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Old October 14, 2014, 09:58 AM   #1
LeftyTSGC
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Why? FMJ vs HP results

I am attempting to find out why the results of shooting two types of bullets are different.

I shoot a STAR30M 9mm. I have noticed that when i shoot Xtreme 124gr HP and MG FMJ at 7yds i get great results from both types of bullets, providing tight 1/2 inch to 1.5in shot groups.

When i get past 10yds, all goes awry (with the FMJ, CMJ, plated RN). At 25 yards with the Xtreme HP i can get 1 to 2in shot groups. But, with the Mg FMJ the best i can get is 8-10inch groups. I have tried seating from 1.160 down to 1.120, and have tried, W231, Longshot and Power Pistol at many different loads, to no avail.

Can someone explain maybe why this happens. I also have two barrels that i have tried and get the same results. Also, this appears to happen only with FMJ bullets, i have tried Berrys and MG RN bullets and get the same results.
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Old October 14, 2014, 10:06 AM   #2
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Therein lies the joy! Finding the variable(s) that are out of whack. Good luck!
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Old October 14, 2014, 10:35 AM   #3
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Measure the diameters of the bullets you are using.
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Old October 14, 2014, 11:13 AM   #4
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Along with measuring the diameters of the bullets, you might want to slug your bore and find out what the diameter actually is. I've seen 9x19 barrels vary from .355" to .359". If yours is on the large side, the bullets may not fit well enough to grip the rifling well.

Hope this helps.

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Old October 14, 2014, 01:51 PM   #5
mdi
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Well, no two different bullets will preform the exact same in any gun. 7 yards accuracy isn't much of a test as round balls will group well at that distance. Xtreme plated bullets by Berrys'? I'm not familiar with MG bullets, Montana Gold?
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Old October 14, 2014, 01:57 PM   #6
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The HP give you more bearing surface over the RN/FMJ. This alone will give the bullet better stability. And is why a lot of BE shooters are using HP at the long line (50yrds). Also with plated if your damaging the plating it is not likely to show up till you shoot it at the longer range.
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Old October 14, 2014, 02:17 PM   #7
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I am going to go out on a limb and suggest that the plated bullets are , upon firing, "gripping" the lands better. They are obtruding better in the bore....( obtrude, to thrust forth; push out )

The plated bullets will certainly deform more readily into the lands than the conventional FMJ's will. So they might be getting a "better" stabilizing spin on them...

How "hot" are your loads ?

Have you tried other weights of conv. FMJ's ?

Any how... what I am suggesting is that the plated bullets better obtrude in the bore... and because of this are more stable leaving the barrel... and better stabilized farther down range.
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Old October 14, 2014, 03:48 PM   #8
LeftyTSGC
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Most of you are saying what i was thinking. I needed to confirm my thoughts.

And yes,
The Xtreme HP are plated
The Berry's are plated (RN)
The Montana gold are FMJ (RN)

I was thinking about slugging my barrel, that may be the issue that the FMJ bullets are not being gripped by the lands as much as the plated are.

I will measure the MG FMJ to check their size.

I tried some 115gn a while ago, but do not remember the outcome.

I was just confused with the vast difference from 7yds to 25yds.

Well i may have 420 124gn MG FMJ to give away after i get done with this.

thanks for all the input.
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Old October 14, 2014, 11:05 PM   #9
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Measure the bearing surface (BS) of your RN bullets and sort them. Keep the group length variations at about .002 unless you have a larger spread in lengths. High quality bullets could have a spread of .004 from shortest to longest so you could have 2 groups. I have seen .018 spread between bullets and went with .003 per group (.241-.244) and my groups really improved.

Make sure you have proper neck tension to avoid bullet set back. Don't flare the case mouth too much.
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Old October 14, 2014, 11:17 PM   #10
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Look at it this way, if you shoot 1" at 7 yards, then you are going to get at least 3-4" at 25 yards simply from the dispersion of the rounds. However, part of your group is your own inaccuracy, and all too many people concentrate more at 25 yards then at 7 yards and shoot almost the same size groups.
Unless you shoot slowly, over a machine rest, you really don't know what you are getting. That, and you need to shoot five or more groups with a given load to have any idea of what the real accuracy is.
I have NEVER had accuracy as good with any plated bullet as I get with MG or Zero jacketed bullets and I very seldom get the same accuracy with a FMJ-RN as I get with a JHP.
9x19 used to have groove diameters that ranged from 0.354-0.362", with lots of guns having groove diameters of 0.358+".
9x19 is also the single cartridge that suffers bullet tumbling/keyholing more than worn-out milsurp rifles that fired corrosive ammunition.
Almost all 9x19 guns are a lot happier with 0.356-0.357" jacketed bullets and 0.357-0.358" lead bullets.
Back when I started shooting 9x19 (around 1972), there were very few 0.356" bullets (made for .38 Super) and almost no 0.355" bullets. We all shot 0.357" bullets and never had a problem and very few ever had an issue with keyholing.
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Old October 14, 2014, 11:39 PM   #11
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Quote:
Originally Posted by LeftyTSGC View Post
At 25 yards with the Xtreme HP i can get 1 to 2in shot groups.
I'd be ordering a boat load of those Xtremes if I were you. Groups like that are simply amazing for a plated bullet.
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Old October 15, 2014, 12:41 AM   #12
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I have been extremely pleased with the Xtreme 165gr HP plated bullets in my XD40. Very consistent and accurate.
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Old October 15, 2014, 12:45 AM   #13
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The BRYs rn are .356 but not a lot of bearing surface on the rifling. The BRY 124 HBRN-TP gives better results and has a much longer sidewall contacting the rifling
The JHPs have a longer straight sidewall that gives more contact. The Xtreme JHPs are thick-plated with a longer bearing surface.

[The MG JHP is an accurate bullet out of a .3555" bore at 1070-ish feet per second.--just saying. Mine are loaded at 1.096" oal. using three different powders ]

These and your bore diameter are some factors affecting accuracy, especially farther out.
Up close, the bullet size and shape has much less effect.

Like noylj said, make sure it's not the operator first.
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Old October 16, 2014, 10:30 PM   #14
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Perhaps the original swaged lead is not concentric????

Idk, just grasping at straws!?!?!
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Old October 17, 2014, 08:51 AM   #15
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I'm just thinking out loud here. The part about "more bearing surface" may be true, but IMHO there is more to it than just that.

The rifling puts a spin on the bullet to stabilize it, the stabilization comes from gyroscopic effect. For a given weight bullet, the more mass you move away from the center and to the outside edge, the stronger the gyroscopic effect will be. I believe that is a big part of why hollow-points or hollow-base bullets tend to be more accurate.

Copper is less dense than lead, so a thick copper jacketed bullet will have less gyroscopic effect than a cast lead or plated lead bullet, since the less dense material is at the outside and the more dense lead is towards the center axis.

A full copper bullet would have to be much longer than a lead bullet for a given caliber and weight. It would make sense that a copper bullet would have to spin faster than a lead bullet to stablize.

Anyway, those are my thoughts, from a relative newbie.
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Old October 17, 2014, 09:14 AM   #16
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Slug your barrel.
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Old Yesterday, 11:49 AM   #17
LeftyTSGC
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Update;

the MG 124gr FMJ measure .355-.356

barrel slugged - i get .352, measured three times

I am going to have to believe that maybe the batch of FMJ's ireceived were not concentric, or not getting enough grip on the barrel to get a good spin. Any way I gave the 420 rounds left away to someone who will try them.

I will use my Xtreme 124gn HP, But would still like to find a good solid FMJ to use.

thanks for all the input and advice.
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