I finally fixed the broken image links due to an ISP change several years ago
I'm a big proponent of substantial neck tension with the 450b, especially when shooting the lighter bullets with Lil Gun. Seems like the words too much and neck tension are an oxymoron when considering this caliber and lighter bullets. That was up until last Friday. Tim (wildcatter) had reported rave results using the Barnes 200 gr XPB loaded as long as the magazine allowed and having a stab crimp applied to the rearward driving band groove. Notice the term driving band as opposed to cannelure. Cannelures are intended to bite into with your crimp for additional neck tension. Driving bands and their respective grooves are intended to reduce the amount of bearing surface between the barrel and bullet.
Here the two are side by side:
In the past, several people myself included, documented the process of modifying the Lee .45-70 FCD to allow using it to produce both good mouth crimps and side stab crimps. That effort left me with one wide (original) jawed and one narrow jawed version. The narrow jawed version being more appropriate for stab crimps. Using the same Lil Gun charges I already documented in Parts I & II, but loading to catch the rear driving band groove with the stab crimp as opposed to the front with the taper crimp, I seated 8 steps of 5 rounds, ranging from 38gr to 45gr of Lil Gun. That seat used as much of the magazine as I felt comfortable with, 2.29 inches COL.
After seating, I ran all 40 cases and 2 additional experimental sets of 5 through the taper crimp set to yield .475 mouths right at the very edge of the mouth, as measured with a quality micrometer, not my less accurate caliper.
After the taper crimp, I ran all 50 through the narrow jaw, modified Lee FCD stab crimper adjusted to catch the rear driving band groove and in the case of the control groups, the rear cannelure of the Hornady 200gr FTX. That's cannelure, not driving band groove. Keep that distinction... Lo and behold and not to much surprise, as a result of the amount of plunge that the case wall makes into that driving band groove being so close to the mouth, the mouths developed a flare.
Out of concern for catching the edge when chambering as well as whether they were too wide now at the mouth to thunk, I re-ran them through the taper crimp again, with just enough crimp to take the flare off.
All being right with the world, Friday morning (I took a day's vacation to get out while it was not hot) I headed to the range in my wife's Taurus. This point marks the beginning of my "cluster-xxxx", wasted, vacation day. On Wednesday evening, my wife and I dropped my F150 at the shop to see if the front end could be aligned without replacing any of the 12 year old front suspension parts and put the key in the drop slot. Those were my instructions to her and I assumed that was what she told Bill the local repairman. During the work week, the truck sits parked due to the cost of fuel and we car-pool. I drop her at the Park-N-Ride and I drive the remainder of the 25 miles to work and back home, picking her up from the Park-N-Ride later in the afternoon. Saves us a fortune in gas. Anyway, I heard nothing from Bill Thursday as he was backed up. Friday morning, I drove up too the gate at the range and have that sucker-punch in the stomach realization that my range keys are in the truck. I drove back into town to the shop and there's a hand written note declaring that they're Closed Friday Due to Funeral. Through the bay door, I could see my truck up on a lift, locked safely away. I returned to the range and waited for some other misguided soul to drive up and let me in with them. After a half hour, I called Ray, the Pistol Range Coordinator, who lives close and asked him to come over and let me in. Of course, while he was in transit, a member showed up and let me in. While I was setting up my gear on the rifle Range, Ray drove up looking disgruntled. After everything quieted back down, I snuck the water shot jugs out of the Taurus trunk and set them up, keeping an eye on the road leading to the Rifle Range.
For clarification: Our club sits on the outskirts of the greater Minneapolis Metropolitan Area and we operate under a tight Conditional Use Permit due to folks living near the range. They're S.O.L. regarding the noise, but we have to be very safety conscious. Nothing but paper targets on the backstops in front of immense dirt berms. Being the Rifle Range Coordinator, I'm supposed to set a good example. Nuff Said...
Having already tried a load reduced in velocity to simulate 300 yards, I brought the next step up in velocity to simulate 250 yards. If you read Parts I & II, guess what? This time, not only did I get to see the water spout out of all 7 jugs, but I got to actually see the dirt puff way downrange as the bullet waived Bye-Bye to the last jug:
I stood there wishing I had packed 7 more jugs in the Taurus' trunk and brought the 200 yard simulation cartridge. Oh well, I still had a fist full of targets and a mission waiting for me that promised hours of fun waiting for the barrel to cool.
The fouling shot using my Gold Standard 225gr FTX, taper crimped over 38gr of Lil Gun. clocked through the traps at 2221fps and hit .5 high .25 right of the bull. Away we go!
I started out with 38gr of Lil Gun and the Barnes with the experimental crimp. Low by standards, but that's how i like to approach changes in what I know that works. Two shots later, I'm checking the chrony which was still in the shade and finally, I shot another fouling shot 225 FTX. Spot on. I finished the remaining two shots of 38gr and poured a cup of coffee from my thermos while the barrel cooled. The thermometer I bring every trip said it was 74 degrees in the shade with a barely detectable 2 o'clock breeze. As I sat there measuring the spent brass with their .503 case head expansion and light ejector marks, while musing over the five shot average that was 137fps faster and 210fps faster at the extreme than the last effort with only a taper crimp, I wondered how I would fare at 45gr of Lil Gun, like Tim reported having shot safely. Never mind the near 3 MOA awful group.
I had with me two experiments. One being the somewhat faster Vihtavuori N110 that I tested last year with lackluster groups despite excellent SDs, using 200gr FTX bullets and the second being 38 grains of Lil Gun and the 200 FTX but instead of seating them short and taper crimping the front cannelure, I seated the to max magazine length and crimped the rear cannelure using the same amount of stab crimp force as the Barnes 200gr ones I just shot. The N110 group had no previous load tested at 38gr of Lil Gun, so nothing to compare to. Same lackluster group.
Next, I shot the five 200 FTX with the rear cannelure stab crimp and they were faster than the previous time I shot them using front cannelure taper crimp and the resulting group was quite nice. File that away for future experiments. Case head expansion was only .5025, so I was also happy with that.
Just a footnote worth mentioning. My resized brass typically mics around .501 to start with. That how my dies came and they still have plenty of wiggle room in the Bushmaster chamber, so NBD.
So, faced with what to do, I chose to try the next step 39 gr of Lil Gun. Again, I saw an increased five shot velocity average of +153 fps with an extreme again over 200fps. Again a ho-hum 2+ MOA 100 yard group and lots of ejector and the beginning of extractor marks on the case heads along with case head expansion to .504 and strong chamber wall imprinting. The highest 39gr velocity extreme of 2595 fps, in loads that previously yielded 2435 and that with a hotter mix of powder left me a little spooked facing 40 through 45gr loads still remaining. Add to that, the temperature was about to go up to the upper 80s as the shade diminished and the sun hit zenith.
Now I'm just a mere mortal. I still have everything I was born with. Some a little worse for wear and tear, but I really like keeping it that way. Not being independently wealthy, I do not have an inexhaustible supply of new rifles and ammunition. I decided to live to fight another day. No telling what would have transpired as I progressed from 40 through 45gr, but I didn't want to find out. It really sucks having to pull down all those nice loads.
...but, they aren't going through my gun. I have no problem milking all the available safe energy from a powder's burn, but I do not want to try to proof out a series of controlled explosions.
I do not re-use powder, primers or bullets once they've been loaded as a rule. I will inspect those expensive Barnes bullets and check their diameter. If they can be re-used, I certainly will, but not if they're off enough to skew results from some future experiments.
In conclusion. It appears that the crimp strength of those deep, sharp shouldered, driving band grooves exceeds what we're accustomed to seeing from cannelures. Perhaps a less firm crimp would yield better results, but it's hard to adjust a variable Lee FCD while applying shim washers to the ram so that they crimp exactly the same pressure every time, at the top of the ram stroke and the repeatability is always a crap shoot after you knock down your setup. I'll be content as a bottom feeder and leave these strong crimps to braver souls. Hating to be wasteful and before I pull these down. If some other braveheart want's to sign a statement of indemnification, they are welcome to shoot these beauties through their gun. Pitted Bore has a bolt gun. You interested Bob?
I don't want the brass back as this style of crimp and bullet leave terribly strong scars that don't iron out.
Strike Three!
I'll be back with other experiments using these fine bullets, just not a repeat of this one. If no one wants to further the cause of knowledge at their own risk, I will pull them and if they're still usable, I will load them long, but with just a taper crimp like we do with the 250's. There is still worth in long loads. I still want to revisit N110 and 2400 is in the batter's box. Also, those 275s are chomping at the bit. They also have great promise. More Water shots to follow.
whew...
Hoot