.45 ACP COR-BON 160g DPX suffers from easy set back when chambering.

This is a discussion on .45 ACP COR-BON 160g DPX suffers from easy set back when chambering. within the Defensive Ammunition & Ballistics forums, part of the Defensive Carry Discussions category; I bought some COR-BON 160g DPX before the ammo shortage got serious. I bought it to use in my XDs because it is supposedly optimized ...

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Thread: .45 ACP COR-BON 160g DPX suffers from easy set back when chambering.

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    .45 ACP COR-BON 160g DPX suffers from easy set back when chambering.

    I bought some COR-BON 160g DPX before the ammo shortage got serious. I bought it to use in my XDs because it is supposedly optimized for short barrels. My initial testing showed the ammo worked flawlessly in the pistol, was pleasant to shoot, and shot to point of aim at expected self defense distances out to 15 yards.

    I rotate the ammo so the same round isn't chambered over and over, and every now and then, not on a rigid schedule, I measure the length of the ammo in the magazines to be sure it's okay. I also put a light scribe line on the bullet at the case mouth so I see it move before it moves very far (as in more than about 0.010").

    The pistol was returned from SA Monday. I took it to the range yesterday. It performed flawlessly with 230g ball, 185g XTP, and 230g GD, which is what I had to shoot in it. I decided the gun is just as good now as it was when it left to be fixed, so I got out the box of COR-BON DPX to reload the magazines. This is ammo that had been in the gun last summer when I carried it. I'd removed it from the magazines and re-boxed it when I sent the pistol to SA right around September 1st (it arrived at SA on 9-3 @ 10:54 a.m. if it matters).

    Out of habit I took the digital calipers to it and measured cartridge lengths from 1.237 to as short as 1.209. I put the 1.209 cartridge in a magazine, chambered it by releasing the slide, then cleared the gun and measured it again. It measured 1.201. I checked the crimp, it's 0.470" which is pretty tight. I wouldn't want it to be smaller than that. I put it in my ballistic bullet puller, gave it one whack and the bullet pulled right out. My reloads (with Speer GD or Hornady DPX and a 0.471" crimp) take 4 or 5 whacks. I decided recrimping to tighten the bullets wasn't in the cards.

    I've reluctantly concluded I'll shoot what I have left of the 160g COR-BON DPX ammo and not buy more of it. The ease with which the bullets set back is, in my experience, both unusual and alarming. I have not had the same setback problem with the 9mm DPX I have in my night stand gun so I'll keep it. I don't think the problem is the bullet. I think, based on comparisons with the factory ammo from Speer and my reloads, the problem is the process at COR-BON and is related to the sizing of the brass before the bullet is seated or the design of the cartridge.

    I did a quick and dirty comparison of the 230g Speer GD with the 160g DPX COR-BON in the next couple of pictures. The first picture shows a factory new 230g Speer GD cartridge with a 230g Speer GD bullet next to it.



    Notice the arrow points to a crimp band around the brass that is right at where the base of the bullet is. The bare bullet is up against the caliper jaw so it effectively shows where the base of the bullet is in the brass. Over my time using the 230g Speer GD in my SIG C3 and the XDs, I've experienced no bullet set back. I still check for it, but none shows up.

    The next picture shows the 160g COR-BON DPX I pulled the bullet from.



    At 1.233" which is close to the longest one I have (1.237") you can see there is a noticeable gap between the base of the pulled bullet and the crimp band around the brass.

    Before the crimp band can begin to stop the bullet setback it will have to slide back to approximately where it's shown in this next picture.



    That's a slip of ~0.073" which will probably cause a pressure increase in the cartridge. It sets the bullet back so far there is a gap between the case mouth and the bullet ogive. It's enough that I don't like it.

    I have 230g Speer GD ammo that's been in the Glock 30 for several cycles that is the same length now that it was on day one. I tried it in the XDs and the bullets didn't move when chambered. My reloads, taper crimped to 0.471", with the 230g and 185g GD don't move when chambered. I just tried the same cartridges in the XDs, C3, G30, and FNX45T and they are solid. The factory 230g GD and 185g GD are likewise solid.

    I haven't tried any other factory .45ACP defensive ammo at this point, and probably won't because I have several boxes of the factory 230g GD. My XDs likes the 185g GD in my reloads so I'll probably look for some of that as ammo becomes available again. Meantime I'll load it with the 230g GD and put it in the carry safe in the closet. The practice ammo clearly isn't a problem because it gets chambered exactly once.

    This is my experience with an admittedly limited sample, but it's enough for me to decide I don't want to use the 160g COR-BON DPX in my XDS. That's a shame because I think, properly assembled it might be the best ammo for the gun.

    Fitch
    “The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety), by menacing it with an endless series of hobgoblins, all of them imaginary.” by H. L. Mencken

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