Air Gun Home :: View topic - 8.2-8.5 .177 grain pellets okay for a 1000 FPS rated break ?

donec · Senior Member

So if you fire a heavy pellet in a springer rifle with the ability to fire a pellet at 1000fps you can break or damage the airgun. To me that means that any air gun that has had a jammed pellet should be considered damaged.

rsterne · Moderator

DeadEye · Member

http://www.grc.nasa.gov/WWW/K-12/airplane/kinth.html

Low boiling point gasses are almost the entire make up of air. I takes very little change in temperature to get them excited. Then the collisions of molecules rebound. Especially when they are trapped.

Slavia · Moderator

Wow, you guys have been busy.

This thread is an amplification of another that came up recently:
http://www.airgunhome.com/agforum/viewtopic.php?t=4456

In trying to analyze all this, I find most of it to be based on credible science and satisfying logic. To make sense of it (and to answer the question regarding heavy pellets), my urge is to whittle it down to what I would call "normal operating conditions." Subtract re-cocking and coil bind due to detonation. Subtract dieseling due to recent lubrication with low flashpoint lubricants. Just consider the normal, stabilized operation of a springer with heavy pellets. I can accept the rest of it as being true, but not usual.

Then subtract "celebrity" opinions. If an airgun guru can provide emperical data, then consider the information. If it's an impression without explanation or support, the discount it - no matter what status they may have in the airgun universe.

What do you have left? Pretty much nothing that helps answer the question. I'm not putting down any of your thoughts; I'm just not satisfied that it adds up to an answer that I can use. So here's what I would like to know:

1. What experience have you all had with damaged springs and heavy pellets? I have had two broken springs - neither related to the use of heavy pellets. One of the guns (a G1+new spring) has since digested an almost exclusive diet of about 2,000 10.5 grain pellets without problems.

2. Do you know of any resources (links) that back up opinions with quantifiable experience (i.e., numbers)?

And here are a couple of questions relating to the Cardew books. The copies I read came to Minnesota from the Seattle library through interlibrary loan, so if any of you have a copy, look it up for me, please. I believe their research was done with a BSA Meteor, which is rated at about 7.5 joules/5.5 FPE:

1. They described an experiment where they shot in a pure nitrogen environment, and recorded a 40% decrease in FPE from a normal (oxygenated) environment with "lean burn combustion." What pellet did they use, what lubricant did they use, and how many rounds had it been since lubrication?

2. They describe that "piston rebound" effect before the pellet starts moving. What pellet were they using?

Good discussion, guys.

Lipoly · Veteran Member

Amigo · Veteran Member

rsterne · Moderator

Amigo · Veteran Member

Slavia:

I'll be happy to send you The Cardew info as I find it.
For some unknown reason, I do not have the option of editing my posts so I'll not have to waste as much time trying to avoid typos if I PM you.

Amigo

Amigo · Veteran Member

Cardew's Nitrogen experiment
The Nitrogen Experiment - Last paragraphs of p.18 and all of p. 19

Establishing the difference between the popgun and the combustion phase is not easy. Clearly there is a big difference between the velocity attainable by a well-oiled gun and one that is dry, the reason for the difference was originally thought to be the friction in the unlubricated condition. We tended to think that a dry leather piston head set up enough friction with the cylinder walls to kill all the power. We did many experiments, some of them quite bizarre, in the hope of isolating the energy produced by combustion from that provided by the spring; a gun was totally cleaned and washed out to remove all traces of oil or grease, then it was rebuilt dry graphite powder as a lubricant - it sounded like a "bag of Washers", but there was still the smell of exhaust. Even a totally dry gun was clearly finding something to burn because the acrid smell of exhaust at the muzzle was very obvious, even using pellets that had been thoroughly degreased still did not cure the smell.

Finally the "Nitrogen Experiment" was embarked upon. A.22 Weihrauch HW35 was stripped, degreased than carefully employing the correct amount of lubrication everywhere. The gun was then fired continually over the chronograph until its velocity had settled to a consistent figure of 636 FPS when shooting a 14.4 grain pellet. That is 12.9 Ft.lbs. We then placed the action of the gun together with a supply of pellets in a long plastic bag and sucked all the air out with a vacuum pump; we left it in the bag for about half an hour whilethe air, and especialy the oxygen was drawn out from the leather piston head and from any other crevices too.

The bag was then firmly sealed around the barrel and a rubber bung pressed into the muzzle to make it air tight so that no air could possibly re-enter it. Finally nitrogen, an inert gas that cannot support combustion, was blown into the bag expanding it to a manageable size for shooting, the gun was then loaded and fired a number of times, of course the bung in the muzzle had to be removed and refitted at each shot so that no oxygen could enter the system - loading the pellets was certainly no easy task. This time the gun only produced 426FPS or 5.8 Ft.lbs.

Once the combustion had been eliminated by the nitrogen the gun's power had dropped dramatically and was only producing 45% of the original power - just under half - without interfering with the characteristics of the the lubrication. The gun was later removed from the bag and fired in air as normal, the velocity soon returned to its original value. This little experiment proved to that whatever lubrication is employed it will not only reduce the friction between the moving parts but also add to the energy within the system by providing a combustion fuel.

All the facts and arguments regarding the four phases apply equally well to spring powered air pistols too. Although the spring power in a pistol is far lower than that in a rifle, the area of the piston is also reduced so the air pressure generated as the pistol fires is about the same, certainly it can be high enough to cause combustion.

Amigo · Veteran Member

Bob:

On the coil bind issue - If a guy has altered his spring preload (or could be called precompress/ed) by adding lubed washers at each end of the spring to reduce spring torqueing, it can already be real close to coil bind at its normally cocked position. Now under conditions we've been discussing add in combustion - not detonation, but combustion as your additional power source and the recipe has the potential for problems.
Hey man, don't worry about or apologize for being skeptical. After all, if someone had not been skeptical of the flat Earth theory, the indigenous people of the Americas would not have had the opportunity to experience the civilized white man's practice of genocide.

Find the post in this thread titled: Cardew Nitrogen Experiment
Using graphite powder as a lube they were getting some combustion.

BTW, unless you're a neighbor to a certain airgunner in Miss. your Moly is probably not in pure unadulterated powder form. It is likely in the form of a paste and what makes it a paste is the petroleum based grease the Moly powder is mixed with.

Again, best regards,

Amigo

Amigo · Veteran Member

Cardew's book 3rd para. p.17 They are covering the 4 phases of airgun operation - Blowgun, Popgun, Combustion and Detonation

A detonation in an airgun produces a very sharp rise in pressure within the cylinder which is often sufficient to cause the walls to bulge in front of the piston. The piston will then be smartly driven back against the spring at a very high speed, often re-cocking the gun, or damaging the trigger mechanism. At the same time the pellet will usually leave the muzzle at high velocity accompanied by a very sharp crack - loud enough to make your ears ring - with plenty of smoke and possibly an orange flame and sparks at the muzzle.
However, although the pellet usually emerges at high velocity this does not always happen, many instances have been observed when the pellet has left the bore below the normal velocity for that rifle. In most instances the extremely fast return of the piston causes the gun to jerk violently, it also damages the spring causing the coils to be permanently forced closer together. The shortening of the spring reduces its energy storage capacity and therefore the future power of the gun.

on p. 18 they do go on to mention that the term dieseling is rather inaccurate as a term for detonation but is becoming accepted.

DeadEye · Member

Lipoly · Veteran Member

Thanks DeadEye.

Amigo, thanks for all that typing, good read! All the theory sounds reasonably sound, but the question remains: at what weight does the projectile start to do damage. I don't see anywhere in the posts you've made here suggesting the 10gr you mentioned before. Also, the posts you've just quoted from seem primarily to talk about combustion (which is part of normal operation) and detonation; not the main topic which is heavy pellets = dorked up gun. I can agree that if you use such as heavy pellet as to induce detonation then you've got a problem, but if you stay below that, I still don't see where the damage is coming from. The main question is again: where does the research suggest that starting at 10gr you run the risk of damaging the gun (in .177)?

donwalk · Veteran Member

i seriously doubt a pellet that weighs in at 10.5 grains or less is going to do any damage to a magnum springer (rated at 1000 fps or more)

keep in mind, most manufacturers use the PBS pellets or some other extremely light pellet, for their posted 'speed' ratings.

it the "real world" most of those springers are capable of propelling a 8.0-8.5 grain pellet at nearer 900-950 fps...which ain't too bad by any standard.

i shoot Benjamin discovery, .177, 10.5 grain, pellets from my Beeman R-10 and RWS 52...and yes, they do drop...but that's what elevation knobs are on scopes for. for what they are, they do hit VERY hard...even at fifty (50) yards.

guys..keep in mind...we're talking about a piece of lead that weighs around 10 grains...it's limited by the propulsion system driving it.

rsterne · Moderator

Even IF I assume that "Combustion" is the normal mode of operation for 1000 fps Springers.... Cardew's description of "Detonation" is obviously what we now commonly call "Dieseling".... and it is that detonation that they describe as harmful to the gun.... (no question there!)....

Are you asking us to believe that using a heavy pellet will take a well settled in gun (which for purposes of this question we will assume is operating in the combustion mode).... and cause it to change to the detonation mode for more than a few shots?....

I personally see no difference between a spring damaged in, lets say, 5 shots with a light pellet, 10 shots with a standard weight pellet, or 15 shots with a heavy pellet.... In every case, it was the DETONATION that caused the damage.... I still see no evidence for your description which I quoted in my previous post: