More on 160-gr bullets: Need for Speed Part B

[pitted bore]

Post #1
This thread is an update describing some of my recent trials with the Barnes 160-grain bullet. (As usual, the verbiage-to-shot ratio is pretty high.)

Standard Warning: For the work described below I used a bolt rifle with a 0.451-inch barrel, which is rather different than the AR-based rifles usually used with this cartridge. If you try to duplicate my results with a different rifle, different components, or different techniques, really bad things may happen to your firearm, or to yourself, or to persons standing near you, or to your dog, or to a passing tweety-bird. Be careful. This information is coming to you via the internet, where untruthful persons post untruths and truthful persons make typing errors.

The last results in my work with lighter bullets was posted on this thread: The Need for Speed, Part A - Preliminary Trials. The objective of the work is to explore what velocities can be safely obtained with the cartridge. Using lighter bullets usually allows increased velocities, but conventional wisdom and techniques do not always work with straight-sided cases.

The lightest .451-452 bullets that are readily available are the Barnes 160-grain all-copper bullets. Last fall, using this bullet with a case full of 2400, I recorded a velocity of 3100 fps on my chronograph at 10 feet from the muzzle. This was obtained using my Springfield 1903 bolt gun with a 20-inch barrel.

Barnes designed these 160-grain bullets for the GAP cartridge. The bullets have been supplied with two different Barnes product numbers: #45165 in boxes of 20, and #45106 in boxes of 40. The first, an XPB type, may be no longer manufactured. The second, the TAC-XP, is the current form. Barnes says their various XPB and TAC-XP bullets are "similar". For the .451" 160-grain bullets, I could find no measureable differences whatsoever.

This bullet creates problems in handloading for the 450B for two reasons. Problem #1: The bullet's maximum diameter is only 0.4500, so that the case doesn't really squeeze the bullet after normal FL resizing, as it would a 0.451 or 0.452 bullet.

Problem #2: The bullet has tapering sides. The taper is intentional. Barnes writes in some of their reloading information: "The Barnes #45165 160-grain XPB bullet has a slight taper on the base to prevent bulging of the case wall once the bullet is seated. Only a slight amount of case mouth belling is needed prior to seating the bullet in the case." From the viewpoint of 450B reloading, there is too much "slight taper".
The bullet tapers from its too-small 0.4500 diameter midway in its straight size to only 0.4450 at the base. When loading, if you taper crimp this bullet after it's seated, the case might grab the bullet tightly at the mouth of the case, but not so tightly down the length of the bullet. This is a problem in this cartridge, because sufficient case mouth tension is critical to getting the powder to burn properly.

The image below may make the point clearer. (The black front end of the bullet is a shadow, not bullet coloring or coating.)

Forum member rohk has noted in another thread that the similar General Bullet 160-grain hollowpoint bullet is consistently 0.451" in diameter. That should make that bullet much easier to work with.

(Continued below in Post #2)

[pitted bore]

Post #2

I've written elsewhere on the forum that I recently took delivery on a bolt gun with a 26" barrel. { LINK} I decided to try some 160-grain bullet loads in the rifle, using 2400 powder. I loaded five rounds with 51 grains in new Hornady brass with CCI #41 primers. OAL was about 2.120".

Even trickling the powder down a 24" drop tube produced a compressed load. Getting the bullets to seat firmly was a problem because of the bullets' taper. Using either or both the Hornady or Lee taper crimp die, a couple of the rounds had the bullets loose in the case. This probably contributed to the observed wide variation in muzzle velocity.

Warning: This load likely produces pressures over SAAMI specs (38,000 psi) for this cartridge. After firing these loads, I measured case head expansion of about 0.0007" just in front of the extractor groove. (In contrast, my measurements of fired factory rounds show zero expansion.) Otherwise, there were no signs of excessive pressure, such as ejector-cavity marks on the case heads, flattened or cratered primers, hard bolt opening, etc. I hope to have some actual psi data for this load before too long.

At the range, on a target at 100 yards the shots from this load impacted about 10 inches above a Hornady factory load. After I lowered my point of aim, the three shots that landed on my target grouped in about five inches. The chronograph was nine feet from the muzzle. Velocities were 3226, 3132, 3226, 3038, and 3179 fps, for an average of 3160 fps, and a very large extreme spread of 188 fps.

Temporary conclusion: 2400 can make these bullets go pretty fast. A faster powder is likely to produce excessive pressures before giving equal velocities. A slower powder like Lil'Gun or 296/H110 will not produce equal speeds before running out of room in the case. Maybe there exists a "magic" powder of approximately the burning rate of 2400 that can produce equal or higher velocities before exceeding available case volume. I've got a couple yet to try.

[pitted bore]

Post #3

Forum member rohk produced some really interesting results in his work with the General Bullet 160-grain clones of the Barnes GAP bullet.
Link. I decided to follow his lead, and made a trial using the 160-grain Barnes GAP bullets with 51 grains of Lil'Gun, CCI 41 primer, COL 2.160, in cases that had been fired 4X.

Cases were FL resized. It was not necessary to use the expander die to seat the bullets. In fact, to try to get the case to hold the bullet, I squeezed the neck a bit with the Lee taper crimp die before seating the bullet. One set of five loads received a side crimp with the modified Lee 45-70 factory crimp diep; the other set of five loads did not.

I used the new Model 70 bolt gun (26" bbl) for testing these loads. At the range I posted a 100 yard target and set up the chronograph at 9 feet from the muzzle.

The uncrimped loads produced velocities of 2846, 2932, 2843, 2871, and 2913 fps, for an average of 2881 fps. The crimped loads were a bit slower: 2824, 2862, 2846, 2880, and 2820 fps, averaging 2846 fps.

Group size of the uncrimped loads was about 2 inches. The five crimped loads went into just a bit less than an inch. Image of the target is below. This looks pretty good, and whether it's a one-time fluke is an open question.

There were no signs of excessive pressure on the cases and primers, or in the behavior of the rifle. I've used up to 54 grains of Lil'Gun with crimped-in 185-grain bullets Link, so more velocity is possible.

More later.
--Bob

[Hoot]

Great work Bob!

I'm surprised though that your velocity went down with the FCD crimp. With Lil Gun, every load I ever did and I admit none were with bullets that light, nor charges that heavy, the velocity went up with the FCD, whether by itself or along with a taper crimp. I always assumed that by holding the bullet back more, the powder got turned on more and that contributed to greater attained velocity. It sure did produce a good group for you. Gotta love those Barne$ bullets. Not cheap, but very consistent from one to the next. At least the ones in the box of them I bought were.

Hoot

[wildcatter]

Doc's work is never boring.

With speeds and groups like that..well..Listen, I've got this ache in my shoulder, can you do anything for that?

I'm with the Hoot, using the SC always gives me, anyway, slightly higher speeds, as it does allow the powder to start cooking very efficiently before it releases from the case. The proof of this is that great group, but then of course, I need some more of that pudding, but just for medicinal reasons, mind you..wink..

..t

[pitted bore]

I'm surprised though that your velocity went down with the FCD crimp. With Lil Gun, every load I ever did and I admit none were with bullets that light, nor charges that heavy, the velocity went up with the FCD, whether by itself or along with a taper crimp. I always assumed that by holding the bullet back more, the powder got turned on more and that contributed to greater attained velocity. It sure did produce a good group for you. Gotta love those Barne$ bullets. Not cheap, but very consistent from one to the next. At least the ones in the box of them I bought were.

Hoot-
I was also surprised that the average velocity was higher for the uncrimped rounds, for the same reasons you state. However, I'm not ready to conclude that the velocity differences are real and repeatable.

Here are a couple of thoughts about it.

1) Because these bullets have the unusual taper from midpoint to base, I modified the usual reloading procedures to try to accomodate this. The Hornady FL sizing die didn't size the case necks enough to hold these bullets firmly down the whole length of the bullets. So, to make the case necks smaller after FL sizing, I pushed them a ways into the Lee taper crimp die. The cases emerged from the die looking somewhat like one of the old black powder cartridges with a body just a bit larger than their straight neck, like a 38-40. I'll try to make some photos.

With these shrunken necks, the bullets required more than the usual force in seating. With this procedure, the side crimp may not have added much to the tension/friction retaining the bullet in the case.

2) The uncrimped loads showed more variation in velocity. For uncrimped, SD=40.0 fps and for crimped, SD=25.4 fps. This result is expected from our thinking about the effect of the side crimp.

With the small sample size of only five observations each, I am not goint to conclude that the uncrimped velocity is really higher. Given the variability in the uncrimped velocities, the average uncrimped velocity might be lower than the crimped average if I were to repeat the trial.

However, I thought the result was interesting enough to report it. I probably should have also given the SD values, which do follow the current ideas about the side crimp.

--Bob

[pitted bore]

Doc's work is never boring.

With speeds and groups like that..well..Listen, I've got this ache in my shoulder, can you do anything for that?

I'm with the Hoot, using the SC always gives me, anyway, slightly higher speeds, as it does allow the powder to start cooking very efficiently before it releases from the case. The proof of this is that great group, but then of course, I need some more of that pudding, but just for medicinal reasons, mind you..wink..

..t

T-
See my reply to Hoot about whether the higher average velocity of the uncrimped rounds is "real". And you're absolutely correct, that more pudding/trials are needed to make any real conclusions. My single small group is indicative, but not conclusive. If the rifle/ammo combination was actually a 3-inch performer, the chance of getting the 1-inch group is pretty small the first time out.

About your shoulder: Stop pounding it with the recoil of your heavy artillery. Forum member "wvcruffler" is a real doc, and will probably tell you the same thing.

--Bob

[Hoot]

...snip...
With speeds and groups like that..well..Listen, I've got this ache in my shoulder, can you do anything for that?

...snip...
About your shoulder: Stop pounding it with the recoil of your heavy artillery. Forum member "wvcruffler" is a real doc, and will probably tell you the same thing.

--Bob

From an old episode of Hee Haw:

Patient: "Doctor Doctor, I broke my arm in three places!"
Doctor: "Well, stay out of those places."


I must have used that exchange a million times since way back when I first saw it. Most often at work when someone is moaning about something they already know the answer to. In Tim's case it was a rhetorical remark, but I still love using that exchange whenever possible...

Hoot