Sierra 142 gr. 6.5mm MK Ogive Length Data Comparison

[M21SNIPER]

Gentlemen,& hopefully some women shooters!),

I have some questions regarding the range or possibly the acceptable variations of ogive measurements associated with the 142 gr. SMK bullet.

First, let me state that at no time in the 14 years that I have been actively using the Match King bullets have I once been disappointed with their accuracy in my rifles, provided I was diligent with my powder charges, case prep., etc. They shoot amazing well in my Garand, M-1A, and my AR Service/Match Rifles!

However, with age comes wisdom and I decided with my new 6.5mm Bartlein Barrel in the works, that I would really try to eliminate all of the variables and see just what the rifle can do in anticipation of 600 yard prone and 1000 yard F-Class matches.

I used a Stoney Point,Hornady) bullet comparator on a set of manual calipers and found some VERY INTERESTING RESULTS,SHOWN BELOW). It is these variations or rather lack of variations in some lots, and wild variations in other lots that I would like your feedback on. AGAIN, I AM IN NO WAY FLAMING SIERRA: ON THE CONTRARY I AM CONTEMPLATING CALLING THEM IF THIS APPEARS TO BE A QA/QC MATTER. Enough said.

Lot #1= 99 Bullets-Ovige measurement in Stoney Point Comparator and analog calipers:

1) 22 bullets @ 1.805" Ogive
2) 5 bullets @ 1.810" Ogive
3) 63 bullets @ 1.820" Ogive>>>>>>>
4) 8 bullets @ 1.821" Ogive>>>>>>>>>> 73% within 0.002"!!
5) 2 bullets @ 1.822" Ogive>>>>>>>


Lot #2= 100 Bullets

1) 1 bullet @ 1.800"
2) 6 bullets @ 1.810"
3) 28 bullets @ 1.816"
4) 15 bullets @ 1.820">>>>>>>>
5) 37 bullets @ 1.821">>>>>>>>>>>>>> 58% within 0.003" :-,
6) 6 bullets @ 1.822">>>>>>>>
7) 2 bullets @ 1.823"
8) 4 bullets @ 1.824"

Lot #3= 100 Bullets

1) 97 bullets @ 1.817">>>>>>>>>>> 97% Dead on!
2) 1 bullet @ 1.805"
3) 2 bullets @ 1.820"

I have sorted the bullets in lot tolerances of 0.003" measurements, example: the 15,37, & 6 bullet counts from Lot #2 all went into the same bag.

I plan on trimming all of the metplats, which I am sure helps quite a bit with uniforming THE WEIGHT of the projectiles, but how can using the ogive to set the jump to the lands, uniform seating depth in the case, etc. be accurate if the ogives are all not uniform???? Obviously, I will be loading in batches to keep like length bullets together.

I would expect quality control similar to Lot #'s 1 and 3, but what happened on Lot #2????? Look at the physical variation in ogive length as well: in all instances it was AT LEAST 0.015" AND IN MOST CASES 0.020". How do Bergers, JLK's, or Lapua's compare?

Anyone with any information regarding these apparently extreme variables, please reply. I am curious to see if the bench rest guys encounter this. Only problem is, long ogive or not, the Sierra's shoot like gangbusters in my rifles! Call it scientific curiosity. Just trying to reduce my vertical stringing at 600 and bullet weight and ogive length seemed like ideal places to start uniforming,bullets, not the brass: it will be weighed as well).

As always, thank you for your time. I look forward to hearing from others who may have encountered this before.....does it matter in the long run??? Please let me know your thoughts and theories on this one. Thank you.

Keep them in the 10 ring!

Regards,

Matt

 

[billmo]

Matt, I am no BR shooter by no means however I do a lot of shooting and have handloaded since 1995-96. I have also seen Sierra's bullets vary almost as much as yours. But, if I sort them by length as you have done like you said they shoot fine. I have measured Bergers, Hornadys, Noslers as well and to be very honset with you, I have found less difference in Noslers weight and ogive length than any bullet I have measured but I only shoot Nosler's BTs. Not trying to degrade nobody's bullets either
by no means. Just my findings. Bill

 

[Spotcheck_Billy]

Matt,
I ran into the same thing with 142 SMK's, as well as with other calibers and weights of the SMK's. I'm not flaming Sierra either. I still use them quite a bit, but in the 6.5mm bore size I've found that 123 and 139 Lapua Scenars are more uniform and shoot tighter groups from my 6.5-284 and 6.5x47 barrels.

 

[jb1000br]

Would this be base-to-ogive? not bearing surface?

JB

 

[M21SNIPER]

JB,

Yes, that is correct. That is the only measurement I can perform at this point, other than OAL bullet length, which is essentially useless as a sorting tool. I was always told to measure off of the ogive when seating/sorting bullets.

Is there a simple way to measure bearing length with a Stoney Point gauge, or is more equipment needed?

Thanks.

Matt

 

[jb1000br]

JB,

Yes, that is correct. That is the only measurement I can perform at this point, other than OAL bullet length, which is essentially useless as a sorting tool. I was always told to measure off of the ogive when seating/sorting bullets.

Is there a simple way to measure bearing length with a Stoney Point gauge, or is more equipment needed?

Thanks.

Matt

Like he said...

http://www.6mmbr.com/catalog/item/1433308/977259.htm

see my pic with the camo netting in the background.


JB

 

[M21SNIPER]

Gents,

Thanks for the info.

That being said, is it wise to still sort the bullets that I measured from boat tail base to ogive, until I purchase a second comparator body?

I would think that is Sierra can make 97 or so bullets in a row almost exactly the same, that it would be prudent to sort those bullets together, correct?

I need to purchase a suitable electronic or heavy duty balance beam scale and start comparing bullet weight as well. I am assuming bullet weight and bearing surface uniformity are both EXTREMELY IMPORTANT for 600+ yard accuracy, correct?

After all of that is done, it's off to David Tubb's site to buy a metplat trimmer....all of this and I have yet to produce one loaded fire forming round for my .260 AI!

I don't even want to think about neck turning yet.... :-, I am sure I will get to that point, but .260 AI is my first wildcat cartridge and I'm a Service Rifle shooter so brass prep. isn't one of my fun things to do...oh well, time and money, right??

Thanks for all of your expertise.

Regards,

Matt

 

[chuckw2]

Gunamonth,

What caliber are you using the Whidden bullet point die on. Are you also trimming the meplats?



Chuck

 

[rvander1]

Hi,
I should start out by saying I'm a beginner at this 1000yd game. I have a good custom gun but have yet to compete with it.
Yesterday I bought 500 Sierra 142s for my 6.5-284. And partly because of the first post on this thread, I decided to weigh them and measure them ogive to base using a Davidson Ogive Gage mounted on a digital caliper. The scale I used seems to me to be very accurate- it is part of my RCBS Chargemaster 1500.

I, found the weight for ALL FIVE HUNDRED rounds to be 142 +/- .15gn . -Well maybe 4 or 5 were .2gn off. In other words 99% were within 1% and maybe the other 4-5 were within 1.4%.

However the ogive measurements were much different:

#420 were .723",+/_ .002")
#80 were .712" ,+/_ .003)

It looked like they "bunched" into two different measurement categories- even though they were from the same lot.

I called the Sierra help desk and one of the techs who is also a shooter- said he gets the same type results sometimes. He said it is incredibly difficult to get a stable ogive measurement when the radius of the ogive can be 15 times the caliber of the bullet. He said even with the same run,lot) if the temperature or humidity changes it can change the ogive like I am seeing.
Nevertheless, he agreed completely with me that this ogive measurement is very important for long range shooting. I seat bullets using a wilson arbor seater- so all my cartridges are exactly the same base,of brass) to ogive,of bullet)measurement.
BUT there can, in THIS lot of bullets,if they were not sorted) be extremes of ogive from a long ogive of .725 to a short one of .709 or 16 thousandths difference which, in this case I think would change the case volume significantly given a few bullets would be seated 16 thousandths deeper into the neck than others, and one-in-five would be seated 11 thousandths deeper!

?? Am I figuring this right?? Please straighten me out if I'm off on this.

-Seems to me that sorting by ogive, if not bearing surface, may be very important in the 1000yd game. The weights seem to be almost spot on- so maybe I don't need to sort by weight? Other opinions- please, from those of you with more experience.,I've only been reloading for 3 years).
Thanks, Bob

I, too, am not flaming Sierra- I understand that it must be EXTREMELY difficult to achieve uniformity in this area with VLD bullets.