Barrel Life: Estimating With Mathematics

People ask me probably 10 times a day, “How long will my barrel last?”. I hate that question. Makes me want to bash my head on a desk because they’re asking me to predict the future and counting on my answer being exactly correct. It can’t. I can get close though and so can you.

Tada: Below is the actual equation that I use (NOTE: I did not invent it and never claimed to have.) to give me an idea of my accurate barrel life. This is really meant to deal with match rifles where 1MOA groups are simply not going to cut it. This is also not something that’s necessarily scientifically precise so please see and use it for what it is, a mathematical MODEL. I’ve shot rifles well past the numbers given by the equation below but they all would soon enough tell me or had already started telling me they’re giving up the ghost.

Variable Definitions:
Powder Heat in KJ/kg (kilojoules per kilogram): H
Peak Pressure in PSI (subtract 10,000psi for Moly: M): P
Bore Capacity = (Bore Diameter^2 * 1000) / 2: B
Powder Charge Grains: C

The Formula for Non-Moly Loads:
((3800/H)^5)*3600/(C/B)^2)*55000/P

The Formula for Moly Loads:
((3800/H)^5)*3600/((C/B)^2)*55000/M

So let’s do the non-Moly math for my .243AI (which is a known barrel burner). Conventional wisdom is something around a 1300 round barrel life. Let’s see what our model says…

First replace all the variables with my numbers.
((3800/3990)^5)*3600/((45/29.52)^2*55000/55000

Next, just like we were taught in math class as kids, do the insides of the parenthesized sections:
(.95^5)*3600/(1.524)^2*55000/55000 = (.7737)*3600/(1.524)^2*55000/55000

Once all parenthesized sections have been reduced, run the equation left to right:
.7737 * 3600 / 1.524 ^2 * 55000 / 55000 = 1199 rounds of accurate bore life.

So yeah, the model is looking very accurate so far. What it cannot account for is how long of a delay between shots or how hot the barrel gets. One varies radically while the other is based on the thermodynamic properties of the barrel and the effect of environmental conditions. I’ve used this model for everything from .223rem, .308win, 7BR, 7MM Rem Mag, .243AI, 6.5BR, 6.5×55, .30-06 and .22LR with substantial success. It predicts a 1.5MM round life with a .22LR. Yeah, that’s about right.

This barrel life calculator is included in BallisticXLR and can even track against how many shots you’ve already fired and logged.

Get out and shoot!

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