Weighing bullets & measuring bearing surface

[CoverDog]

I have just started to weigh my bullets for 1,000yd shooting. A box of 100 Lapua 139gr 6.5's weighed from a low of 138.88 to a high of 139.12 a .24gr difference. The majority of them (87%) were within .14gr of each other (138.94 to 139.08). To separate them into groups how low in gr.'s do I need to get. I can split up the 87% into two additional groups which would get the difference down to 7/100th's of a gr. difference between them having 45 bullets in one group and 42 in another. How anal do I need to be?

And when measuring bearing surface how much variance do you give to your bullet groups.

That Original Pennsylvania 1000yd BR Club 1000yd Shooting School I attended 3 week ago has created a monster!

Thanks to all who have listened and especially to those who will respond with suggestions.

 

[tenring]

A quarter inch difference in weight will mean nothing. I used to do it and feel it is a waste of time. After you separate those bullets, shoot the best in one group and the worst in another. I would be surprised if you find any difference.

I have also separated bullets by bearing length for my groundhog match rifles. I found that good custom bullets are so close in bearing length, that again it is a waste of time. Do the same testing suggested above and make your own decision.

Who said what on this subject at the Williamsport BR school?

 

[dreever]

I agree with Tenring. I used to sort all my bullets, had little plano fishing boxes with compartments. Sorted by weight, bearing length, base to ogive, etc. The worst shot as good as the best so I came to the conclusion that lifes to short to worry with this. Same goes for meplat trimming, stopped doing that also. I still use pointed bullets but even that I'm not convinced about. The human, and enviromental variable from day to day has more of a bearing on how well you shoot on any given trip to the range.

Danny

 

[FergusBailey]

I have not weight sorted long range bullets. I agree that custom bullets generally do not need any sorting, however do find that sorting commercially produced long range bullets will benefit from base to ogive sorting. I try to batch the bullets within a couple of thou and find you will end up with 3 or 4 batches in a box, including a small batch that are way off the others. I just shoot the batches individually, and save the really weird ones for fireforming cases.

I agree with the other comments that you need to prove the difference on paper, but for me base to ogive sorting reduced random flyers that I was getting in my groups.

 

[dogdude]

+1 for FERGUS dogdude

 

[6BRinNZ]

This is some info from Brian Litz on the bearing surface for a .260

"The problem will be in the BC variation that accompanies the shape variation. Typically, if the bullets have less than 3 to 5 thousandths of variation in base to ogive, it's very difficult to tell the difference in group size at 1000. If the variation is greater than 0.005", then you might see some benefit in vertical group size from sorting them.
Best of luck,
-Bryan"

Also comment from German Salazar

"Finally, bullets themselves can have a large effect on MV variance. The biggest thing to look for is consistent length of bearing surface."

In terms of weight, put the variances into a ballistic chart to get a gauge on what the weight change alone would do, assuming all else being equal....I think you will find that weight sorting isn't likely to offer much.

Good luck

 

[ar15topgun]

It is best to remain silent and thought a fool than to speak and remove all doubt.

 

[tripcrow]

Gotta disagree with what some are saying. Especially for 1000 yard shooting. I'd keep them separated in as small a grouping as you can measure and feel comfortable doing. It is all about what you personally are comfortable with or willing to do. It looks like a quarter grain difference in bullet weight would probably yield 3 FPS difference in velocity if running a 6PPC and 65g & 68g Bergers in Quickload is used for a comparison. Try finding 3fps, even with a very good crony and a big box of ammo. Shooting a handful of groups will statistically prove nothing. And hey, 3fps here, 3fps there, and the next thing you know you'll have an improvement you can readily see. Besides, common sense will tell you the more everything is the same the better they'll shoot. Not that common sense is always right mind you.

Unless they're all measuring a rare +/-.001", I keep my bearing surface sorted sorted bullets in the boxes of .001" they were originally sorted into. Hey if they're sorted out already why mix them back up. That sure ain't going to make them shoot any better. Then you can sort those bearing surface lots into weight, and then into diameter, and then into OAL, and then into base to ogive, and then point to ogive, and then into....and then you'll have those 1000 bullets or so sorted out into a bunch of little boxes like Danny is talking about and be trying to figure out what order they should be shot in. Have fun.

 

[bozo699]

Gotta disagree with what some are saying. Especially for 1000 yard shooting. I'd keep them separated in as small a grouping as you can measure and feel comfortable doing. It is all about what you personally are comfortable with or willing to do. It looks like a quarter grain difference in bullet weight would probably yield 3 FPS difference in velocity if running a 6PPC and 65g & 68g Bergers in Quickload is used for a comparison. Try finding 3fps, even with a very good crony and a big box of ammo. Shooting a handful of groups will statistically prove nothing. And hey, 3fps here, 3fps there, and the next thing you know you'll have an improvement you can readily see. Besides, common sense will tell you the more everything is the same the better they'll shoot. Not that common sense is always right mind you.

Unless they're all measuring a rare +/-.001", I keep my bearing surface sorted sorted bullets in the boxes of .001" they were originally sorted into. Hey if they're sorted out already why mix them back up. That sure ain't going to make them shoot any better. Then you can sort those bearing surface lots into weight, and then into diameter, and then into OAL, and then into base to ogive, and then point to ogive, and then into....and then you'll have those 1000 bullets or so sorted out into a bunch of little boxes like Danny is talking about and be trying to figure out what order they should be shot in. Have fun.

Absolutely

 

[6BRinNZ]

Weight is absolutely used to derive BC...Brians book "applied ballistics" contains the formula.

Bill - I agree with your sentiment and it is of some interest as all the little things do add up, measuring/ weighing will definitely highlight if there are any exceptions that will make a known differencene, not to mention the mental confidence of knowing everything is technically perfect.
Much of what we discuss though is categorised by reward vs effort and hence some of the comments. A lot does come down to as you say what you are comfortable with. For fairness sake it would be worth running the quickload numbers of .25grn against 139 grns as the variance as a percentage is significantly smaller. Like a lot of things such as bullet pointing etc the improvements gained for the effort vary per caliber/projectile....often as shooters we seem to pigeon hole effort vs reward when it really needs to be put into context of the shooting discipline, caliber etc.

OP - good luck its a fun journey

 

[bozo699]

Bozo-

A bullet with a Ballistic Coefficient of say .500-G1BC that weighs 110gr will have the same "Drop & Drift" as a bullet of 240gr at the same Coefficient and Velocity.

In the ballistic world, bullet weight effects "energy" but has NO effects to path and drift. Velocity and BC are the two major variables to "time of flight" (which is drop and drift).

As much as you post here on this site, I would have guessed you would have better understanding of ballistics, especially something as basic as "bullet weight"..........
Put equal Velocity and BC into what ever ballistic software you have and enter huge variances to the weights. What you will see weight effecting is energy only.

DM

Donovan,
I do understand Ballistics to a certain degree, I think you would have to have a weird love for advanced math to completely understand all aspects of it, if you do then my hat is off to you, also I enjoy your posts and I know by your posts your a intelligent man and I apologize for my sarcastic remark, I guess I was in a mood and should have kept my mouth shut, I will remove the post when I am done here. I do however believe weight matters, in my sarcastic post I said ,...So a 30 cal. 110 grain bullet in a 40 mph full value wind will have the same point of impact a a 240 grain bullet loaded with the same charge in the same conditions, if they were going the same velocity then you would be correct,...BUT
we as precision shooters (at least I do ) very carefully measure each load to assure the velocity stays the same. On a not so ridiculous scale lets say we were loading 107 grain SMK bullets in a dasher at 3050 fps then accidentally got a 107 Grain SMK that was defective, it didn't have the right lead core in it and it weighed 97 grains, same bullet shape, same base to ogive measurement, would it go in your nice little 5" group at 1000 yards???.... NO it would have several inches of vertical at least because it is now traveling 3115 fps, your SD/ES will be WAY off! I agree small weight amounts won't have the effect that base to ogive will, BUT in the accuracy world we always try to remove or reduce variables and weight of the projectile is a variable! I have quite weighing all but my LR loads as I don't believe it makes a huge difference. Just a side note Two weeks ago I won closest to X by .001 I was .246 and Jack Peterson .247, if my measuring made that difference then it was worth it to me as my envelope had $115 in it and Jacks had $70 in his Anyway our opinions may vary but I wish all the best shooting to you as well.
Wayne.

 

[mikecr]

I just have to ask because I've yet to see it;
Has someone tested bearing variance over a chrono to demonstrate affects one way or another?

 

[BOBC]

I'm with you Danny. Tunnel tested 30 cal match bullets shot in a return to battery rest rig used to test bullets. Bullets varied a full gr. total indicator reading.
The three 5 shot groups averaged .138". Bullet weight error equates to .00595%. I still have these groups the ballistician sent to me.
I'd find it hard to believe we have long range shooters that can shoot and or call shots with those kind of variences. However, the tested bullets only
varied .002" TIR from land contact to base.

 

[mikecr]

Ok Donovan, thanks but;
I'm really lookin for chrono results from bearing variance.
NOT target results from nose length variance.

Have you tested this?

 

[6BRinNZ]

Donovan - where/how are you measuring to get the nose variations?

Thanks

 

[6BRinNZ]

Received a bunch of A-maxes and scenars today (for .260) ...measured 200 A-maxes all were within .001" variation.

Similar number checked for the scenars - these had variances over .005" in bearing surface. As mentioned in an earlier post Brian L (ballistician) suggests this variation is enough to show up at 1000.

Ballistic/tolerance arguments aside what it says to me is - there is no harm in checking...

The A-maxes were meant for club days and the Scenars for the important events...

 

[mikecr]

I think it could be counterproductive, or even detrimental, to cull bullets based on single variables, without actually understanding their overall contributions.

For instance, if you cull based on 5thou of extra bearing surface, what are you actually culling?
ES?(still searching for any proof on that). BC?
You should notice that Bryan qualified the deviations with seperate scenarios. That is, if 5thou of extra bearing = 5thou less nose length, then yadda, yadda.
Well, have you qualified your variations?
If not, then for all you know that 5thou extra bearing is just what's needed to counter 5thou smaller meplat, or 7thou longer boattail and minus .3gr weight.

I don't believe you should get all picky with a single part of a picture, while assuming the rest is perfect. You should look at the whole picture, before taking any actions.
If that's too much work(it might be), then just what is your plan here?

 

[Ont0001]

When "sorting " bullets albeit ,weight,bearing surface,Juenke DU's,etc. my main objective is not to necessarily try to sort to perfect identical bullets....but more to find that "ONE" or two really way out of spec bullet that would "kill" your averages in score or any chance at match standings.
Generally most "match " grade bullets are close enough as a group to shoot very well. However, I've found a lot of boxes of match bullets will contain one or two "WTF happened to that shot?" if loaded into match rounds.
If in fact, no deviant aberrations are found in the sorting process,I have eliminated a possible "mechanical" variable and gain confidence in the bullets standard performance.
To what extent one sorts (look at percentage vs actual number for a mean average) is up to the individuals discretion and time,but I feel a worthwhile endeavor.
JM2C
Gord O

 

[FergusBailey]

For me, the motivation for ogive sorting was the reduction of unexplained flyers on the target. After sorting, I consistently shot 5 shots into a group, where 1 in 5 was dropping out of the group before sorting. I am going purely by results on target when I say it made an improvement to group bullets into batches of 2-3 thou.

 

[6BRinNZ]

Mikecr - I agree with your statements - to me it simply stated that I am probably dealing with a batch of quality bullets that have lower than expected tolerances when using bearing surface as a baseline indicator (yep it can be argued that the nose or BT or meplat would be a better place to start). I may get lucky and the sum of the critical measurements may balance out - to me its just a red flag.

From here I can choose to just go and shoot or measure each of the critical areas, or finally make some assumptions based on effort vs reward and put my time elsewhere. Starting somehwere in the measurement game is at least letting me make informed choices.

The jury is out for me on which approach is best at this stage, but I guess that is in part what this thread is about...