doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com burn rate and psi

Miller, I understand what you are saying. My question is what wears at the gun more. A constant or increasing pressure down the barrel or a greater pressure in the chamber that falls off sharply.
Geno, I am not ready to pay for that,but might if provoked enough. 7625 is very expensive and getting to be a pain to find consistently.

You won't live long enough to determine the difference. Neither type of powder will wear the gun out. Keep the wear points clean and freshly lubed and don't worry about the type of powder. Reasonable velocity(1150-1200fps),light shot loads(7/8-1oz) and pressures as 2P suggested will do the job, nicely. A faster burning powder will be cheapest in the long run.

I have Larry's articles. Mr. Bell's article compares the presure of various black powder loads with low presure smokeless loads @ 5 points along a 12 ga barrel. none of these loads were above 6000psi so we can't say for sure what would with the 7k load vs. the 48oo psi load. But it was very clear that his 7/8 oz 4800psi load was 100psi higher at the chamber gauge and lower thruogh the rest of the barrel than BLACK powder. Without srtain gauge measurement @ varius places along the length of the barrel. If someone has the results of such an experiment please sare. Mark

I have a Pressure Trace with strain gauge.the first bought in 2005,direct wired, and failed this year.The second, wireless Blue Tooth and just installed.I reported results in 2005 and received comments about calibration and tried to explain how that is done with a strain gauge.Some just cannot understand,but if you wish,go to the Pressure Trace site and read or have someone read it to you. Anyway,the curves are as described above and I will need to print them out,use my planimeter (a very good one )and maybe report(slower is lower at the chamber,but higher further down the barrel when compared to faster) .Today,the experiment is to base line new AA's-6453,6403,5798,6151;5949 psi.The curves look to be the same, but peak at:.45 for one,.6 for three;.8 for one.This all in millisecs as the PT measures in 1/10,000th sec intervals for a three millisec total.Next, the same shells will be reloaded,shot,reloaded,shot,etc. to see if there is any change in pressure etc. as shells are reloaded many times (I think crimp may be a problem).BTW, Armusa low pressure are(5000 psi),Wallyworld are not(hot);fast is faster than slow but not alot( sorta like the first place Olympic 100 meter guy is fast and the fourth place guy is slow)

Mark, thanks for looking that up! Most of the time, I can remember the basic conclusions Bell reached, but not the details.

It's really quite simple. Here is a quotation from the PressureTrace web site;

"PressureTrace will generate PSI estimates without calibrating the system to a factory load!
Using factory ammo or a load reference with known pressure to verify results is always recommended but we recognize each chamber will produce different pressures and wildcatters may have nothing for comparison. PressureTrace uses both thick and thin wall open vessel algorithms to provide reasonably accurate pressure estimates from barrel, chamber and brass dimensions. Unlike other products PressureTrace does not require a large correction "fudge" factor for pressure held by the brass but the system can still be calibrated to match other pressure systems. For safety, NEVER exceed the loads in a reputable load manual.

Note: If a barrel is not cylindrical at the chamber (where the gage is glued) the system MUST be calibrated against a load of known pressure. This is particularly true of double barrel shotguns with a strong flare near the locking mechanism, octagonal barrels, etc."

Your strain gauge is not calibrated and produces only SWAG estimates of the pressures inside the barrel to which it is wired. RSI admits as much; '...reasonably accurate pressure estimates...'.

None of this is necessarily bad, so long as we don't start treating SWAGs as if they were accurate measurements.

If you find any of this difficult to understand, perhaps it will help if you 'have someone read it to you.'

Well, thanks to Jim Legg and Mr. Apperson,and 2-piper, I will try a "faster" powder,probably the Clays formula seen in the recent thread on this site,and will not expect to knock a piece of the breech face off my gun.
Thanks all, Justin

I used fast and slow and now 700X for everything low-pressure 12 gauge.

Thak you William for saying so well what I was trying in my feeble way to say. Everyone understand when I mentioned the higher bbl pressures of the slow powder loads This was not meant to imply they would "Spike" to dangerous pressures, but simply that what was lost at the beginning would be caught up further on, the pressure will not remain lower all the way down the bbl, the curves will in fact cross. The attempt is actually to more or less replicate Black powder performance which when loaded to the same terminal ballistics will also have a higher "Barrel" pressure than will a fast smokeless. The big fly in the ointment here is that while black will burn at essentially the same rate under any imaginable pressures, these slow smokleless powders loaded to very low pressures can become exceedingly unreliable.