NEW TOPIC: Increased Air Pressure on the Front ..

[Lindy]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

I was referring to the way Lex Talus FFS uses the DK, which you want to compute at the longest possible range, and then not change.

I don't have Infinity 6 running on my current system, which is running a Vista OS. Sierra doesn't guarantee that Infinity will run on Visa. I quit running Infinity years ago because it wouldn't ouput settings in mils, and I may be misremembering how it works. It would seem odd, though, that they would publish multiple BCs in velocity ranges, but their program wouldn't use them.

 

[Triggerfifty]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Yes, if you put a different ammo temp into the program (70 is the standard), the program will vary the MV based on the ammo temp. This is based on military cartridges that are selected on a curve or temp range variations. It's not perfect as there are thousands of powder combinations, but it's for military applications anyway.

For example, if you put in an ammo temp of 100, the MV will be adjusted by 100 fps for the military .50 ammo. All other outputs will be adjusted accordingly, elevation and windage.

Trigger

 

[Tribe]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Not to throw a fork in the road... but I've been trying to come to terms with this "Transonic Zone"... and how to determine where it actually lies, and what effects it truly has, for some time now.... seems to be somewhat of a moving target...

Trigger... you frequently refer to that final percentage of supersonic flight, as a critical region, and where all factors seem to jump to the fore... if you don't mind, could you throw out a "meat and potatoes" overview for the unwashed?

Thanks
C

 

[The Mechanic]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

it floats like fog on a lake.

 

[Triggerfifty]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Sure,

A couple of examples of this zone are:

7.62mm M118 and M118 LR rounds, 1000 yards supersonic range, the final critical zone of the supersonic range is 900-975, guesswork is okay to 750, past 750 requires math and serious thinking.

300 Win Mag with A191 round (190 gr. Sierra MK @ 3000 fps), 1400 yards supersonic range, critical zone is 1300 - 1375 yards, anything past 1200 requires math and serious thinking, (computer calculated solutions)

338 Lapua with 300 gr. Sierra MK, 1600 yards supersonic range, critical zone is 1500-1575 yards, anything past 1400 yards requires math and serious thinking.

Another way to look at this is that any school trained shooter can handle 75 % of any gun's supersonic range 75% of the time in 75% of the conditions. Anthing greater than that approaches the definition of luck (if you believed in luck) or computer support for a 1st or 2nd round strike.

Another way, the shooter is the most critical part of a sniper team in that first 75% scenario, in the remaining 25%, it's the observer with the fire control that has the more difficult job, the shooter is relegated to pulling a trigger and making sure the gun is loaded, but with a bolt open on a hot chamber

Does that clear anything up? I've trained and used this explanation for so long that sometimes I don't bake it down enough.

Trigger

 

[CoryT]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

With the Pejsa method and DK, the change in the closer part of the curve is less than an 1/4 minute, therefore it's basically invisible. The advantage to this system is the ability of the user to create the values based on actual observed performance, without the need for Doppler radar. Multi BC's are nice, but require a bit of random poking about to get calibrated. The ABC software, (now sold via Aquilo International http://www.aquilointl.com/ and called FieldCraft) has the BC's already in place, but what if you use a bullet not in the library?

QuickTarget is only on the desktop, but uses a Cd, or coefficent of drag rather than the G1 or other drag functions. That's a very accurate system, right till the bullet stops moving, but very few mfg's have Cd data for their bullets.

 

[CoryT]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Trig, I think that explanation of the 'zone' covers it perfectly. While I always have the computer it really only becomes a requirement at the extended range of the cartridge, when the data in a dope book is just not enough info to compute the actual solution with a high degree of reliability.

Some people shoot so often in a limited set of conditions that then can in fact get a good solution out there, then feel that it's really no problem. Throw in a nice 5000 foot change in elevation, woodland to desert terrain and watch the fun begin!

 

[Triggerfifty]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

That's for dang sure. Reminds me of an ex-wife that was so flim flam at life, she thought it all happened on autopilot, and was "entitled" to blah blah blah (enter glib statement here). Wait, I must still have issues with her

Nice butt though!! Like the T-shirt says "I hate to watch her leave, BUTT I love to see her go" or something like that, applies either way you bend it.

Duck, or wear thicker armor...

Trigger

 

[Dogtown]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Triggerfifty</div><div class="ubbcode-body"> Anthing greater than that approaches the definition of luck (if you believed in luck) or computer support for a 1st or 2nd round strike.</div></div>

On a side note, I think this is a very good definition of luck: variables at play.

 

[Tribe]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Is the critical range in the above BC table, right around 2,100 yards? Where the BC's begin to drop, and also seems to coincide with last 25% of max range as listed?

 

[Triggerfifty]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Tribe,

Good observation, the above .50 round is the M8 API, which has one of the highest BCs of the conventional .50 rounds. It is better than the much talked about Mk211-MOD-0 round. The average 3000 yard BC is .709, well above the .660 of the Mk211 round, giving you more supersonic range than MK round. Supersonic transition in the posted BCs, however, do not accurately reflect the stability of the round at supersonic transition. Conventional projectile shapes like the military rounds actually "handle" the transition better and may stay stable through transition.

This can't be translated to other conventional designs though and seems to be established more by bullet weight (lighter conventional designs don't handle the transition as well, the 168 gr. Sierra MK for example begins to tumble right at transition range).

Seeing a gradual climb in the BC values after transition is normal in all designs. Here's the paradox, VLD designs such as the AMAX, 773 Gr. Lost River match and the Barnes solids handle the transition less well, and destabilize faster than do ball rounds. BUT, the tradeoff is that the VLD designs have a farther supersonic downrange point, so it's always a tradeoff.

One thing not yet discussed here (though it's not part of this subject) is that barrel interface with the VLD bullets is critical. The controlled spin patent aspect of Cheytac's bullets may arguably no longer exist because of changes in barrel specs. The 408 is a better near range grouper as a result of these changes, but downrange supersonic range has gone down at some point.

Recently though, 408 419 gr. projectiles manufactured by Cheytac in their Jamison Internation facility in South Dakota are so well refined that the BC of the 408s 419 gr. bullet is now a higher supersonic average number, giving the 408 a supersonic range of just under 2400 yards, up from the previous value of 2200 yards SAC. A rough average BC supersonic value of this better projectile is .960, up from the .932 average from 2001-2002.

Things to ponder.;.

Trigger

 

[The Mechanic]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

I think a lot of that is due to the tungsten core (very dense better than lead) on the API a many have used these in matches to great success. They shoot very well out of my windrunner even when pulled and resized they will group at or below 1MOA and seem to be very stable no matter what distance shot at.

 

[Triggerfifty]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Mechanic... touchdown. The tungsten core does raise the SD of the projectile, same length as the Mk211 and M33 Ball, but because of the badly selected 1:15" twist for nearly all .50 BMG barrels, the higher SD is better stabilized over the long range than are the M33, Mk211 rounds. The barrel twist is a compromise with all these varying weights, but works the best witht the SD and metal comosition of the M8 API round. DM4 and DM43 headstamps shoot incredibly well through guns, even the M107 POS (Piece of Shit). 1:16 works better with the M33 and Mk211 rounds. In my data tables, I use the same data for both of these rounds.

With the twist rate in mind, the AMAX round and the 773 gr. Lost River bullet would both have much higher BC values if they were correctly stabilized with barrels of a tighter twist, giving better downrange stability. Right now, with the 1:15 barrels, both rounds loose supersonic range and the ability to stay stable through transition downrange.

Trig

 

[Triggerfifty]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Here are a couple of examples of how fast the 300 gr. and other long projectiles can destabilize. The 1540 yd group is about 50 yards short of the calculated transition point. 1500 is about 50 yards PAST supersonic transitional range. It was cold, about 20 degrees, with some dense air, no wind. So, now why the LEFT deviation of shots, even with spin twist calculated into the shot placement?

 

[The Mechanic]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

20 degrees I would say velocity went down unless barrel and ammo temp was kept up. Also dense air lowers supersonic even further. Keyholes seem to be in same direction so maybe magnus got them started and destabilized in one direction?

 

[Triggerfifty]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

The ammo temp did go down, H1000 was the powder in those loads, which is temp stable for the most part. Biggest issue was much denser air at that air temp. Not sure about the angle of the keyholes, it's in the subsonic range. You can see what happened to the size of the group from 1400 to 1500, 2 of the 3 are on the target, 40" apart, 3rd was off the target. From sub MOA to more than 3 moa in a short distance. Seems to be the nature of the 300 gr. bullet tho. It's a great bullet as long as it's supersonic.

 

[The Mechanic]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

It seems as though both keyholes are point left

 

[Triggerfifty]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Just a wrap up on this subject.

This phoenomonon continues to happen. It is partly controllable with some planning and assumptions. Trouble is plans never survive first contact, assumptions are, well we all know about assumptions. It is a narrow spectrum event, and if the assumptions are carefully managed, you can shoot into these zones.

Just like ignoring sping drift and the earth's rotation (at ranges that mean the difference between a stike and a miss, you can't ignore them. It's about keeping the circular capability of the gun and shooter centered over the center mass of the target. Assuming that the little 6" error is "no big deal" means that the 6" is now outside of the error budget of the shot, or meaning, your shot checkbook is now half as valuable as it used to be

Not good.

Observations:

Long and high BC bullets of the VLD design are more susceptible to this event. Shorter, heavier, and standard configuration bullets like the military .50 bullets (M33, M8 API (choice), M20 APIT, Mk 211, are better at handling this zone.

Longer and higher BC bullets have trouble transitioning from supersonic to sub-sonic flight without destabilizing totally and going end over end by the time they are transonic.

Error budget, error budget, error budget...

 

[lrs50bmg]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

I could be mistaken, but I always understood the M8 API to have a hardened steel core (Magnanese-Molybdenum Alloy), not tungsten.

The M8 API does have a greater sectional density as the greatest proportion of the core is the penetrator. In the Mk211 you have multiple components, and the penetrator is much smaller in relation to the M8. I will try to post a schematic to show the differences.

Scott

 

[Triggerfifty]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Yep, Scott you're right on the MK211 having smaller parts. The BC of the MK 211 is also lower than that of the M8 API.

.675 3000 meter average for the MK211

.735 3000 meter average for the M8 API (DM43)

All of a 29" 1:15" twist barrel, so these BCs are a bit flawed. Cause 1:15 is a bit fast for both of these projectiles.

 

[lrs50bmg]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Here is a schematic of both rounds:

The real winner would be the Canadian C88 APIT round:
A true tungsten core, albiet at 900 grains!

Scott

 

[Greg Langelius *]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

The Pejsa calculations deal with a 'break velocity' and the internal program notes comment that for most bullets, this velocity corresponds to about 1300fps. I think it goes without saying that this velocity will likely be significantly affected by density altitude, and I believe that the given figure was chosen with some healthy 'fudge factor' consideration. For my purposes, I enter a value of 1100fps; and count on the individual bullet's characteristics to navigate this zone with better than average panache. I also think that actually driving bullets into this zone at around 1100fps carries an accuracy penalty that may not be present when shooting into this zone with an additional 100-200fps of velocity.

Greg

 

[Triggerfifty]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Greg, not sure I understand. The fps speed is a speed zone. 1125 fps understandard air conditions is the supersonic threshold. The distance downrange at which this point occurs is the issue. I agree that there is an accuracy penalty at 1100 fps becuase this is after transition to subsonic flight.

The issue being the DISTANCE downrange at which this velocity transition happens. Can you explain what you're indicating with what you say...

"I also think that actually driving bullets into this zone at around 1100fps carries an accuracy penalty that may not be present when shooting into this zone with an additional 100-200fps of velocity."

Trigger

 

[The Mechanic]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

I ripped the penetrator out of an AP and I use it for a center punch. It seems heavier than just hardened steel. But the profile is the same as your diagram of the M8.

 

[The Mechanic]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

OK Looked on BiggerHammer and it looks like they did have a tungsten core.

 

[Greg Langelius *]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

I think that playing in the transonic risks the consequence of reduced stability. Better to stay above 1300fps; very little more to my meaning.

While I realize that going transsonic is not good for accuracy, I also think there will be bullets which handle this transition better than others, and that going transsonic, and subsonic, is not necessarily a death sentence for accuracy. The more critical issues may involve terminal performance, moreso than basic accuracy.

This subject is not really inside my comfort zone these days, my practical application suffers from a lack of suitible venues that I can reach in my current situation. I tend to be tethered a lot closer to home lately, and the one near enough facility I frequented is no longer available.

Greg

 

[lrs50bmg]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

The diagram you have from BH is for the M2 AP (Black Tip), not the M8 API Silver tip. I was only referring to the M8. Note also the core is listed as a tungsten/steel alloy. Definitely heavier than other steels, but still not as heavy as a pure tungsten core. The M2 AP's were the most accurate of all the old military projectiles. None of the more modern API projo's do quite as well.

I would love to get my hands on about a thousand of the M2 AP projectiles!!!

 

[The Mechanic]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

This is were I got my M2's
http://www.hi-techammo.com/hitech.zkb?menu=0&method&home-page
shows to be temp out of stock but hi tech almost always have them. Most of the time I can just tell them as from the weight difference 640 to 650 as apposed to 690 700 for the tungsten. I do see what you mean on the tungsten chrome steel designation instead of a pure tungsten core. They are just real accurate out of my Windrunner even the pulled and resized ones have all been under 1 MOA and have had 200 yard 4 shot last time out close to .5- .6 so at the price you just cant go wrong.

 

[Triggerfifty]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Greg, I agree that some projos handle transition better, absolutely. From our radar measurements, it's the conventional designs, not the long nosed VLDs. The VLDs just push out the supersonic range given a bullet of the same weight and velocity through increased BC.

lrs50...

I like your observation, the M2AP also did very very well with a 3500 meter BC average of .732 and a SSR range of 1600 respectable yards, about like a 338 Lapua pushing a 300 Sierra MK.

Mechanic... gotta love those windrunners huh? You need a shroud like cheytac uses on the M200 series guns, makes the windrunner such a damn sweet shooter!!

Kind of busy at the hospital this week, guys, sorry for not posting on the other topics, good discussion going here.

Trigger

 

[lrs50bmg]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Mechanic,

I just picked up ~ 350 M2 AP's down here in Raton. I'm here for the FCSA Nationals, and one of the vendors had a partial can. It took a little talking to convince him to sell them all to me, but I prevailed

I agree they are the best bet in a mil projectile.

Scott

 

[The Mechanic]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Are they already sized? that I guess is the key to them. I would pick up a sizer but all of the ones I have bought so far have already been sized. I tried out ones with some pretty deep scratches just to see what they would shoot like and they have all shot well.

 

[lanwickum]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

Another solution for your first problem trig.

Don't think the wind direction at shooter has much to do with this and is usually fairly calm when this happens. Air layers near mountain terrain. Cold or warm air layers near mountains. At 1800 yards the bullet has a fair arch to it. As the bullet skims through these layers it has a slight deflection to it, maybe up or down depending on how it hit that layer. When the top of the arch of flight is just hitting another layer of air is when this is greatest. All kinds of rather drastic vertical deflection going on here. This can be pictured well with fog coming off mountains.

This have much truth to it?

 

[JRose]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

My head hurts... I'm gonna come back to this when I don't have so much stuff on my mind so as to absorb / decipher some of this.

 

[lrs50bmg]

Re: NEW TOPIC: Increased Air Pressure on the Front ..

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: The Mechanic</div><div class="ubbcode-body">Are they already sized? that I guess is the key to them. I would pick up a sizer but all of the ones I have bought so far have already been sized. I tried out ones with some pretty deep scratches just to see what they would shoot like and they have all shot well. </div></div>

Mech,

Sorry for the delay, was driving back from Raton (1250 miles).....
These were already sized. They also had the scratches on them from the puller when they were disassembled. Good to know the scratches don't affect the accuracy.

Scott