Cold barrel shot about 30-50 fps slower in a Witness Match .40

[Skydiver]

After downloading the data from my chrono to check for powder temperature sensitivity, I noticed that all the cold barrel shots out of my Witness Match .40 were about 30 to 50 fps slower than the average of all other shots. Fired 90 shots through the chrono: 1st mag to ensure chrono function, 2nd and 3rd for baseline temp, 4th and 5th to test warm rounds, 6th and 7th to test cold rounds, and 8th and 9th for post test baseline temp again. In all cases, the first round fired from each mag was much slower then the rest.

Is this really an issue of a cold barrel? Or is it powder placement within the cartridge after putting in a fresh magazine? 5.4 gns of Universal Clays only fills about 1/3 of the case.

[CHA-LEE]

I have noticed that the very first shot out of the gun for the day (Pull the gun out of the bag and shoot it) is some times up to 20fps slower than following shots. But after that first round is fired its pretty consistent, even when waiting several minutes between tests.

Do you clean the barrel completely before every range session? Maybe the way slower first shot is due to the barrel being too clean and a lot of gas is escaping round the sides of the bullet as it fires? I have seen this happen with my gun when comparing a perfectly clean barrel verses dirty when chronoing rounds. When I chrono rounds I try to make sure that my gun is as close to match conditions as possible. So I will usually not pull it straight out of the bag and chrono but instead shoot some practice stuff first and then chrono after. That way everything is at its "Normal" operating temp.

If you are going to a USPSA match that chrono's the rounds its within the rules to ask the chrono guy to fire a couple of test rounds through the gun BEFORE they start doing the actual chronoed rounds. This eliminates the chance of "Cold Barrel" syndrome at the chrono station.

[Skydiver]

I normally clean the barrel completely before every range session, except for times when I know I'll be running the chrono. For chrono sessions, I leave my gun in the dirty state as it was at the end of a match or a plate shoot so that I can simulate the stop at the chrono station in the middle of a match.

For the session above, the gun was dirty from the previous evening with about 100 rounds fired after cleaning the barrel before the plates shoot. To both test the chrono function as well as get the gun up to "normal temperatures", I fired my first mag of 10 rounds. As described above, I then proceeded with the rest of my chrono session. Between 10 round magazines, I would pause for about 2 minutes. This let the barrel slightly cool, as well as to give me a consistent amount of time to pull the warm bullets out of the thermos bottle, or the cold bullets out of the ice chest and put the bullets into the mag.

I'd not originally interpreted Appendix C2, #48, as a way to get the barrel warmed up. Reading closer though, there is nothing that prevents me from asking the chrono CRO if I can take advantage of C2, #48 to shoot 6 shots into the berm/target before they test my rounds.

[CHA-LEE]

Knowing the rules is a good thing