Impact Change Due To Heating

Dear pundit of powder, primers, pellets, and Perazzi’s that go POW:

We exchanged comments last winter about barrel cryogenics and the probability of barrel heat-up in the course of a trap round affecting POI.

I performed a highly scienterrific experiment last Saturday, the results of which I share below:

Ambient temperature was 68 degrees f, sunny, calm, dry, with high, thin cirrus clouds in the northwest. The gun was fired twice at no target to burn out any oil film from the thorough cleaning an hour previous. It was allowed to cool for 10 minutes

1. I fired 1 shot carefully at pattern paper #1 from 20 yards with full choke

2, 10 trap loads were fired as fast as could be cycled through a single shot BT-99

3. I then immediately fired one shot carefully at pattern paper #2 . (Same distance as first)

Steps 1, 2, and 3 were repeated resulting in 4 shots on separate papers, 2 hot barrel, 2 cold barrel.

My fellow practice squadmates (who were anxious to end this boring excercise) and I examined the results and came to the unanimous conclusion that all 4 shots had points of impact that were within a 2 inch circle i.e. nothing was going on here when the barrel got hot.

This is the same gun that I previously complained about going haywire (missed targets) after 10 or so shots. I have recently shot this gun after swapping to another and noticed that after 10 shots a spot on my shoulder gets kinda sore and my gun mount seems “uncomfortably wrong”. I now believe this factory Browning pad with its pointy ends is the culprit. My next scientific endeavor is to replace the pad with a flatter one and re-shoot (I recall you recommend the Sorbothane variety) to satisfy my need to put this subject to bed.

Advancing shooting science is dirty, tedious work but then someone must carry the knowledge base forward.

John, Chelmsford, Massachusetts

Dear John,

I was heartened to hear that your particular single bbl gun did not change POI with heat and that you can now blame it on the pad. We ought to send copies to all the cryogenic firms out there who claim that they can cure heat induced wandering POI by freezing things.

Personally, I have never thought much of the argument that hot barrels changed POI, but I guess that it would be possible. If you do all your shooting out of one barrel of an O/U the stresses are bound to be uneven. I don’t know what effect that would have though. The bottom line is that every gun is different. If a barrel is badly made and contains significant uneven stresses, it might be possible for heat to change things. I just have never experienced it myself to any extent that I could notice.

Also, you never got your barrel REALLY hot. I was once in a “hot” corner of a dove field in the Cauca Valley in Colombia. In the course of less than two hours I fired slightly over two full cases (not flats) of shells. I was using a Browning B-80 gas gun (Beretta 302 clone) so all those bullets went down one tube. The ambient temperature was also in the 90s at the time. Trust me, that barrel gave a new meaning to the word “hot”. Although game shooting is in no way as precise as patterning, constant dove shooting like that can give you a pretty good idea of where your POI is. I could detect no change in impact as the barrel heated to the point where it was literally “smoking”.

Best regards,

Bruce Buck
Shotgun Report’s Technoid
(Often in error, never in doubt.)

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