Air Venturi Tech Force M12 combo: Part 5

by Tom Gaylord, a.k.a. B.B. Pelletier

Part 1
Part 2
Part 3
Part 4

Air Ventury Tech Force M12 breakbarrel air rifle
The new Tech Force M12 breakbarrel is a new midrange springer from Air Venturi.

Today’s report is an important one, but it may be confusing until you hear the whole story. The last time I reported on this Tech Force M12 combo was back on November 19 of last year. A lot has happened with this rifle since then, and I’ve kept daily readers informed of what’s been going on, but it would have been easy to overlook and even easier to forget. So I’ll summarize.

The M12 I’m testing is a drooper, and I first had to solve that problem. Once I did, I noticed it threw fliers. I cleaned the barrel — but it got no better. I tightened all the screws — again, no change. I cleaned the barrel with JB Non-Embedding Bore Cleaning Compound — and still there was no improvement. Then, I shot the gun just to break it in — again, no change.

All of this work took a lot of time, as I was testing and reporting on other guns. I also set the rifle aside for weeks at a time out of sheer frustration. In late January of this year, I decided to have another go at discovering what the problem was. I had to locate a drooper scope because, by this time, I’d used the scope that was on this rifle for other tests. I reread the early reports and discovered that this rifle had shot very well at 10 meters with JSB Exact RS pellets. So, that was the pellet I tested, but at 25 yards.

Pay attention!
At 25 yards, I got several groups that had a bunch of shots close together and then some fliers. But one group stood apart as extraordinary. Seven of the 10 shots were in an extremely small group, and 3 others were huge fliers. This was what I had been looking for. When you see something like this, it tells you the rifle wants to shoot, but something is interfering intermittently.

Tech Force M12 breakbarrel air rifle 25-yard target
The group at the top left with the one shot that isn’t quite touching is 7 shots from 25 yards. That’s a 0.439-inch group. The other 3 holes are fliers shot at the same time. This is a clear indication of a problem.

I looked down through the muzzlebrake with a powerful flashlight and saw the real barrel muzzle deep inside. It appeared very rough, plus I could see bright bits of lead clinging to the inside rear edge of the muzzlebrake. I showed this to Edith, and she confirmed what I was seeing.

Apparently, the crown of the muzzle of my rifle was uneven and was causing pellets to wobble just a tiny bit when they left the barrel. A few of them were hitting the inside rear edge of the muzzlebrake, causing them to destabilize in a big way. Those were the random fliers I was seeing.

I communicated this to Pyramyd Air. Gene, the tech manager, took apart an M12 to look at the crown. He said it looked rough to him, as well. He crowned it and sent me the barrel to exchange with the barrel in my rifle.

The barrel Gene sent is .22 caliber, while my rifle is .177, but that makes no difference. One barrel works as well as another, as they’re the same size on the outside. I followed Gene’s instructions and switched barrels in 15 minutes. I didn’t have to disassemble the rifle because of how it’s made.

Once I got the original barrel out of the gun, I could see that the muzzle wasn’t as rough as I’d thought. I had seen grease on the end of the muzzle when I looked down inside, and it looked like rough metal to me. The muzzle is finished rather well, but the actual crown, which is a chamfer cut into the bore, is cut on an angle rather than perpendicular with the bore. It allows compressed air to escape the muzzle on one side of the pellet before the other.

Tech Force M12 breakbarrel air rifle 177 muzzle
The muzzle of the .177-caliber barrel that came in the rifle was crowned lopsided. The chamfer appears narrow at the bottom of the muzzle. That’s not an optical illusion — it really does grow narrow there!

Tech Force M12 breakbarrel air rifle 22 muzzle
It may be hard to see in this photo, but this crown is even all around the bore. This is the .22-caliber barrel sent to me by Pyramyd Air.

Following the assembly of the barrel to the rifle, I remounted the scope and proceeded to start my sight-in. I decided to test the .22 barrel with JSB Exact RS pellets, as well. One shot at 10 feet was all it took…and I was on target. Two more shots at 10 meters and I was sighted-in. Next, I shot a 10-shot group. The rifle behaved very stable and did not appear to throw any wild shots.

The 10-meter group I shot was consistent, if not terribly small. But the lack of fliers, even at 10 meters, gives me hope that the crowning of the barrel has solved the problem.

Tech Force M12 breakbarrel air rifle 10-meter target
Ten shots at 10 meters gave me this group with the recrowned .22-caliber barrel. This gives me hope that the problem has been fixed.

Test is not finished.
By no means is this report finished. I still need to shoot several groups at 25 yards to see what the M12 can really do. I have no idea what the best .22-caliber pellet might be. After rereading the first two parts of this report, I see that I very much liked the way the gun handles. That’s still true. It lacks the two-bladed Mendoza trigger — and that’s a shame, but the trigger it has isn’t that bad. Obviously, I’m able to use it.

I now have both a .22-caliber barrel and a .177-caliber barrel that fit on the same powerplant. If I can hold onto them both, I may be able to get a little more milage from this gun. First, I could do a redneck crowning job on the .177 barrel and report how well that works.

Next, I could test the .22 barrel for velocity and then swap barrels and retest the .177 barrel to get a comparison between calibers from the same gun. I’ve always been able to do that with my Whiscombe, of course, but this is more of a real-world air rifle to which many can relate.

I know there are several shooters who wanted the M12 to be a great buy, and my early tests didn’t bear that out. If they’ve continued to follow this blog, they’ll get the chance to see how the story ends!

65 Responses to “Air Venturi Tech Force M12 combo: Part 5”

  • Victor Says:

    B.B.,

    Sounds like a potential for QA issues with this rifle. Of course, I don’t know how different things would be for this rifle, versus most others. But wow! that 7 shot group is great for 25 yards. Sure would like to see that repeatable with 10 shot groups, should you fix the crown. The price is right, IF the back crown was a fluke. I’d venture to say that this rifle is in the moderate power range for a .22, so accuracy test’s at 25 yards, and maybe even 50 yards, would be interesting.

    Victor

  • duskwight Says:

    B.B.

    Crown is the king, as usual. Very impressive results.
    I wonder what would this rifle show with some extra work like bedding, spring guide/gas spring, anatomic heavy stock etc. It could be interesting – to upgrade every rifle up to its possible top and then test them to compare. Of course that doesn’t mean making recoil-compensating rifle out of D350 or converting TX-200 to gas spring (I’ve seen and shot both cases :) ). Just making everything top-notch, keeping rifle’s basic shape and constructive features.

    duskwight

    • B.B. Pelletier Says:

      duskwight,

      That would probably help the gun, but I don’t have a plan to do it. I do, however, plan on re-testing the .177 barrel with this series.

      B.B.

  • twotalon Says:

    B.B.

    Looking at those muzzle pics this early in the day was not a good thing.
    What’s worse, is that the second pic that you say was recrowned by PA….. looks horrible.
    I don’t want to know how they did that, or what it looked like before that if they thought it looked bad enough to do THIS recrown to.

    twotalon

    • B.B. Pelletier Says:

      TT,

      The PA crown is better than the original. I’m sorry that my photos don’t convey that fact.

      When you are seeing is the crown cutting into the rifling, which it is supposed to. The Mendoza crown has thrown up a uniform burr and you can’t see where the rifling transitions.

      B.B.

      • twotalon Says:

        B.B.

        My 48 HAD a crown that was quite a bit like the Mendoza. There was no transition, and the edge of the bore was not clean and sharp. I fixed that.

        The crown job on the other looks so rough that it sure looks like snag city. Wish I had some pics of some of the crowns that I have done. Was thinking about that just a few days ago.

        twotalon

      • twotalon Says:

        B.B…..
        How about a fast and dirty tip ????
        If you have a new barrel or have done a recrown there is a chance that the edge of the bore has some small fuzzies in it. You can’t see ‘em, and the Q-Tip test will not always spot them. Shoot a few PBA pellets through it and see if it makes the groups tighter when you switch back to lead again. I have seen this work. I think the hard pellets knock off a lot of the fine fuzzies.

        twotalon

        • B.B. Pelletier Says:

          TT,

          Good tip.

          Thanks,

          B.B.

        • duskwight Says:

          TT,

          Yup, I second that :) Another method is to use short and a tad expanded by skirting bits of 4,5 mm pure copper wire (or just hammer some 5 mm pieces through some steel drawing-block – it will also form the skirt). This way you can shoot really powerful springers without risking to overstress the spring and stock screws – they are heavy.

          duskwight

          • twotalon Says:

            comrad duskwight…

            There is also one of my latest tricks. I guess I could call it “slow motion ‘almost’ fire lapping”.
            It involves repeatedly pushing tight fitting lead pellets through the bore with polishing compound. Smoothes a lot of the roughness out of the bore and rubs the fuzzies off of the crown.
            Often there will be some fine fuzzies extending from the crown after this procedure. I can feel but not see them. A tiny bit more polishing of the crown very lightly will remove them. I use a crowning tool consisting of a steel ball and polish in the crown with bore polish. Then push a few more pellets with polishing compound and recheck the crown.

            twotalon

            twotalon

            • duskwight Says:

              Just like prescribed by The Party, comrade!
              However our local Committee someties opts for a bit different worker’s tradition for HQ barrels – run the upskirted pellet dry almost to the end and then apply some very fine toothpaste-liquid polishing compound at the very crown and then just push it out.

              duskwight

              • twotalon Says:

                duskwight…

                Just like back in the 50s….the Russians always thought of it first….

                I get the whole barrel.

                twotalon

  • Frank B Says:

    For some crazy reason BB,I’m actually excited that you have a barrel that may show a dramatic response to a good redneck crown job! Get out the acorn nut & lapping compound.

  • J-F Says:

    I think it illustrates perfectly the differences between rifles like this and the Wlather LGV of yeterday and why you pay a premium for the LGV and why I would buy the LGV before this one any day.
    I think that’s what John was failing to grasp yesterday.
    Not that there’s anything wrong with getting this one instead of the LGV. If you want a cheap capable rifle that needs a little love and attention to shoot it’s favorite pellet accuratly get this M12.

    If you’re looking for that perfect rifle that will shoot most of what you throw at it with extreme accuracy, feels solid and will last you a life time right out of the box go get an LGV or TX200.

    J-F

    • kevin Says:

      J-F,

      I’m in your camp on this BUT…….I’ve learned that there are many airgunners that are primarily attracted to this hobby because the aspect of airgunning they enjoy most is tinkering. Spending long hours in their workshops getting an airgun to perform it’s best. Many times this means taking inexpensive airguns and addressing/fixing the manufacturing shortcomings that made them inexpensive. Once these folks succeed in making a decent shooter from a poor shooter they’re bored and onto the next airgun fix-it challenge.

      I admire these guys. It’s just not me. I’d rather spend my time shooting.

      kevin

      • J-F Says:

        I know and I even understand it! That’s what I meant by “a little love and attention”.
        I know some people like to do that and there’s not anything wrong with that way of thinking.

        People upgrade Mustang and Camaros all the time, making them look, handle and perform way better than when they came out of the factory but if I can afford a Porsche 911 turbo I’ll be buying one and spend my days driving rather than under a car trying to upgrade it to the Porsche level.

        Now older cars/rifles it’s not the same thing, thinkering with those is keeping them alive and bringing old memories back.

        So brand new, I’ll take the Ferrari of airguns if I can afford it
        Vintage, I want the old workhorses, the icons, the diamonds in the rough and the forgotten ones that can still prove why they once were so popular or the cream of the crop.

        J-F

  • Victor Says:

    B.B.,

    So how do you do a crown? Wouldn’t you need a lathe? I haven’t used a lathe since machine shop over 35 years ago. Can it be done with a hand tool, like a Dremel? Yup, they don’t get much more ignorant about this kind of stuff than me.

    Victor

    • B.B. Pelletier Says:

      Victor,

      You don’t need a lathe and a Dremel tool is not the way it’s done. A hand drill is all you need, together with some know-how.

      I guess I will do a Redneck Crown Job for this blog.

      B.B.

      • Victor Says:

        B.B.,

        I think a blog on a Redneck Crown Job will be both interesting and useful. Think about all those air-rifles that could use one. If more people had a clue as to how they might restore accuracy, and thus usefulness from an air-gun that otherwise will sit in storage forever, they might actually be willing to try it. I would.

        Victor

        • twotalon Says:

          Victor…

          Just make sure that you don’t do it to a good shooter in an attempt to make it even better. THAT can cost you !!!!

          twotalon

          • B.B. Pelletier Says:

            TT,

            That is the reason I’ve never done one here. Some people read an article, see the results and imagine they will always get a benefit. Then they order a new rifle from a reputable maker and screw it up with all their “fixes” until they have ruined a good gun.

            B.B.

          • Victor Says:

            twotalon,

            I wouldn’t think of experimenting with a good shooter. I think it’s worth trying on a bad one, and especially something that was otherwise deemed hopeless, and thus condemned to some corner, never to be shot again. I think there are lots of rifles out there that fit this description.

            I know from experience what a good crown job can do. My Anschutz 1413 had a crown job done on it, and it was amazingly accurate, even for an Anschutz.

            Victor

            • twotalon Says:

              Victor…

              Yup. The hopeless ones would be the best candidates. But check out some things first….
              Push a few pellets through and feel out what the bore is like. If it is horribly rough, or gets loose at the muzzle, then a new crown may be worthless. If the bore is just too loose for any of the better pellets, then a crown is not going to do much for you.

              twotalon

  • Victor Says:

    B.B.,

    Regarding the MAV 77. I noticed that Crosman still has it in their website, but you can’t find it through their online catalog. I really hope this happens because I was hoping that this rifle could be a great way to introduce people to field target shooting, including myself. I’ll eventually own a TX-200 III, but I’d like to see something more affordable for others who find it harder to justify something like a TX-200.

    In a nutshell, the promise of what the MAV 77 offers is a big deal, I think.

    Victor

  • john Says:

    This rifle is showing why I avoid Tech Force guns. I don’t disassemble barrels on these types of guns and try and correct factory errors. If it comes with a problem that makes the gun inaccurate from the start it remains inaccurate to the end. It will likely just be put in a gun rack and left to deteriorate and gather dust along with quite a few really great guns that I rarely ever use anymore. Sadly I can’t seem to sell the guns I no longer want. But the guns I really like that I don’t want to sell I have a freind that will beg me to sell them to him until I finally say OK just to get him to stop. I guess I’m lucky he hasn’t decided he wants my condor. That would be one he never gets from me. I got way too much love into that gun to part with it.

    • chuckj Says:

      /Dave,
      Nice looking wood! We tried to warn you about our disease. What’s your prognosis for this beautiful chunk of art?
      -Chuckj

      • /Dave Says:

        Well, Chuck, I never had a flintlock… The chunk is 63″ long, Oregon black walnut with one void in the toe that I think I can work around. The curl in it tells me something Pennsylvania, but in walnut instead of curly maple. I studied under a traditional Pennsylvania Dutch gunsmith for a while about 30 some odd years ago, and built a couple of kits that turned out well, so after stumbling across this on gb I decided it’s time to get serious. I was actually looking at a smaller piece from the same guy when I clicked on this auction and only had a few minutes to decide. So, $200 later, here I sit with a grin on my face, staring at this chunk of wood, waiting for it to tell me what it wants to be (you woodworkers will understand that statement…). :-)

        /Dave

        • chuckj Says:

          /Dave,
          I know, you just carve away anything that doesn’t look like a beautiful flintlock stock. (I’m sure you’ve heard that one before)
          -Chuckj

    • BG_Farmer Says:

      Flintlock!

      • /Dave Says:

        BGF,

        It’s definitely gonna be a flintlock! That much I know for sure, and a looonnnggg one,… but which variant? The guy I got the wood from was going to do a Fowler, but I kind of like the Isaac Haines rifles on Jim Chambers’ site. The Fowlers are pretty nice too, but I’m pretty sure I want a rifle.

        /Dave

        • BG_Farmer Says:

          I tried to post you some helpful links, but they may be hung up waiting for moderation — they show up at the bottom of the comments section with the addition of “Your comment is awaiting moderation”. I hope I’m not in trouble with Edith!

          • /Dave Says:

            Thanks, BG. I’ll check them when they show up. If they don’t, you can email them to me at: dmagee1 @ hotmail. com (take out the spaces…) I’m looking at pictures and stats of late 1700′s flintlock rifles to see which might fit both my taste and the piece of wood. Once I narrow down the field, I’ll start making paper templates to lay out on the wood to be certain that they fit and then make my decision.

            /Dave

  • Herb Says:

    BB,

    Wow – Great job! You have really worked hard to get this one to shoot well.

    Herb

  • /Dave Says:

    I’m afraid I’m with tt on this one. That is really an ugly, rough crown job! Properly sharpened tools can make a world of difference and it’s no harder to sharpen properly than it is to sharpen improperly…

    /Dave

    • twotalon Says:

      /Dave….

      So what’s wrong with “galling in” a crown with an old rusty pipe reamer ?????

      twotalon

    • B.B. Pelletier Says:

      Dave and TT,

      You don’t always cut a crown. Sometimes you use an abrasive, which is what this is. That will leave the marks seen here.

      B.B.

      • /Dave Says:

        BB,

        I know. And I can’t wait for the (abrasive) redneck crowning blog! I just hope there are a bunch of people who ruin good guns after reading it, thinking just what you’re afraid of…. That way I can pick up some good deals on the yellow… JK! :-)

        /Dave

  • Victor Says:

    B.B.,

    You recently said something about re-lubing/greasing an air-rifle so that it was smoother, but then added that it would also drop the velocity some. What kind of grease, or lube, are you talking about and would recommend. I’m thinking that this might help with my most powerful air-rifle, which also happens to be my least accurate. I’m not much of a tinkerer, but this could be worth a little effort.

    Thanks,
    Victor

  • Matt61 Says:

    The old crown job, eh? Is this still a Chinese gun? That would explain the QC.

    Thanks for the explanation about the upended car although in terms of the third force law about action and reaction, I don’t quite see how running into a cable could flip the car up unless the cable was being actively moved. Any guesses as to the first thought of the cows after they fell out of the truck? Let me set up the problem, if you hook yourself up to a monkey’s consciousness and what comes out is a lot of swearing, then if you hooked yourself up to one of the cows, what comes out would be…

    Michael, yes bad-mouthing the Hells Angels could be interpreted as courage but also a drugged state or maybe insanity. Thompson’s .44 mag is surpassed by his tommy gun, but hunting pigs with it turned me off. Did you know that baldness is supposed give an impression of great strength? I understand this was the reason why Mussolini was bald since he was otherwise rather short and unimpressive physically. “Power perceived is power achieved” as it said in a bad martial arts movie whose title I can’t remember. It was pretty bad. In the finale, a guy tries to escape his pursuers in a gym by climbing up a rope suspended from the ceiling. That’s smart. They bad guys surrounded the bottom of the rope and one of them even climbed up another rope to chat with him. In another scene the mercenary hero is greeted by a new employer in his house who then releases a thunderous flatus. “Fiber is great for you,” he says. The things a mercenary must do…

    Genetics has a more optimistic take on baldness. The concept is that traits that have no obvious benefit or are even disadvantageous like blue eyes (light sensitive) or baldness (?) persist because they are linked on a chromosome to traits that are so desirable that make them worthwhile. :-) Hence the great achievements of the bald ones.

    Matt61

    • B.B. Pelletier Says:

      Matt,

      This Tech Force was made by Mendoza — despite the Chinese name. Mendoza makes very good barrels, as a rule.

      B.B.

    • J-F Says:

      Geez you guys are starting to make me feel ashamed to have hair all over my head!

      So R. Lee Ermey, Chuck Norris, Muhammad Ali and so many more are lesser men because they’re not bald???
      I was told that baldness came from overthinking people :P ;-)

      The most popular bald guys right are probably Vin Diesel and Jason Statham but I suspect the washboard abs may have something to do with it…

      J-F (the non-bald guy)

      • Herb Says:

        J-F,

        If you want to waste your hormones growing hair that is your prerogative.

        :-)
        Herb

      • Victor Says:

        J-F,

        So what does this say about someone who isn’t balding, but has always had a relatively thin head of hair?

        Victor

        • J-F Says:

          It means your hair are too long or you should stop wearing a hat.
          I was like that and so did my grand father when he was young, his doctor told him to stop wearing hats and keep his hair short, I did the same thing and now no more thin hair line.

          J-F

  • kevin Says:

    Today reminds me about the stories and opinions we shared about The Importance of a Crown awhile back:

    http://airgun-academy.pyramydair.com/blog/2011/09/the-importance-of-the-crown/#comments

  • Vince Says:

    Off topic – BB, did you say that Crosman was coming up with more options for an AR upper?

    • B.B. Pelletier Says:

      Vince,

      I did say that. And I have asked Crosman once again if there is anything in development along these lines. I now have a greater interest, since I have an AR lower, so I will be watching and waiting for this to happen.

      B.B.

  • BG_Farmer Says:

    BB,
    I’ll be more convinced if the .177 barrel shoots the same way after a crown job. There are a lot of other things in a barrel that can cause problems and some nasty looking crowns can shoot (as we Connoisseurs of Clunk know)! I think it is important that the problem is less one of muzzle/crown “finish quality” and more that the pellet was being deflected enough to bounce off the inside of the extension!

    • /Dave Says:

      Yeah, I’ve got a couple of ugly ones that I won’t mess with because they already shot fine.

    • B.B. Pelletier Says:

      BG_Farmer,

      I think everyone is overlooking the most important fact inn this report. Some of the pellets were hitting the rear of the muzzle brake and THAT is what was causing the poor accuracy. It wasn’t just the crown, but what it was making some of the pellets do.

      I don’t have permission to pull the brake off the test rifle, so I’m trying to fix it like Pyramyd Air would fix it for a customer.

      B.B.

      • /Dave Says:

        Not really overlooking that, BB. Just looking at the crown. As you said, the bad crown may be causing the pellet to hit the muzzle brake…

        /Dave

      • john Says:

        B.B.

        I would be interested to see how to face a muzzle perpendicular to the bore without removing the brake. Sounds like magic.

        john

  • BG_Farmer Says:

    I’d say southern rifle, but then that is all I care about :)!

    There’s a lot of variations (PA, VA, other). Start here:
    http://www.kentuckylongrifles.com/html/antique_rifles.html

    Visit here (and look through the virtual museum also):
    http://americanlongrifles.org/forum/index.php
    and here:
    http://contemporarymakers.blogspot.com/

    This vendor is great (I call them the PA of ML’ers):
    http://www.trackofthewolf.com/Index.aspx
    This man can help by inletting the barrel and drilling rr hole if you don’t want to try yourself:
    http://knobmountainmuzzleloading.com/

    If you see anything you like, let me know, as I may have better pictures from a book or something.

  • Ton Says:

    BB,
    A re crowning blog would be well appreciated.
    I think I have said it before but i’ll say it again – that stock is beautiful so it would be a pity if the rifle does not shoot.

  • joseph Says:

    Hello again from New Zealand, allow me to stir the “crowning”pot even more.Recrowning is best done on a lathe after the muzzle has been looked at closely to see the markings on the lands, these should be even on all of them,ifnot,enough of the lands should be removed to get a even reading.This should be done by an experienced machinist as it involves accurate setting -up of the barrel so it runs dead-true to the INSIDE of the bore. the breech-end of the barrel is also very inportant.As most breechblocks have a slant the pellet does not seat properly and will get damagrd on closing the breech. Again Iset my barrils up in the four-jaw chuck and dial dead-true to the inside,then with a small dead-sharp single-point tool cut enough of the rifling away so as to form a perfect circle perpendicular to the barrel axis.From the bottom of this cut advance the tool under 20 degrees to form a taper lead-in into the rifling, This makes shure that the pellet enters the rifling concentrally. (read up on how Harry Pope loaded his breech loading rifles !!)
    A question on another topic:when does a pellet leave the barrel as only lung pressure alone can move it,therefore there is no air cushion when the piston slams into the breechblock, why use such very strong springs? My suggestion is to redisign the breech of the barrel so as to retain the pellet until maximum air pressure has been achived and the pellet is spat out(as in precharged and pump-up rifles) instead of blown out. just a thought from DOWN UNDER Regards Jeff. Ps Christchurch is a long way from Auckland, 2 days by road and 4hrs by ferry!!!

    • B.B. Pelletier Says:

      Joseph,

      The way a spring gun works, the pellet doesn’t start to move until the piston has almost come to a compete stop. Regardless of the power of the spring, the pellet can’t start moving until the pressure overcomes its inertia. That’s why deep-seating is not recommended for the more powerful guns.

      B.B.

      • Vince Says:

        Is it correct to say that the pellet can’t start moving until the pressure overcomes the initial static friction or resistance? This resistance doesn’t come from inertia, but rather the rifling biting into the pellet and the slightly oversize skirt getting squeezed down to fit the bore.

        In a powerful gun, if a pellet is deep-seated much of that initial resistance is already overcome and the pellet might start moving too soon. The powerplant never gets the chance to build up the pressure needed to maximize power.

        • Wulfraed Says:

          OTOH: deep seating is going to reduce the compression ratio, lowering the peak pressure.

          Not by much, i concede, given the size of the piston versus the chamber.

          Let’s say we have a 1″ diameter piston with a 6″ stroke. That’s ~4.7 ci of air. Let’s say a.177 flush pellet has (let’s ignore conical base) .15″ diameter and .15″ depth… .0026ci. Assuming the piston fully stops before the pellet moves we have a compression ratio of (4.7 + .0026) / .0026 => 1808:1

          Now assume deep seating by a quarter of an inch. That makes the chamber volume (including pellet hollow) .0062ci and compression ratio (4.7 + .0062) / .0062 => 759:1

          Less chance of diesel combustion (even if a real diesel engine doesn’t hit 20:1 compression ratio <G> )

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