OCW - Max Capacity and Fouling questions

[Break Bad]

Two questions for those who are experienced with performing OCW test:

I always wondered why so many shooters load so close to or above max, then I read the OBT Paper:
"Any systematic effect that varies the chamber pressure or volume during the initial stages can dramatically change the pressure peak time. If a load is not very heavy and the case is not very full, the initial stages last longer than in a load that is near max. All the OCW loads developed with this theory have been found to work best when the powder charge is near max volume for the case and bullet combination. This also explains why variations in neck tension and seating depth can have an (sometimes) adverse affect on accuracy and velocity variations. Granted, this is not at all new, but now there is a consistent explanation for why this is so."

When you start your increments, do you even bother with the lower end? EG: 123 Scens and 4350, min 40 max 44.8. Start at 43 and go to 45 in .5 increments?


Reading the OCW , I raised an eyebrow at step 10 in the instructions:
"10. Your barrel should of course be clean before starting. Depending on the number of rounds you will fire, you may decide that it is necessary to clean half way through the string, fire a couple foulers, and allow a couple of minutes to cool before continuing. With custom barrels, you may be able to fire 25 shots or more before fouling begins spoiling group sizes. With factory barrels, I wouldn't fire more than 15 to 18 shots before cleaning... This is all relative, of course."

I was wondering fouling after 25 rounds is really a factor? @ 100 yards?

I wasn't planning on cleaning since my barrel has 'only' 50 rounds since the last cleaning. Now I'm not so sure.

 

[AtOne]

I personally don't start at the bottom but that's really dependent on your comfort level with reloading. If you do start there you'll get more info on other OBT's at the lower end but again you may not want to go there due to the lower velocities.

Cleaning only happens for me when groups start opening up and that's a lot of rounds down the barrel. Two completely different views on cleaning out there choose which one works for you.

I also do OCW's in .3 grain increments and 5 shot groups, that way I have all the info I need when I get home and don't question if one shot was pulled or not. If you screw up one shot in a 3 shot group its much more difficult to figure out which one it was vs. in a 5 shot group and its really not that many more rounds down range in a OCW test but its a heck of a lot more info to view when your done.

Good luck with it !

 

[Break Bad]

Gave it a go today. Was going to do it at 100 but changed my mind last minute and backed up to 200, so naturally forgot to change my elevation...first three shots 3 clicks low are marked up 1 in. Couldn't get comfortable with the parallax, but gave it my best. Not really helpful data but may see how 44 shoots.

 

[Macmathews]

You may want to re- read the theory.
You should only be firing 3 rounds per target at a distance of 100 yards

Kyle

 

[oldfatguy]

^^^^^^^^^^^^^^^

Changing from 3 to 5 round groups and shooting at 200 yards vs 100 really does not improve the program. Of course everyone is entitled to their own opinion.

OFG

 

[Break Bad]

Thank you for the feedback.

After shooting this test i'd have to agree, doing it from 200 yards was a bad choice. But, I feel I have to add an extra shot to the groups because 1.) fairly new to shooting 2.) its a new stock, trigger, scope.

There is vertical spread at 43.6 and 44.2, book max is 44.8. Considering another test, this time from 100 yards, in .1 gr increments from 44.2 to 44.8..which is near book max. Sighters and test rounds show'd no pressure signs at 45.1.

Any further thoughts appreciated.

 

[AtOne]

Definitely start at 100 especially if your new to shooting and your equipment.
1/10 of a mil at 200 equals .72 inches so any slight change in your POA and you could have groups that are twice as large by being 1/10 on either side of your POA.

Loading in .1 grain increments at this point is a little excessive. Find the node first then fine tune it.
Don't sweat loading a couple extra for each grain weight, I'm sure Dan Newberry won't penalize you any OCW points by doing what works best for you as long as you get to the end result your looking for.

.3 grain increments will get you there with plenty of info from 100 yards, Give it a go again and have fun with it.