in the bore.

..............My understanding is they copied the shape of the F-16 (looking up or down) for that design.

................Buckshot

[Nelsdou44]

I'm glad Maven raised the topic because I think it sheds some light on an undersized bore rider I have.

It's a David Moss design 50/50 bore rider to drive bands w/drive bands that are fairly wide-narrow lube grooves. After doing some effort to ensure the drive bands engage the lands on seating and striving to keep the case necks/boolits aligned as straight as possible I got some decent groups at 50 yds. But the same load and technique at 100 yards goes to minute of barn. So I believe I'm still getting some amount of nose tipping in the barrel.

My guess is that the first boolit length of engraving into the barrel is critical that "sets" the axis of the boolit as opposed to its true center of mass. This also makes me wonder about the roughness of the throat as being a factor. In comparison, my Lee 175 8mm has narrower drive bands than the Moss design.

Could narrow drive bands "help" getting the boolit launched straight and true?

Nels

[Bass Ackward]

Could narrow drive bands "help" getting the boolit launched straight and true?

Nels

Nels,

Could. Suppose that you had a fair amount of slop in your throat. A thin band would allow you to crush fit and it would also offer less resistance to moving forward into the bore.