To clean the barrel, or not to clean? Not a question...

S

semi_problomatic

New member
I'm not asking if I should clean my barrel or not.

Basically I used my chrono (CED M2) on some factory ammo, had a deviation of >15fps for 5 shots.(new bore, first few shots out of the rifle) After shooting 50ish rounds with no cleaning, (hand loads that powder weight was increased by .5 grains per 5 rounds) I shot a few more factory rounds through the chrono (from same box of factory ammo) and there was an 80fps difference. I get the concept, not cleaning leaves residue in the barrel, could constrict the bore, which would increase pressure...which would increase muzzle velocity.

1 random occurance isn't gospel. So has anyone else noticed this? I've seen the whole spectrum of barrel break in procedures...from cleaning every shot to every few shots to never cleaning at all. At some point this leap in velocities would have to stop or stabilize. So if you cleaned your barrel wouldn't there be a jump in velocities as you shot between cleanings. In reverse, if you didn't clean your barrel would the increases in pressure make your velocities rise as you line your bore with copper. Also, from not cleaning, wouldn't it turn into shooting from a chrome lined barrel (not the chrome lining, but the uneven layering of copper down the bore having the same effect on trajectory as the uneven chrome lining).

I know this is a lot of assumption and jumping to conclusions based off one random occurance I wasn't even looking for, just wondering if anyone else has come across this as well.
 
I don't know all of the reloadin mumbo-jumbo but many people don't clean until accuracy drops off. The fouling lends to more consistency, as the barrel is only clean for one shot.
 
Well the reloading mumbo jumbo was just to illustrate that I wouldn't be able to notice an increase in velocities as I shot because I was increasing the powder charge every 5 rounds.

I try to keep my reloads at a >10 fps spread, and the highest deviation I had that day was 7 fps between 5 rounds.

In reality, at 100m I doubt an 80fps difference between rounds would be a noticable difference. It probably wouldn't come into play until beyond 300m, depending on round type. According to my ballistic calculator a deviation of 50fps would be a +/- 10" verticle spread at 1000m.
 
I've never noted that much difference under those exact circumstances. It could be a combination of several factors.

The dirty barrel could increase velocity, but I doubt that much without other factors coming into play.

Some powder is quite temperature sensitive. Shooting loads in early morning when it is cold, and more loads later in the day after it is warmer can make a pretty big difference with some powders. As much as 100 fps between temps in the 20's and colder vs temps in the 90's.

The chronograph relies on the shadow of the bullet passing over the sensors. As the amount of daylight changes during the day and the angle of the sun on the chronograph changes it can make for small changes in recorded velocity.

I'm not saying for sure what caused this. But it could be one or more of the above in combination.
 
Some powder is quite temperature sensitive. Shooting loads in early morning when it is cold, and more loads later in the day after it is warmer can make a pretty big difference with some powders. As much as 100 fps between temps in the 20's and colder vs temps in the 90's.
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This...

The chronograph relies on the shadow of the bullet passing over the sensors. As the amount daylight changes during the day and the angle of the sun on the chronograph changes it can make for small changes in recorded velocity.
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...and this, is what I was thinking.
 
This kind of discussion always fascinates me. I'm not a reloader so I would never even investigate something like this. It's a little off the original topic too, but I've been waiting for a chance to ask this

Here's the question: what is your margin of error for your measurements? For a 30-06 15fps is a small fraction of a percentage point of difference.

So what is the margin of error?
 
So what is the margin of error?
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The chronograph is an invaluable source of information, especially for the handloader, but ultimately it's the results downrange on the target that counts. Every now and then a load with a larger SD and ES will print on paper (at 100 yds.) better than other more "consistant" loads (in a particular rifle).

Notice all the disclaimers? Every rifle is different.
 
The factory loads I was using were the hornady SST's with h4350 (don't have box in fron of me) but its supposed to be very stable through out temperature ranges. And the temperature was near identical. I think the CED's margin of error was +/- 5 at the time, but I'd have to open it up and look at it again. I didn't notice the difference until I was at home, transfering the info from ced's program to excel so I could have a hard copy. When I down loaded the info I still had the older reads from the factory test and some 45-70 rounds I had made and tested.
 
Some powder is quite tmperature sensitive...

True enough...and few people consider that as you fire a string of shots, the action (and barrel) is heating up with each round fired. And if you chamber a fresh round, then wait for several seconds before firing it, the powder inside that round is heated by transfer of heat from the action/chamber. Result is a higher velocity with each successive shot. The more rounds fired in a string, and/or the longer a round is held in the hot chamber before firing, the more the velocity increases.

The cure for this problem is to cool the rifle between rounds, with the action open, while leaving the next round in the (cool) magazine until ready to fire.
 
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