Some OCW testing questions

[ReaperDriver]

OK, so I'm going to try out the OCW method for testing some new rounds tomorrow and as I'm reading through Dan's instructions a couple things don't make sense:

It appears that he is doing his testing without a chronograph and settles on an OCW regardless of MV. If that MV ends up being too low or less than desired, say for getting out to 1K with decent energy to buck the wind - is the OCW REALLY the best charge?

The 2nd thing is he starts with published max numbers and backs off 10% and then works back up. We all know, or at least I've found from experience that the manufacturers max #'s are notoriously slow and very conservative. At least in my rifle (20" SPS-T), I'm finding there is no way I'm coming close to the MVs of even the published max loads in the Sierra manual and others. I'm usually in the 150-200 fps under range. So what's a girl to do?

 

[landcbeitner]

Re: Some OCW testing questions

I use the OCW as described here...
http://www.shoot-farther.com/My_Homepage_Files/Page8.html

 

[918v]

Re: Some OCW testing questions

The whole point to OCW is to be able to throw the powder charge from a measure and still have good accuracy. You don't want a sensitive load. You want a forgiving load. If such a load won't get you to 1000 yards, tough. Develop a different one.

Understand the limitations of your platform.

 

[okiefired]

Re: Some OCW testing questions

You can only get an OCW within the paramiters YOU set. If your OCW is too slow and there are NO presure signs, go up in charge weight. Again, watch for presure signs. Max presure is different from rifle to rifle. Be careful, keep records and watch for high pressure.
Not sure of your experience so if you already know this, I'm sorry. Remember OCW is done round robin. 5 targets. Shoot load 1 an target 1, load 2 at target 2, load 3 at target 3, load 4 at target 4, load 5 at target 5. Repeat. In the end, all 5 targets should have five ( or three if you prefer ) shots of the same charge weight increasing from target 1 to 5. Exemple; target 1 at 42.0 gr, target 2 at 42.3 gr., target 3 at 42.6 gr, etc. I like .3 gr increments. Please remember , watch for pressure sighs. Good luck.

okie

 

[ReaperDriver]

Re: Some OCW testing questions

How long do you guys wait to shoot between each shot? Do you let the barrel cool between each shot? when I was doing ladder tests, I would let the barrel cool down between each 5 shot string. But since each shot is a seperate target, I wonder if I should wait longer between individual shots.

 

[Unsichtbar]

Re: Some OCW testing questions

2 Minutes

 

[Swan]

Re: Some OCW testing questions

Also be sure to get up from the gun and stretch ur legs a bit between targets. I was lying down way too long and noticed neck fatigue by the time I was on last two targets of the OCW test. Probably slightly affected the groups I think. You will find a low node and probably one at a higher charge as well.

As far as getting more velocity from your SPS-T, do what I did, find a 26" barrel and never look back.

 

[DaveV]

Re: Some OCW testing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body">How long do you guys wait to shoot between each shot? Do you let the barrel cool between each shot? when I was doing ladder tests, I would let the barrel cool down between each 5 shot string. But since each shot is a seperate target, I wonder if I should wait longer between individual shots. </div></div>

Read this thread and you decide:

http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=1409737&page=1

The most important post, IMHO, is Lindy's:

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">I wouldn't expect to see much of a POI shift at 100 yards as the barrel and/or ammunition heat up.

It might be useful to note that the trajectory of a .308 zeroed at 100 yards is essentially flat - within 0.1 inch - from 30 yards from the muzzle to 109 yards from the muzzle.

However, those effects will be more pronounced at greater distances - which is why in handloading we strive to produce rounds with low standard deviations of muzzle velocity.

I have measured changes in muzzle velocity with ammunition temperature which range from 0.6 fps per degree F. to nearly 5 fps per degree F.

Plug those kinds of numbers from a marked temperature shift into a ballistic program, and one will find significant deviations in POI at ranges beyond 700 yards.

Bramwell, referenced earlier in the thread, speculated that chamber temperature might have a quicker effect on primer performance than on powder temperature. It would be nice to have a good way to isolate primer performance with temperature. I can't think of one immediately, but I'll probably have dreams about it.

</div></div>

So it really depends on what distance your are testing at. Temperature effect will increase with distance. The only way to know for sure is to chrono at different temps.

Cheers!