OAL and its affect on extreme spread & standard deviation

[31B]

I am having problems finding a consistent load for 308Win. and I would like to hear opinions and advice from more experienced people than I.

I am getting huge variations in extreme spread: 164.4 to 35.47 and standard deviation: 33.12 to 9.27 with the same amount of powder.

I am using an older Lee Turret Press,three die head) and a Redding Comp Seater Die for a 308 Win. and the cartridge OAL varies from .001" to .004". That looks like too much to me for consistent load. The turret head flexes and shifts in its fitting a lot when seating a bullet. Could that be the problem with the huge extreme spreads?

I'm using: Lapua cases, Fed 210M, 175 SMK. I've tried RL 15, N150 and N550 and I individually weigh each charge. Regardless of the powder charge weight they have all been inconsistent.


If anyone thinks that the press is the problem what other turret press would you suggest? Does the Redding T7 head flex and shift in its base? Would an "O" frame press be better?

Any suggestions would be greatly appreciated. Thanks in advance.

Regards,

31B

 

[Forum Boss]

How many loads on your Lapua brass?,If this is new brass, you can get high ES if you don't run a same-caliber expander mandrel down the necks the first time.)

What are you using to size the necks and/or body?

Are you chamfering the necks before seating the bullet.

Where is the bottom of the bullets' bearing surface,if it's right down at the neck-shoulder junction, you're in the "donut zone" where it's hard to maintain uniform neck tension).

 

[31B]

The brass is new. I've reloaded it two times.

I'm using a Redding neck die. I have not full length re-sized the cases.

The OAL is 2.8" to fit through the magazine.

I do not know where the bearing surface is.

Thanks,

 

[jb1000br]

sounds like you are jumping a fair bit before you hit the lands...so the 4 thou variation in OAl won't affect much...

How do the groups look at range?

What kind of chrony are you using...weird numbers could easily come from the chrono...

JB

 

[31B]

I'm using a Shooting Chrony,alpha model.) It's about six years old and has not been used for several years until recently.

When I do my part I have been getting groups under 1/2 MOA at 100yds. I have not gone past that. The 1000 yd range is a 2 hour drive and I think it would be a waste of time to record W & E data when I'm having this much inconsistency on the chrono.

Thanks for the help.

Regards,

 

[jb1000br]

I'd bet $$ it is the Chrony...ran mine against my Oehler 35P,simultaneously) and was amazed how inconsistent the Chrony was...could easily get you that 100fps ES, when it was not in reality...I would suggest you try it at range, or at a bare minimum to avoid the drive, shoot over another chrono.

I'll try and dig up exact numbers from that test...

JB

 

[31B]

I appreciate the suggestion. I will definitely ask to borrow one that is known to be reliable.

Is Shooting Chrony a low quality product or did I just happen to get a bad one? Are they worth the shipping & handling to return it to the factory for a repair or should I thing about an Ohler instead of a new turret press?

I appreciate the suggestions. This has really been frustrating chasing a bunch of different loads with out results.

Regards,
31B

 

[jb1000br]

Oehler 35P vs. Alpha Chrony: Simultaneous readings, Chrony immediately in front of O35...

6BR and varget ladder:

O35 --- Chrony
2724 2745
2772 2794
2767 2794
2795 2809
2804 2824
2816 2844
2811 2851
2855 2890
2864 2888
2876 2908

6.5-284/142/n160 Ladder

O35 --- Chrony
2841 2742
2859 2833
2865 2760
2892 2919
2902 2666
2897 2865
2918 2877
2958 2937
2948 2972
2971 2982
2971 2990

H4350 ladder

O35 --- Chrony
2896 2898
2912 2915
2929 2922
2952 2938
2971 2970
2976 3727
2989 3013
3001 2841
3021 2841
3029 no read
3032 no read

There are no typos...those are the actual readouts...

See how the Crony can be a little inaccurate?

JB

 

[31B]

I appreciate you detailing the comparison between the two chronos. I am still getting varied readings w/ my Shooting Chrony. Five or six rounds will be within 10 to 15 fps of each other and then the next couple of rounds will be up to 125 fps slower.

Unfortunately I have not been able to borrow anyone else's chrono to check if I am making a mistake when I reload of if my chrono is bad. A new Ohler may be a future purchase though.

Thanks for the info.

Regards,

31B

 

[jb1000br]

31b -- what is the load...if it is within "safe" in my 308, I can shoot them over my Oehler if you think we can use that data to draw a parallel...

JB

 

[31B]

JB,

I appreciate the offer.

175 gr SMK; 42.2 gr Viht N150; Fed 210M primer; OAL 2.8",OAL varies between .001 to .004" with my Lee turret press); Fed brass. I realize that Fed brass may not be the most consistent stuff. I have gotten inconsistent fps w/ Lapua brass out of my 20" .308 as well.

I fired 10 rnds. The Shooting Chrony showed an error for the first 3 rnds, then 4: 2572; 5: 2492; 6: 2607; 7: 2609; 8: 2608; 9: 2617; 10: 2610. This is from a 26" Hart bbl w/ 1:10 twist.

I don't know if I am making a mistake when I reload or if the chrono is the issue. The erratic results are from two different rifle.

I was happy w/ the groups w/ the 42.2 gr of N150 at 100Yds. I think I am going to load up 50 to 100 rounds and make the drive to the 1000 yard range in the next couple of weeks and see how it goes.

Once again, I appreciate your suggestions.

Regards,

31B

 

[onehole]

Since you are taliking about chronys I remember an occasion during my old air rifle field target days when here in the UK we had severe comp restrictions to stay within the 12ft lb law and everone strived to get as close as possible to this and not go over.Nearly everyone had a chrony in those days and at one meeting about six chronys were lined up and compared!!!all six gave different readings and a total variation overall of nearly 40fps and thats a lot when you consider the precharged air rifles only varied some 2 to 3 fps on each shot so no error there just one chrony would say 800fps and the next 830 or so!There were quite a lot of arguments at some meetings when chronographing was done and some people disqualified or banned from the comp.I still use a chrony for firearms work shes a bit battered now but have recently compared to another newish make and got same readings so for now i will stick with it.I use it mainly to work out appx trajectory but always check out under field conditions anyway.cheers onehole

 

[ChrisNam]

31B, as far as I know Oehler no longer makes a commercial chronograph. Pitty!!!

 

[JimmyO]

I read somewhere the the Millenium CED with 8 foot screens was actually very close to the 35 as far as measuring ES and the best currently availible unit under 1K. I wish I could remember where I saw it.

JimmyO

 

[tightneck]

I'm pretty sure Oehler still makes the model 43PBL,personal ballistics laboratory). As you may have guessed from the name, it's quite pricy. Glad I got the 35P while the gettin was good.

 

[31B]

As I've been looking into this a little further, Oneshot's experience is not surprising. Since Oehler is no longer making commercial chronos I have decided to stick with my Shooting Chrony for now and accept the fact that there will be a little variance.

I appreciate the replies and have happy newyear's eve.

Regards,

31B