Some experimenting with tips and boat tails

[SendIt]

Sharing the results of a little experiment inspired by conversations here on the condition of projectiles.

People get fussy about bullet tips, and the idea that a nick in the boat tail has much more of an effect has been put out there too so I did up some loads to test the pair of theories.

Test was done with a Howa 1500 Varmint in .308 which when I'm having a good day shoot's 1.1" - 1.2" groups at 200m. Shooting 150gr Nosler BT.

For comparison I had the following loads:

• Load A - Tips and tails in good condition.
• Load B - Tail in good condition, tips bent, pinched or squashed around a little with plyers.
• Load C - Tips in good condition, dented boat tail.

To dent the tails I pressed a flat head screwdriver into the corner edge of the bottom of the base, not the side so no impact on the rifling. Pushed about half a mm deep at an angle so there was a little dent and a little bur sticking up.of about the same height.

Shot 3 groups of 4 shots for each load all at 200m, results were:

• Load A
  • 1.2" (didn't actually shoot these again on the day because have done so before more than once.)
• Load B
  • 1.3"
  • 1.2" with 1 flyer
  • 1.3"
• Load C
  • 1.3" with a flyer
  • 1.5"
  • 1.4" with a flyer

So strong indication for paying more attention to the tails than the tips in this case.

Hope it helps somebody.

[Chronos]

That's interesting send it. I would have still fired off the rounds with good bullets simply as a control. No data is truely accurate without a control but with suck a small sample size the data is just an indication of what you were trying to prove.

What shape do the groups show? Is the increase in group size more vertical or just radial?

I've often wondered about SP bullets than can have their points flattened upon recoil in a box magazine and how that may affect drop at longer ranges.

Chronos

[tom604]

so unless your benchresting no noticeable difference , good groups by the way, even the bad ones

[SendIt]

Chronos,

I had used the Load A "good bullets" on a dozen occasions before, that's why I didn't bother as I was confident stating their accuracy as I have - For the purposes of this test anyway. Fair enough point though to rule out factors on the day.

Radial size increase to the groups, as well as directions of flyers. They just landed wherever. I didn't break it down to this level but if you wanted to get extremely technical I suppose you could do the test again and mark which side of the bullet the dent was on, and always load that facing the same direction.

Maybe I'll do something with soft points the next time I get curious about something.

[SendIt]

so unless your benchresting no noticeable difference , good groups by the way, even the bad ones

This was with an adjustable front rest and rear sand bag. Very stable and I'd say I was shooting well on the day so shooter error in this would be as minimal as I can achieve.

[Westy]

Like Chronos I found this very interesting and enjoyed your hard work Sendit

[Timb0]

Are we talking about Nosler Custom Competition projectiles here? If so I take it the damage to the copper hollow tip would look quite severe?

[SendIt]

Nosler Ballistic Tips were what I had loaded for this testing Timb0.

[Lyam]

You might have a new tool to sell to the meplat uniforming boys.

A boattail uniformer on the other end?

[Lorgar]

I haven't done anything like this level of testing buy I've seen a few indications of the same behaviour too from damaged tails.

I don't batch bullets and aren't very fussy, but if there is an overly wonky tip or flaw in the bullet they go in one box. Good loads go in another.

The wonky ones get used for plinking or whatever fun. Same indications as above, a few more flyers with them than you'd expect.

[Jessie]

Maybe I'll do something with soft points the next time I get curious about something.

A lot of the hunters would appreciate the results I'm sure.

[Mich]

Very interesting results Sendit.

I don't think I've ever even thought about giving the tail any attention.

Might do some testing myself to see if I can support the theory here.

[Jack V]

Good work . It's something that bullet swagers have always known but it's not always easy to get good clean obvious results .
Results also change at longer ranges where a bad meplat degrading the BC starts to compound the issue .

[BRNOmod2]

Good work - its great to see someone doing some tests and collating the results - of much interest to many of us no doubt

[SendIt]

Worth doing in the end I think. I've done a little more since and am while it's not 100% scientific I'm sold that the tails warrant as much if not a little more attention than the tips.

I've been dividing my loads more with the condition of the tail the priority and separating any with flaws and it seems to be adding something.

[Jack V]

When a bullet flies at high velocity a shock wave is formed infront of the meplat . This tends to create a dead area and shields the meplats inconsistencies from greatly affecting the bullets progression through the air and because it's rotating anyway at high rpm even if one side of the meplat is longer than the other it is still essentially a round profile as seen by any laminar flow of air .

Also boat tail spire point bullets tend to fly slightly nose up on the first half of the trajectory which is not presenting a square face of the meplat to the actual trajectory or any laminar air flow anyway . Again the negative effects of this trait is reduced by the shielding shock wave effect for the highest velocity parts of the trajectory anyway .

However as the velocity falls the shock wave moves back the bullet tips over more inline with the trajectory axis and it becomes less of a shield so the meplat inconsistencies start to affect the BC more and the trajectory .

Meplat trimming is more about getting a square meplat that can then be closed accurately . Meplat closing is about increasing the BC to get flatter trajectory and hold velocity at longer ranges which also helps fight wind effects .

Test don't have to be overly scientific to be very useful and it's better if they are not because then we can understand better the results.

The air flow at the base of a bullet is turbulent for a flat base and less turbulent for a boat tail but at short ranges the difference is not so noticeable but as the range increases and velocity falls the boat tail settles the turbulence down somewhat but the turbulence on a flat base stay about the same .

Any damage , inconsistency or non concentric form in the base or edge will upset the turbulence and act like a rudder . It can also disturb gas flow from the powder pressure as the bullet leaves the muzzle and cause yaw and it can also if bad enough upset the gyroscopic stability (rotational stability ) of the bullet .

[Swarm]

Test don't have to be overly scientific to be very useful and it's better if they are not because then we can understand better the results.

[Jack V]

Test don't have to be overly scientific to be very useful and it's better if they are not because then we can understand better the results.

So what's your problem mate ? Can't you understand that most people don't have a degree in ballistic science .
Make the tests too complicated and no one will be able to follow them . Did you miss the words "overly scientific "

[Swarm]

Pfft, whatever. Lose the attitude.

You said it's better if tests are not overly scientific. That's plainly false. The more thorough and accurate the test the better and more useful the result. Period.

People not having the resources to perform such tests is a completely different thing and doesn't support your silly assertion that less scientific is better as a philosophy for testing procedures.

[Jack V]

Pfft, whatever. Lose the attitude.

You said it's better if tests are not overly scientific. That's plainly false. The more thorough and accurate the test the better and more useful the result. Period.

People not having the resources to perform such tests is a completely different thing and doesn't support your silly assertion that less scientific is better as a philosophy for testing procedures.

Out.

You lose your attitude sport . A test can be accurate without being ÖVERLY SCIENTIFIC " and complicated to a point that no ordinary shooter can understand it . What the OP did was very good and jerks like you are ruining the thread and his work effort .

[Swarm]

What the OP did was very good and jerks like you are ruining the thread and his work effort.

Read it again. I never uttered a syllable against SendIt, what he did, or his results. Just your comment. I guess you "cant understand".

As for attitude, you're the one that opened with 'what's your problem' and the condescension. God forbid someone question your wisdom, right?

Anyway, not wasting any more time on this so I'm out. You need to have the last word anyway so I'll leave you with it.

Keep up the good work SendIt