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trimming the bullet meplay for better BC

 
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  #15  
Old 11-27-2003, 06:42 AM
*WyoWhisper*
 
Posts: n/a
Re: trimming the bullet meplay for better BC

Jeff,

I must admit I often wondered about the inconsistencies. But I am not areo expert so I figured it must be no big deal cause these guys are shooting tiny groups at 1K...

So Jeff where does a guy get a tool like the one you mentioned???


and I thought I was anal when I debur the flashhole from both sides and bevel both the inside and outside edges of them. [img]images/icons/wink.gif[/img] [img]images/icons/grin.gif[/img]
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  #16  
Old 11-27-2003, 07:12 AM
Bronze Member
 
Join Date: May 2003
Location: Townsville Australia
Posts: 98
Re: trimming the bullet meplay for better BC

WyoWhisper,I understand Your own Dave Tooley sells a unit to trim meplats but i have not seen one so i don't know how his cuts or if it changes the point dia..If his 1K groups are enough proof i'd say it's a beauty...I don't think u need to be an Aero expert to want to change things,i started in trying to make my life a bit simpler in having bullets nearly all the same length...When u see the points after doing this the meplats all look different so i made a cutter to even them,sort of evolution...1 of the true brains of L/R bench shooting is Henry Childs in your country and he went another way and instead of cutting the point he repoints it with a die ..I am presently makeing one for my 187 BIBs as we speak,will let it be known if it's a better "mouse trap"..JR..Jeff Rogers
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  #17  
Old 11-27-2003, 09:02 AM
 
Posts: n/a
Re: trimming the bullet meplay for better BC

We're testing the Tooley tool to uniform meplats on a number of bullets at the USAMU. So far any loss in BC is miniscule -- all we're doing is uniforming the points and bullet overall length.

We've tried it on 7mm Remington Short Mags, 6.5 x 284, and both 80 and 90 grain 5.56mm bullets.

We machine rest test all ammo at 300 and 600 yards. We're moving our 1,000 yard concrete block and will get our 1,000 yard machine rest capability back in February.

Groups are indeed shrinking slightly, and I think it's because the bullets are now more consistent length- and point-wise.
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  #18  
Old 11-27-2003, 05:22 PM
Bronze Member
 
Join Date: May 2003
Location: Townsville Australia
Posts: 98
Re: trimming the bullet meplay for better BC

G'day From Aust Dave,Your machine rest has got my interest...Have you tried checking the bearing surface lengths??,i have found this area to be the most productive in reducing the vertical dispersion from a conventional rifle ....With Full cartridge preparation i can hold V.D. of less than 2.0 ins at 1K in fine shooting conditions with my present gun...Do you find that a ballisticly inferior projectile will perform better after meplat modification than a unit with a higher bc proportionately speaking???...How do you uniform the points after the length classifying is done??...JR...Jeff Rogers
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  #19  
Old 11-27-2003, 05:51 PM
Silver Member
 
Join Date: Sep 2003
Location: Central Virginia
Posts: 141
Re: trimming the bullet meplay for better BC

Hi guys,

I have been doing this for a few weeks now, after reading the post at BR.com, I had Dave send me one. All I can say is it works.

I guess old Two Shoes at SH would have a field day with this one. LOL but it does work.

By the way droped the whistle pig but it's still me.

Good luck, Vern
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  #20  
Old 11-29-2003, 02:21 PM
Silver Member
 
Join Date: May 2001
Location: NC
Posts: 352
Re: trimming the bullet meplay for better BC

Brent,
Again sorry for the delay. Below are my attempts to answer your questions as accurately as possible.

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Have you guys experimented with cutting the tips way back, or just enough so they all clean up square vs. the wild uneven ones etc.<HR></BLOCKQUOTE>
So far, I don't see the numbers saying that cutting them back to far has any deterimental effect, but I'm sure at some point it has to have some affect on the negative side.
We have only cut back enough to cleanup the tip only when shooting across the M43.
One guy that shot in these tests with us, definitely cuts his tips back a lot further than the rest of us. But on paper he hasn't lost anything except for some BC loss. That's an experiement for the future and it would take a lot of rounds to statisitcally prove or disprove this and I'm not sure we have enough guns, barrels, bullets, and setup to tell anyway.

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Have you played with boring the HP out larger and it's effects either?<HR></BLOCKQUOTE>
We haven't specifically bored out the HP per say but after cutting the tip flat we all clean up the burr using different methods.
Myself, I use my dremel tool with a wire wheel attchement that rounds the inside and outside edges very nicely. I do deburr the inside of the HP on the 338 bullets with a small number drill first before putting the wire wheel to it.

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Do the really wildly uneven tip always reduce BC by a certain amount?<HR></BLOCKQUOTE>
There is a reduction, but I don't have the hard numbers calculated to give them to you. We not worried about the loss only about the consistantcy and that's what our tests have been concentrating on.

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Have you all established a baseline BC ES for the squared tiped bullets and compared them to the ES of random selected out of the box bullets?<HR></BLOCKQUOTE>
Yes. but, I don't have a lot of the raw data fully compiled due to work restraints right now. But during these tests we would take 1 rifle, same lot# of bullets, powder, primers etc and fire strings of unaltered, trimmed, and tipped bullets for comparison. This same test was fired for 4 different calibers between 6 to 8 different proven BR rifles/barrels.

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>I'm curious, do you guys leave the acoustic target set up, or use a stand for it that is always a set distance from the bench? I don't have this type of permanent setup, it's a real PITA to get accurate measurements without this.<HR></BLOCKQUOTE>
Unfortunetly we can't leave it setup. So all of our numbers are comparable within that particular test for BC comparison. But it's not that critical being we're only looking for relative changes within and not what the actual true BC. Though we do take out time to setup as accuractly as possible so that we are pretty close.

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>As I'm sure you're aware of, the distance is very critical for absolute BC numbers, relative ones for tests like you're doing would be easier, if that's all you were after.<HR></BLOCKQUOTE>
Oh yea... afterward we went in a plugged in some different numbers, jsut changing a distance here or there by fractions of an inch and it would definietly affect the number in a big way.

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Do you guys use a seperate frame for the acoustic target just ahead of another target frame to icsolate the sound traveling through the frame. It does travel faster through the wood than it does through the air, and often the target backer material will transfer this noise to the sensor before the mach wave reaches it.
The sensor will sometimes trigger too soon in this case.<HR></BLOCKQUOTE>
I'm trying to think exactly how these were setup the last time we did this. We did see a couple of the 338 bullets give obviously wild numbers for TOF but the velocity readings on the chrono and proof screen said everything was fine so we suspected something with the acoustic setup. We also has a slight rain come and go that morning so there were many variables to consider.

hope this answered some of your questions. BTW: I don't hear you bragging about how nice the weather is up there this year as compared to last winter! [img]images/icons/grin.gif[/img] I was chilly enough that I had to throw on a flannel shirt the other day to go to work. But we haven't had a frost yet. [img]images/icons/tongue.gif[/img]

I've got pictures of the trimmer and stuff coming shortly.

Steve
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  #21  
Old 11-29-2003, 02:40 PM
Silver Member
 
Join Date: May 2001
Location: NC
Posts: 352
Re: trimming the bullet meplay for better BC

Here's some images of the actual tool and some of the actual bulets I fired through my LG rifle during this test session of unaltered, trimmered, and tipped bullets.

Dave Tooley's trimmer (L -&gt;R) cutting head with stop coller that sets the amount of cutting depth, next is the body that the cutter rotates in and has a plastic collar pressed into the opposite end that is cut like a throat would be in your rifle. This is the stop that the bullet seats against while being trimmed. Last is the bullet itself.


Next is how I hold it while trimming. The cutter sticking out the right side is turned by hand or can be chucked up in a drill for power if your doing a large batch.


next is a picture of 30 rounds of ammo for my LG just before firing, showing the unaltered meplats, trimmed meplats, and plastic tipped meplats.


Steve

[ 11-29-2003: Message edited by: Steve Shelp ]
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