Ultimate Neck Tension

[Hoot]

I've said this before, but it bears repeating. If the bullet and powder are a good fit, neck tension doesn't factor in that greatly in velocity and accuracy. Lucky for us that Lil Gun is a wide ranging powder for the bullets we generally use. Still as you go toward light for it, neck tension does factor in. Similarly, if you go with a slower powder, neck tension once again becomes an issue. I have tried several times to get AA1680 to work with the common 300gr bullets at our disposal, walking away from it as simply too great a mismatch, then coming back with a different approach. Today, I tried the ultimate neck tension solution and my final attempt at getting those two to get along. I seated my bullets so as to engage the lands of the rifling. That's not anew trick in terms of maximizing accuracy, but probably so for trying to get the pressure up high enough to burn the powder efficiently in my 20" barrel.

I did not feel the endeavor was reckless as 1680 is a sleeping giant of a powder that has so far not managed to get going with 300gr bullets using other tactics. Starting a tad lower, I worked up through excessive waste. From the first step, I was already throwing powder out the bore so bad as to have to move the chrony 22 ft away from my muzzle (as far as I could go) in order to escape the ERR01 and odd, low readings 701-706fps. Luckily I brought 5 sighters with me to work that out before running for score. In my particular chamber, I could feel the leade start dragging on the bullet at 2.15 COL using the Hornady 300gr XTP Magnums and at 2.22 COL I ran into the hard stop of the lands. That's what I went with for this test. Here's the brief range of loads I tried:



That's the standard template I use for up to 8 loads. As you can see, despite the bullets all being right up at the doorstep of the lands, velocities were still all over that place and more importantly, the velocity change per 1 grain steps are less than they should be. Using the 250 FTX with Lil Gun, that 4 grain range would have resulted in several hundred fps change. There were no pressure signs whatsoever and the feel was that these were gentle recoiling loads for such a heavy bullet.

Despite loading to the lands usually being the ticket for some particularly accurate results in smaller, bottle necked calibers, it was no panacea for these 300gr hollow points. I get much better groups from the 240gr XTP Magnum.



While I'm certain some of you may differ with me on this opinion, I believe that for our 1:24 twist rifling, you need more RPMs to stabilize them and tighten up the groups with a 300gr bullet than can be achieved at velocities I was able to achieve with 1680. My particular barrel loves 2200fps. It also likes 38gr of Lil Gun. When you can get one, the other, or both in your load, it seems like it's hard to go above 1.5 MOA at 100 yards, providing you do your part. Regarding that, I had near ideal conditions today. Starting temp was about 65 degrees, zero wind, reasonable humidity and best of all, no one else at the range. Those kind of conditions are conducive to me finding my groove and staying in it. Despite feeling like that was the case, the groups were not what I'm accustomed to achieving. As a matter of fact, the couple of times I ran these and other 300s over either 296 or Lil Gun, though they felt fast for that weight of bullet and more finicky, I did manage better groups.

I've served my time with both the 300gr class of bullets and with AA1680, as in the last straw. I'll leave future development of them to others who are more interested in throwing heavyweights down the range. Though my results were less than stunning, it was rewarding to finally scratch an itch I've been wanting to do for some time and that was shoot some load in this caliber with the bullets loaded to the lands. You really can't do that with tipped bullets unless you're running an Olympic UMAR lower or shooting a mag with the C_bass16 single stack slot mod done to it. If I ever get those black followers, I will entertain modding one of my mags to do just that. Admittedly, I never tried IMR4227 with the 300s, but I've already got more powder now than I really want for this caliber. If they were a weight I was actually interested in, perhaps I would have tried it, but IMHO, they're excessive for white tail hunting and it's hard to fine the wallet once again under those circumstances.

Another plus from today's range visit was to test out my latest iteration of my spin on gunnut's recoil reducing stock sing my home made spring weights. In this case, the several smaller diameter, longer weights in parallel and utilizing different strength springs produces a pleasant buzz in place of the kick we normally associate with this caliber. There are four 19/32 diameter tubes of different lengths cast into fiberglass resin. The shortest one is still empty, as I slowly scrounge up enough mercury to to try in it for additional interaction with the recoil impulse. That's a lot of surplus mercury wetted relays, old thermostats, old thermometers, etc to scrap out, but I'm getting there. Then again I digress.

Good Luck to those who walk the path of the heavier choice bullets in this caliber. I will enjoy reading of your exploits.

Hoot

[Wicked Hunter]

I may have to try some more of the 300's through my 20" Bushmaster. My Trident upper shot its best groups using the 300gr XTP Mag bulets over 39.5gr of w296.

[Hoot]

When I typed this last night, I forgot to mention something. I am usually a proponent of loading bullets with cannelure so that the taper crimp at the mouth is driven into it. Given their length you can load the 300gr XTP Mag all the way out to maximum magazine capacity and still have at least half the caliber inside the case. There is a caveat in my report that I didn't emphasize. For those who like loading any bullet that can be loaded to maximum COL, all the way out there, read on.

If all your chambers are cut the same as mine, then in the case of this bullet. If you load it to 2.26 COL or more, you will probably wind up driving the bullet back into the case during chambering due to it running into the lands while the cartridge is still being driven from behind by the bolt. My chamber has around 1650 rounds through it and may have begun eroding slightly. Hard to say as my only experience with that has been in the arena of bottle neck calibers. The point being that your chamber and especially the point where the lands occur may be even shorter than mine, which equates to pushing the bullet even further back into the case, wedging it tightly in the barrel, or both.

Besides the inconvenience of having the bullet stuck in the barrel should you need to extract the cartridge without firing it, the other concern is incurring a different pressure than you intended for the load you're working through. I highly recommend that folks who reload buy themselves a Hornady (Formerly Stoney Point) Overall Length Gauge and case for the 450 Bushmaster. It allows you to check how long a particular bullet can be loaded before engaging the leade and lands. A very useful tool. I have cases for every caliber I load for.

Luckily, only a few of the 45 caliber bullets (mainly the heavyweights) have stubby noses and are long enough to still obey the "half caliber" insertion depth rule of thumb, yet run into the lands. So this is not what I would call a prevalent issue in this caliber in an AR platform. This got a lot wordier than I intended, but I felt it rated mentioning in the name of safety and as always, that's part of being Hoot.

Hoot

[Hoot]

Copied from another thread:

...snip...Question for Hoot. Those loads, wherein you were hitting the Lands, were you out over 2.260 oal? My question is because we are supposed to have a .200" free-bore, so it should be impossible to hit the lands and still have the cartridges stay "Inside" of the mag??
..t

The 300gr XTP Mags are .82 inches long. seated .295 inches into the case, those blunt noses go from the case's 1.695 out to 2.22 OAL where they stop firmly against the lands. If you turn the bullet around backwards so that it's heel first (IE immediately .452 not tapered), you start encountering taper at 1.961 COL, or .266 from the mouth with the case inserted until it thunks, as opposed to being held closely to the bolt face.



Luckily we're not shooting wadcutters. As a reference to chamber depth for my particular rifle, the maximum case length my chamber will allow the bolt to close upon is 1.74 or 4/1000 past spec for the chamber lip, so there's a little leeway but I'm not complaining. For those with a Hornady/Stoney Point overall length gauge I referenced, if you want to compare apples to apples, the Hornady 250gr FTX bullet, deployed in my rifle, hits the lands at 2.45 COL.



So, loading the 250gr FTX to 2.26 COL, it jumps .19 to the land. In the interest of scientific objectivity, despite the fact that I'm a fastidious cleaner every 20 rounds during load development and JB Compound every 200 rounds, there's always the remote possibility that I have buildup in my rifle. I have never had it scoped, but my gut feeling is that buildup is not a significant factor in my readings.

Hoot

[Siringo]

This is probably off topic but --- I have found the best method for good neck tension is a clean neck. No powder residue ----- I bought a ultrasonic cleaner and could not believe how dirty the inside of my cases were. One set had to have been shot upward 15 times, plus run thru a tumbler ---- I had to wash them several times to get all the burn up carbon out of the inside.

With the 300's I found in my carbine that a resized 300 grain hornady .458 diameter shot the best groups. Nice short bullet --- which seems to stabilize in the 1/ 24" twist. The worst was the 300 grain FXT -- that bullet is to long. The best load was 30.5 grains of LG w/WSR primer for the Hornady 300. However, I have come to the conclusion for my usage that the best bullet is ---------------------------------------------- the 250 grain FXT.

Regarding Tridents barrels --- they are not a direct comparison to the bushmaster barrel. If I recall, they have a 1/16" twist and are .451 inch diameter. That would be a big help with the 300's and maybe explain why the throw better groups with that bullet versus the bushmaster barrel.