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Education / Training New BKL mount adjusts for barrel droop: Part 1

New BKL mount adjusts for barrel droop: Part 1

by B.B. Pelletier

Announcement: Due to a mix-up, the most recent Big Shot of the Week winner wasn’t announced last Friday. Jeffrey Aaron Demers is this week’s winner of Pyramyd Air’s Big Shot of the Week on their facebook page. He’ll receive a $50 Pyramyd AIR gift card.

Jeffrey Aaron Demers is this week’s Big Shot of the Week. Congratulations!

The optional BKL bubble level is mounted on the left side of the new BKL adjustable scope mount. This view shows the rear of the mount raised up to compensate for this rifle’s barrel droop.

Today, I’m going to show you the new BKL adjustable scope mount that will soon be available. I mentioned this mount in the Part 3 test of the new RWS Diana T06 trigger last week, which is where the first picture comes from. I’ll show all the nuances of the new mount and discuss how it works.

Looking up from the underside of the mount’s rear ring, we see the two legs that slide up and down for elevation compensation. Note that the ring has two cap screws.

The front ring is captured, so all it can do is rotate as the rear ring goes up or down. This prevents stress on the scope tube.

These first two detail shots show how the mount works. The rear ring moves up and down on forked legs that are open on the bottom. Two screws on the sides of the legs jam the ring tight in position when the right elevation is achieved.

The front ring is captive and is only able to rotate when the rear ring moves up and down. This prevents stress on the scope tube.

The black elevation pad is a Delrin screw that the scope tube rests on. It’s located just ahead of the rear ring.

Another key feature of this mount is the elevation pad, located back by the rear ring. The scope tube rests on this pad, which is used to make very small adjustments to the elevation of the scope. A small Allen wrench inserted into one of the holes in the periphery of the elevation pad lets you turn it up or down like a capstan, providing tight control over the elevation changes made. When the scope rests on the pad, it provides additional support against random movement once the scope ring screws are properly locked down.

Does it work?
I tested this mount on an RWS Diana 34P that I’ve retained for tests just like this. The rifle in question has 21 inches of droop at 20 yards (the only sight-in distance I use, since the pellet strikes the same place as the 30-yard point of intersection when it crosses the line of sight for the second time), making it a severe case of barrel droop. When I developed the UTG droop-compensated scope bases for RWS Diana spring rifles, this rifle was the worst test case, against which the base for the RWS Diana 34 base was designed. If the BKL mount can fix the droop on this rifle, it can fix anything you’re ever likely to encounter.

And fix it, it did! With the mount adjusted about as far up as it could go and still be locked in position, the scope was sighted-in dead-on at 25 yards, which is in the center of the 20-30 yard sight-in distance. And, the scope was in the center of its click-adjustment range. This was an acid test that the BKL mount passed with flying colors.

Another factor I was watching was the BKL mount’s ability to hold its position on a heavy-recoilling spring rifle. When the mount was given to me for testing, it had already withstood the jackhammer recoil of a Hatsan 125, which is even harder on scopes and mounts than the UK-produced Webley Patriot. Indeed, the scope that had been in that test was destroyed, but this mount held fast.

On the RWS Diana 34P, the mount also held fast under two different scopes, the intial one that finally gave up the ghost during my test and the replacement scope. Hundreds of test shots were fired without a hint of scope mount movement or scope movement in the rings. Despite there being just two screws per scope cap, both scopes remained in place throughout the test.

Additional features
This mount also offers 11mm dovetails on both sides of its base. If you want to attach a laser, tactical flashlight or rangefinder, your base for them is built right into the scope mount. Because BKL recesses the Allen screw heads into the base, both sides of the scope base have this feature and can be used in this way.

Here you can see one of the two 11mm dovetails in the base of the BKL mount. There’s another one on the other side, and recessed screw heads make it accessible for this purpose, as well.

The final feature this scope mount offers is the facility to mount a bubble level to the base of the new mount. It attaches to one of the three spreader holes in the base, though I think you’ll choose the hole that’s farthest from your eye so you can focus on the bubble. I used this level in the test of the RWS Diana 34P, and it worked well.

An optional BKL scope level can be screwed into one of the three spreader holes (the center hole in each group of three) on the base of the new BKL scope mount.

If you need to spread the base of the mount to get it on a gun, the ring screws also have to be loosened. Then, the base can be spread evenly by the three spreader screws.

The best part
I’ve saved the best for last. When this mount was shown to me at the BKL factory, I was told that the motivation for making it the way they did wasn’t an air rifle, but a popular air pistol! The cuts on the mount are specific to clear the front sight on the Beeman P1/HW 45 spring air pistol.

The profile of the new BKL adjustable rings was made to accommodate (to clear) the front sight of the Beeman P1 pistol.

The Beeman P1 was the inspiration for the new BKL adjustable scope mount.

Because this is the first mount I’ve seen that was made for the P1, I think I’ll order a BSA pistol scope and give it a test. Whatever scope you select has to fit into the two rings that measure 4.0625 inches apart on the outside. Because this is a one-piece scope mount, those rings cannot be moved, so pick your scopes accordingly.

author avatar
Tom Gaylord (B.B. Pelletier)
Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.

76 thoughts on “New BKL mount adjusts for barrel droop: Part 1”

  1. B.B.

    A great report and a great product. Reading it I was waiting for “survivability” report but when I read about surviving on Hatsan-125 – well, I need no other proof, it’ll really survive anything. I just wonder how many shots it took to destroy the scope. Maybe today’s accessories makers must invent a sort of “hatsanproof” quality mark, just like “bulletproof” mark in late Middle Ages 😉
    Did you test it on any other “scope killer” like Diana 54, that has a sort of reputation for destroying optics?


    • duskwight,

      The scope was already on its way to being broken when I received it for testing. It only took about 150 shots on the 34P to finish it. I don’t know how many shots were put o it with the Hatsan, but they were a lot.


    • Duskwight,

      How come you consider the Diana 54 a ‘scope killer’? I thought the recoil slide mechanism actually diminishes the effect of recoil on scopes. At least, I’ve never had any problems with the big Leapers scope on my 54. Can you tell me why you think the 54 is harder on scopes than a similarly powerful rifle (say the 350) that does not have an anti-recoil mechanism?


      • You miss the point of what the anti recoil mechanism is for……
        It reduces recoil felt by the shooter and also reduces the necessity for the shooter to hold the rifle right.

        The scope rides along with the action without the extra weight of the stock to help snub recoil, so the shock to the scope will be greater than with a 58 or 52 which have the same action and power level.


        • Moreover, it (m54) may inflict bidirectional recoil effects, depending on just how well timed the piston and slide action are…

          The slide moving backwards is a “normal” recoil to scopes (firearm scopes are designed for that direction, optics braced from sliding to the front of the tube); the spring piston jars the scope forward (and internal optic to the rear of the tube) (which is the recoil air-gun rated scopes are designed to survive).

          Combine the two and you get any combination of:
          A jar when the slide starts moving (normal recoil), a light jar if the piston hits while still sliding (airgun recoil), a second jar when the slide stops moving (airgun recoil);
          A jar when the slide starts moving (normal), a jar when the slide stops (airgun), and a jar when the piston hits (airgun);
          A jar when the slide starts moving (normal), a hard jar if the slide stops all the way back AND the piston hits at the same time (airgun)
          A jar when the slide starts moving (normal), some indeterminate jar if the piston hits while the slide is moving AND the slide is adjusted such that this hit stops the sliding action …

          And since the mass of the stock (and shooter) have been removed from the equation, these action-only jars are much harsher (consider the recoil of a 10lb action/stock/scope combo vs a 5lb action/scope when the 5lb stock is not part of the unit)

          • Wulfraed/TwoTalon,

            Is there no benefit derived from the fact that the slide actually has to travel a fair distance (2 inches?) before it reaches the end of its travel range? Moreover, the slide does not hit its stop hard (or I would feel that as recoil) but offers resistance all the way, resulting in less bidirectional acceleration and more of a dampened shock? I’m not entirely convinced by your arguments. In B.B.’s recent series on the 54 and all of the comments thereto, nobody remarked particularly on the 54 being hard on scopes.


            • It is going to depend a great deal at what point in the rearward travel that it changes direction . If the rearward travel is still in motion and stops and changes direction before it hits the back, then you will probably not feel any recoil other than a slight nudge from the friction in the sled.
              Then there is forward recoil. At what point does the piston get stopped before the sled can hit the front? Does the piston stop long enough before the sled can hit the front that inertia is the only driving force (with sled friction slowing it down) or is the piston still in motion as the sled hits the front and jackhammers it?

              It really does not matter when compared to a 48, because the 54 does not have the weight of the stock tied to the action. The scope on the 54 is always going to take the worst beating from recoil because of this.

              So is it a bad scope eater? Compared to a 48, yes. Compared to other rifles, maybe yes or no depending on the rifle and what kind of scope is used on each.

              Based on comments from other websites, I could conclude either way that I want to about if it likes to eat scopes……
              One guy can claim that his has eated a half dozen scopes, while another guy claims to have shot thousands of pellets without a problem using the Wallyworkd centerpoint. Well gee whizz. I lost two of them on lesser powered rifles (and in short order).


            • All I can go by is some stuff I’ve read, and my own experience: 1) that all normal spring guns have that reverse recoil pulse which standard (firearm) scopes are not designed to withstand; 2) since the m54 stock and shooter (unless holding really really loosely) are taken out of the recoil equation means /faster and sharper/ recoil effects on the action (which, BTW, only moves about a thumbwidth).

              When I pulled mine out this spring I noticed the BSA AIRGUN scope’s reticle was rotated some 15 degrees relative to the turrets… I’m fairly certain I’d have noticed that when first mounting the scope [I returned a Leapers that arrived with a 5-10 degree rotation]

              This on a gun that had less than 100 pellets through it over 15 years (it actually doubled that count when I took it to the range to sight in a new scope — though I’m no where near to even grouping at the Kennedy Dollar size at 25 yards. Lack of a proper rifle bench may be contributing factor — I was on a pistol box with only the fore-end having any support. When a changed out the mount for the UTG custom base I found signs the stop screw was gouging out the socket.

      • Alan,

        I’ve got nothing to add to twotalon’s words, except for the fact that IMO Leapers is one of the sturdiest low-price scopes on the market.


        • I’ve had a Leapers 3-9 AO on my 54 for years without a speck of trouble.
          But I also agree that some guns are death on scopes and that many people, especially newcomers, might be unaware just how hard springers are on scopes. They just make uninformed decisions when buying a scope.
          I can see devising a Consumer’s Report test for springer scopes. You’ve seen those desk science toys with the line of 3/4″ ball bearings suspended on strings. Pull one back and release and the one on the opposite end pops away and the cycle repeats and repeats until all the energy is dissipated. The scope test could be very similar, where the scope is mounted on a bar suspended by similar strings set in the middle of the line of balls, with 5 balls suspended at the right end and 5 balls suspended at the left. Pull and release one ball for a light recoil gun. Pull and release all 5 balls for a Hatsan 125 test, banging it forward and backward multiple times.

            • BB,
              Thanks for that link to the Leapers scope article. I will look around there some more because there are a lot more interesting looking articles.

              No wonder the Leapers scopes hold up so well. Both the drop hammer and the vibration tests are very severe and I must say that I am impressed! I have witnessed lots of equipment being destroyed in very similar tests, and often you don’t know what the weak link is until you break it.
              Thanks again,

  2. BB,this looks well thought out and made.Can I get a measurement of height to the ring base?? I think this may be usefull on a .308 for long range shooting….but I’m concerned about clearance of the objective bell (just in this application…full barrel shroud).Thanks!

    • Frank,

      The base is now mounted on a P1 and the closest estimate of height I can get is 0.868″. That’s from the bottom of the jaws to the bottom of the ring.

      But since this is an adjustable mount, remember that the scope will slant down when mounted, which will affect things.


      • Yeah,that’s why I asked…..I have a real issue with it shooting low right now.Just came back from the maiden voyage with scope #2….a Tasco custom shop BR 8×32.It turned out the Airforce 4x16x50AO
        was just out of vertical adj. range.Agressive shimming will be the next rabbit out of the hat.Issues at 50yds have kept me from using the 185 yds I have available.I’ve spent years dreaming of having this kind of distance to shoot….and only 5 minuites from the house.Thanks for the measurement!

        • Frank B

          Have you tried this scope mount?


          The price put me off of it for awhile, but I finally ponied up the cash. It is rock solid so far, and has windage and elevation adjustments and a stop pin. They are made by Sportsmatch in England. I am probably telling you things you already know.

  3. B.B.

    I think you have me convinced to pick up one or two as soon as they hit the shelf.
    It looks close to being a high mount in one profile, and close to being a medium in another profile. What is it closest too?

    I am not familiar with the Hasan 125. My only experience with Turkish is the Daisy Powerline 1000 that W-Mart sold quite some time back. It had a butt ugly stock, and was brutal in recoil. It tried to tear the rear ring from the rifle after only a couple dozen shots. It was visibly leaning.

    I never click center a scope anymore after I had two that it clearly did not work with. Click centered left both of them way off center and at the limit of positive control. I only do optical centers now.


  4. twotalon,

    It’s a medium-height mount.

    The Hatsan 125 is a powerhouse. Not so fast in velocity but 75 lbs. cocking effort and it kicks like a slide hammer. It was what Webley attempted to foist off as the “new” Turkish-made Patriot, but nobody bought it. It’s the worst recoiling airguns ever made.

    Click-centering doesn’t work. The scopes have to be optically centered to be in the true center of the range. Click-centering is like trying to drive in the fog by keeping the car in-between the turn signals.


    • B.B.

      There was also another problem with the two scopes in question…

      Even at optical center they were at their limits. Can you say “BAD SCOPES” ?
      I was having combination problems and nothing seemed to be fixing anything…until I started working down a long list of anything I could think of as a possibility. Much hair pulling and work later things finally came together as everything done helped a little (sometimes a lot).


    • B.B.

      My two cents:

      In my experience Hatsans have the worst barrels ever. Uneven rifling and grater-like surface are their trademarks. Not many Chinese can match this abscence of quality. Overall quality is low and design is ugly. Even their power cannot compensate their inaccuracy.
      Besides that previous-generation Hatsans were prone to accidental discharge, as they had badly engineered and badly made trigger mechanisms, with sears too soft and grinding themselves away. As far as I have heard, that caused at least one serious injury in Ukraine. Current generation’s triggers are some copies of Record type, but still they are crude and their metal brings doubts.


      • I’ve seen quite good result from their AT44 line of PCP’s… The low powered springer I have from them seems to be well made, I’ve had it for over 10 years and it still works good, without much maintenance… It isn’t very refined but usually hits what I’m aiming at. Again being in Canada this might be due to the lower power.

        I’m not saying they have the built quality of German rifles but it does it’s job.


        • JF

          Maybe AT-44 is better-made, but being a springer fan I have more experience with their springers. Well, I try not to have any experience with their springers 🙂


      • They must be careful what they ship to who, then. I’ve had 2 Daisy Powerline 1000’s that had a plethora of faults – but accuracy was never one of them. Considering the heavy trigger and nasty recoil the PL1000 was crazy accurate out to the 60 yards I tested at. Almost as good as the best of my breakbarrels.

  5. Very clever design. I especially like the black delrin elevation pad for fine adjusting and additional support.

    Sure hope BKL plans on adding a two piece adjustable to their lineup. Double strap rings on these adjustables would be nice too.


  6. Cowboy Star Dad,

    Well, I finally heard back from the place you sent me for Slavia parts. I copied their response here:

    I am sorry, we cannot help you. We do not have any Slavia parts and we do
    not shop out of Canada.

    Fortunately I did find an old 631 parts gun and am having it sent to me now. So I think I got all the parts I need.

    Thanks for your help.


  7. BB,
    Nice report and excellent detail photos of this mount. I like the bottom view that shows the spacer washer in between the tabs that get pinched by the elevation lock screws. That should make for a tight lock-up without distorting the tabs.
    The mill finish aluminum color is pretty unusual for a scope mount, isn’t it?

  8. Edith,
    I see the change in the blog reply limit. Thank you very much! Today, the 50 count is perfect. For me, if I get farther behind in my reading than that, it’d take me more than a day to catch up and 50 is a good day’s worth. I can’t imagine more than a 100 being needed for my purposes except to cover a long weekend, maybe.

  9. It’s nice to see John at AirForce come up with another good product. You won’t find anyone who works harder at his business than him. I am glad they were able to buy the BKL and not only continue to provide the best mounts in the industry but to improve upon them with new models.

    David Enoch

  10. Can’t wait to see the results of the P1 scoped test.
    I took a look while at Bass Pro Shop in Hampton VA and they only had 2 models… at 300$ each! A bit too expansive for a test to see how they hold on a spring air pistol.

    On an off-topic note I just bought a Tanfoglio Witness 1911 BB gun /product/tanfoglio-witness-1911-co2-bb-pistol-brown-grips?m=2534
    it’s AWESOME, I love it, I’m even thinking of selling a few of the others I have because they won’t be getting much use from now on.
    The single action trigger is so nice compared to all the double action other BB guns provide…
    If you like the Walther PPK for it’s realism, weight, all metal, blowback, field strip, single action options you won’t regret buying this one either.

    So I looked a similar airgun and found the GSG 92 being tested right now /product/swiss-arms-p92-co2-pistol?m=2035
    and the SIG sauer P226 X5

    I know the SIG field strips like the real thing (like the Tanfoglio and Walther) and was wondering if the GSG has the same option? If it does I’ll buy both of them.


    • I just re-read the GSG 92 part 1 report and it does disassemble… but I think it can be taken apart further than what’s showed on the pic. Sorry for not looking better before asking, guess there are stupid questions after all…

      Edith, I know PA won’t ship airguns to Canada but what about airgun parts, like say a mag for a BB gun? or pellets, would they ship me pellets?


      • J-F,

        I think they ship some things. For some reason, it sticks in my mind that they can’t ship optics (at least not scopes) to Canada. I might be wrong on that, but that’s what comes to mind.

        I’m pretty sure they can ship some parts and ammo.


  11. In theory, the bubble level seems like a good idea, but I worry about too much information. Just like an overmaginified scope can make things more difficult with the reticle jumping around, I suspect that changing your focus around to compensate for the bubble might do the same thing. Even if your first shots were better, you might get fatigued faster in the long run. It will be interesting to see how this product pans out.

    CowBoyStar Dad, interesting comment about how you exhale while shooting with a slow shutter. You dare not try that while shooting an airgun or firearm, but that is exactly the technique used by traditional Korean archers, and I believe that the Koreans do disproportionately well at the Olympics. It does seem to help when I’ve remembered to do it. I had one great session at 20 yards where I was exhaling on release and those arrows were buzzing in exactly where I aimed them.

    That’s a great photo today and maybe it shows the wild and crazy Russian commando that Fred was talking about who shot his own trainer. I would say that he needs the attention of the Master Chief in G.I. Jane who tells a Navy Seal candidate, “Sergeant XXXX, however short your time may be with us, there are two words you will learn to put together, ‘Team work.'”

    All, I’m here to warn you about the dangers of heat stroke. I was celebrating last Friday by flying my plane and helicopter in the 100+ degree temperatures and then going for a swim and sitting poolside staring at the moon through the palm trees. I polished off the evening by watching my new Star Trek DVD (Epidsode 19 with the Gorn containing the worst fight scene ever filmed and Episode 20, the Alternative Factor) into the wee hours. Later that night, I had this terrible upset stomach, extreme nausea, then uncontrolled vomiting that went on until daybreak. Lying down brought no relief but instead these unendurable hunger pangs that I couldn’t stand at all although crawling to the kitchen and eating bread brought no relief. I was considering calling the emergency room, then I finally figured out that what I was feeling was not hunger but thirst. Somehow, my enthusiasm for rc flying, the pool, air conditioning, and maybe even the Gorn masked severe dehydration. It’s a good thing that I figured this out before the confusion and disorientation of heat stroke set in. When you don’t have an Edith around you are as good as a Mountain Man by himself in the woods. The water took the edge off the problem, but not right away. I poured in the water all weekend but was still bedridden and hardly able to lift a finger. Boy, was I in a bad way. However, I am on the mend and about to realize my dreams of walking out to buy some buillon broth.

    Notwithstanding all this and girded by a sense of mission, I hauled myself off my sickbed to pick up a new acquisition which is now sitting on my living room floor. You will freak out when you learn what it is–especially Mike. I will divulge all tomorrow.


    • matt,
      I don’t fixate on the bubble level, I merely glance at it to orient the rifle and get the feel for a level stock. Once I have the rifle level it’s not necessary to constantly check. I may glance at it three times: once to orient the stock, once before I take the deep breath, and I may glance at it after follow through if the shot is off. If you have the internal level there isn’t even any glancing, it’s right there in your face in your peripheral vision.

    • Matt61,

      Re: “In theory, the bubble level seems like a good idea, but I worry about too much information”

      If you’re just plinking I understand. If you’re in anal mode and trying to discover your guns utmost accuracy I must ask “Are you serious?”

      Too much information?? It just takes a glance and what I usually learn is that the hold I use, although comfortable and easily repeatable, usually has too much inconsistent cant for ultimate accuracy. An anti-cant device (whatever form or shape it takes) should not just be viewed as “one more thing to pay attention to while you’re shooting” but rather a training aid to ingrain a proper hold that eliminates cant. After awhile you will not need the anti-cant device if you train yourself, with the aid of the anti-cant device, to hold the gun correctly.


    • I worked in the Grand Canyon as a boatman. Making the wrong calls about heat and exertion could result in death for you or one of your passengers. You have to take in a lot of water continuously, of course, but also eat A LOT of salty foods. Salt tablets are not very useful. A close second behind salty foods are the Electrolyte Replacement (ER) drinks, of which the most effective is Cytomax (mixed 50% of their recommended formula). I find the Cool Citrus flavor least obnoxious. The easiest technique for self-monitoring is to take in that level of fluid that allows you to pee a light straw-yellow color. The worst I’ve gotten to was walnut brown, when ordinary surface scratches would not bleed; they finally started bleeding three hours later, when I got back to water and started pounding it down. Through the summer months down there I figured on a daily intake of approximately 2 gallons to remain comfortable.

  12. me thinking of getting a scope for a hatsan 125.. ideas? trying to go for the
    “Barska Varmint Hunter 3-9×40 ”

    and can you let me know a good adjustable scope..

    meaning the scope is a 20mm and the hatsan railin is 22

    sorry if im saying it or it comin out wrong.. first scope and i kinda want it to last 🙂

    • janaka,

      If you want the scope to last, don’t get a Barska. They are inexpensive and lightly built.

      You need a good Leapers scope for a powerful air rifle like that Hatsan 125. Like this one:



    • Mrven,


      Above is the link to the BKL 388 mount on Pyramyd Air’s site. This is the same one you located on BKL’s website. It does not fit 14mm bases. It fits 3/8″ or 11mm bases (flexible enough to fit both dimensions). It accommodates scopes with 30mm tubes. It will fit an RWS 34P. You will have to inquire with Pyramyd Air’s tech department to determine if it has enough clearance for the objective bell of the UTG 4-16×44 rifle scope. I assume this is the one you’re referencing (which comes with Weaver rings):


      Email the tech department at tech@pyramydair.com or call them at 888-262-4867, ext. 5.


  13. In light of yesterdays blog about jargon, I’d like someone describe headspace so I can understand it and then I’ll let you know why I don’t understand what you’re saying, if I don’t.

    • Chuckj,

      Headspace is the space between the breechblock or end of the bolt when it is at its most rearward travel (bolts and breechblocks do move during firing) and the head, or base, of the cartridge. When a cartridge fires the pressure of the expalding gas presses the cartridge case against the walls of the chamber. If the headspace it too large, the cartridge head will move back while the cartridge body remains locked to the walls of the chamber. That leads to case separation at the head, or base, of the cartridge. In rimfire cartridges, the head is very thin and will blow out (rupture) if there is excessive headspace.

      In semiautomatic guns the cartridge must release its grasp on the chamber walls and be able to be extracted from the chamber, so the breechblock in those guns does move — but only after the pressure has diminished enough that the cartridge body is not still pressed against the chamber walls.


  14. Thanks Tom,
    I think I misspelled breech in my previous comment. I spelled it breach.

    I have not done any research on this so my questions are from complete ignorance. If you don’t want to answer these because I didn’t even take the time to research on my own first I will understand and not be offended by the silence.

    1. I know what a bolt is but not a breech block. Which guns have bolts and which have breech blocks? I assume the breech block is on any gun that doesn’t have a manually operated bolt? My Savage Mark II BV has a manually operated bolt but my semi-auto Ruger 10/22 has a breech block?

    2. You said “…and the head, or base, of the cartridge”. Which is it the head or the base? Because in my mind the “base” is like where the primer is and is against the bolt or breech block while the head is at the other end where the bullet is. See, that is confusing! Two normally diametric terms describing the same thing. SO THE “HEAD” OF THE CARTRIDGE IS POINTING TO THE REAR OF THE GUN?

    3. Not a question but one of those pearls this rookie gets from this blog: the expansion of the cartridge grasping the walls of the chamber is a revelation to me. It explains the why of head-space issues.

    4. Once the bolt is closed or the breech-block positioned (or what ever it does) why would there be any space at all between it and the cartridge? Isn’t the bolt still putting pressure on the cartridge after it’s cocked?


    • Chuckj,

      The end of the bolt forms the breech block. Maybe in the future I oill think of a way to show you other breech blocks, but all of them — bolts included — are just walls that stop the rearward movement of the cartridge case.

      A bolt might press forward on the base of the cartridge, but the bolt is not fixed absolutely immobile. When it is under great thrust to the rear, the bolt or breechblock does move. And this is where headspace comes from.

      The base of the cartridge is the part that contains the primer. The “head” of the cartridge contains the bullet.

      Does that clear things up or do you need more? And, since headspace is not an airgun term, I have to ask, what caused you to ask this question? If I knew what you were trying to understand I might be able to explain it better. My explanation has been generic so far.


      • Tom,
        Not to worry. Your generic answer is sufficient, at this time. This comment was a result of your blog on jargon you posted on the 25th. The jargon term headspace/head space/head-space was a term I had seen a lot (and even on this blog site) and it was one of those terms that puzzled me, until now. You did a good job explaining it, but like all answers, it generated more questions.

        I was confused about “head” and “base” because in your answer to me on the 26th it looked like you used “head” and “base” to describe the same area of the cartridge. At any rate, you have just moved me up to second-string on headspace jargon.


        • One possible point of confusion is that the measurement “point” differs depending upon the cartridge type — that is, what part of the cartridge “stops” it from going too far forward..

          Rimmed “straight wall” (some have a taper) like the .38Special, .357Mag use the rim itself — everything from the rim to the bullet tip just “floats”, and headspace is determined from the rim to the [revolver] shield. A thick rim cartridge will show less headspace than a thin rim cartridge.

          Mouth style — .45ACP, .30M1 Carbine — use the edge of the case mouth against a lip in the chamber. You can’t use a strong bullet crimp as the rolled case mouth wouldn’t “stop” against the lip. In these, improperly trimming the case length will affect headspace.

          Bottleneck (most rifle calibers — .223Rem/5.56mm, .308Win/7.62NATO…) use the flare of the neck as the stopping point (measured from somewhere mid-point). Resizing brass to different lengths at the flare would affect headspace.

          In the case of bottleneck and “mouth” cartridges, there are standard specifications for what is too long or too short to be used in a standards compliant chamber. If the chamber and the cartridge are up to spec, then incorrect headspace is a fault of the bolt or breech face. While not safe for use with general ammo, small excesses could be handled by the trim and resize operations — letting one form cases specific to just the chamber of the single gun.

          I don’t think anything can be done with rimmed pistol cases — no sizing/trimming operation is going to make a rim thicker to compensate for excess headspace.

  15. Dear, I have a HW90 which makes very high shots, le istale a mount Diana Bulleyes zr mount which comes with a droop of ponpensacion but down, so disarm and invert it so that the sight is always pointing mostly up , My question is if with this assembly “BKL mount adjusts” I can install it inverted, so that the sight is pointing more up ??

  16. thanks for your prompt response B.B. Pelletier

    as I need a mount that raises the vision of the scope because my barrel (HW90) pulls very high, weigh to acquire this adjustable mount but mount it upside down so that it points more upwards.

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