Bullet Jump

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Bullet Jump

Postby Avenger10 » Wed Oct 08, 2014 11:47 am

Hello all-

I guess I'm the newest newbie here... but I been reading you guys for a while.

To the point. I have started shooting my new 450 BM and immediately notice that the bullets jump .018-.024 out of the case when I close the bolt with full battery. As I am shooting factory Hornady ammo I spent a dime and had me a conversation with a nice young gentleman goes by the name of Seth out at the Hornady factory. After explaining my observation he looked up the push/pull data from my ammunition lot number and verified that they were within spec for that production run. He said they would like me to return some samples for them to dissect.

Then the stupidity part of our conversation... he spoke with one of the ballistic engineers who told him my rifle probably has an excessive head space problem and the extra couple of thousandths is allowing the added inertia to lunge the bullet forward when the case mouth meets the end of the chamber. Now I'm not a genius but I did sleep at a holiday inn express last night and I believe that the case mouth always meets the end of the chamber with authority when we close the bolt on our rimless, shoulderless AR platform cartridges.

You guys having the same experience?
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Re: Bullet Jump

Postby Hoot » Thu Oct 09, 2014 4:17 am

The bullet pull is not unique to your batch. It's been going on for as long as I've been coming here. At issue is the crimp employed by the factory and many who reload for the caliber. It is not as robust as we'd like it to be. If you chrony your rounds, you'll see velocity SDs that would make a bottleneck caliber enthusiast cringe. Not at all uncommon to see velocities vary by as much as 7%. What's amazing is the rounds group tight despite the spread. One solution available for reloaders is the stab crimp instead of the taper crimp. That method was developed by Wildcatter via a modified 45-70 Lee Factory Crimp Die. It essentially stakes the bullets into the case which has a two fold effect. It anchors the bullets in the case better and a secondary effect is that it holds them back a little longer during ignition. That allows the pressure to grow more controllable rate before the bullet releases and that contributes to velocity conformity. Not perfect, but better than just the taper crimp. If you reload for your 450b, there are instructions for modding a 45-70 Lee FCD die in the stickies on the reloading for the 450b sub-forum. If you do not reload, one thing that helps reduce pull is to not chamber, remove and re-chamber any one round too many times as the pull effect is cumulative. If you reload for other calibers, do consider reloading for your 450b as well. It opens up a whole new universe of options available to us for tailoring your loads to your particular mission. Up here we don't have hogs. My 450b is primarily used for brush hunting white tails. They're much easier to kill than hogs. In that mission, its hard to beat the 200gr bullet. Shoots faster, flatter and has the same frontal area as the factory 250. Knocks a white tail arse over tin cups. Lot less perceived recoil than the heavier bullets.

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Re: Bullet Jump

Postby Avenger10 » Fri Oct 10, 2014 7:31 am

Hoot-

Thanks for the info, I'll get started with the 45-70 mod. I spoke with a nice lady goes by the name of Stephanie over at Lee and she said she could make me a custom one for the 450b if I would send her a dummy cartridge. Price was ~ $25.

How well does the stake crimp work with the 250gr Hornadys as they do not have a cannelure band?

Also, have you experimented with not using the expander die to increase neck tension? The Hornadys have a generous bevel on the back end, I doubt we need to use an expander to get these bullets to start straight.

Also, has anyone experimented with the Corbin Cannelure tool on the Hornady 250's?

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Re: Bullet Jump

Postby Hoot » Sat Oct 11, 2014 6:01 am

IMHO, the hardest part of modding a 45-70 die for stab crimping isn't getting the length right. It's narrowing the width of the bite that the collet makes. A narrower bite provides a more assertive hold on the bullet while not disturbing the case and bullet as much as a wider one. I have many Lee FCD for other calibers that I reload. They all are made with a fairly wide bite width. I mention this because I'm not sure that having Lee make you a die, will result in them getting the bite width correct. If they can do that, then the $25 price is quite reasonable.

It would be enlightening for someone to send them a sample case with a narrow bite width and see what comes back from them. The issue for a reloader who does not have a modded die in the first place, to produce a sample case for them to use as a guide. Kind of a chicken and egg conundrum.

If you want to "go the dough", I can produce a narrow bite example for you to send them.

WRT bullets that do not have a cannelure or driving band groove, the stab crimp requires more pressure to produce a worthwhile improvement in bullet hold and it disturbs a little more of the case and bullet, but it does work. In reloading for the 450b using Hornady dies, almost everyone here who does that, does Not use the flaring die. It's not necessary with jacketed bullets and adds additional work-stress to the case mouth brass.

Edit: I forgot to address one of your questions.
Again, IMHO, tools that impart a rolled cannelure after the fact, do not produce the same result as having the factory do it. If you look at a factory cannelure, it is down into the bullet and the jacket on either side is relatively undisturbed. In the home made cannelures I've seen, some of the copper displaced by the cannelure is pushed back up out of the trench causing a ridge on either side of it. That could potentially catch on the case mouth when seating, possibly shearing off small bits that lodge between the bullet or resulting in less consistent neck tension than we already encounter. This is purely speculative as despite having seen home made cannelures, I have actually never reloaded them myself. If a tool can produce a cannelure just like the factory ones, in already manufactured bullets, without allowing the displaced material to rise up on either side, then that would be a useful tool for this caliber.

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Re: Bullet Jump

Postby Jim in Houston » Sat Oct 11, 2014 4:12 pm

Yes, I agree with Hoot (dangerous not to agree with him on this board - you will probably be wrong). The expander die is not required when reloading the 450 BM.

BTW, I have not seen any range reports on the 450 BM's with and without the stab crimp. I have reloaded some of both with the 250 gr and the 225 gr bullets, and as soon as hunting season is over, I will be at the range to chronograph them and will report back.
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Re: Bullet Jump

Postby Hoot » Sat Oct 11, 2014 4:44 pm

Jim in Houston wrote:Yes, I agree with Hoot (dangerous not to agree with him on this board - you will probably be wrong). The expander die is not required when reloading the 450 BM.

BTW, I have not seen any range reports on the 450 BM's with and without the stab crimp. I have reloaded some of both with the 250 gr and the 225 gr bullets, and as soon as hunting season is over, I will be at the range to chronograph them and will report back.


My experience A/B'ing identical loads using stab vs taper crimp has been that the taper crimp yields slightly better accuracy, but the stab crimp yields slightly greater and slightly more consistent velocity. Most of the bullets we load are just as terminal at say 2200fps as 2250fps, so I opt for the taper crimp. Another issue is adjusting your stab crimp for one load, adjusting it for another and then trying to get it back to the first setting is not as cut and dried a process. Better off making several stab dies and keeping one set for each load. Another positive for the stab crimp is that it is not case length dependent. A stab crimp applied to a case that's 1.680 will be the same for a case that's 1.700. That is not true for a taper crimp. With the taper crimp die set at the same spot, the 1.700 case will get a tighter crimp than the 1.680. That's why I sort my brass by resized length whenever possible. I have a large Plano box with large compartments labeled for example, <1.68, 1.68-1.685, 1.685-1.690, 1.690-1.695 and >1.695.

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Re: Bullet Jump

Postby Jim in Houston » Mon Oct 13, 2014 9:41 am

Thanks for the info, Hoot. I would opt for the accuracy of the taper crimp over the higher velocity of the stab crimp. I do not, as yet, sort my cases by length, but I guess I should start and maybe that will bring my SD down a bit. The breakdown into .005" groups is good info.
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Re: Bullet Jump

Postby wildcatter » Thu Oct 16, 2014 4:23 pm

Ok, something not said yet about the various crimps, is..

The Taper Crimp is good and is usually deployed on Straight-Rimless Cartridges (45acp, 9mm lugar, 450b, etc.), but has some bullet drift problems. The Roll Crimp is much better and is usually deployed on rimed cartridges (357mag, 41mag, 44mag, 45-70, belted magnums, etc). Using a roll crimp on a Straight-Rimless Case is a recipe for inviting excessive head space and is dangerous in nature.

Buttt.. The LeGendre-Side-Crimp solves both of those problems and though it isn't unique, it is effective. By deploying this "Stab-Crimp" (if you will) you still get the effects of normal head spacing and a much more effective crimp, albeit further down the case wall, and is, as I said much more effective, than say the Famous Roll Crimp, making the LeGendre-Side-Crimp the best crimp (over-all).

Of course, one could manually load your 450b rifle, putting the cartridge fully into the chamber, then let the bolt fly, snapping the extractor over the rim. In this way you usually won't get any or much bullet drift? But then even this method is fraught with occasional problems. I like the LSC so well I use it on nearly any cartridge and fit my needs well. Unless you are a benchrest shooter the LSC is your Baby..

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Re: Bullet Jump

Postby Texas Sheepdawg » Thu Oct 16, 2014 11:03 pm

The first thing I do is that I taper crimp my rounds (.476"-.475").
Then I apply the LeGendre Side/Stab Crimp. See video.
Then after I apply the LSC, I taper crimp one more time (.475"- .474") to remove any possible bell that the LSC might have created.
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Re: Bullet Jump

Postby Jim in Houston » Fri Oct 17, 2014 1:13 pm

I side crimp first, then do a taper crimp to .475 +/- to remove any "belling." I do not do the first taper crimp mentioned below.

There are instructions on how to use the taper crimp elsewhere - http://450bushmaster.net/viewtopic.php?f=5&t=685. The video shows placement of the crimp, which was always a question and is somewhat subjective, except, of course, it needs to be on the bullet and close to the casing mouth.
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