Q. On barrel heating and accuracy

[Busta Capp]

When testing loads, how much time do you leave between shots? Is it generally assumed that as a barrel heats up, the groups open up?

I was doing some tests today on loads, and my process was shoot group of 5 pausing only to mark bullet placement in the order shot. First five shots were a tight-ish .75MOA. I continued on in this manner and each successive group opened up. Hard to tell if this was the loads, or the barrel heat, so thought to ask the pro's.

How much time do you leave bewteen shots? Do you let the barrel cool between batch tests? I know my barrel is not free floating right now, so this may be on of the main culprits. Any thoughts?

 

[sunray]

"...Do you let the barrel cool between..." Yep, but let it cool, completely, between strings of 5. No rapid shooting at all when you're load testing
A rifle may or may not shoot better with a free floated barrel. The only way to find out if your rifle likes it is to try it. Fortunately, if you lose that .75" group(I wouldn't do anything with that rifle), putting the pressure point back in isn't a big deal. Use a bit of epoxy bedding about 1 to 2 inches aft of the end of the forend. Don't forget the release agent.

 

[maynard]

The rounds that you are testing should be fired in about the same time it would take to shoot a match. The number of rounds in your test should also be what you would fire in a match. This might mean in a TR/F Class match you fire 2 sighters and 10-15 for score. If you get a fast marker shooting two to a target you might fire a shot every minute. With a slow marker and slow shooting partner(s) and fickle conditions it could be 3 minutes between shots.
Testing with the number of shots that you would fire under match conditions will give you a better idea on what your rifle will do as it heats up. You don't want to find out your rifle is a tack driver for 5 shots, then opens up to the four ring for the next 5 shots as it gets warm.
You are correct about the barrel heating up and the groups open up. The hole is getting bigger with more heat. I am not sure how hot it has to get for it to open say .001", likely around 300-400 F. Any engineers here that want to run the numbers?

 

[Busta Capp]

Good points maynard, as it is F Class (M) that I was hoping to shoot when I get this part figured out.

My next experiment is to narrow in on that load that was giving me the best group, 23.5 gr of H4895. I was going to build loads from 23.0, 23.2, 23.4 and 23.6. I will shoot these at 2 to 3 minute intervals and see how the barrel reacts over time/groups.

I also wanted to vary the OAL to get as close to max OAL as possible, but will do this afterwards. Is there any other tests that you run to "shake-out" a load for F Class competition?

 

[sunray]

"...narrow in on that load that was giving me the best group..." If 23.5 was the best load, go back to 23 and work up by 1/10ths. There's no point going to 23.6 if 23.5 gave you the best group when you worked up by half grain increments. You know 23.5 works.
Five rounds of each load starting at 23.0 and work up to 23.5.
How heavy is your barrel?

 

[jkajfes]

deleted

 

[jkajfes]

Good points maynard, as it is F Class (M) that I was hoping to shoot when I get this part figured out.

My next experiment is to narrow in on that load that was giving me the best group, 23.5 gr of H4895. I was going to build loads from 23.0, 23.2, 23.4 and 23.6. I will shoot these at 2 to 3 minute intervals and see how the barrel reacts over time/groups.

I also wanted to vary the OAL to get as close to max OAL as possible, but will do this afterwards. Is there any other tests that you run to "shake-out" a load for F Class competition?

ya run the test at different times of the year. As much as the powder makers say they're insensistive to temperature your mileage may vary! A load put together in the spring or earlier might not shoot come july and august with a temperature change of 25 degrees. As much as you'd like to think 1/10th or two of a powder change are going to narrow groups down keep in mind, Do you want to be working in this narrow spectrum? Find a node that's more forgiving.

If you shoot international matches where the rules can be different as in single stringing it all changes...

when you've got your load testing done... some are probably going to need a new barrel and then you start over...

 

[Busta Capp]

How heavy is your barrel?

It is a stock Savage 110FP, so heavy barrel but not super heavy.

This brought up another thought. What are the rules regarding F(M) and barrel replacement? I would imagine this is fine as long as it is the same barrel as the original OEM one. Tried to find this on the DCRA rules page but I didn't have any luck. Anyone know the answer to this?

 

[maynard]

F(M) is really designed to get the new shooter into the game for the least amount of $$$. By the time you burn out a barrel, or start shooting better then your equipment, is when it is time to move up. For a .223 you might get 3000-4000 rounds out of the factory pipe before accuracy starts going downhill.
By this time you might want to get off the porch and play with the big dogs.
If you swap out your barrel and stick with the .223 you can shoot in F(F).

 

[Mystic Precision]

You should find a point of diminishing returns using the factory pipe. Just use a load that is consistently accurate. Likely you will have two loads a few tenths apart that will alternate between being the best load. Factory pipes aren't match barrel consistent. Go with the one that shoots best at the longest distance you will compete in. Don't just do your load development at 100yds.

200yds is my min and 300yds is even better. You are looking for load stringing. A 3/4" diagonal group looks great at 100yds but by 500yds, could be 10" across.

Test as you would compete.

When finalizing a load for F class, I will run through the max numbers of rds I would ever shoot as fast as I can. How did it shoot?

Then I will let it cool to 'medium' hot and retest. This time I will shoot slower but leave each rd in the chamber for 30secs or so.

I am trying to simulate any condition I can think up for a match.

What changes will I face as the rifle gets hot?

Maybe there is a screw up and I get called to shoot the next relay much sooner then expected and my rifle doesn't cool?

Maybe conditions are horrid and I need to wait but forget to take the rd out of a hot chamber?

Shoot in the rain. Shoot in the sun. Wind. whatever condition you will likely face and see how your rifle reacts.

I would rather shoot a 3/4MOA dead reliable/consistent rifle, then a finicky bug hole shooter. I don't care if the next shot touches the first. I just care that they all go into the X or 10 ring.

Jerry