I'm starting a thread, that may end up being very short, but it's germane to my current endeavor and some here will be able to help me through it.
This is a spinoff from the long but otherwise excellent Long Range Rifle Discussion thread. Some will remember that in that thread I recently experienced something not quite an epiphany, more like a revelation, when offgrid brought up the Hornady A-Tip bullets in the discussion. I dismissed the Hornady bullets out of hand due to past experience, but fritz brought up facts and good arguments in favor of the A-tips, something frowned upon in Internet discussion groups. Since I respect both offgrid and fritz, I went off and did some research.
What I found out caused me to actually order some A-tips and start looking for a load. (Yeah, offgrid and fritz were not wrong; in fact they were very correct.)
Now, I mentioned on the thread that 230gr is heavy for F-TR, where the .308 Winchester is the biggest caliber allowed, but I would try them any way, due to the allure of the BC, .823. This is a full 140+ points higher than my current bullet, the 210gr JLKLBT. I should also note that I am forced to look for another bullet due to the fact the sole maker of the JLK bullets sadly passed away about 4 months ago. Whatever bullets I have left in my stash are the last of the JLKs.
So, I started doing some research and experimentation to come up with a load. My first stop was Hodgdon and of course they do not have a load for a 230gr bullet in .308 Winchester. The heaviest is the 208 A-Max, from which I derived my 210gr load.
So, I turned over to Quickload and discovered that what I was envisaging as a starting load would produce pressures of 80,000 PSI. Not good. The load that would provide by with a velocity of 2500FPS produced 65,000 PSI. I wanted to be closer to 62,000, the maximum SAAMI pressure for the .308 Winchester. My current load with the 210, produces 59,500 PSI according to Quickload.
I was falling into the old geezer trap of focusing on an issue and ignoring the importance of the parameters. I wanted to be at 2500FPS, which was 100 FPS less than my current load, but it would produce the same elevation and 1MOA less of wind displacement at 1000 yards.
I kept thinking that the faster the bullet goes, the less time is spent in the conditions and the less a bullet is affected by the wind. I wanted to stay at 2500FPS because my JBM run gave me 1MOA better wind at 1000 with that compared to my current 2620FPS of my 210 JLKs. In my mind, if I slowed down the bullet, the drift would increase and I would lose the advantage of using this beautiful, heavy, expensive bullet.
This morning I woke up with an idea germinating in my head. I took my usual 2 mile walk during which I continued to mull this over to the beat of 1970’s disco sounds. I was working out in my mind that BC is the criteria, not speed. The amount a bullet is moved by conditions is a function of the differential between the time spent in travel in air compared to the time spent in travel in a vacuum. Even though the 230 would start slower than the 210, it would arrive at the target at the same time as the 210 and at a higher terminal velocity. That’s what JBM showed me.
The fact is, the difference between air time VS vacuum time should be consistent; it should make no difference how fast I started the bullet, provided it was fast enough to get there in the first place.
So when I got back, I started punching numbers in JBM and sure enough, at a saner velocity, pressure-wise, the windage for 10MPH, full value, is 5.7MOA compared to 6.9MOA for the 210 @ 2600FPS. Over 12 inches less wind at 1000 yards.
The elevation will be a little more, another MOA or so, but I have a dial on top of the scope for that eventuality.
I've known for a long time about the difference between ToF in air and ToF in a vacuum is what BC is all about. I think my issue is that this REALLY comes into pay when you get into big BC values and there's a significant difference in BC values between bullets. To me, it simply was not intuitively obvious that velocity played a lesser role here.
This is where it's important to understand the parameters and play out the scenarios ahead of time. Now, my plan is to load up 5 different loads and take them to the local range to try them out on paper to see what the results will show and then take the best one and load up for a match. I have the cases all ready for this and I will be loading this up in the next week or so to test next weekend and be ready for the next 1000 yard match.
Another aspect of the load is the seating depth of the bullet. I like my bullets to be seated where the pressure ring, if there is one, or what it should be if there was one, is just below the junction of the shoulder and the neck. This leaves the boat tail only to intrude in the case.
As it turns out, the boat tail of the 230 A-tip is the same length and size as the boat tail of the 210 JLK. I have been playing with the comparator to see if I can have the bullet seated at that length and still be able to clear the lands. As it turns out the ogive on the A-tip is extremely long so that there is very little difference between that bullet and the 210JLK from base to ogive.
More testing and measurements to follow.
I have 6 loads ready to test. That is one long bullet but the ogive profile is such that I cannot set the bullet to touch the lands in my rifle. That's probably a good thing.
I will run the loads on a ladder test this weekend and pick the best one and load up more for the next 1000 yard match.
Here are some pictures:
I was able to do a quick ladder test today and I found a very interesting load that produces less than .25MOA of elevation and out of a 5 shot group, i essentially have one ragged hole with another hole to the left at the same elevation.
The velocity is about 60FPS less than what Quickload predicted, but I believe that may be due to somewhat loose neck tension.
I'm going to try some rounds at 1000 tomorrow after some maintenance work on the range. If the elevation works out as predicted by JBM, we are in business.
I find what you are doing, majorly intriguing and have always had a very deep respect for snipers and their ability and need and ability to adjust for wind and conditions and consider it amazing that someone can hit targets with precision at 1000 yards or more/less. Can you post some of your targets and groups?
The longest range in my entire county is 100 yards. I can't image a 1000.
|Knows too little |
about too much
TL Davis: “The Second Amendment is special, not because it protects guns, but because its violation signals a government with the intention to oppress its people…”
The urge to save humanity is almost always only a false-face for the urge to rule it. -H. L. MENCKEN
‘70s music? I feel so old...
Do not meddle in the affairs of wizards, for thou art crunchy and taste good with catsup.
I have stated many times in the past; I am NOT a sniper, nor do I have delusions of being one, play one or TV or would ever be able to be one.
That said, I am simply a long range competitor with a few medals, titles and plaques to my credit.
I do not ever posts targets or groups. We shoot for score on a well-understood target, with published dimensions. For example, the X-ring of the 1000 yard F-class target is 5 inches in diameter (just under 0.5 MOA.)
Yesterday I went to the local range to do the quick ladder test. This morning, I left the house at 5:15AM on my way to the big range to do some work on the targets and to try out a few rounds after the work was finished. JBM had specific predictions for come up differences from my current load and a terminal velocity number. My mission was to see if I could confirm those figures. I dragged my rifle and a minimum amount of ancillary equipment to the firing line after the work was finished. I was exhausted and literally soaking (dripping wet)from sweating profusely. The sun was very hot this morning and we were out in the open, no cover, for the work. I was shaking a little bit. (Age + heat + outside work = exhaustion ). I took my first shot and nothing showed on the target. I had forgotten to put in the come-up difference (age). I held at the top of the target and the second shot recorded nicely. I put in the elevation correction that JBM had predicted and took a third shot help center and fired. Nothing on the target. I realized I had turned the elevation knob the wrong way and corrected that (heat exhaustion). I took the fourth shot holding center and got perfect waterline elevation. I took the fifth shot holding the waterline and applying for wind and shot an X, a dead center X according to the display. By that time, some of the other guys were coming over to sniff around, I closed my ammo box and stopped firing, I was done for the day. I was ready to pass out anyway and I had my numbers.
This stuff is working out precisely as predicted by JBM using the figures from the manufacturer and the MV as measured with my MagnetoSpeed V3. It was awesome to see the bullets going precisely where the exact corrections were predicting. We are talking to the 1/8th of an MOA here. I spoke to one of the F-Open shooters (not someone who would compete against me,) and we discussed the numbers and the results. He's a little bit of a scientific shooter like I am with the numbers and the observations and we have a lot of fun discussing this subject. He was taken aback by the results.
If you remember the comments in the OP of this thread, where I was talking about the difference in the velocity in air versus the velocity in a vacuum as being the measure of the efficacy of the BC in a bullet. I told him what my MV was and the final velocity at the target (a by-product of etargets.) The rule of thumb for high BC bullets is 100FPS per 100 yards of travel. Put another way, an excellent bullet will lose 1000FPS over 1000 yards. He has heard of some newfangled bullets cutting that down to 900FPS for 1000 yards. My delta is quite a bit less than 900FPS, and at sea level. My current load with the high-BC JLK 210 bullets has a delta in velocity of just under 1000FPS for 1000 yards.
Mission accomplished, thanks offgrid and fritz.
More info to come, but I am playing this one a little close to the vest here. BTW, the recoil was very nice, it's a shove not a sharp hit and the cases look very nice with no bolt lift issues whatsoever. This leads me to believe QL was being very conservative here, we shall see.
I said '70s DISCO music. There is no such music from the 50s and 60s.
|Retired, laying back |
and enjoying life
You and fritz need to keep your heads down because if the prairie dogs ever find out it is you two I'm learning so much about hitting them out where they think they are safe they are going to put out a contract on you two. Please keep the info coming.
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A question that is somewhat tangentially relevant to the BC topic. I have a .308 semiauto that I've been able to take out to 300 yds. After trying numerous hand loads and high vs low BC bullets I've actually found that my hunting bullet (150 grain Nosler partition) shoots the tightest groups. I have shot factory loads and hand loads of various powders and bullet grains on many different occasions but the Nosler partitions always group sub MOA and better than any other load. Any idea why this low BC bullet is shooting tighter groups? My initial thought is that it is due to barrel vibration or resonance.
A quick answer is that BC has nothing to do with the precision of a bullet. Benchrest shooters are notorious for using low BC but highly precise flat base bullets.
I'm uncertain I deserve any real credit, as I just relayed what I saw and what was stated to me -- by shooters with greater understanding of flight ballistics than I.
My frustration began with the poor tracking of Hornady 6.5mm 147 ELD-M to JBM ballistics. Then discussing it with a squad member who was shooting quite well with 150 SMK loads. Then I heard he did just as well, if not a little better, with Hornady's new A-tip bullets.
I'm just a weekend warrior who wants factory ammo to shoot reasonably close to factory ammo. Maybe one day it will occur.
I hope the A-tips work well for you, NikonUser.
Every barrel is different. I have one AR-15 barrel that shoots its tightest groups at 100 yards with Hornady 55 Vmax ammo. But I don't compete at 100 yards.
I need ammo that holds wind well at 300-600 yards, with good vertical consistency. Bullets that weigh 69, 73, and 75 grains drift a whole let less than those 55 grain bullets. What little -- if any -- that I lose in vertical consistency is greatly overshadowed by the heavier bullets' ability to reduce horizontal wind drift.
As I explained in the other thread, I was simply not aware of the A-tips; Hornady is just not a bullet company to which competitors look for long range F-class level bullets. That market is owned by Berger, with a few boutique bullet makers who charge very high prices. My last experience with Hornady was 10+ years ago with their A-max bullets and their inflated BC value; that had soured me on Hornady.
What you and offgrid did was to make me look again and get past my long-time disdain of all things Hornady. You each carry enough weight that I really would have been a fool to ignore your observations on Hornady in general and some reports on the A-tips in particular.
I explained how I had to get it through my head again about the benefits of ultra high BC values. The consensus in F-TR right now is a Berger 200-20x as fast as possible. It's a game of MV with the hope that a so-so wind call will not hurt as much as the bullet spends less time in the wind. I'm looking here at a velocity that's a couple hundred FPS less than their loads, but the BC is so much higher the A-tip will arrive at the same time as their bullet, with a higher terminal velocity and a whole lot less lag time. Wind reading is still critical, but I may save a point or two per match, and that counts.
Good friend gave the 230 A-tips a go in his recently built 300PRC. No buenno on the A-tips.
Rifle specs: Kelbly Black Bear action, 28" Brux barrel, NF 7-35, 338 CIP mags (max OAL 3.8ish), TBAC Ultra338 suppressor, McMillan A5. Chamber freebore cut for the 225 ELD's.
He worked up loads with 4 bullets. Order of performance. Hornady 225 ELD, Berger 215 Hybrid, Sierra 200 SMK and Hornady 230 A-tips. He does all his initial load work up at 850yds then goes to 1350 and 1660. Range is on private land 5 minutes from his house. I didn't write down how far he was jumping the A-tips to mag feed, jumping them a lot. He also single fed them with a few different jump length... Rifle was built to shoot a 2100yd max Magnum match in Raton, single feeding not a problem. He wanted the A-tips to work because of the BC. Published BC did track at 1650. The 225 ELD's at 2900 is no slouch in the BC department. He's giving the remainder of the A-tips to another friend with a 300 Norma Mag who shoots the Berger 230 Hybrids with good results.
I shot this rifle a few times. The Kelbly Black Bear is very nice action, very smooth cycling, fit and finish first rate.
Thanks for the report, offgrid. I noticed that you did not give the most important datum on the barrel, the twist rate.
Also, I know this is going to expose me to ridicule here and get me banished from Wisconsin for the cheese festival but I'm not a fan of Brux barrels. I'm not saying that's the reason. Just a comment.
At any rate, if the barrel does not like the bullet, then you look for another bullet. I stop at 1000 yards anyway.
On the other hand, I am a huge fan of Kelbly's products.
So, has a Brux barrel out shot you in a match?
A little slow, but that's not the problem, methinks.
As for Brux barrels, I'm sure they are fine now. I just have a long memory and I'm a big fan of Krieger barrels.
I've been beaten by all great brands of barrels, and I've beaten all brands of barrels.
Keep in mind our altitude. We do load work up at 5200' on the private range. Magnum match in Raton 6700' another match in Wyoming 7500'-8000'. My home ranges 7700' and 8500'.
Most everyone around me has or is shooting a 6BR. We have a saying when comparing calibers, loads... Is it BR (6BR) accurate? BR easy to tune? It shoots OK, it ain't no BR. My buddies 300PRC with the 225 ELD or 215 Hybrid is BR accurate.
I too been beaten by all the great brand barrels and have beaten them all.
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