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Old December 4, 2009, 06:36 AM   #1
draggon
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Paper targets, same bullet, different holes.

Just came back from the range where I spent a pleasant afternoon with my son, both of us shooting 9mm's.

My reloads in both guns, his a Glock and mine a Norinco CZ clone. The bullet was a polymer coated, 124 gn conical nose in front of a HS6 load.

Noticed for the first time that the holes punched in heavy card targets were different from the two guns. Barrels are both about 5 inches.

The Norinco (said to have a chrome lined barrel) punched holes with little radial tearing whereas the Glock punched much more ragged holes.

Didn't have a camera but has anyone an explanation for this?
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Old December 4, 2009, 08:27 AM   #2
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I'll suggest a couple of possibilities:

One is velocity--how different are the two guns? Faster is cleaner.

It seems unlikely to me that they'd be that different, which brings me to

Two is tumbling. Keyholing is from a tumbling bullet. Is one gun fairly worn and not producing good rotation of the bullet? Is one barrel leaded quite a bit which would lead to less stabilization of the bullet in flight?


You don't say at what range these targets were shot, nor whether there was any difference in accuracy.

To check, I'd repeat the experiment with a distance of at least 10 yards, and I'd assess the above factors.
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Old December 4, 2009, 08:49 AM   #3
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I agree with Mongoose. Velocity difference due to different chamber and bore dimensions is most likely. Keyholing, if you have it, will be more apparent if you set up some 50 yard targets and look at the holes made from that distance. I suppose shallow rifling might have trouble with the polymer coating? Don't really know?
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Old December 4, 2009, 09:09 AM   #4
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Ranges varied out to 25 yards and the difference was evident at all ranges.

The guns are both near new, around 1000 rounds each and both started out the day with clean barrels and fired about 200 rounds each.

The holes don't look like keyholing/tumbling, just really ragged edges for the Glock vs the Norinco.

The Norinco is consistently the more accurate gun, it is also much heavier and easier to hold than the Glock and has a better trigger, at least for me.
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Old December 4, 2009, 09:10 AM   #5
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Don't the Glocks have a polygonal rifling or something like that. Could that make such a difference?
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Old December 4, 2009, 11:01 PM   #6
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"Don't the Glocks have a polygonal rifling or something like that. Could that make such a difference?"

Ah, now we're closing in on it, methinks.

Yes, there are some Glock barrels that apparently don't respond well to lead rounds (and polymer-coated count), with the polygonal rifling. Good catch!

OP: Try comparing the two again, this time w/ FMJ rounds and see what happens.
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Old December 5, 2009, 08:24 AM   #7
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Will try again next week with jacketed bullets to see if there is a difference.

The bullets I was using were Westcastings Gold Match, rated to 1700 fps and promoted as suitable for Glock & HK barrels.

In 1000 rounds fired with cleaning at about 2-400 round intervals there has been no leading in either the Glock or Norinco barrels.

Is it possible that the relatively sharp engraved rifling on bullets fired from the Norinco "cuts" the paper as it punches through versus the Glock without the rifling impression "tearing" the paper more.
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Old December 5, 2009, 07:56 PM   #8
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No. You're getting more velocity out of the Norinco. Not being a Glock owner, the polygonal rifling didn't occur to me. I think that rifling and the use of a slow-ish (for caliber) powder are combining to cause the problem. I expect it is easier to drive one of these bullets into the Glock barrel. That will mean the problem is the Glock rifling isn't giving you as much resistance for start pressure as the Norinco. That means the powder won't burn as early or as completely as it does in the Norinco and the peak pressure will be lower. With that drop in peak pressure comes a drop in velocity.

The solution will be to increase the charge in the Glock a little or to move to something faster burning than HS-6. Universal will probably work well.
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Old December 6, 2009, 04:26 AM   #9
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Have IR sensors on the way for the CED chrono so I'll check comparative velocities also.
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Old December 9, 2009, 04:41 PM   #10
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I love those screens. They can even pick out my little .177 cal airgun pellets in the basement. Thats how I found that after only 35,000 rounds, my old Feinwerkbau needed new springs. 100 fps extreme spread from about 325 fps to 425 fps is not good. By comparison, my inexpensive single-stroke pneumatic Baikal has an ES of about 6 fps. I chinced out on the battery pack, though. Bought a motorcycle battery and small inverter so I can keep the screens and my laptop running to dusk at the range.
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Old December 18, 2009, 04:41 AM   #11
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Finally got back to the range with both pistols today.

Tried a range of jacketed cartridges, all of them factory, Nato FMJ, Win bonded in 124 and 147gn and Rem Sabre in 124 and 147gn.

All of them exhibited the same difference in target holes. The Glock punched ragged holes and the Norinco much neater holes. It is not just this particular Glock. Just before I used the range a group of security guys were requalifying on the range using company Glocks and had left their targets up. Same ragged holes, perhaps even more ragged and they have shorter barrels so it doesn't seem that more speed means more ragged. (Polygonal rifling is said to give a better gas seal and higher not lower velocities compared to conventional rifling.)

The CED IR screens arrived but someone has "borrowed" the club chrono so I didn't get a chance to check velocity but it doesn't seem to be that.

More and more it appears to be a characteristic of the polygonal rifling.

Last edited by draggon; December 18, 2009 at 04:51 AM. Reason: additional information
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Old December 18, 2009, 10:20 AM   #12
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Sounds exactly like velocity to me, probably due to less bullet deformation resistance by the polygonal rifling not letting chamber pressure build as high. You just have the effect of velocity backward. Less velocity means more ragged holes. Faster velocity means cleaner holes. That's how my target rounds have always performed. More powder gives more velocity gives cleaner holes, and that's all from the same gun using the same bullets.

The faster you hit something the more reaction force it presents. The higher that reaction force, the more its mass is resisting yielding to the push of whatever is hitting it. You get a more sharply defined cut because the resistance causes the target to be broken off rather than stretched into a tear. Take a piece of cardboard and push the dull claw of a hammer through it. It will normally tear or rip open if the claw isn't too sharp. Hit it fast with the same hammer claw and it pokes a hole rather than tearing. Same principle sped up applies to the bullet holes. Faster means a cleaner hole.
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Last edited by Unclenick; December 18, 2009 at 10:27 AM.
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Old December 18, 2009, 11:30 AM   #13
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What kind of target were you using?

If the targets were stapled (taped/adhered) to a backing, was the backing indentical? Were the targets equally taut?
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Old December 18, 2009, 11:01 PM   #14
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Shaun, heavy weight paper targets on a corrugated cardboard backing, stapled. Shots were fired on same target to exclude any differences so that's not the solution.

Unclenick; Don't disagree with your statement that faster equals neater and that is evident in the other shorter barrel Glocks vs ours. The issue then is whether it is purely a velocity thing or a polygonal barrel thing. You're saying that polygonal barrels shoot slower whereas Wikipaedia and others are claiming that polygonal shoots faster.

I'll try and settle that aspect next week by trying to get the CED IR screens to work with my Pact chrono, assuming the CED chrono can't be found.
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Old December 18, 2009, 11:42 PM   #15
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Draggon, if your patient and have access to a snow bank and can shoot into it safely you could fire 10 or 20 rounds from each gun into the snow and when the snow melts you will have [if you kept them apart] 2 piles of perfectly preserved projectiles ready to help you understand the interior ballistics of the firearms they were fired out of, you will be able to see how the different types of rifling distort the bullets, but I guess this would all depend on where you live
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Old December 19, 2009, 11:57 AM   #16
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Remove a cartridge that has been chambered in each handgun to see if the nose of the bullet was somehow damaged/deformed by the feed ramp.

I doubt there are significant enough velocity differences between each handgun to produce the results you're oberving.

Perhaps the broach cut rifling of the Norinco produces rifling marks on the bullet shank that are more abrasive which "cut" a circular hole in the target paper as the bullet passes through.
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Old December 19, 2009, 12:17 PM   #17
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Draggon

It's the rifling in the Glock barrel that is causing the differences. Replace the barrel in the Glock with a after market barrel or use copper jacketed bullets only. (no plated or coated bullets)

Jim
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Old December 19, 2009, 05:46 PM   #18
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Jim, Type of bullet doesn't make a difference, same effect with jacketed.

Shawn, Already checked for bullet damage on chambering. None evident from either gun.

I am also inclined to think it is largely due to the rifling difference rather than velocity differences. I suspect that if there were huge differences in velocity due solely from the rifling then the manufacturers would use that as a marketing ploy against other brands and reloaders wanting the last 10 fps from their reloads would be recommending (for or against) Glock/HK vs all the others.

I will eventually get round to checking the velocity, hopefully next week but in the meantime can't help wondering if what I am seeing makes any difference in real life on animate "targets". I guess it would be small in any case and hard to quantify.
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Old December 19, 2009, 07:16 PM   #19
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Life is short, don't worry about it. The round isn't keyholing.
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Old December 19, 2009, 07:46 PM   #20
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Draggon,

I don't mean to suggest the polygonal rifling is universally slower. Speed will be a function of bore resistance and the bullet mass and choice of powder. The bullet nose shape has to be identical to make the comparison valid, though. I'm not sure how the shorter barreled Glock's bullet's shapes compared to yours? If I shoot a lead SWC out of my .45 at about 750 fps, it will cut a cleaner hole than jacketed hardball going 850 fps. So it does have to be apples to apples in that regard.

Velocity and bullet shape are really the only two variables here. Unless that polygon squeezes the nose form appreciably, I don't really see how that alone would do it? Could be wrong, of course, but I just don't see why it would be true? Let us know what you find?
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