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Help With Boattail Bullets

 
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  #8  
Old 11-14-2007, 04:02 PM
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Quote:
Originally Posted by Boss Hoss View Post
If your shooting is 300 yds or less then boattails are a waste of time.
Agreed, though not so much a waste, but not a necessity either, especially at these velocities.

Quote:
Look at the BR guys NOBODY uses boattails in the 100 or 200yd game...
Good point, but then NOBODY shoots a 6.5-300 Wby *that* close . . . ;-)

Quote:
BT have to fly approximately 300 yards before they become completely stable in flight
I'd respectfully disagree with this generalized statement and would say: "NOT if everything is correct."

I have a fast twist .243 shooting 105 Scenars, a .260 and a 6.5-284 shooting 140 Bergers and a 6.5-300 Wby shooting 123 Scenars and ALL of them punch bugholes at 100. If they didn't, they'd go back for correction.

If your bullet is not stabilized at closer distances, and needs to "go to sleep" (sic), the throat geometry is clearly allowing in-bore yaw to occur. In-bore yaw produces a bullet that is not rotating around it's center of gravity at the muzzle and at closer ranges. No more mystical than that.

The combination of an elongated ogive in conjunction with a boat tail produces an extremely short bearing surface. This is exaggerated in VLD-style bullets. This short bearing surface requires a close fitting leade or ball seat area of the chamber to produce a straight run to the rifling. If the diameter of the ball seat area is too much greater than the bullet diameter, the bullet's short bearing surface is not long enough to keep itself straight. This problem allows the bullet to slump slightly off center as it accelerates forward and it is then in a slight yaw attitude when it engages the rifling. This yaw continues to the muzzle.

When the yawed bullet emerges, it rotates around it's center of form, while it's center of gravity is eccentric to this rotation - yuk. After a certain time of flight, the bullet is forced by it's rotational forces to begin to rotate more so around it's center of gravity and it stabilizes somewhat, but, it will NEVER be as accurate as a bullet that emerged correctly to begin with.

Groups at distance will typically not be bigger at the same rate as it would as the result of linear angular dispersion. Due to this mechanism, your 300 yard group may be about the same size as a 200 yard group, but it will never be smaller.

As BuffaloBob points out, this problem can definitely be a product of freebore, which accentuates any in-bore yaw by allowing it to continue longer and to a greater degree. The 6.5-300Wby is originally a 1,000 yard BR wildcat cartridge based on the necked .300 Wby and does not typically use the same "Weatherby Freebore" illusion as the legitimate members of the family. If you did not specify exaggerated free bore with your build, it should not be present in this long range precision BR cartridge chamber and on the reamers commonly found for it.

The very first thing I would do is suggest that expectations be aligned with the **hunting** bullets you are trying to get to perform. What level of accuracy is expected? What are you getting? 1/4 moa may be unreasonable, while 1/2 to 3/4 moa may be more in line with the game bullet's limitations.

Ever try "good bullets"? I never had amazing accuracy with GKs in my own 6.5-300Wby, and it may due to forces vs bullet construction. Nosler 120 BTs shot great in my rifle, perhaps due to the hard base resisting setback deformation better.

If best accuracy with a 140/142 SMK or 139 Scenar exceeds 3/4 moa in a custom rifle, this in itself may be a problem and something is likely broke.

I would suggest checking and/or touching up the muzzle crown, which is considerably more critical to accuracy with boattails than with flat base bullets. In fact, we're really not sure at this point that it will shoot FB bullets any better anyway, right?

How many rounds are through it? Throat erosion will enlarge the ball seat area and it might benefit by a slight setback. My own 6.5-300Wby had to go back at 750 rounds, and we had to take almost 2" off to get it to indicate with enough runout to provide proper reamer piloting for a decent chamber again.

I would next try seating the boattails longer, as close to the rifling as possible. This will negate as much slump as possible while not changing bullets.

The problem will be more apparent with a bullet like a Scenar, which will be a little "skinny" at .2635" or so, and a "fatter" bullet can sometimes help, but 140 SGKs are typically a little fat already and it should shoot them.

You might also consider trying moly-coated bullets, which generally show better results when there is a geometry problem. This is because the coated bullet enters the rifling with less resistance and less potential deformation. It straightens itself out better, stabilizes sooner and leaves the muzzle with less difference between it's center of form and center of gravity. While the resulting effect is sometimes attributed to the moly being "slipperier" in the air, while it is actually because the coated bullet stabilizes faster, thus achieving it's published BC sooner, thus giving less drop/drift.

Another obscure problem inherent to these rascals is the hard carbon ring, which will both increase pressure prematurely and will also reduce throat diameter enough in some cases to deform the bullet. The slow powders necessary for this guy WILL leave some serious crap behind, a diamond-hard combination of carbon and calcium-based deterrent coating residue.

Considering the reasoning process behind getting a 6.5-300Wby, it **should** shoot boattails and I personally would be very unhappy to be forced to shoot flat-base bullets in it. What's the point? If you try these things and see no improvement, it may be time to take it back to the builder for correction.
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  #9  
Old 11-14-2007, 04:08 PM
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Quote:
Originally Posted by Steve Shelp View Post
Hank,
I've got experience with the 6.5-300 WWH. It's been about 5 years since I've fired mine though. ;^(

How long is your barrel and what is the twist? What load did you use to get 3650 with a 140gr bullet? I have fired mine just a hair over 3500fps with a 30" barrel but basically wrecked the cases after 2-3 firings.
This speed demon has never set the accuracy bar really high to begin with because of the speed it runs at. So what type of accuracy are you getting with it? Maybe it's par for course? If your shooying a lot of pressure with the slow burning powders, the pressure at the muzzle is going to be elevated and will affect boattail bullets more than flatbase bullets if your crown if off-square just a little bit.

The best accuracy we ever got out of the 6.5-300's I've owned or buddies rifles have been shot with IMR7828 loaded down to around 3200-3300fps. Maybe try that jsut to see if the accuracy improves to help evaluate the accuracy of your hunting loads? Just a thought.

Steve
Hey Steve, FWIW, my 6.5-300 Wby used 83.0 H-870 to drive a 140 SMK to 3,400 and into 1/4 moa groups. The same charge sent a 120 Nosler BT at 3,500 and also into 1/4 moa. Sid Goodling built and refreshed it for me.

After setback, I quit using H-870 due to the fouling. I also lost almost 3" total barrel length, between 2" at the chamber end and a re-crown.

I found IMR7828 way too fast and am currently using 74.0 Retumbo to drive a 123 Scenar at 3,400, which also yields 1/4 to 3/8 moa accuracy. I had decided to quit making it sore just playing with it and stopped working on new loads there.
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  #10  
Old 11-14-2007, 05:53 PM
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I am just summarizing what one of my friends of many years who I shoot competitively with who is also a ballistician at one of the better known bullet companies and that is what their development testing has borne out. What empirical data source are you citing with all of the opinions you have presented here specifically the “moly” one?

If you take care of your barrels properly then the carbon ring is or should be a non issue. The bore scope does not lie.
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  #11  
Old 11-14-2007, 05:56 PM
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I'd put the crown under a magnify glass and see what it looks like?
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  #12  
Old 11-14-2007, 06:49 PM
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Howdy Boss Hoss. I am sorry if you have taken my comments above personally.

First, my own first hand experience with match grade and benchrest quality custom rifles has proved to me that it is very simply NOT indisputable fact that all boat tail bullets are inherently inaccurate at ranges inside the magical 300 yards cited.

I have already stated this above, and given examples of no less than four custom rifles I currently own that shoot well with boattails at any given range. This personal experience in itself is enough for me to respectfully disagree with your absolute and all-inclusive statement.

Will they compete with a fresh 6PPC at 100 or even 200? No, but not many rifles will, bullet choice notwithstanding. All rifles mentioned above are indeed capable of turning in 1/4 moa groups with boattails, though.

Regarding the in-bore yaw as my reasoning for this, a series of articles in Precision Shooting magazine that have appeared over the last year or so discussed in-depth the throat geometry information I cite, replete with drawings demonstrating the mechanism. The articles had made many things that had been rather difficult for me to understand suddenly quite clear, especially why a couple of my rifles will NOT shoot Bergers inside of 1-1/2" at 100 yards, yet drive Nosler BTs into 1/2" groups at the same range.

Further, I had a series of e-mail exchanges with Mr. Walt Berger regarding this phenomenon and he suggests throat geometry is a major factor as well. I doubt Mr. Berger would agree his bullets will not shoot well at any certain range, and the fact that I was doing my preliminary accuracy testing at 100 yards was not an issue.

As my 6.5-300 throat was going, I experimented with it, trying to keep what accuracy I could before tying it up at the 'smith's for the couple months a re-work takes. It quit shooting Bergers, then quit shooting Scenars, then quit shoot Nosler BTs. By "quit", I mean accuracy went to over 1/2 moa. This pattern, taken with the information gleaned from the article, focused it quite crisply.

The statements I made above, regarding moly coating vs quicker stabilization/less in-bore yaw, is taken from the same series of articles, and I regret I was unable to play with any of my rifles enough to get a feel for it myself. The best I could do was take my well-worn 6.5-284, which had had 800 moly 142 SMKs through it at that time and try both uncoated 142s and Berger 140s and all I could really prove is that neither shot as well as the moly'ed bullets. I felt that there were too many factors to draw any conclusions from this, including the moly deposited in the bore that would not seem to completely come out. The case made for moly helping to make the best of a bad situation is compelling enough to cite it here as a possible solution. This rifle has since been rebarreled, but I plan not to waste my time with moly, as it has not proved itself to me to be worth the hassles in a correctly chambered rifle.

Taken with the rest of the author's experiments and assertions and the logic behind it, it makes perfect sense to me that this "going to sleep" had a scientific reason behind it that could be influenced by changing throat geometry and was not the "fault" of any given bullet design.

There has never been any truly scientific evidence that any sort of bullets produced tighter groups at longer ranges, nor any solid reason to think a certain type of bullet has some weird aerodynamics that prevented accurate shooting at closer ranges. After reading this and fooling with it some, I feel that my confusion about "why" of some of this stuff is "so" was gone and it was enough to cause me to quit parroting the same rather old info about boattails being unstable at close range just because they were boattails, *especially* when it does not happen with all rifles. The minute it cannot be repeated in even ONE gun, it's just not "true".

Regarding the carbon ring, I do understand your point about "proper care" and insinuated neglect, and I do understand bore cleaning as well as the next guy, however, these HUGE doses of slow powder in the 6.5 bore are quite another animal and no amount of scrubbing, even with JB, would touch it.

I cleaned the rifle religiously every time out, with **no more** than 20-30 rounds passing between cleanings, using customary techniques and for all practical purposes, it was "clean". It was not visible to the naked eye. Sweets patches came back white. JB just made it shiny. Regrettably, I do not (yet) own a bore scope, or this problem may have become apparent sooner, but as it was, the carbon and deterrents accumulated to a point of affect performance before I understood it's nature and presence.

I would be interested in your friend's take on this new information and would encourage you to check into it also - it opened my eyes.
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  #13  
Old 11-14-2007, 09:42 PM
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Thanks for the response and I will discuss this tomorrow with him as well as my friend and builder who has set world records and is in the BR HOF. I do not have his list of credentials but have won a State 1K Championship last year and finished 4th this year even with a dead primer on a target of record string and I have only been competing 3 years now. The statement about cleaning the carbon ring out is just plain incorrect and I have posted Speedy’s instructions in the past about cleaning methods that work and I have a bore scope to verify all of this as well.

It is just a fact that most people are really pretty clueless about cleaning a barrel properly. I cannot tell you how many times people have come into the shop swearing that their barrel was absolutely clean to watch their jaw literally drop when the bore scope was inserted and the results put on the monitor. One guy swore that the “patches come out clean with no blue” but turned green when the monitor came on showing the layered fouling (IOSSO for that). What follows is a method that will get the barrel clean and I have several rifles that use close to or over 100grs of powder as well as my competition tubes that are fired so rapidly that they will literally burn you hand severely if you were to grab them. It does not matter what you shoot if you do not properly maintain your bore it will foul period. Some people feel better just thinking that it cannot be helped but that is just ignorance so read this and give it a try it works….

IOSSO is the best stuff I have ever used for the carbon ring and for severe copper removal (IOSSO works on it as well but takes a little longer) is another trick I learned from Speedy. Run a very well soaked brush with Sweets through the bore several times then run patch soaked with Hydrogen Peroxide very slowly through the bore. The chemical reaction causes the copper to go into suspension and be harmlessly removed. You will see a large amount of foam forward of the patch when it approaches the muzzle. Performing that trick on severe copper fouling has caused more than one person to shake their head in disbelief.


S.G.&Y. BARREL BREAK-IN & CLEANING INSTRUCTIONS

Many of our customers upon taking delivery of their new gun or barrel are in a quandary as how to go about breaking-in that new barrel for maximum life and accuracy. With so much written in magazines these days stating use this, don't use that, brush, don't brush...what's a person to do?? At S.G.&Y Precision, we have a unique opportunity to inspect many barrels on a daily basis with our video borescope. Consequently, we see the results of a variety of break-in as well as cleaning procedures, and most of them leave the rifle owners with their mouth agape when they see the fruits of their misinformed labor on our color monitor. We have seen practically new barrels ruined with less than a hundred rounds shot through them by some of the crazy and sometimes humorous break-in methods. Anyway here goes for what it's worth.

Bore guides - If you don't have one get one!� Without a good bore guide you are just wasting your time trying to break-in a barrel or cleaning it for that matter. More barrels are destroyed by cleaning without a bore guide than by shooting. There are many types and brands of bore guides available on the market and range in price from $5.00 to $50.00. The only one we recommend is the Lucas two-piece bore guide. They are the best insurance you can buy for that new barrel. All other bore guides in my opinion are only good for keeping the solvents out of the trigger and action.

Solvents - We recommend Sweets 7.62 for copper and a solvent mix of our own (Actually Pat McMlllan gave me this formula) for powder fouling and for cleaning/storing your gun for the next match or season. This Speedy Formula is made as follows: Mix 2/3rds Hoppes # 9 Plus Black Powder solvent with 1/3rd Regular Hoppes # 9 Nitro solvent. Let this mixture set overnight and it will form a sort of gel that adheres very well to the brush and cuts powder fouling to a minimum.� Note: Butches Boreshine may be substituted for this Speedy formula.

Procedure for "Break-in"- Before firing that first shot, clean the barrel as if it had been shot by following these simple steps:

Step1 - Insert Lucas bore guide into receiver and chamber. If you don't have one stop here and get one, if not, just shoot your gun and forget trying to take any care of your barrel at all.� Lf you do have one, proceed and give yourself an "At-A-Boy" for being astute enough to have purchased the proper tools for the job. Note: One "Aw-****" wipes out all your "At-A-Boys". �

Step 2 - Run one wet patch of Sweets through the bore and let soak for approximately 30 seconds. Do not patch this out.

Step 3 � Next, run the brush through the barrel only enough to expose the entire brush. Yes, I know that you still have 12 more inches of cleaning rod you could push out the end of your barrel but we want to protect that new crown. Also. if that rod hangs out that far, you will eventually start wearing down the rifling at the crown from about 4 to 7 o'clock. This is very bad "JU-JU" for accuracy. OK, back to our next step. Once the brush is exposed, saturate it well with our Speedy Formula or Butch's Boreshine and SLOWLY run the brush through the bore 10 complete back and forth passes while keeping the rod as straight as possible. This is when the Lucas bore guide really pays for itself.� Remember, the key word is slowly. We are not trying to break any speed records. Let this sit a minute or two and proceed to the next step.

Step 4 - After you have let the barrel soak for a few moments, saturate a patch with the Speedy Formula or Butch's Boreshine and pass it through the bore. Follow this with 2 dry patches and then dry the chamber with Brake Kleen or lighter fluid.� Next, gently wipe the crown off with a soft cloth and lube your bolt (lets not gall the lugs just yet). Now. your ready to shoot your first shot. Then follow the schedule below to complete your barrel break-in.

1. Clean barrel / lube bolt / 1 shot.
2. Clean barrel / lube bolt / 5 shots.
3. Clean barrel / lube bolt / 10 shots.
4. Clean barrel / lube bolt /10 to 15 shots and clean again.

Additional Cleaning Tips

Each time you clean you may also follow the last dry patch with a patch soaked with LOCK-EEZ. This is a graphite powder suspended in a quick evaporating carrier that coats the bore slightly before passing that first round through a completely dry bore.

We are always asked about powder fouling and how to remove it. The only product that we have seen that really does a good job on powder fouling, especially on the carbon ring that forms just ahead of where the neck ends in the chamber, is IOSSO Bore Paste. This is used with a Pro-Shot nylon bristle brush and worked slowly in the neck and throat areas, then slowly down the entire bore. Follow this up with a few wet patches, then dry the bore as usual. and your ready to shoot.

Follow the outline above for your regular cleaning program and I promise that your barrels will deliver their greatest accuracy and life without a lot of grief and hours of wondering if they are clean.

Good Shooting,
Speedy Gonzalez �
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  #14  
Old 11-16-2007, 01:29 AM
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Thanks for all the help and explanations. I believe that this reamer was origanally for 155 match bullets. That would fit the problem that has been sited. The velocities that I have gotten, 3600 fps with 92.0 grs of AA8700 and 140 sgk, 28" bbl, make me think that it has some freebore or at least a long throat. I will get my smith to cut me a false chamber, split it and measure it.

What premium bullets, that would be acceptible for hunting, would you recommend? Sierra bullets have shot very well for me over the years and work great on our Texas deer and hogs.

Thanks again, Hank
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