450Bushmaster.net

Okay. So I'm not that great at freehand drawing, you've probably seen better art in a fifth grade art class. But it's the best I can do without my mechanical drawing tools. So let's just move on to an observation and possible alternative regarding the taper crimp into the cannelure/band on The COP 200 Grain all copper bullet.
I've been examining the design of this bullet and the performance obtained by Hoot so far.
The crimping band/cannelure on this bullet is really deep. (0.023") sounds great, right?
But the average case mouth thickness of a 450 Bushmaster case is 0.015". You see where I'm headed with this?
The observation that's bugging me is that if I taper crimp into that banding groove, am I compromising the ability of the cartridge to headspace on the case mouth? The reason is when the case wall that is 0.015" is taper crimped into a band groove that's 0.023" the case mouth could be buried/recessed almost 0.008" too deeply into the cannelure groove. So how can I achieve a decent head space? In theory, I may have just done the same thing as apply a heavy roll crimp and there's no case mouth to headspace on.
See image 1.


Now I'm wondering if it might not be better to seat the bullet just a bit deeper putting the cannelure into the case, allowing the case mouth to rest just above the groove where there's a 0.065" section, right before the bullet starts to taper, then align the LeGendre Side Crimp to crimp into the banding groove, then taper crimp the case mouth to .475"?
See image 2

Now there's a definite hold on the bullet and the case mouth is back in a position for a final taper crimp into that area right above the cannelure where there's about 0.065" for the taper crimp to bite, yet allow the cartridge to still headspace on the case mouth? With such a positive crimp, the powder will get a good start, the case should expand well and soot should be minimal and the powder burn might be more efficient. And at 38 grains of Lil Gun, it should perform well.
Right now it's all just a theory, but I plan on testing this theory if nobody sees any issues that I may be missing. What do you guys think?

I think it would also be possible to just seat the bullet so that the case mouth is above the cannelure and taper crimp to .475. This would not be as tight a hold as adding the side crimp, but this would be the same as a taper crimp on the 250 gr FTX, which has no cannelure and should give acceptable, if not optimum performance. Only the chronograph will be able to tell what the benefit of adding the side crimp is.

I have got some 250's and 225's loaded with and without side crimps. I hope to get to the range to compare them sometime soon.

Wow, I never checked the cannelure on them. I would think as long as you checked your case lengths to be sure they were the same you should be safe. Your idea sounds like it would definitely work though.

The driving band groove is not a cannelure in the strictest definition of the term, it just allows us to use it that way. At least that's the impression I got. It's real easy to see what minimum case mouth diameter it will take to compromise the headspacing. Taper crimp an empty, cast off case down until it will no longer catch the lip and measure the diameter. A while back I did that experiment, stopping at something like .460 and it still caught it sharply. That's way less than the benefit diameter needs to go. Keep in mind that a true cannelure has rounded shoulders and a driving band groove, which is cut, has a near 90 degree shoulder. That equates to a much more secure grip on the bullet than afforded by a rounded shoulder and a shallow groove such as cannelures have. With the the COP 200 I loaded, I took them down to .474 and tried pulling the bullet I using an inertial puller. After ten hard whacks on the concrete floor, it had not budged! Heavier bullets might dislodge more easily, given the additional momentum.

Hoot

Thanx Hoot. But do you think it's okay for a test run? I'm itching to try this.

Texas Sheepdawg wrote:Thanx Hoot. But do you think it's okay for a test run? I'm itching to try this.

As long as you don't stab crimp too deeply, there's no reason to be concerned. I've done stab crimps into XPBs and they ran very well. Great velocity SDs IIRC. As for the mouth taper crimp, just use enough to get the belling out. Again, IIRC, the stab crimp into the groove held on really tight, so start low and work up.
Hoot

Thanx. I seriously don't intend on pushing these harder, like I do the FMJs. I'm counting on the 30 less grains of bullet weight and my prediction that somewhere between 37 and 39 grains is going to be a sweet spot and send those little copper monkeys right at the velocity I'm wanting. I will load a couple and post specs here.

The finished product.