OCW question

[Dildobaggins]

So this weekend I'm going g to do an OCW test for my 6mm creedmoor. First time ever doing one of these. Read up on Dan Newberry OCW test. Then went on some forums and researched more.

When doing round robin, I have seen people say and read, they wait two minutes per shot, some say 5 mins, others say nothing about weighting for barrel to cool between shots.

So what is the general consensus on this? How long do you wait? Because I'm going from 40.6-42.6 grains of H4350. if I'm waiting 5 mins between shots this is going to take like 4 hours

Thanks fellas

 

[nn8734]

I stop and take a break when barrel miraging occurs and starts to impact my sight picture. 5-10 minutes is what i take then resume

 

[6.5SH]

Something like this and some vinyl tubing that fits your chamber will greatly speed up the cooling time:

 

[nn8734]

Something like this and some vinyl tubing that fits your chamber will greatly speed up the cooling time:

Hmmm…Worth considering, especially in the warmer months.

 

[Dogtown]

The whole point of doing it round robin style is to spread the heat across multiple strings, avoiding bias from earlier cool strings and later hot strings. Just take your time shooting each round as consistently as possible, and then take a short break once you start to see some mirage. That way each charge weight should get a decent spread of barrel temps and not bias in either direction.

 

[Doom]

The time depends on what the ambient temperature is and to some extent how many charges you are shooting. With a heavy barrel in 308 and 223 and temperature below 70 I wait about a minute between shots. When it's above 70 I usually use a temperature gun and keep barrel temp below 100F. If it were a pencil barrel I would probably weight longer. As noted the round robin is intended to limit the effect but it doesn't always eliminate it. You really don't want a cold barrel unless one only want to shoot the load with a cold barrel. Hence the 3 foulers.

Seldom will my groups be especially small doing an OCW test. Remember it average points of impact that you are comparing. Try and stay on the rifle during each round. Waiting between rounds means you probably come off the rifle and move. It's hard to get back exactly as before so the groups may open up some. Seldom are my groups much less than .5 MOA but the load determined is often capable of ~.3 MOA or less. for 5 shots.

 

[Doom]

As for you loads, I usually load and shoot 1 round per increment checking for pressure until I get to 94% of maximum, then shoot 3 per charge. For 6CM the increment should be 0.3 grains. I am usually looking for a node below max.

 

[ShtrRdy]

I don't do the round-Robin thing but rather shoot the group for one charge weight while in one position, then wait a few minutes and shoot the next group.

 

[straightshooter1]

So this weekend I'm going g to do an OCW test for my 6mm creedmoor. First time ever doing one of these. Read up on Dan Newberry OCW test. Then went on some forums and researched more.

When doing round robin, I have seen people say and read, they wait two minutes per shot, some say 5 mins, others say nothing about weighting for barrel to cool between shots.

So what is the general consensus on this? How long do you wait? Because I'm going from 40.6-42.6 grains of H4350. if I'm waiting 5 mins between shots this is going to take like 4 hours

Thanks fellas

As mentioned, a lot depends on the configuration of the barrel and the ambient temperature you're shooting in. In cool temperatures with the heavier barrels, one doesn't need to wait long, if at all, between shots, but after 4 or 5 it's very likely a pause for a couple minutes will be needed. It really helps to monitor the temperature of your barrel, which can easily be done by attaching a temperature strip to the barrel just above the action. I use as temperature strip this way and don't let the temperature get above 104°F (as shown on the strip), which is not hard to do in cool ambient temperatures.

 

[Doom]

I don't do the round-Robin thing but rather shoot the group for one charge weight while in one position, then wait a few minutes and shoot the next group.

This can work, and I have to admit I have done it myself, but I will add that the issue is repeatability between the groups. IF the shooter has issues with repeatability when getting on and off the rifle it may be a problem.

 

[Dildobaggins]

This can work, and I have to admit I have done it myself, but I will add that the issue is repeatability between the groups. IF the shooter has issues with repeatability when getting on and off the rifle it may be a problem.

Yeah, I'm definitely going to do round robin then, haha.

 

[Precision Underground]

This can work, and I have to admit I have done it myself, but I will add that the issue is repeatability between the groups. IF the shooter has issues with repeatability when getting on and off the rifle it may be a problem.

This. So many ppl gloss over shooting RR and think it doesn’t really matter but there’s a very important reason for it. I’m nearly 100% confident in my ability to be consistent group to group and I still shoot RR because it’s too easy for a small variable in one group to completely throw the test off. If you see a pattern on a target shot RR you can be all but sure the ammo caused it. There are several things that can easily cause a pattern on a target shot group by group.

OP, time between groups is 100% dependent on how heat affects your barrel. ARs and thinner barrels can be more prone to heat shift. Thicker bolt gun barrels aren’t usually as susceptible to it.

 

[Dildobaggins]

This. So many ppl gloss over shooting RR and think it doesn’t really matter but there’s a very important reason for it. I’m nearly 100% confident in my ability to be consistent group to group and I still shoot RR because it’s too easy for a small variable in one group to completely throw the test off. If you see a pattern on a target shot RR you can be all but sure the ammo caused it. There are several things that can easily cause a pattern on a target shot group by group.

OP, time between groups is 100% dependent on how heat affects your barrel. ARs and thinner barrels can be more prone to heat shift. Thicker bolt gun barrels aren’t usually as susceptible to it.

For this first one I'm using a bolt, with a light varmint barrel. Thanks for the info. I'm ordering an ELR 3d bag tonight. Been using a protektor rabbit ear bag with a bipod in the prone position and it ain't doin it for me. Gonna give yours a shot.

 

[2aBaC̶a̶]

Yeah, I'm definitely going to do round robin then, haha.

Just so you're clear round robin has a higher risk of user induced poi because of getting on and off the rifle.

 

[Dildobaggins]

Just so you're clear round robin has a higher risk of user induced poi because of getting on and off the rifle.

But if I had an issue with repeatability, then it sounds like it's 6 of one half dozen of the other.

 

[nn8734]

But if I had an issue with repeatability, then it sounds like it's 6 of one half dozen of the other.

Just take your time and you’ll be fine.

I load an extra round in each charge weight just in case I need to take a mulligan at any point. I also zero with 5 or so rounds at one of the charge weights before hand so my poi is at least in the general neighborhood of the POA, especially if I’m using a completely different case/powder/bullet combo than the rifle was previously zeroed with.

Take a break when feeling a bit fatigued or barrel mirage appears and resume once it’s gone.

 

[Dildobaggins]

Just take your time and you’ll be fine.

I load an extra round in each charge weight just in case I need to take a mulligan at any point. I also zero with 5 or so rounds at one of the charge weights before hand so my poi is at least in the general neighborhood of the POA, especially if I’m using a completely different case/powder/bullet combo than the rifle was previously zeroed with.

Take a break when feeling a bit fatigued or barrel mirage appears and resume once it’s gone.

Good call I'll definitely load an extra for each charge tonight. I planned on doing some sighters with a charge right in the middle.

 

[Doom]

The attached target is one that works well for load development.

 

[Dildobaggins]

The attached target is one that works well for load development.

I really like that target, been looking for one with a red diamond for awhile now that had 1/4 bullseye and can't find it. I have an Arken SH4, and with the center dot at 100, the reticle just blends right into the black diamond.

 

[Doom]

I just put an SH4 on my Rugar American Rimfire and I have to say I love the reticle on that scope. Haven't used it on that target yet.

 

[Precision Underground]

Just so you're clear round robin has a higher risk of user induced poi because of getting on and off the rifle.

Shooting RR doesn’t meant you have to shoot 1 round each time you set up. The way to do it is load one of each charge weight into the mag and shoot one round at each POA. So you are still shooting the same number of strings but each string has one of each charge weight. It’s best to use a small target with small spacing between POAs so once you’re set up for a string you don’t need to move much to get to your next target.

 

[John Glidewell]

Free downloadable targets for 6mm BR Norma and 6BR benchrest and Long Distance shooting. Targets for 100 to 1000 yards and varmint hunting.

6mmBR.com offers free targets for precision benchrest and long-range shooting. Downloadable targets for 6mm BR Norma benchrest, varmint, and 6BR 1000 yard. PDF and Word format targets for accurate printing. 6mmBR.com is for 6mm BR Benchrest shooting, with 6BR FAQ, Reloading, Message Boards...

www.6mmbr.com

The red diamond targets are 1/2". I print them with a laser printer on heavy paper.

 

[straightshooter1]

The attached target is one that works well for load development.

That's a good one for development. Attached below is one I like to use for load development:

 

[straightshooter1]

I really like that target, been looking for one with a red diamond for awhile now that had 1/4 bullseye and can't find it. I have an Arken SH4, and with the center dot at 100, the reticle just blends right into the black diamond.

Though I like the target I posted (mainly for all the data I can record on it), I've found that for OCW load testing a large sheet of white paper with just horizontal and crossing vertical lines does well (POA being where the lines intersect). Such a target is really helpful in interpreting the vertical and horizontal locations of the groups as they relate to each other. Interpreting changes in location and the shape of the groups relative to the POA is important when trying to determine what the OCW test can tell you about your loads.

 

[Doom]

Though I like the target I posted (mainly for all the data I can record on it), I've found that for OCW load testing a large sheet of white paper with just horizontal and crossing vertical lines does well (POA being where the lines intersect). Such a target is really helpful in interpreting the vertical and horizontal locations of the groups as they relate to each other. Interpreting changes in location and the shape of the groups relative to the POA is important when trying to determine what the OCW test can tell you about your loads.

Yep. That works too. I haven't used it because I like the 6 on 1 sheet. The thing I like about the target I posted is it's easliy scanable. BUT your point on location is spot on.

 

[kthomas]

Shoot at a pace that you normally would - otherwise, what's the point? Just let it cool down when it starts to get toasty.

Personally I'm not convinced that these tests provide any meaningful data, but will be a good learning exercise regardless.

 

[BearNaked]

As others stated, depends on your barrel thickness and ambient temp. heavy barrels i usually run between 7-10 shots before a break and my AR's i run about 5. Maybe 1-2 mins between shots. I write down speeds, notes if i pulled it, check brass, etc to waste the boring wait time between shots. once the barrel is warm, i run a chamber fan on it for a good 10-15 mins then do it all over again.