SBR Noise

[GRIFFIN ARMAMENT]

So in my original hypothesis of creating ammo that from the get go has lower original chamber pressure, wouldn't that allow 'decorking' to occur at much lower PSI and thus (maybe) mitigate some of the PSI blast and allow for slightly better suppression?

YES absolutely you would reduce the sound of the firearm both with and without the suppressor. This would be similar to 300BLK. It produces a somewhat sedate unsuppressed numbers for SPL.

Re decrease in pressure and value of pursuing it:

YES of course- a decrease in pressure will cause a decrease in sound. You will probably also lose velocity with the pressure decrease though. That's probably why people don't pursue it.

Re comment on oil:

Yes I change the oil on vehicles every 3000 miles. Despite the fact that the transmission usually ends the vehicle and the engine would probably run on 150K more miles. So I'm probably actually wasting some money and 3000 probably isn't the perfect number, given other major components will end the life of the vehicle ahead of time.

[Joelski]

Ditch the dino stuff. I put synthetic in the tranny, diffs and transfer case too. Crankcase lube gets changed yearly and still looks good.

[alamo5000]

OK so I did a little bit of experimentation... I bought a pound of Winchester 748 because that one has the lowest listed CUP value out of all the powders on Hogdon's reloading data.

According to Hogdon's data a 55gr SPR SP has a CUP value of 39,000 at max load...

Well I didn't use Speer Soft point bullets... I bought a box of 1000 Hornaday FMJ 55gr and tested with that.

The only other bullet that they have listed at 55gr that compares the powders is a Barnes TSX FB... with that bullet the CUP values are much closer...48,500 vs 50,300 at their max loads...



Long story short I loaded rounds to almost identical (pretty close) velocity averages and there was marginal, if any, difference in sound. Of course I don't have a meter but there was no discernible difference in sound.

Anyway I almost satisfied my curiosity about the Winchester powder...It actually works great for plinking ammo and it meters really well. I just basically finished off the pound of powder so I have a couple hundred loaded 55 grain rounds now.

On a side note the powder was somewhat cheaper than some of the others and as I said it meters really well so later on up the road I might get some more to make plinking rounds with.

[alamo5000]

I am getting way over my head here but I am reading about CUP vs PSI and those two are NOT the same thing. At best they have a rough correlation to each other. From what I can tell CUP values are estimates only whereas now they are actually measuring PSI in some cases.

CUP generally measures peak pressure...so basically my theory is that the properties of the powder do make a huge difference in CUP and in PSI. So say you had a powder that had a violent expansion...the CUP would be pretty high...but if you had a powder that had more of a controlled burn the CUP might be really low. That said the actual PSI to get the bullet down range is obviously still present although how it gets there is slightly different. Google and read up on how they measure CUP if you are curious about it. It will make more sense...

I learned something but this is getting too nerdy even for me...

Long story short myth busted.

Also don't use CUP and PSI interchangeably like I was thinking... they are not the same thing.

[Former11B]

Did you learn that 160 dB sounds the same no matter which powder you use.

[alamo5000]

Also if you notice on the data on their reloading page that I pulled... one is listed in PSI (the Barnes) and the other is listed in CUP (the Speer)...

I didn't notice that until just now. The measurements for the Barnes now seem like they are more accurate across the board because it is two entirely different measurement systems.

[alamo5000]

Did you learn that 160 dB sounds the same no matter which powder you use.

I learned that they way they measure pressure is entirely different. I was comparing apples to oranges...

CUP does not equal PSI

[alamo5000]

Basically from what I gather the measurements for CUP have been around quite a while... they have a test barrel with a small piston attached to the chamber. On the other end of that piston they place a carefully calibrated piece of copper (or lead for some rounds). When the gun goes off it forces the piston up and it crushes the copper. From that they determine CUP pressure estimates.

PSI on the other hand is just what it sounds like... PSI...

So basically as I said before... if your powder has a quick 'flash bang' component to the design of it the CUP will be more... but if the powder is designed to be more of a controlled expansion then obviously it won't send that piston up to crush that piece of copper nearly as hard...hence 'less peak pressure'...but by the time that bullet reaches the end of the barrel though there still is substantial PSI.

At the end of the day though PSI is what matters. Under pressure then the decork=the boom.