Group size vs. Bullet Speed

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Group size vs. Bullet Speed

Post by mikemyers on 10/31/2017, 8:50 am

I used to think that group size was proportional to the distance - a 4" group at 25 yards would also result in an 8" group at 50.

This article talks about accuracy, and group size would affect that:
https://gundigest.com/how-to/training/ballistics-initial-bullet-speed

Elsewhere in this forum, I've been reading that the groups open up more than double, because of bullet speed, and there is a difference between bullets that are heavier or lighter, based on how they are slowing down among other things.

I'm trying to understand this...  ...without completely interrupting the other thread.
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Re: Group size vs. Bullet Speed

Post by BE Mike on 10/31/2017, 9:09 am

I remember someone saying that at the short line, "a load of bubble gum and talcum powder will hold the ten ring". The long line takes some effort. The only thing I'll add is that standard deviation doesn't give a reliable indication of accuracy at 50 yards. The only way to find out how your load will shoot is to test it at the long line.
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Re: Group size vs. Bullet Speed

Post by Wobbley on 10/31/2017, 9:28 am

Just to make the theorists go tilt, there has been more than one rifle and load combination that has shot consistently smaller proportional groups at 300 yards than the same rifle at 100 yards.  Rare, but it does happen.

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Re: Group size vs. Bullet Speed

Post by dronning on 10/31/2017, 9:35 am

Remember too your hold/gun is never stationary you are imparting lateral forces to the bullet so it will never follow the MOA rule (1" @ 25yd = 2" @ 50yd...).  A not so smooth trigger release may put you 1" off target @ 25yd that might be 3" @ 50yd.
- Dave
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Re: Group size vs. Bullet Speed

Post by Ed Hall on 10/31/2017, 10:05 am

Here's some extra info to help your brain hurt:

I mentioned in another thread about the trajectory of the bullet being an arc with a diminishing radius as it slows down toward the target.  There is another component to that path that I did not include, but it exists.  It is a slight deviation in a helix pattern around that initial path described by the diminishing arc.  It is caused by the spin that is imparted by the rifling.  The spin works by containing the error within a smaller area (the helix).  Today's bullets are much more balanced, but there are still things like drag and pressure waves to contend with.  Really good bullets have a tight helix, but they also have a sweet spot of rpms, which is governed by several factors, e.g. muzzle velocity, barrel acceleration and air quality, etc.  This is why the group size can be greater than the expected doubling for twice the distance.

Can a velocity increase help decrease the group size at 50 yards?  It can, but a decrease can as well.  There is a sweet spot for each system (gun, primer, powder, bullet), etc.  In longer ranges the sweet spot may only exist for part of the trajectory, making it even more complicated.  The helix can vary in complicated ways as the bullet stabilizes or destabilizes along the path.  The off-hand sweet spot has to be evaluated also.  If you find the muzzle velocity of a .45 bullet is most accurate at 890 fps, but you can't handle the recoil in sustained fire, it's not going to help.  All things need a balance.


Last edited by Ed Hall on 10/31/2017, 10:57 am; edited 1 time in total (Reason for editing : I didn't like the way the original read.)

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Re: Group size vs. Bullet Speed

Post by Magload on 10/31/2017, 11:55 am

Dang Ed it is surprising we even hit the target.  BTW there is also a point in the bullets flight that it is said it  goes to sleep.  I it been 50 some years since the basaltic lexture  I gave but I believe that is the point that the rotation causes the bullet to have it's best stabilization.  Does that have anything to do with us shooting handguns and BE.  It could be why velocity effects group size.  When picking my load for the LL in my LB WG for the Zero 185gr JHP I took what was recommended on this site and started .3grs lower and went up .1grs each load.
I first shot 5 10 shots groups with Federal Gold Match as a reference as that is what was used with the 1.6" test target group.  Before that I settled the gun into the RR with 30 rounds.  I then shot the test loads 5 10 shot groups.  Each load decreased in size till I hit 2.4gr and after that they started to open up again.   Might have just used what the Masters said and saved the ammo.  BTW the Federals only shot 1.75" i didn't get 1.6" but the bench I have available is not very good.  Don
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Re: Group size vs. Bullet Speed

Post by TomH_pa on 10/31/2017, 12:26 pm

removed.....not fundamental info


Last edited by TomH_pa on 10/31/2017, 4:10 pm; edited 1 time in total (Reason for editing : wrong topic)

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Re: Group size vs. Bullet Speed

Post by mikemyers on 10/31/2017, 1:05 pm

Copy this into a browser window:

Code:
http://www.the-long-family.com/shock%20wave%20theory%20summary%20explanation.pdf
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Re: Group size vs. Bullet Speed

Post by jmdavis on 10/31/2017, 1:51 pm

Guns often have accuracy nodes with regard to charge, seating depth, bullet weight, etc. it ften times there will be accuracy nodes at different charges. One might find that 4.5 of BE works great at 50 yards in slowfire. The same load may or may not be as accurate at25 yards where recoil control becomes more important. 

A .1 charge change with all other variables being the same may open or tighten a group more than a 25fps variation would suggest. You have to test your gun, with your oal, your bullet and your charge, to know what shoots best. But you can't get wrapped around the axle with the details of the load and ignore the shooting process.

Ed Halls advice should be taken very seriously. He will try to steer you right. I just wish I could shoot leg matches beside him without his brass bouncing off my head. Smile
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Re: Group size vs. Bullet Speed

Post by CR10X on 10/31/2017, 2:19 pm

If you think this is an appropriate topic for the Fundamentals area, then I might as well give up ever making any comments again.  Rolling Eyes

I do however find it slightly amusing that in the search for getting better, a large number of individuals will get distracted by physical things rather than focusing on the part of the shooting equation that demands the most work.

I will leave you with one small observation from the past X number of years shooting damn near everything.  Almost every gun I've seen shot better than the person shooting it.  And those times when the person was better than the gun, well, they generally won anyway.   

But don't let that stop you all from chasing group size versus bullet speed as a Fundamental discussion.   Smile Laughing

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Re: Group size vs. Bullet Speed

Post by AllAces on 10/31/2017, 2:42 pm

After all the ballistics, physics, statistics and testing.............there is the Cone of Silence which occurs right after the bullet rips through that thin sheet of paper, followed by the sound of sucking air, followed by an expletive-deleted.
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Re: Group size vs. Bullet Speed

Post by dronning on 10/31/2017, 3:26 pm

CR10X wrote:I do however find it slightly amusing that in the search for getting better, a large number of individuals will get distracted by physical things rather than focusing on the part of the shooting equation that demands the most work.

But don't let that stop you all from chasing group size versus bullet speed as a Fundamental discussion.   Smile Laughing

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^^^^^ This!!!  The amount of time pontificating all this crap if I was training I probably could have improved my score a couple of points - bye!
I am going to practice dry fire and hold now!
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Re: Group size vs. Bullet Speed

Post by Tim:H11 on 10/31/2017, 3:29 pm

Don’t chrono. I shoot what I can shoot well. When I have settled on something I may chrono it so I know what it’s doing. But its mostly out of curiosity. Just me.
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Re: Group size vs. Bullet Speed

Post by Wobbley on 10/31/2017, 4:25 pm

The key to success in bullseye pistol.  Get an accurate set of guns.  Find ammo for them that shoot well enough to fit well inside the ten ring at 50 yards.  Then go practice and train—A LOT.  

You’ll go much further much faster shooting decent guns and ammo than continually searching for the best setup.

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Re: Group size vs. Bullet Speed

Post by Magload on 10/31/2017, 7:18 pm

I have said it before.  Testing is just another fun part of shooting.  At least I enjoy it.  I may never be good but I will have fun trying to get there.  Don
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Re: Group size vs. Bullet Speed

Post by USSR on 10/31/2017, 7:44 pm

Magload wrote:I have said it before.  Testing is just another fun part of shooting.  At least I enjoy it.  I may never be good but I will have fun trying to get there.  Don
Have to agree.   And, if you want to take it even further, take up casting your own bullets.   Very rewarding.

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Re: Group size vs. Bullet Speed

Post by Magload on 10/31/2017, 7:55 pm

USSR wrote:
Magload wrote:I have said it before.  Testing is just another fun part of shooting.  At least I enjoy it.  I may never be good but I will have fun trying to get there.  Don
Have to agree.   And, if you want to take it even further, take up casting your own bullets.   Very rewarding.

Don
Nope no way.  Not going there I have cast fishing sinkers and back in the 60s a friend and I cast 55 pounds of 12ga deer slugs and swagged riflings on them till the swag broke.  non rifled ones shot just as well anyway.  No interest in melting lead now that I have to buy it.  My friend had around 500 pounds of lead panels.  Besides I am retired I don't have time to make bullets.  Don
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Re: Group size vs. Bullet Speed

Post by USSR on 10/31/2017, 8:14 pm

I dunno, loading match .45 ACP for $.06 per round appeals to me. Smile 

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Re: Group size vs. Bullet Speed

Post by Ed Hall on 10/31/2017, 10:15 pm

Oh, Oh, I must consider myself scolded for perpetuating this thread when I actually was thinking of adding something along CR's lines and didn't.  But, I do get wrapped up in having to find the reasons for many things instead of just training, e.g., why is the hold factually better than it looks?  Some of this, as well as learning how to do a lot of my own work, caused me to take twelve years to reach High Master.

BTW, the reason your hold is better than it looks is because we "see" extremes and often when we "see" the sights wander into the white, what really happened is the extreme edge of the dot or front sight touched the white but if we really thought about it, the actual sight was still well within black.  Also, everything we perceive is in the past, so if we are true to accepting our hold and operating the trigger without hesitation, by the time it fires chances are we are back into the black and enjoy success.

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Re: Group size vs. Bullet Speed

Post by BE Mike on 11/1/2017, 9:04 am

CR10X wrote:If you think this is an appropriate topic for the Fundamentals area, then I might as well give up ever making any comments again.  Rolling Eyes

I do however find it slightly amusing that in the search for getting better, a large number of individuals will get distracted by physical things rather than focusing on the part of the shooting equation that demands the most work.

I will leave you with one small observation from the past X number of years shooting damn near everything.  Almost every gun I've seen shot better than the person shooting it.  And those times when the person was better than the gun, well, they generally won anyway.   

But don't let that stop you all from chasing group size versus bullet speed as a Fundamental discussion.   Smile Laughing

CR
Yep, bullseye pistol shooters were shooting 2600 and higher when the standard for accurizing a 1911 pistol was 3" groups at 50 yards.
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Re: Group size vs. Bullet Speed

Post by fpk on 11/1/2017, 10:20 am

Ed Hall wrote:Also, everything we perceive is in the past, so if we are true to accepting our hold and operating the trigger without hesitation, by the time it fires chances are we are back into the black and enjoy success.
Being someone that completely over thinks the process of shooting and is currently struggling with training a smooth trigger pull, this is really helpful.  This gives my brain something to chew on as counterpoint to the shouting that goes on in there to "PULL THE TRIGGER NOW!". Thanks you!

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Re: Group size vs. Bullet Speed

Post by mikemyers on 11/1/2017, 10:41 am

(Oops, sorry that I posted this in the wrong forum.   Maybe the thread can be moved?  It wasn't intentional, I just lost track of which forum I was in.)
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