Seal to pellet corealation question?!?!

[tjk]

Ok folks here's a mystery I can't figure out,...or I just discovered something here!?!?!?! Here's a bit of back-ground info. Last weekend I re tuned my Sierra-Pro rifle. Now I've shot this rifle ALOT,...bagged many BT's with it to boot!!! Come on huntin'season!!! But any ways. After spending some time re working this rifle,...different spring coil count,...altering the spring seat,...I decided to stick with the original seal. Now I've shot every pellet in my armory,...Beeman SB's, RWS DS's, JSB exacts, Peak pellets, Beeman FTS's,..and even a few CPHP's,....but all of these pellets leave alot of dieselled vapor inthe barrel,...as well as inconsisting shots,...a few close to POA,...and then some flyers.....,and boy did they fly all over the place!!!!!. So I decided to remove the scope and take her back to the 'OR' and re-place the seal with a new apex,..or even a tesle seal. Buuuutttt I forgot my wrench-box at the shop,...and it has my metric allen wrench set in it!!!! I replaced all the stock screws with allen cap bolts,.....Well I decided to shoot it 'shot-gun' style at my indoorhall-way range,..with the Beeman Cro-mags. A little more back-ground info,...These are all I ever shot thisrifle with excusively,...and guess what,...no dieselling in the barrel?!?!?!?! Even the same/or close to grain weight Beeman FTS's dieselled,...but the Cro-mags???,......not a bit of vapor to be seen!!!!!! Now I really wish I would have left the scope on it. But it was getting dark outside so I didn't think to try them out earlier. So here's my question,....If a seal is accustommed to shooting a pellet of a certain grain weight,...and specific skirt diameter,...such as the Cro-Mags,...would this be a "set-seal" phenomenom/effect?!?!?! TJK

PS Upon inspecting the old apex seal during the tuning process,..it was in perfect condition,...and comparing it with the New Apex seal,...I couldn't see or measure(with dial calipers)any difference,...besides some lube stains/use. Anyone got a clue on this,...or a logical exsplainationwith this reaction/result??

[speedturtle]

I have used both the original G-1 seal and replaced it with JM's small red apex seal. What I have noticed after replacing the stock seal with the apex is that there is an immediate reduction of dieseling or the presence of smoke in the barrel. IMO the apex seal is more rigid which means it can hold its form and exerts more outside pressure to the compression chambers I.D. than the stock seal. The after effect would be a more consistent FPS and P.O.I. Another benefit is that any excess oil or lube behind the piston seal can't be immediately carried over by the seal since there is a tight fit on the I.D. of the chamber hence the immediate reduction of dieseling smoke.

If we will just base our comparison on visual inspection we would say the stock seal is still OK after so many pellets shot. What we don't know or quantify is the ability of the seal to maintain its sealing force on the chamber. If you want to find out if the stock seal has lost its sealing ability you would notice it when you take out the piston unit from the receiving tube. The whole piston unit comes out easily. Another manifestation is that when you are using lighter pellets you would notice that the sound of the piston hitting the transfer port plate is more pronounced. That would probably indicate that you are losing valuable air pressure behind the seal instead of concentrating it all to go out via the transfer port.

Just my opinion on your inquiry TJK.

[tjk]

Thanks for the imput ST. No we're not losing any pressure from around the old APEX seal at all,  nor did the piston slide out of the action with ease. So going on what you said,...our seal seems to be working in perfect order!!! No smoke coming from the  action cocking slot either.  Maybe the weight and the shirt diameter of the Cro-Mags is enough resistance to keep whatever lubes in the comp chamber from escaping into the barrel. I just thought this was an interesting observation while comparing them to pellets with the same weight that dieselled. Hell I don't know,..just thought I'd throw this out there. tjk

[leadbottom]

tjk - 7/2/2009  10:57 AM
I just thought this was an interesting observation while comparing them to pellets with the same weight that dieselled. Hell I don't know,..just thought I'd throw this out there. tjk

This is interesting.  I wonder if maybe the non-dieseling pellet is a looser fit in the barrel and is allowing a lower pressure build-up in the compression chamber to the point where dieseling pressure is not reached.  Just speculating...

[tjk]

Sounds as good as any reason so far!!! LOL's Let the spit-balls fly!!!tjk

[tjk]

Latest test results. Hitting the high 890's to 920's with 8.8 grainned Beeman Cro's. This with an old APEX seal,...and zero dieselling!!! About the same velocities as the RWS SD's at 8.3 grains with a slight bit o' vapor in he barrel,...Go figure?!?!?!?! BT's beware, SP's PO'd and ready to slay!!!!  tjk