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Not really a gunsmith question, but I thought somebody here might know. Does shortening a shotgun barrel reduce the chamber pressure with all other things being equal?
Chamber Pressure Shortened Barrel
- Thread starter SurplusMan
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Blastattack
CGN Ultra frequent flyer
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- Winnipeg MB
No. Velocity will also be virtually unchanged as well.
It would depend on the original length and how much you shorten it but basically no. I have seen pressure reduction at the gas ports on a semi auto when cutting a barrel from 30 inches to 19 inches but I doubt that loss reached the chamber where it all started.
Peak pressure (chamber pressure) occurs after the bullet has traveled between 1/4" to 3" depending on caliber. 1/4" is for very small capacity handgun cartridges, to over 3" is for large, overbore magnums. From that point on down the barrel, pressure continuously drops.
Yes, the powder is still burning, but it can't keep up with the expanding volume behind the bullet.
Here is a QuickLoad graph (not mine) for 30-06. Red line is pressure. Note that peak pressure occurs at about 2-1/2" bullet travel.
Yes, the powder is still burning, but it can't keep up with the expanding volume behind the bullet.
Here is a QuickLoad graph (not mine) for 30-06. Red line is pressure. Note that peak pressure occurs at about 2-1/2" bullet travel.
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Thanks for the info. I've been contemplating if I want to shoot an old beat up Damascus barrel shotgun that has had it's barrel chopped some years ago to about 20" and i was wondering if that might make it any less dangerous with modern shells. Man I can't wait for some mini shells in canada.
Blastattack
CGN Ultra frequent flyer
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Unless the shotgun is Nitro rated, you SHOULD NOT under any circumstances fire commercial shotgun loads out of it, unless said loads are SPECIFICALLY loaded for Non-nitro proofed shotguns.
If the action of your gun is in good condition and not loose and floppy or the barrels deeply pitted you should be able to shoot the gun but only with handloads. If it is a 12 guage, I use 80 grains of 2F and 1 1/8 oz of shot. Important to use fiber wads and no plastic wads when shooting black powder (the heat melts the plastic). I use prelubed fiber wads intended for muzzle loading in my cartridge shotguns. Also I would recommend a card wad over the cushion wad (to prevent pellets being imbedded in the cushion wad). Also use plastic shells (Winchester AA stand up well) because paper shells are much thicker and raise your chamber pressure and more importantly because your chamber is probably 2 5/8" and the thick shell mouth 1/8" into the forcing cone will increase pressures. I do load and shoot smokeless in my damascus guns but I choose powder and loads that keep the pressure down around 7000 psi. There is a powder which will burn at 4000 but it also leaves a lot of unburned powder in the barrel. I do not load smokeless in my 20 guage guns because I don't know of any low pressure combinations for that guage and the chamber pressures in a 20 guage are higher than in a 12 guage
cheers mooncoon
cheers mooncoon
Chamber pressure is wholly unrelated to or affected by bbl length. How could it possibly be? Peak chamber pressure occurs within the first couple of inches of the bullet's travel. After that the volume behind the bullet continues to increase which, following the Gas Laws results in lowered pressure.
No you haven't. What you have seen is a reduction in the pressure dwell time. It is physically impossible to affect the pressure at the gas port by altering the barrel length past the gas port. Peak pressure at the port will occur as the bullet passes the port and allows maximum pressure gas into the system. After that the bullet moves forward which causes an increase in bore volume that continuously lowers the gas pressure. Not to mention that the now open gas system is rapidly leaking gas pressure as well.
