Why have low pressure limits on modern guns????
Lets assume a cartridge was totally encased in the chamber, had a solid seal to the bolt with no part of the case left unsupported. Case failure would then not be the limiting factor for pressures. Several modern rifle designs are very close to this encased design.
Why are pressures kept to a SAMMI maximum of about 65,000 PSI in firearms. It seems that pressures of at least 100,000 PSI would be safe in a firearm made with steel in the 200,000 PSI class. The MV would skyrocket from what we have now. 5,000 FPS here we come.
Where am I going wrong???
Why are pressures kept to a SAMMI maximum of about 65,000 PSI in firearms. It seems that pressures of at least 100,000 PSI would be safe in a firearm made with steel in the 200,000 PSI class. The MV would skyrocket from what we have now. 5,000 FPS here we come.
Where am I going wrong???
0
-
The limiting factor to propel a projectile much past 4500fps in a rifle isn't pressure, but rather the modern conventional smokeless powder. IIRC, the powder just runs out of oomph. 0 -
The standard answer: Because the ammuntion manufacturers always have to consider the possibilty that modern, very powerful ammo will chamber and be fired in an older, weaker gun without the design attributes you admire. Metallurgy has improved greatly in the last 20 years, but that doesn't strengthen the older guns.
A sightly different answer: Assuming new guns made out of modern materials that chamber a cartridge unique to themselves, there is no reason why your dream can't be fullfilled. We are seeing the beginnings of this happening in cartridges like the Winchester Short Magnums, and the Lazzeroni line. Stick around--there will be more, high intensity cartridges appearing in this decade. But-just how much can your shoulder take? They have not redesigned or improved shooters.0 -
Can't keep the bullets together.
I WOULD RATHER BE DUCK HUNTING.0 -
I think Duckhunter has stated the answer.
From what I have read on the subject, the limiting factor is not so much containing peak pressures in the firearm, but is a question of maintaining the integrity of the bullet. Sporting bullets subject to such velocity tend to disintegrate.
It is possible to build a bullet that will endure these forces as has been demonstrated and used by the US military in some of their ultra velocity munitions. But then it isn't a sporting arm or sporting arm configuration. Even if a bullet of such durable construction is fabricated (which is possible) barrel life would be dismally short.
Regards,
Heavyiron[8D]
"If I don't see you nomore on this world, I'll meet you on the next one, and don't be late!" - Jimi Hendrix0 -
As "dergerbirsjaeger" and "duckhunter" point out, the combination of internal and external ballistic pose limitations in what is practical and not just feasible. Centrifugal forces in the bullets tend to distort them and tear them apart, especially on regular lead or thin jacketed bullets. Then there is the actual air resistance as speed increases, making it exponentially harder to accelerate or maintain any speed and stability...etc. Reaching a good performance ballistic formula takes into consideration much more than just peak chamber pressures. 0 -
Aren't chamber pressures normally expressed in CUP (copper units of pressure)???? I don't believe I've ever heard of them expressed in PSI (pounds per square inch)..???? 0 -
Jim
The methiod of expression depends on the equipment used to measure the pressure. Copper crusher systems use the CUP (or LUP if a lead pellot is used) "Copper Units of Pressure".
The newer Piezzo and strain gauge systems use PSI (pounds per square inch).
ANSI lists some cartridges with CUP limits only, some with PSI limits and some with both. There is also the European system CIP, again it uses both types (crusher and Piezzo) but measured in the throat area instead of through the case wall like ANSI does.
There are some approxamation formulias for converting between the systems, but none are perfectly accurate (sometimes CUP is higher than PSI, sometimes it's lower).
223Rem 52000CUP, 55000PSI, 370 CIP crusher, Not Specified
22-250 53000CUP, 65000PSI, 350 CIP crusher, 405 CIP transducer
243Win 52000CUP, 60000PSI, 360 CIP crusher, 415 CIP transducer
6mmRem 52000CUP, 65000PSI, 370 CIP crusher, 430 CIP transducer
444Mar 44000CUP, 42000PSI, 310 CIP crusher, 355 CIP transducer
Bpost Check out hoop stress/strain, bolt thrust/shear strength, cyclic fatigue, and other engineering considerations. Besides, as one other poster pointed out, It's not the peak pressure, it's the pressure/time/distance (work under the curve) that is the main limiting issue. The powder gasses only expand at around 5500fps and so that's your limiting factor (unless you can figgure out how to get additional fuel/gas into the reaction as the bullet travels down the barrel, like the Germans did on a prototype cannon in WW2).
Some guys like a mag full of lead, I still prefer one round to the head.0 -
There are practical gains to be had out there. The 30-06 factory load is loaded to a Sammi pressure of 50,000 because of older rifles that chamber this cartridge. The standard 270 is loaded to 55,000. Any gun thats ever been chambered in 270 can handle this higher pressure in 30-06. A handloader can load the 30-06 (in his modern rifle) up to the 55,000 level with no problems. This gets the 150 gr. bullet up to about 3100 ft per second instead of the standard 2950. Like all load testing you want to slowly work your way up looking for signs of high pressure. Also other problems come into play with higher pressures. In a pump or lever rifle you may have problems with extraction. But I have done this for years with no problems and have read articles in gun mags where some writers have done it too. 0 -
Guys; All of you seem to have missed the point that the PRIMER is the limiting factor! Having blown a number of primers in my younger days, this is not something you want to take a chance on. The gas from this has blinded a number of shooters in the past. ALWAYS WEAR
EYE PROTECTION WHEN SHOOTING!!!
Active old guy who lives with two dobermans.0 -
I read the above reasons and they are well taken. I agree that before we can go to 100,000 CUP we will have to redesign the primer. They will not stand that much pressure as they are right now. Second we will have to come up with a new case. Brass begins to flow at around 52000 CUP pressure and it will only accellerate as the pressure goes up. Also, I will have to be convinced that the modern rifles will stand 100,00 and high CUP. I've read about rifles that blew up with partial bore blockages --not completely plugged to give too much credence to the theory of unlimited chamber pressures. If you think I'm wrong, just load your 30/06 or .270 with 2400 powder at your load weight for 4064 and see what happens to it when you touch it off. But please do it from a safe distance with a string to trigger as I don't want to hear of your injury or demise. 0
Please sign in to leave a comment.
Comments
10 comments