I know this topic has been beaten to death and that the general thought is that, as LL demonstrated, POI does not (or should not) shift as the barrel heats up. Moreover, if there is shift, then its likely that the barrel was poorly made (not stress relieved etc.).
However, I think there's a new factor worthy of consideration: <span style="font-weight: bold">the length of time a cartridge has been in the chamber especially when using a temperature sensitive powder.</span>
I say this based on observations made shooting this past weekend. In short, my barrel got pretty hot and likewise, the chamber was just as hot (Remington 700). With the barrel/chamber still hot, I loaded the internal mag with 4 rounds. I chambered round 1 and it took me about 30-45 seconds to get on target and fire round 1. I chambered round 2 immediately but this time it took me >1 minute to fire round 2. Round 2 impacted about .3 to .4" high at 100 yards. I immediately chambered the next round and fired round 3 in about 30-45 seconds. Round 3 clovered with round 1. I immediately chambered round 4 and like round 2, >1 minute passed before firing. Round 4 clovered with round round 2 on the target.
I was able to repeat this another couple of times, which is difficult given that I had to "throw out" any group to which there was discernible shooter error.
My load: 175 gr SMK, Lapua brass 3x fired (neck size only), 43.1 grs RL-15, CCI 200 LR primers.
RL-15 is known to be temperature sensitive (opposed to Varget). Ambient temperature was about 55F and ammo was kept in open box (so figure ammo was exposed to 55F). I believe this makes sense since loads developed in the winter time can be "hot" when shooting that same load in the summertime. Here, the cartridge is heated up just like in the summertime except that it is the length of it's <span style="font-style: italic">duration in the chamber prior to firing </span>. The more time the round sits in the chamber, the more likely the internal temp of the powder rises, which increases the velocity and hence the shift in POI.
The purpose of this post is to see if this is (1) repeatable by anyone else, and (2) to keep in mind of how long a round has been in the chamber if there is a significant pause between shots relative to pauses between other shots in the same string/group.
To see if this is repeatable by anyone else here, whenever your barrel gets hot, fire a string of rounds but hold every other round in the chamber 30-60 seconds longer (heat up the ruond) and then fire. Shots that were held in the chamber longer should impact slightly higher and/or have higher velocities.
This is limited to circumstances when: not sufficiently letting the barrel "cool down" between shots & using temperature sensitive powder.
However, I think there's a new factor worthy of consideration: <span style="font-weight: bold">the length of time a cartridge has been in the chamber especially when using a temperature sensitive powder.</span>
I say this based on observations made shooting this past weekend. In short, my barrel got pretty hot and likewise, the chamber was just as hot (Remington 700). With the barrel/chamber still hot, I loaded the internal mag with 4 rounds. I chambered round 1 and it took me about 30-45 seconds to get on target and fire round 1. I chambered round 2 immediately but this time it took me >1 minute to fire round 2. Round 2 impacted about .3 to .4" high at 100 yards. I immediately chambered the next round and fired round 3 in about 30-45 seconds. Round 3 clovered with round 1. I immediately chambered round 4 and like round 2, >1 minute passed before firing. Round 4 clovered with round round 2 on the target.
I was able to repeat this another couple of times, which is difficult given that I had to "throw out" any group to which there was discernible shooter error.
My load: 175 gr SMK, Lapua brass 3x fired (neck size only), 43.1 grs RL-15, CCI 200 LR primers.
RL-15 is known to be temperature sensitive (opposed to Varget). Ambient temperature was about 55F and ammo was kept in open box (so figure ammo was exposed to 55F). I believe this makes sense since loads developed in the winter time can be "hot" when shooting that same load in the summertime. Here, the cartridge is heated up just like in the summertime except that it is the length of it's <span style="font-style: italic">duration in the chamber prior to firing </span>. The more time the round sits in the chamber, the more likely the internal temp of the powder rises, which increases the velocity and hence the shift in POI.
The purpose of this post is to see if this is (1) repeatable by anyone else, and (2) to keep in mind of how long a round has been in the chamber if there is a significant pause between shots relative to pauses between other shots in the same string/group.
To see if this is repeatable by anyone else here, whenever your barrel gets hot, fire a string of rounds but hold every other round in the chamber 30-60 seconds longer (heat up the ruond) and then fire. Shots that were held in the chamber longer should impact slightly higher and/or have higher velocities.
This is limited to circumstances when: not sufficiently letting the barrel "cool down" between shots & using temperature sensitive powder.
