Scope mounting: Mounting a scope directly onto the barrel?
any thoughts on what effect mounting a scope directly to the barrel
might have? The barrel is a featherweight contour, drilled and taped to
take the bases. I am wondering if having the scope attached to the barrel
like this will have any adverse effect on accuracy or harmonics etc. thanks
WA USA - Friday, October 23, 1998 at 22:13:27 (EDT)
Re: "mounting a scope directly to the barrel" -Rich
A couple of things come to my mind. First off, barrel harmonics will be affected. That said, they may be beneficial or harmful to accuracy in your case. You are adding some weight to the barrel and so vibrations "should" be slower. But then again it may add a sub-harmonic to the equation. Who knows.
I would be concerned about the barrel heating up with the scope clamped down tight. This certainly will do no good as stresses will build up, and this could cause unusual results in point-of-impact after a several shots are fired. Now exceptions can always be found. Take for instance the long Redfield 3200 scopes that were solid barrel mounted on smallbore rifles for many years. Of course the barrels didn't warm up too much. Champion shooters used them this way with fine effect. I sold my 20X 3200 a few years ago. If mounted on the action there was a terrific amount of overhang. I'm talking a foot and a half or so. Too much for my comfort. If solidly mounted on the barrel it prevented the barrel from freely doing its thing. So I reluctantly gave it up and bought a Weaver T-20. More trade offs. The Redfield had a very flat field, crisp and clear. But a very small field of view relatively speaking. Three and a half feet at 100 yds. Now the Weaver T-20. Very good clicks, but as someone else said "Coke bottle optics". A benchrester I know once won a Weaver T-30 or 36. Not sure. This scope was virtually unusable. Extremely dark for one thing and not even good for paper punching on a sunny day.
Many Camp Perry long range target shooters mount the long Unertl scopes partially on the barrel with no handicap. Of course these are the suspension type mounts and stresses can not build up in this system as the scope tube actually "floats" within the mounts. Spring tension pushes the scope tube into a type of V-block situation. Hard to describe in print. All things considered, a very good system, (in my lowly opinion). Any system (floating or solid mount) has its advantages and disadvantages. What you gain on one end, you lose on the other. Just like with scope optical qualities; magnification, eye relief, light gathering, etc. When you gain in one spot you lose somewhere else.
This is more than you wanted to know. Sometimes I get a little carried away; ……..sometimes a lot!
That's all for now.
Ron N. <email@example.com>
USA - Saturday, October 24, 1998 at 05:42:23 (EDT)
Rich - I discourage greatly the mounting of the scope onto the barrel. You will get a harmonic change that problably would not be repeatable within the system due to the difference in the metal. Remember, you have a scope, rings, and base that must vibrate as well. The barrel will not match that vibration and accuracy will be degraded. Yes, scopes have been mounted on barrels but they were low power small scopes for african big game at ranges shorter than you will normally shoot and at targets much bigger than you will shoot. The damage to a normal scope, not designed to be mounted on the barrel would also be a problem in the near to long term, depending on how long it would take for the flexing to pop or miss align the reticule and erecter lens. Ron is quite right on the small bore scopes, they don't produce the same harmonics, and was designed for that set up, and the Unertl is designed for the front to mount on the barrel. The sope body is suspended in the rings/adjusting turrets with a shock spring in front. The scope must be slipped back into battery after every shot. These scopes were used to some extent in SEA with success.
Fayetteville, NC USA - Saturday, October 24, 1998 at 15:12:35 (EDT)
This is not meant to be a flame, but I don't understand some of your reasoning.
> "I was at a loss as to why his weapon would start throwing high rounds after about 6 -7 shots then after a break of about 15 to 20 minutes return to the orignal (sic) impact point".
I'm pretty certain that Knight still uses Remington barrels and most likely are still hammer forged (unless Custom Shop). Not a great way to make a barrel and certainly not in the class of "match grade" as we have come to know and expect. Full of stresses for one thing. They start with a little slug of metal with a drilled hole (and probably not reamed) about a foot long. A reverse image mandrel is inserted into it. Rotary hammers pound the metal tightly to the mandrel forming the rifling and elongating the barrel material in the process. Barrels that have stresses built into them tend to change their point-of-impact when they heat up and this is well known. And I'm sure you know it. Now I'm not saying that great barrel 'can not' be made by that method, it is just that the method is normally chosen because it is cheap and fast. A German or Swedish made hammer forged competition barrel is much different than a American made production barrel. It is rumored that Remington has about $13.00 invested in each production barrel. Don't quote me on this as it comes second hand from another list. But even if it costs Rem 4 times this amount ($52.00) it is still not a barrel that I would want to take to the Nationals. I've kept score for a few people who have used Rem Varmint Specials (7-08s and .308s) at 1000 yds. Once things settled down they did creditable work. I don't know how they make the 40X barrels anymore, but they used to be button rifled. A much better way.
>"As the barrel and chamber heat they get smaller".
If I were to have a ring of steel with a hole in it exactly .500" in diameter and wanted to force it over an object that was .501" I would heat the ring and make the hole LARGER; not smaller. I know, I've heard the stories from physics students stating that the opposite is true (that a heated ring actually shrinks), but in real life it is the other way around, at least with steel. Maybe other metal products shrink when heated, but I doubt it.
>"That is until he told me it had been reamed using a tight Obermeyer with a short throat".
I along with many others have used the .308 Obermeyer reamers (or chambers) with good success and never a sign of over pressure with peppy handloads or factory match ammo. I do not want to speculate on someone else's pressure problems.
>"As the chamber gets smaller the pressure becomes greater and the muzzel (sic) velocity increases."
Muzzle velocity increases slightly as the barrel heats up (less heat is absorbed into the relatively cold steel). I've seen it a few times on my Oehler 35, but you have to have a load that has a relatively small extreme spread to show it and shoot 10-shot groups or more. If one has wild variations in velocity then trend probably will not show up.
This is about all I know on the subjects.
Comments and criticisms welcome.
Ron N. <firstname.lastname@example.org>
USA - Sunday, October 25, 1998 at 00:50:28 (EDT)
Ron N. I could agree with you more on your theory of when things heat up they expand (no sexual pun intended.) This is a common law of physics which we learned in 7th grade. On many of our match rifles we cut chambers to National Match specifications, having a .340 diameter neck and hardly any free bore at all. As a matter of fact when I take a Federal factory match bullet, insert it in the chamber, and then extract the bullet, rifling marks are definitely visible. With this on a Douglas Air Gauged barrel, I have spectacular result. Heavy barrel contour also makes a difference to "absorb" more heat. Fluting - ah-h-h-h well that is two schools of thought. I like it! When camming a live round in the chamber, it is tight, wiht no slop! I'm ready for Storm Mountain now!
Also - DON'T - I REPEAT DON'T mount that scope on that feather weight barrel. There would be more problems than you can imagine, especially once you start to drill and tap that featherweight barrel.
Al Ostapowicz <email@example.com>
The Poor Side of Town wiht D. West, but in Beautiful, Ohio USA - Sunday, October 25, 1998 at 07:45:07 (EST)
Ron - Everyone needs to be flamed once in awhile, just to keep things interesting and the thought processes from becoming stagnant. I'm not sure if I understood the Physics of it all but I believe that a ring made from a rod or "wire" will react the same as a milled block of steel. In as much as a ring will expand on the longitudinal greater than in width. This causes a ring to actually open in diameter as opposed to closing. The chamber of a rifle will close, I believe, because the longitudinal is now the length of the bore and as the metal swells the chamber closes and becomes tighter. The SR is a custom with Krieger barrel and obermeyer chamber that was short throated. We shoot rounds at a rather "fast" pace and weapon heat up is normal. All of the M24s stayed on zero while the SR climbed 3 to 4 moa at 600 meters. This made it very challenging for the observer to keep him on target. After the 5th to 7th round he started blowing primers due to chamber pressures. He was firing 175s and with a cold gun they grouped well. After the gun heated up they became erratic. I have seen this problem before with tight chambers and short throats and that is why I was upset that I hadn't figured it out sooner. When the round is fired the case expands and locks into the chamber for a moment. The less the case expands the greater the chamber pressure. Then again, I was kicked out of college so can't claim to be real smart on these issues. Heck, look at the way I spelled muzzle!!
Oh well, enough fo now. Flame on Ron and I'm always willing to learn new and exciting things! Jump in Al, I think you have a good background for this as well.
Fayetteville, NC USA - Sunday, October 25, 1998 at 21:51:07 (EST)
As a follow up. (longish)
>"The chamber of a rifle will close, I believe, because the longitudinal is now the length of the bore and as the metal swells the chamber closes and becomes tighter".
Still can not see what the longitudinal length has anything to do with a chamber growing smaller.
>"All of the M24s stayed on zero while the SR climbed 3 to 4 moa at 600 meters".
I do not doubt that the phenomenon took place. You saw it. It happened. Period. However, it is dangerous to draw conclusions based on a sample of one, or even two. There may have been something unusual about this Krieger barrel; hard to speculate. The Obermeyer chamber has been in use for many years with no idiosyncrasies. It is merely a S.A.A.M.I. minimum with a shortened and a smaller diameter throat. And perhaps the lead angle optimized. Two consecutive 300 yard rapid fire strings will definitely warm a barrel up too. And the distance is enough to show any unusual tendencies. But then again, this is iron sights and not a good way to prove anything.
Ron N. <firstname.lastname@example.org>
USA - Monday, October 26, 1998 at 09:31:38 (EST)
On the issue of chambers getting tighter as barrel temp increases, I believe that the reason this might occur is that he barrel is being heated from the inside out. As the temp of the inner surface increases the metal will want to expand in the direction of least resistance. Since the material further away from the chamber surface is still not yet heated and rigid, this direction would be toward the center-line of the chamber. Conversely if you heated the barrel from the outside the chamber would then grow in diameter,but then I'm no physicist.
Laszlo Markos <email@example.com>
Round Rock, TX USA - Monday, October 26, 1998 at 11:43:40 (EST)
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