The Need for Speed, Part A - Preliminary Trials

[pitted bore]

Post #1
This thread is a report of some initial trials with lightweight 160-grain bullets trying to obtain high velocities in the 450 Bushmaster.

(Standard Warning: For the work described below I used my bolt rifle, which has a 1:16" twist barrel with 0.451" grooves. I don't worry about pressures for reliable semi-auto operation. If you try to duplicate what I did using different rifles, different components or different techniques, bad things may happen. Be careful. Don't forget that this information is coming to you via the internet.)

After I made my first post in mid-May 09 on the calguns.com 450B thread, our fearless Wildcatter pointed out the possibility of working up to some pretty giddy high velocities with the bolt gun. He specifically mentioned 3000+ fps. I was interested, and started to look for light-weight bullets that might be up to the job, since lighter bullets generally go faster than heavier.

The lightest weight bullet I could easily find in catalogs was the 160-grain Barnes bullet manufactured for the 45 GAP. It was a bit pricey for a lot of trial-and-error exploratory work. I spent my initial efforts with the 185-grain Hornady fully encapsulated SWC instead. My intent always was to use the 160-grain Barnes bullets after learning enough to try them without wasting a lot of them.

I finally obtained 3000+ fps with the 185s and reported it here in May this year. LINK. The load was a compressed charge of Lil'Gun with a heavy crimp. Accuracy was about 5 moa.

After breaking the 3000-fps barrier, I decided I was ready to try the 160-grain Barnes bullets. Here's an image of that bullet linked from Midway's web site:



These are made with a fearsome-looking hollow point that is really deep. Measured dimensions on the lot of these bullets that I purchased: Length = 0.6655 +/- 0.0005"; Diameter= 0.4500" +/- 0.0001". The depth of the hollow point was about 0.40", or 60 percent of the bullet length.

I've attached some photos I made of the bullets.

Barnes TAC-XP 45 GAP 160 Grain Hollow Point Lead-Free Bullet

gap_top2.jpg (22.5 KiB) Viewed 16876 times

Barnes TAC-XP 45 GAP 160 Grain Hollow Point Lead-Free Bullet

gap_top3.jpg (22.68 KiB) Viewed 16876 times

Barnes TAC-XP 45 GAP 160 Grain Hollow Point Lead-Free Bullet

gap_top1.jpg (35.96 KiB) Viewed 16876 times

edited to update link to Midway image - June 2013

[pitted bore]

Post #2
For the initial shooting trial with the 160-grain bullets, I assembled five rounds in 4X fired Hornady brass with Win SR primers, using 51, 52, 53, 54, and 55 grains of Lil'Gun, the same weights of that powder I had used with the 185 grain trials that gave more than 3000 fps.

COAL was 2.125". I used the minimum neck expansion that would allow the bullet to enter the case. The bullet pressed solidly onto the powder in the last two charge weights. I did not want to compress the loads, since as far as I know no firm decision has been made about the desirability of compressing fine-grained powders. I crimped the bullets with the Hornady taper crimp die, but not with the modified Lee 45-70 Factory Crimp Die.

An image of a loaded round and bullet is attached below, showing for comparison a Hornady factory 450B round and a 250-grain FTX bullet.

I shot the loaded rounds in May 2010, with the temperature at about 50 F. The chronograph screens were 10 feet from the muzzle. The barrel was fouled with about 20 assorted rounds previously fired. Velocities and observations were as follows:

• 51 grains = 2746 fps, sooting half the length of the case
• 52 grains = 2805 fps; sooting a third of the length of the case
• 53 grains = 2932 fps, sooting a quarter of the length of the case
• 54 grains = 2913 fps, ditto
• 55 grains = 3011 fps, ditto

There were no signs of excess pressure. I shot these at a 50-yd target, and the last three shots went into 7/8 inches.

This was encouraging. However, the sooting and lack of pressure signs even with a case full of powder indicated that perhaps Lil'Gun was too slow for this bullet weight.

[pitted bore]

Post #3
Because Lil'Gun appeared too slow when used with the 160-grain bullet, I decided to move to a faster powder. According to several burn-rate charts, after Lil'Gun the next-faster powder in my cabinet was 2400. I'd tried this powder in some work with the 185-grain bullets, but had encountered pressure signs before achieving velocities equal to Lil'Gun. I made up five cartridges using 43, 44, 45, 46, and 47 grains of 2400, loaded as above.


I fired the series in mid-May, with the temperature at about 55 F. The chronograph screens were 9 feet from the muzzle. The barrel was fouled with about 25 assorted rounds previously fired. Velocities and observations were as follows:

• 43 grains = 2826 fps
• 44 grains = 2863 fps
• 45 grains = 2900 fps
• 46 grains = 2983 fps
• 47 grains = 3014 fps

Again, there were no obvious signs of excessive pressure, but there was little case sooting. On my 50-yd target the group was about 3" center to center (6 moa).

[pitted bore]

Post #4
Since 2400 had behaved reasonably well with the above series, in August 2010 I tried another set of 5, beginning where the above series left off, loading as above using 47, 48, 49, 50, and 51 grains of 2400. These were fired with the temperature at about 82 F. The chronograph screens were 10 feet from the muzzle. The barrel was fouled with about 40 assorted rounds previously fired. Velocities and observations were as follows:

• 47 grains = 2940 fps
• 48 grains = 2971 fps
• 49 grains = 2991 fps
• 50 grains = 3064 fps
• 51 grains = 3100 fps

Again, there were no obvious signs of excessive pressure, but I'll not go higher. Pressure at 51 grains was sufficient to expand the cases so that they did not rotate in the chamber when I unlocked the bolt. On my 50-yd target the group was about 4" (8 moa).

Preliminary Conclusions
The max for my setup is about 3100 fps. I won't try for more than this with 2400 powder. Perhaps there' s a powder between 2400 and Lil'Gun that could support more speed with this bullet weight in this case, and I'll entertain suggestions. Meanwhile, I'll try to obtain more positive accuracy estimates, and try to recover some of these bullets from expansion media to see how they look. After all, the 160-grain bullets are intended for less than half the speeds to which I'm driving them.

The gaping hollow point should guarantee a good SPLAT, but the solid base construction might permit some notable penetration. I hope to find out.

--Bob

[BayouBob]

Those loads ought to just short out all the circuits on an old boar hog!

[wildcatter]

Bad Bob, PM me for an address. I have my pressure goodies set up and running. I have Certification Loads, directly from Hornady, so we will have very accurate read-outs and totally Apples to Apples comparisons. If you'll send me ten cartridges, I'll get you pressures for your top load(s) of lil-gun and 2400

A thought here: have you dedicated a case with a 1/4" hole through the primer pocket, so you can get the exact amount of powder, in grains, in the case? I assume you have and you can't get any more lil-gun into the case. For you guys that don't know what I'm talking about, here goes.

The goal here is to determine the maximum a mount of a particular powder that can fit into a case. CAUTION, just because we have found the max amount of a particular powder that will fit into a case, DOES NOT mean that, that amount of powder is necessarily safe to use. However, what it can tell you is this, if you do hit the max powder wall, by slowly working up the load, safely, and you still don't have enough pressures, determine by any number of acceptable ways, then another powder is indicated. As always, this is not for the new guy to try, for there is much to be determine, in order to keep you weapon in one piece and your health intact.

Sacrifice a case and drill a 1/4" hole through the flash hole. Now seat the targeted bullet to your chosen OAL. Now carefully fill the case, with powder, through the flash hole. When the case is full, place the cartridge between the your middle finger and thumb, with the thumb covering the flash hole. With the cartridge pointed toward the floor, use the back of a kitchen knife and tap the case many, many times. Now when you take your thumb from the flash hole, you'll find that the powder has settled and that you can get more powder into the case, do so, and repeat the process, until there is no more powder can fit into the case. After repeating the process, many times, empty the powder from the case and weight that charge. That "Particular" charge weight, for your bullet, that was seated to your chosen OAL, now generally represents the perfect amount for a max charge, with minimal compression and will be a reference point, only, for future work, with that powder and bullet combination, again, this is not necessarily a safe load and is only a reference tool, for working up a loads. This is but one tool, there are many other considerations when reloading, if you are new to reloading, you must read all of the reloading manuals and discuss much before you starting shooting YOUR recipes, for if you have a blow up, don't even think about suing, because you are the only perpetrator to that crime.

..t

[wildcatter]

Bobber, with that long dissertation, I might have not made the point. If you can get more lil-gun into the case and if you'd do a LeGendre Side Crimp AND a Taper Crimp to boot, you might get much better bullet pull, thus igniting the powder more efficiently and stop the sooting altogether, and this with low enough pressures, maybe, maybe not. Assuming you can get more powder into the case and keep the pressures within limits, as per my Tapping suggestion, to see what is the maximum amount of lil-gun that will fit in our case. Knowing you, you've already done all this and my suggestion is redundant, but it never hurts to make sure.

And, when you singled loaded the mags, using your 2400 loads, did the action lock open? For you new guys, this the best indicator that the load might be a good working load, assuming it isn't locking open because the action is over-working?..t

[pitted bore]

And, when you singled loaded the mags, using your 2400 loads, did the action lock open? For you new guys, this the best indicator that the load might be a good working load, assuming it isn't locking open because the action is over-working?..t

T-
You're slipping there, guy. A couple of months ago you managed to remember that I'm shooting a 1:16" twist barrel, and here you are now forgetting this is a bolt rifle. <grin>

If my action should lock open, I'm in deep doo-doo, 'cause an open bolt will mean the bolt has sheared off the two front lugs and the safety lug, and the mortician will have to tug on the bolt to try to get it out of my brain pan.

Back when this rifle was another caliber, some too-stiff loads locked the bolt closed and I had to yank pretty hard on the bolt handle to get it open. That was a major oopsie, with too much powder and pressure. And that's why now I'm pretty cautious in working up loads with increasing powder charges.

I've described above my stop-and-back-down point - - When a case expands on firing so that it doesn't turn in the chamber when the bolt is opened; then it's time for me to quit upping the pressure. In this rifle this locking occurs at pressure levels below any other signs of too much pressure. The factory loads don't expand sufficiently to cause this, and until I've got actual pressure data, I'm not inclined to push past this point.

While I haven't done the test for max powder capacity you describe, I'll agree that it's a pretty good one. What I have done in the past is use a 3- or 4-foot-long drop tube made from taped together plastic soda straws for trickling stick powders like IMR-4350 into bottle-neck cartridges; this can produce even tighter packing than tapping for those combinations.

However, the tapping technique you describe works well with ball powders, and does permit a squidge more (like 0.2 grains) powder to be crowded into a case than an ordinary slow trickle, with or without a drop tube. But, as I have said, I really don't want to compress ball powders like Lil'Gun. When I've broken down some of my unfired heavier Lil'Gun loads, I've had to dig the powder out of the case even when I've tried my best to avoid compression.

PM being sent.

--Bob