position of meplat pin hole in bullet holes

[goodi]

the attached 500 metre fly target (with 5mm coreflute backing) was shot with BIB flat base projectiles

as can be seen, for all holes the pin holes are quite central in location.

the slight apparent tears on some holes are not pin hole related, the target bullet hole serrations were not completely flattened out for the photo.

 

[johara1]

Were there any bullet holes in the backing ? jim

 

[goodi]

hi jim

no

to my knowledge, Townsville LRBR competitors are the only Australian shooters who have used BIB's over a long period of time.

they report that BIB's produce similar bullet hole orientations at 500m, 600yds and 1000yds.

they have confirmed that at these ranges, VLD projectiles behave as per this discussion.

 

[goodi]

today, just for a matter of interest a target frame was set up at 1000yds.

on the frame 2 new IBS 1000yd BR targets were taped front and rear and spaced around 3-4 inches apart.

given the reasonable conditions, using some guessimation ( and some luck) 2 groups were fired.

not the clearest photo - 105 vld group upper centre 108 HPBT group to right and slightly lower

the 5 shot left hand group are 105 berger vlds

the 6 shot right hand group were berger 108 HPBTs.

following are some close up photos of the paired front and rear paper sections for both groups.

105 vld face target

105 vld rear target

105 vld both targets mounted side by side

108 HPBT face target

108 HPBT rear target

108 HPBT both targets mounted side by side

not that any definite conclusions can be drawn from this simple test but it seems that pin hole random orientations continue to occur for both the 105 VLD and 108HPBT.

for some reason, I was expecting the 108HPBT's (being tangent ogives - I think ??) to possibly provide central or more central pin holes, but as can be seen, this did not occur.

it also appears that projectiles can pass through 1 sheet of target paper, travel about 3-4 inches, and impact the 2nd target face without any apparent keyholing or noticeable enlargement of the bullet holes on the 2nd sheet.

it appears that the pin hole position and orientation for the 1st and 2nd target papers also seem to coincide.

food for more thought and additional questions ????

 

[johara1]

The BIB's are a non VLD., so it would be common with boat tails ?What material is your backer made of? are these all trimmed and pointed bullets?..... jim

 

[goodi]

g'day jim

the BIB's were 30 cal 187 Flat base

the Townsville members have sent a photo of a HG IBS 1000yd BR target shot by jeff Rogers. I will post it asap.

apparently centre pin holes with the BIB's was a common occurrence at 1000yds..

all the projectiles used today were lightly trimmed and pointed.

there was no backer as such, the only materials the projectiles passed through before impacting the mound were the 2 spaced IBS paper targets.

cheers
dave

 

[johara1]

Dave, Just maybe it's from shooting upside down LOL...... I need to look into this more but right now the weather and my wife had surgery and I have been to busy to do much outside. Try a piece of non corrugated cardboard behind it. Did you try flat base bullets ?... jim

 

[goodi]

Jim, I am thinking of you both and hope your wife has a full and complete recovery.

unfortunately I don't have any flat base projectiles in any calibre to test at long range.

I do have thousands and thousands of VLD's and HPBT's which all shoot superbly when I load, tune, clean, hold and read the conditions correctly.

a mirror on the muzzle will highlight my greatest cause of inaccuracy.

cheers
dave

 

[johara1]

Any of your buds have any old BIB 108 flat base...... jim

 

[JFrank]

Gents
As a novice I find this interesting also if I may say that my bullet tip holes are not exactly centered to begin with so a spinning projectile would rarely line up dead center on the paper at any distance. Does it affect accuracy? Could I shoot the difference if they were perfect?
Or just a curiosity?
Jim
Addendum- maybe I got lucky on this one

 

[Mozella]

I'll have to go to the range and make a special one-round test because I normally shoot 5 shot groups and they always go through the same hole. Therefore, I can't measure this wobbly meplat phenomenon. That's my story, and I'm sticking to it.

 

[alinwa]

Absolutely FANTASTIC Goodi...... that is a sort of the test I'm hoping to do if I start seeing the off-center tips. I have capability to set two frames up to 15ft apart.....

This is the most fascinating thread I've seen in years


Yo Jim.... this statement (( "also if I may say that my bullet tip holes are not exactly centered to begin with so a spinning projectile would rarely line up dead center on the paper at any distance. ")) Could you expand on your thoughts please? I'm not understanding your point.......

 

[JFrank]

Absolutely FANTASTIC Goodi...... that is a sort of the test I'm hoping to do if I start seeing the off-center tips. I have capability to set two frames up to 15ft apart.....

This is the most fascinating thread I've seen in years


Yo Jim.... this statement (( "also if I may say that my bullet tip holes are not exactly centered to begin with so a spinning projectile would rarely line up dead center on the paper at any distance. ")) Could you expand on your thoughts please? I'm not understanding your point.......

I'm probably not phrasing this properly however when I look at my bullet tip they just are not uniform, they may in fact be centered. They just don't look like it. In my mind I picture the bullet rotating with the center out of alignment. Sorry my brain isn't working better today.

 

[alinwa]

View attachment 1068344
I'm probably not phrasing this properly however when I look at my bullet tip they just are not uniform, they may in fact be centered. They just don't look like it. In my mind I picture the bullet rotating with the center out of alignment. Sorry my brain isn't working better today.View attachment 1068344

See? Now That's why I ask for clarifications I couldn't get the sense of that from your post.

NOW I see where yer coming from!

Thanks

al

 

[Ned Ludd]

As far as I can tell from all the pictures that have been shown, it looks to me like it is the smudges around the bullet hole that are not concentric/uniform, not that the bullet hole isn't centered. I am wondering if the grooves in the bullet bearing surface aren't grabbing/twisting the paper slightly as the bullet passes through, so that the smudges aren't uniform around the entry hole, making it appear to be "off center".

 

[alinwa]

As far as I can tell from all the pictures that have been shown, it looks to me like it is the smudges around the bullet hole that are not concentric/uniform, not that the bullet hole isn't centered. I am wondering if the grooves in the bullet bearing surface aren't grabbing/twisting the paper slightly as the bullet passes through, so that the smudges aren't uniform around the entry hole, making it appear to be "off center".

Well..... they can't twist the paper cuz they're rotating 'wayyy too slow. And the rifling grooves can't really touch tha paper anyways..... I misdoubt they even rub paper

 

[Ned Ludd]

Well..... they can't twist the paper cuz they're rotating 'wayyy too slow. And the rifling grooves can't really touch tha paper anyways..... I misdoubt they even rub paper

Way too slow??? Bullets lose linear velocity far faster than rotational velocity and if they're supersonic at the target, they most likely haven't lost more than about half their linear velocity. If they started out rotating at 200,000 RPM or better, chances are good they're still rotating at better than 100,000 RPM when they hit the target in many cases. Even though that's worth less than one full turn as the bullet passes through the paper, it doesn't mean the they couldn't twist the paper as they pass through. Further, some part of the bullet is clearly touching is touching the paper, otherwise there wouldn't be any smudge marks around the pinhole. I'm not saying that twisting the paper is beyond any shadow of a doubt the reason for the off center pinholes, but it's just as reasonable as some of the other explanations I've seen posted so far. It sure as hell isn't because the meplats are off center.

 

[goodi]

Jim
I am not aware of anyone out here with a supply of LRBR 6mm match quality flat base projectiles.

Nedd
For whatever reason, either by eye examination or by measuring, it is most noticeable that for centre pin holes, the bullet holes are round.

For off centre pin holes the bullet holes are definitely oval,with a direct relationship betwen the degree of ovality and the axis of pin hole off set.

The identification of the force or forces causing this situation are yet to be clarified.


.

 

[JFrank]

What ever is causing it doesn't appear to effect what little accuracy I have so I'm going move on and just not worry about it.
J

 

[RGRobinett]

Bryan Litz addresses that in this section of Vol I - ie the slightly rounded heel. He machined it off a number of 185 Juggernauts and hey presto, the yaw disappears and BC is slightly improved. As he says though, there is at present no way of economically manufacturing BT bullets in bulk in this form.

A return to long-range flat-base bullets in the future, maybe? Increased base-drag but a more stable and consistent performer at long range potentially. There are some such custom designs around, aren't there?

Been there, done that, got the T-shirt. Such bullets (FB) were used, by a hand-full of individuals, to win/place//show, & set records in 1K bench-rest competition - at a rate greatly disproportionate relative to their opportunity (usage). Still, wasn't/isn't a FB going backwards? Despite their record, people just wouldn't buy them . . then, the grim reaper knocked on the door, jackets became unobtainium, and time marched on.

I have long been called an idiot for my belief - based upon empirical results - that regardless of FB/BT, the heel should be sharp - as sharp as possible. That said, most of the ball-tailed [contemporary BT] bullets seem to work well enough. Brian's books expose a good deal of myth and mystery - great works especially in conjunction with the works of Robert McCoy and William C. Davis Jr., great works.

BTW, the FB bullets weren't great because I made them - it's simply a GREAT design. At known distance, BC is highly over-rated - I'd bet that only the upper tier of the ultra elite could observe a 0.070 difference in BC - maybe.

Imagine how quickly an engineer would get demoted, or, canned, for proposing the addition a FB bullet to the long-range line-up! Perhaps Dave Tooley, or some of the other instagators/users will chime in. aJR, from Down-under could offer some useful dope. RG