Moderator: FYI, our new guide to the 6XC cartridge and 115gr DTAC bullet, written by David Tubb, is now on-line: 6XC Cartridge Guide.

You may also want to check out 115gr DTAC bullet specifications by Henry Childs in our enhanced Articles index. Click on the "Articles Archive" tab on the left margin.

Last Edited Guest on Nov 6, 2004 9:58 AM

Thanks for the update. We received an email from a visitor to the site asking how much the throat needed to be extended. I replied we would measure the bullet (David has promised samples), but we were guessing the 115 ogive would be between .040 and .050" closer to the lands than a 107. Looks like that was a pretty good assumption.

Depending on ones seating length for a 107 smk, that might not be an issue, given the long neck of the standard case. But with a Dasher case, as you point out, one would probably have to seat the bullet down into the powder.

Thanks for the good words but it is a bit of a stretch to say I helped design Tubb's 115 grain, 6mm SMK. David sent me 50 to try. I ran various tests on the 112 grain and 115 grain, offered a couple of suggestions which Mr. Tubb did not adopt.

Henry

Last Edited HBC on Oct 29, 2004 4:37 AM

3-------1.302" long
17------1.303"
91-----1.304"
171-----1.305"
85------1.306"
32------1.307"
10------1.308"
2-------1.309"

The base to ogive length of fifty bullets were measured and found to vary no more than 0.0005" which is exceptional compared to other SMK bullets. A 0.210" diameter comaparator was used to reduce the wedging of the ogive into the comparator and giving false readings.

Henry

Last Edited HBC on Oct 30, 2004 5:29 PM

7/18/2004
(16) rounds, avg. muz. vel. 2372 f/s, avg. BCg1 = 0.543

8/2/2004
(10) rounds, avg. muz. vel. 3053 f/s, avg. BCg1 = 0.563

Rev.: From the above data, the best fitting drag function is G2 w/BCg2 = 0.270 (based on tables from SAAMI)

The second best fitting drag function is G5 w/BCg5 = 0.352 (Based on tables from SAAMI. Also choose G5 drag function in the Oehler BEX program and input BC = 0.352.)

Henry

Last Edited HBC on Oct 31, 2004 7:06 AM

Yes, I have measured the 6mm, 105 grain Scenar at BCg1 = 0.51 over 288 yards. That is close to what Lapua reports, which is a BC of 0.50.

I believe the Tubb 115 gn. would have a little BC advantage over the 105 Scenar (considering that the Scenar would have roughly a 5% higher muzzle velocity over the Tubb 115) but I would choose the bullet that shot best in my rifle, based on significant testing, preferably long range testing since it is likely there are not too many chronographs that can accurately measure velocity extreme spreads and SDEV's.

Henry

Last Edited HBC on Oct 31, 2004 10:22 AM

Paul

No tests on the .224, 90 gn. JLK but Otto Holmberg gave me one to measure. It looks like a mineature Berger, 6mm, 115 grain VLD and weight wise it scales to the same form, i.e. (.224/.243)^3*115 = 90.08, thus the BC should be very close to (.224/.243)*0.60 = 0.55. That BC for the JLK should be pretty close because both bullets appear very similar in form. I have measured the Berger 6mm, 115 VLD at BC = 0.60.

Rev.: Looking into my data, I find that all dimensions for the .224, JLK 90 grain bullet are entered and the estimated BC is 0.51. Thus it appears one could expect a minimum BC of 0.51 and possibly as high as 0.55.

Henry

Last Edited HBC on Nov 1, 2004 3:54 AM

I have not used the newer versions of the Sierra program but believe the older versions did use the G1 drag data with multiple BC inputs for various velocity ranges.

If the Infinity version also uses G1 and you input only one BC value and that was 0.58 then I believe it would give you drop values too low for the .224 JLK 90 grain VLD bullet. I believe the BC of that bullet would be well below 0.58 if determined from the G1 data.

Another point in trying to determine BC based on sight "come up", it is very important to establish the accuray of your sight adjustments then carefully determine the come up from at least a 10 shot group at say 100 yards then another 10 shot group at say 600 yards and carefully note temperature, site elevation and corrected barometric pressure readings for both groups shot. And of course the velocity of both groups would have to be measured with an accurate chronograph. If possible also note relative humidity but it will have little effect.

Rev.: I would also measure your sight radius, measure the sight movement for the adjustment you made at Phoenix, then calculate the actual moa' adjustment. Also, a stated M.V. of about 2800 f/s does not sound too close.

Henry

Last Edited HBC on Nov 3, 2004 3:13 PM

Ok....the Army Marsmanship unit has determined the BC of the 90gr JLK at
around .560-.565, not too shabby!....Now if you take a trek over to the
Florida Highpower forum there are several threads including a monster of 500+
posts on the 90 in a .223 bolt action with a 30" palma contour barrel, as well
as load data and general highpower type experiences with the bullet. I'd give
it a look just so you can get an idea of what works and what doesn't ...German
Salazar describes the 90 in the 30" barrel as a mini magnum or balistically
superior to a 300WM with 190gr sierra MK, he is getting about 2900fps from the
combo.

My recommendation would be a .22 Dasher with a 28-30" barrel 1:6.5 twist or
1:7 (marginal)using a slowish powder like VV N550 or N560 you should be able
to get 3000-3100 fps with no stress on the case, and being a BR case with some
"improvement" accuracy should be very good...one thing I do know the jlk's
like to be in the lands a fair bit 20 thou in is a good place to start, they
are a little fussy about loading but once you have them working they hammer.
Incidentally the 90 is made with 6mm jackets so they should handle velocity
well..

Henry
I have a 1in7 twist barrel do you think it will work ok with the 90 in a Dasher?

Paul

Last Edited paul on Nov 3, 2004 3:48 PM

Your comment, "marginal" for 7" twist was good.

At 3050 f/s muz. vel., 80 ft. AMSL, 50 F, the .224" cal. 90 grain JLK would have an Sg = 1.29 per my calculations. That is too low. I would not want to shoot in a long range match with anything lower than Sg = 1.4 and would prefer 1.6.

For the same conditions and a 6.5" twist, Sg should be around 1.5, which is much better.

Rev.: Here is a test for the 90 grain JLK and someone who has an 8" twist barrel and lives at around 2000 ft. AMSL or a little higher. For a muz. vel. of around 2800 f/s and temp. of 50 F or higher, Sg for the conditions in this paragraph would be about 1.06. At 10 to 20 yards the bullet would likely yaw baddly, making oblong or key holes but at 100 yards or more, Sg should have increased enough that the bullet holes are round, if you can hit the target.

Henry

Last Edited HBC on Nov 3, 2004 5:03 PM

One way to look at BC claims is to calculate the form factor, which is sectional density divided by the BC. Many of our long range match bullets have form factors of around 0.55 and down to around 0.48. The Berger 6mm, 115 grain VLD, when one finds a lot with a very small meplat, has a form factor of around 0.46.

I have placed magnesium and aluminum tips on 6mm 107 grain MatchKings which increased the length to over 1.30" and reduced the meplat to 0.010" to get the form factor down around 0.41. The machined Lost River cupronickel bullets in 6mm have form factors down around 0.40 but they have meplats of around 0.010" also. It takes a streamlined bullet as well as small meplat to get form factors down in the low 0.4's.

A 90 grain cal. .224" bullet with a BC of 0.58 would have a form factor of 90/7000/(.224)^2/.58 = 0.442. That is a very low form factor for a bullet with a 0.055" diameter meplat. The sample of the 90 JLK had a 0.055" dia. meplat but of course that can vary from lot to lot. About the smallest meplat diameter I have seen on a commercially swaged bullet, without pointing the meplat in a special die, is 0.050.

Contact the folks who measured the BC of the JLK at 0.58 with Oehler Mod. 43 equipment and ask: What was the sky screen spacing and what was the distance over which the BC was measured? Also, did that 0.58 value represent the high or the average BC of ten rounds or more?

If the meplat diameters on the .224" cal. JLK 90 grain bullets you are shooting is around 0.030" then I would agree that it would likely have a BC of around 0.58. But with a meplat of 0.055", I don't think so.

Rev.: One word of warning on the very small meplat bullets (meplats less than 10% of bullet diameter): The BC can be increased by placing an aluminum tip on the bullet, increasing the bullet length and reducing the meplat to below 10% of bullet diameter but high BC variation will result. I have seen BC variations in a 10 shot group, with the very sharp pointed bullets, vary as much as 13%. A BC variation of 13% will kill a group at 1000 yards with lots of vertical stringing. I know from experience.

Here is a quote from R.L. McCoy's book MODERN EXTERIOR BALLISTICS, p 71, just below Fig. 4.24: "sharp pointed ogives are utterly impractical for either ordnance or sporting use." McCoy recommends a minimum meplate diameter of at least 10% to 15% of bullet diameter.

Henry

Last Edited HBC on Nov 4, 2004 9:07 AM

It finally dawned on me the M43 BC test you were refereing to. Larry sent me a copy several years ago. It is a bit difficult to navigate since the tests are identified with only a sequential number. I found the test for the JLK 0.224" cal., 90 grain bullet over 1000 yards. The sky screen spacing was 8 foot, which is not bad but not good either but 10 rounds were fired for an average BCg1 = 0.502, with a high of 0.507 and a low of 0.492.

Here is the data (average for the 10 rounds) if you want to calculate BC w/your program:

Altitude---3935 ft. AMSL
Temp.------53 F
R.H.-------55 %
Baro.------30.24" corrected (26.16" Hg uncorrected, or local absolute pressure)
Instr. vel. @ screen #2-----3138 f/s (avg. of two M43s)
Distance from sky screen #2 to acoustic target---999.23 yd.
Time of flight from screen #2 to acoustic tgt.---1.321605sec

Henry

Rev.: Sorry, had temp. wrong, 53 F is correct. Also did not include instrumental velocity (kinda hard to calc. BC w/o that.)

Last Edited HBC on Nov 5, 2004 9:49 AM

Does velocity make a lot of difference to usable twist? I see the 22Br produces about 3050 with the 90 JLK, I guess a Dasher should be capable of another 100 or 150fps would this help with a 7” twist?

Thanks

Paul

Not much of an effect on the gyroscopic stability factor, Sg, at least per my estimate below:

.224" caliber, 90 grain JLK VLD out of a 7" twist, 800 ft. AMSL, 80 F, 78% R.H.:

3050 f/s-----Sg = 1.41
3200 f/s-----Sg = 1.42

To really answer your question would take equipment and tests that are not available to me.

Read McCoy's article in the 1996 P.S. Annual about the 30 cal. 168 grain smk. I know that is a different bullet but he has plotted a curve in that article showing the overturning moment Coefficient, Cma, versus Mach number, p.183. The rate of change of Cma relative to Mach number would be roughly similar to other hpbt match bullets. That curve relates inversely to Sg. In other words Sg is proportional to 1/Cma, thus at Mach 3, Sg would achieve its highest value when launched from the same twist barrel since at Mach 3, Cma reaches its lowest value.

In the region of Mach 2.5 to 3 you can see that Cma does not change much, percentage wise. The percentage change for Sg would be exactly the same as Cma but with reverse sign.

Henry

Last Edited HBC on Nov 6, 2004 7:15 AM

No, for shorter ranges I would probably shoot the Clinch River 6mm, 100 grain VLD but I have also used it for 1000 yard BR with good results.

Henry

Given that the 105 Berger and the 107 Sierra bullets have quite close BC values. It follows that the form factors should be quite simmilar since we are looking at nearly identical sectional densities. One could conclude that the difference in ogives between the two bullets is not a major fator in down range performance. If this is the case, it seems then that one should only consider group size and velocity in choosing between the two bullet types. Find the one that gives the best velocity(fast and very consistent) and shoots the smaller groups and your home.

If this view is too simplistic, I would love to hear why.

Thanks,

Scott Parker

Last Edited SP on Nov 6, 2004 2:19 PM

Yes, I think you are correct but there is another dimension. The bullet that does not make it to the target will have a devistating effect on score or group. The Bergers shoot very good but I have had far too many did not make it to the target and I am not alone in that experience.

Henry

Rev: There are multiple reasons after reading Henry's post below. Don't you love it when you learn something
RCole

Last Edited RCole on Nov 6, 2004 10:33 PM

Yes, it is true that the Bergers use thinner J4 jackets. The JLKs do also. However, the JLKs for what ever reason make it to the target as often as the Sierras. It either has to do with the manufacturing process or it has to do with that teeny tiny little rebate on the boat tails of the JLKs. Henry, if you have some insight here, please share.

Thanks,

Scott

Believe me, I have studied the problem of bullets blowing up or probably more accurately stated, distorting in the barrel, than most any sane person would.

It is far more than thin J4 jackets. Bullet makers who extend the lead core far into the ogive are asking for problems. When the bullet reaches maximum chamber pressure of around 60,000 psi, the bullet, depending on mass, bore diameter and friction between the barrel and jacket, is accelerating at around 150,000 g's. That means the mass of the bullet lead core in the ogive is generating a lot of force and pressure. Pressure that the ogive jacket must contain, because the ogive jacket is not supported by the barrel bore. With such high internal lead core pressures, the ogive jacket can distort or crack open and allow the lead core to flow out.

The maximum height a pure lead column can extend upward without collapsing upon itself while accelerating upward at 150,000 g's is approximately 0.065".

I think also, as you do, that the J4's are part of the problem. I have measured the ultimate compressive strength of J4, Sierra and Lapua jacket and find that in some cases the J4 jackets are harder than most. In forming bullets in the point up die, cracks are created in the ogive portion of the jacket. A harder jacket is likely to have cracks form in it than in a jacket made of a more ductile jacket material. When a bullet with lead extended high in the ogive is subjected to 150,000 g's and that bullet also has cracks in the ogive jacket as a result of forming in the point up die, I think you can visualize what might occur to that bullet.

Henry

Henry

Your examination is exhaustive it seems and does make sense.However, how can one justify the fact that I have shot a few thousand 6.5mm 120gr Sierra Spire Points out of my silhouette gun with great accuracy and not a single bullet failure. All shot with high pressure and velocity loads.

My laymans point of view is that there is no single reason for the bullet failures but a synergestic effect of several reasons. Thin jackets, long bullets with the lead cores protruding well into the ogive, and very high rpm required to make the bullet work add up to a tenious existance.There are probably others. Then there is always the slight chance of a manufacturing defect inside the bullet,.... no I do not even want to go there as simply the wind is enough to keep me occupied during a match.
Just imagine the 90's being shot at 3050 fps in a 6.5 twist barrel. The mind boggles at the rpm that the little pill is traveling at and the stress it is being exposed to while accelerating at 150,000 g's . I am utterly amazed that even ONE bullet goes through the paper, but they do with astounding regularity.

Well enough of my rambling.

RCole

Last Edited RCole on Nov 6, 2004 10:11 PM

Exposed lead tip bullets tend to have much shorter ogives than VLD match bullets. One has to consider the actual acceleration of a particular bullet, jacket thickness and the amount of lead that the ogive jacket must support. And there are a lot of other factors, such as condition of the throat and barrel, barrel friction, residue buildup in the barrel, jacked hardness and tensile strength and more.

Henry

Thank you for the reply( replies?). I guess you cannot really compare apples to oranges.

Could copper buildup( fouling) be a contributing factor to bullet failures and if so how much.

RCole

I ahave a Pact professional chronograph. Can this be used to give any reliable velocity information; SD, ES and such? For example, are lower extreme spread values(15fps) from this chronograph any different in reality than higher values(45 fps)?

Thanks,

Scott

I would think copper build up might cause problems with a fragile bullet but how much build up can, I can't say.

Scott,

With today's sky screens, I believe one should have at least 12 foot sky screen spacing to measure velocity extreme spreads with reasonable accuracy. That would give a chronograph resolution of around 4 f/s. A 4 foot screen spacing would give roughly a 12 f/s resolution, which is too much error.

There is an example of sky screen error in PS, June 2001, p. 14. Two chronographs with 8 foot screen spacing were set up and fired across simultaneously and the two #1 screens were close together. The difference in the average of ten shot groups of those two chronographs ranged from 1 f/s to 11 f/s. That is based on 10 shot averages, if individual rounds had been compared, the difference would have been greater. Only about 1/2 f/s of that difference can be accounted by the bullet loosing velocity over the short distance from midpoint of one set of screens to the midpoint of the second set of screens.

Henry

Here is a Berger test:

BC TEST 7/21/2003
Berger 6mm, 105 grain VLD, moly coated, received 6/17/99 from Berger Bullets, Glendale, AZ.

Cartridge: 6mm WMSC, 49 grain water capacity Load: 39 gn. H4350, WLR, virgin Lapua brass turned in lathe for 0.002" total clearance. Bullet TIR 0.002" to 0.007" for 0.005" avg. near meplat. Base to ogive dimension of bullets from this lot was very consistent, varying less than 0.002". Thus, the longer bullets have a longer ogive and smaller meplats than the shorter bullets.

Barrel: Hart 28" long, 8.3" twist with 942 rounds fired previous to test.

Test equipment: Two Oehler M43's w/sky screen spacing of 24 feet, acoustic targets at 101.6 yards (Unit A) and 287.6 yards (Unit B).

Conditions: 79 deg. F, 84% R.H., 30.00" Hg corrected and 130 feet above mean sea level.

BCg7 measured to: Unit A at 101.6 yd. // Unit B at 287.6 yd.

Round # / Bullet length inches / BC@Unit A / BC@Unit B / ft/sec @101yd / ft/sec @287 yd
1* 1.218 .499 .500 3004 3003
2 1.224 .523 .520 3032 3032
3 1.225 .514 .515 3041 3040
4 1.225 .534 .533 3034 3033
5 1.225 .520 .522 3032 3031
6 1.228 .526 .526 3033 3032
7 1.228 .525 .525 3040 3039
8 1.229 ---- .532 ---- 3029
9 1.229 .539 .536 3039 3038
10 1.230 .544 .542 3038 3037

Avg. 1.226 .525 .524 3032 3031

ES .012 .045 .042 37 37
ES excl. #1 9 11

*Round #1 was fired in a barrel cleaned, dried and then followed by a final patch with Lock Ease the day before the test.

Last Edited Moderator on Nov 9, 2004 4:02 PM

As a continuation of the subject on chronograph error, it is interesting to see, in the test above, that even with 24 foot screen spacing on two chronographs testing the same bullets simultaneously, there is about 1f/s error due to the chronograph sky screen detection error.

The two sets of sky screens were close together, that is, the center to center distance on the two #1 sky screens was 2.2" as it was on the #2 and #3 sets of screens. Thus the bullet lost only about 0.1 f/s from #2 sky screen in unit "A" to #2 sky screen in unit "B". Units "A" and "B" are defined in the test in the post above.

One other interesting point is the fact that the first round out of a clean barrel is virtually always the lowest velocity round, which the test data above clearly shows.

Henry

Last Edited Moderator on Nov 9, 2004 4:00 PM