Still beating a dead horse: About different bullet weights and points of impact

[Walt Sherrill]

We've had two lengthy discussions here in recent months on the effect heavier rounds have on point of impact. The consensus was that with revolvers, where recoil against the frame is immediate, the barrel starts to rise as soon as recoil begins.

In the case of semi-autos, where there is rearward movement of the slide and barrel, there is some delay of recoil force to the frame, and only modest contact with the frame (via recoil spring compresion) until after the bullet has left the barrel. With semi-autos, some here claim that barrel rise is immediate, while others claim it is trivial, with little effect on the point of impact. Barrel rise is very obvious after the bullet has left the barrel (which typically happens before the slide has moved a small fraction of an inch [.10"]). In super slow-motion videos, barrel rise is not obvious until after the bullet has left the barrel, but even seemingly trivial amounts of barrel rise can have a big effect down range.

So we've had lots of opinions and claims, but no real evidence offered. (It was JUST OBVIOUS to parties on either side of the debate.) I've been on both sides of this debate, and have been called all sorts of names on other forums for even questioning whether heavier bullets do, in fact, hit higher when fired from semi-autos.

I tried my experiment yesterday -- after finally finally finding the necessary ammo at a Gun Show this past weekend. None of our local shops had 124 or 147 gr 9mm rounds (except in the higher $dollar SD rounds, and I'm not flush with cash...)

These results are NOT definitive, and I may not have done things correctly, but I'll show the results, here. You folks can then tell me what I did wrong, and offer counter evidence to show the errors of my attempt. I posted this on another forum earlier today. I wish the groups were smaller -- but with my impaired vision I was happy to be hitting the black center at 40 feet.

Your main conclusion may be that I'm not that great a shot... and I'll agree. The gun was more up to the task than I was.
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About different bullet weights causing different points of impact with semi-autos.

I had stated, earlier in this discussion, that I had never really questioned the claim that heavier bullets tended to hit higher. I didn't change bullet weights that much and didn't hand load. I never really noticed that much difference between 115 gr and 124 gr rounds, and almost never shot 147 gr.

I knew that points of impact did rise with weight in revolvers, but accepted it to be true with semi-autos.

I gave it a try, yesterday, and I'm not sure I did anything to resolve the issue, except to show that at the distance I was shooting, there wasn't an OBVIOUS difference.

In every case I used the same gun (an M&P Pro 9mm with a lot of Apex upgrades) and tried to get exactly the same sight picture and point of aim on the the targets. I shot seated, from a rest, with my hands resting on a firm padded rest.

I loaded up 16 rounds of 9mm: one 115gr (for the first shot, off target) then 115gr, 124gr, 147 gr, 115gr, 124gr, 147gr, repeated four times. I moved from left to right, one shot on each target, and the moved back to the left to the first target and repeated the shots. All three targets were mounted on the same target hanger. (I had to pull them off to run them through my scanner...It doesn't like a very WIDE (or long) document.

I had the targets set at about 40' -- not the 50' indicated on the targets. The lighting at the indoor range where I shoot is mediocre for precision shooting, but great for combat-simulations. At about 40' My eyesight is at its limits. (I get cataract surgery next spring for my "strong" eye -- I'm right eye dominant -- and that should help me a good bit.) I had left eye cataract surgery done several years ago, and it was great.

Before I started I tried using my Merit Optical Attachment (an aperture that can be attached to your glasses with a suction cup.) It worked for me in the past, when my eyes were better, but it wasn't a help today -- while it did make the sights and target a bit clearer, it also proved more aggravating than helpful. I took it off.

Here's the results of my efforts, five shots per target, weight of bullet noted at the top of each target. ONLY that weight bullet appears on that target. Maybe if the distance was greater, the results might have been more obviously different.

Note: at one point, I jerked a 124 gr. shot, marked it on the target -- high left -- reloaded a 124 gr round, chambered a 115 gr round to reset the gun (fired off target), and continued. When I scanned the targets, I covered that errant round, which was near the handwritten "24" at the top of the target. (Duh!)

 

[David R]

The merrit thing did now work because there was not enough light. Try it on an overcast day outside.

It looks from YOUR sample they all impact about the same. I need to try it from my 5" 45. The last targets I posted were from a 3.5".

David

 

[Nanuk]

I have always found the POI and shifts were more related to a specific gun or barrel than the load. Some of my guns are more forgiving and some the POI radically shifts with different loads.

I do not think you proved anything but that the bullets all behave in a similar manner in that gun.

 

[JDBerg]

Think About Ammo Power Factor Rather Than Just Bullet Weight

I have an STI Trojan 9mm 1911. While I do not compete in IDPA ESP class with it, I know a few guys who do compete with my gun, the STI Spartan V 9mm 1911, the RIA 9mm 1911, and the DW Pointman 9 1911. To make these particular guns run properly, try thinking in terms of power factor for a 9mm load, rather than just bullet weight.

I took the following from the Wilson Combat website...

"...5) Ammunition - Some pistol ammunition works well in the 1911 and some doesn’t, choosing the proper ammunition will go a long way toward reliable function. In general, longer cartridge length (basically as long as will fit in the magazine and seat fully into the chamber) and more pointed bullets will result in smoother feeding and more reliable function. Additionally how powerful the cartridge is affects function to a great degree. Very light loaded ammunition of under 124,000 power factor (bullet weight X muzzle velocity = Power Factor) may not reliably eject and/or lock the slide to the rear on the last shot in the magazine. Some commonly available 115 gr. FMJ RN ammunition unfortunately fits into this category. Ammunition with a power factor of 128,000+ will be required for IDPA or USPSA competition and will properly function your pistol."

So as a general rule of thumb I think I should stick to the higher power factor ammo for this particular gun, but I think the rule can apply to many of my other 9mm's.

 

[Walt Sherrill]

I do not think you proved anything but that the bullets all behave in a similar manner in that gun.

And I may not have proved that, either. As I said, it was NOT a definitive result.

All I can say is that there was NOT a big difference in points of impact given generally the same points of aim -- and my eyes were equally bad regardless of bullet weight or muzzle velocity.

I was shooting Georgia Arms 115 gr hardball, which they rate at 1150 fps
and North Georgia Firearms 124 gr hardball, which they rate at 1100 fps
and North Georgia Firearms 147 gr. hardball, which they rate at 950 fps

All of these are above the IDPA minimum power factor for SSP and ESP the divisions.

 

[cougar gt-e]

Unless you mount the gun in a ransom rest, the variation in poi from the shooter will swamp out any potential raise / drop induced by the ammo.

 

[Limnophile]

Walt,

You need to record the elevation (above or below the center of the bullseye) for each shot on each target, then perform an analysis of variance to see if there is any statistically significant difference between target (bullet weights).

My calibrated eyeball, for what it's worth, doesn't see a difference, except maybe the 147-gr bullets are hitting higher. Shooting at targets at 25 yd would make any difference more obvious.

 

[Radny97]

I'm not a statistician but I have some college education in that area. I think that you need to shoot more in order to really determine if there's any difference.I would recommend at least 50 shots over various targets at each bullet weight. I also think you will need to spend some effort ensuring that your grip of the gun is at the same pressure for all shots so that you aren't limp wristing it or gripping it too hard or different between shots.
I commend your effort! That was a very interesting discussion that we had regarding muzzle rise before the bullet has exited the barrel and I'm interested to see more information on this issue.

 

[Walt Sherrill]

You need to record the elevation (above or below the center of the bullseye) for each shot on each target, then perform an analysis of variance to see if there is any statistically significant difference between target (bullet weights).

My calibrated eyeball, for what it's worth, doesn't see a difference, except maybe the 147-gr bullets are hitting higher. Shooting at targets at 25 yd would make any difference more obvious.

As you can see in my write up, I didn't claim to offer a definitive answer to the questions we've been asking. Or even a "maybe" answer. I have never shot a lot of 147 gr rounds in the past -- they weren't easily found in local gun shops, and I shot cheaper stuff at the range that is generally found mostly in 115 gr or 124 gr.

Until the related discussions that prompted my exercise above started, I would NOT have been surprised if heavier rounds hit much higher than lighter, faster ones.

Re. your comments:

1) As for 147 gr being maybe a bit higher? The differences you see could simply have been human error -- my limited vision or my obviously less-than-stellar trigger work. I'm far from a machine. (Some of the 115 gr. rounds were high, too...)

2) The only range I have easy access to is an indoor range that is limited to 50'. The lighting at 40' and 50' is not great. Perhaps I'll try again with a different target and a smaller bull? (Using a 6 o'clock hold on a smaller center might give better results.)

3) my eyes are good enough to do the measurements you mention, or to shoot IDPA-type courses of fire at greater distances than 40', but they aren't good enough to do a consistent sight alignment when precision is important. Beyond 40' I'm at a disadvantage. Maybe in the Spring, after cataract surgery? (That said, I hope we have some better answers sooner than that.)

Someone with better eyesight or access to superior shooting conditions is welcome to do the same sort of test, but at a greater distance. It's not a particularly expensive drill.

• Having all three targets on the same hanger seemed like a good idea, too: basically the same conditions, distance, lighting, etc.
  
  
• I thought it important to do a registration shot before starting any string of fire so I fired the first shot of the magazine off target. I know that the first shot with a manually loaded round may not lock up the barrel and slide quite the same as when the fired round powers the mechanism.
  
  
• The ideal solution would be the target at 20-25 yards, using a Ransom Rest, with the gun manually sighted for each shot...

Sighting the gun with each shot offsets the problem of testing a polymer-framed gun in a Ransom Rest. I do have a Sphinx I could have used, and took it with me, but the sights needed adjustment and I didn't have the needed mm tools to adjust the sight. Polymer frames are a bit more flexible than metal frames and don't always return to the exact same stating position after each shot. Aimed fire makes that less critical.)

Radny97's comments about the need for a larger sample is valid -- but I wasn't really trying to do that sort of analysis -- I was trying for a Scientific Wild A$$ guess-type result.

I'll leave BETTER (more replicable) tests to someone who has better eyes and who is a better shot. Another participant here is planning to do a similar test, but has been tied up on the job, etc. Maybe he can throw some more light on the issue.

I want to try shooting my 9mm 1911 with the recoil spring removed, too -- so that there is no significant contact with the frame until the barrel slams back -- long after the bullet has gone.

.

 

[reddog81]

Based on those targets it would appear that both 115 and 147 have a higher point of impact than 124. Also it looks like 147 shooters better for you assuming the torn sections of the target represent multiple hits and not a keyhole.

 

[Walt Sherrill]

Based on those targets it would appear that both 115 and 147 have a higher point of impact than 124. Also it looks like 147 shooters better for you assuming the torn sections of the target represent multiple hits and not a keyhole.

No keyholing. The range where I shoot uses small cardboard strips across the top attached to the motorized holders. I use cheap copier paper to make the targets (on my printer). The targets are taped to that strip. You can get some big tears which distorts things.

If I do this again, I'll tape the holes shut before I scan them so they are more easily seen.

Only five shots to each targets displayed.