R243MBS Problem

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tchepone
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R243MBS Problem

Post by tchepone »

Gun: Rossi, Single Shot, 243 Winchester, 23" barrel, 1:12 twist, 3x9 scope, firing done with scope at 9 power.
Problem: Vertical stringing of shots. The stringing is exhibited with many different weights and lengths of bullets. Horizontal variation is less than 1" +/- of center. Vertical variation is from 2.5" to 5". I have tried numerous loadings, bullets from 75 to 100 grain, different bullet manufacturers, different powder & primers. Have used only Federal cases. Chronograph readings show all groups of 5 rounds to have extreme spreads of 11-55 fps, shot to shot. Most loads are in the 25-35fps variation. Velocity has been 200-350fps, below the published velocity range for the load, (per Sierra, Lyman & Hornady manuals). The loads look good on the Oehler chronograph.
Stony Point tool shows maximum cartridge overall length to be 2.521" with a Sierra 100gr semi-pointed bullet, (ogive touching the rifling).
The barrel crown does not show any anomalies with a 30 power magnifying glass. The scope is tight, mounts are tight. Shooting was done at 100 yards, from a solid bench, by a NRA master class shooter. Firing was done at a rate of approximately 1 round per minute for each 5 round string, with 3-5 minutes between strings.
Anyone have any suggestions where to look to find the cause of this vertical stringing? Forearm pressure issues?? Gun has a non-wood stock and forearm. (rubberized plastic?). It has been a frustrating experience to date. All suggestions appreciated. And why did they put a 12" twist on this gun? Remington learned years ago that it did not work with long bullets. Thanks!! tchepone
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Re: R243MBS Problem

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I would start with trigger maybe lighten her up and should see better groups but be cautious as to not make her unsafe if you plan anything other than bench shooting. I had a new england .223 single shot years ago and it did same thing until I lightened my trigger pull to around 2.5lbs it was 7.3lb trigger out of the box. Also how is the breach claw the metal part that fits to the reciever and rocks open and closed. Take the forearm off and when the barrel is closed on the gun see if there is any horizontal or vertical movement of barrel from reciever I have seen this on some and it will cause your shots to go all over so I do not think this is the case here. They should be rock solid when closed. also try switching scopes to I have had scopes that have given me greif because I was cheap on the glass it cost me alot of wasted rounds down range. I am not rich I get what I can but I try to verify it will do what I need.
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Re: R243MBS Problem

Post by Ranch Dog »

Welcome to the forum! You might want to read through this article to see if any of it might apply.

6mmBR: CURES for VERTICAL STRINGING
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Re: R243MBS Problem

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Thank you all for the suggestions. I will look into each. Ranch Dog, Thank you for the article by Speedy Gonzales, it contains a lot of good information. It may seem geared to a higher quality gun but is applicable to any and all rifles.
This is the first break open type single shot rifle I have worked with. I had not given the "breech claw to receiver fit" and "lock up" much thought, but what you indicate makes a lot of sense. I will check that.
The scope is not an expensive brand and I know they can be a source of problems. I plan to change it out with a different brand and re-fire.
I don't feel the trigger is the source in this case. It is not a bad trigger, heavy, but it breaks clean without a lot of gravely creep.
One thing I forgot to mention in the first post was, I have fire lapped the barrel with a NECO kit. It is very smooth and cleans up easily.
Loads, I have tried many variations. They all vertically string. The chronograph indicates the loads are good, with low extreme spreads and low standard deviations. I felt this pretty much pointed me to a gun problem.
Again, Thank you all for the suggestions. I have more things to look into. tchepone
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Re: R243MBS Problem

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Keep us posted to any results or issues you find so we all can learn.
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Re: R243MBS Problem

Post by Ranch Dog »

akuser47 wrote:Keep us posted to any results or issues you find so we all can learn.
Yes, exactly please! We need more Single Shot info here on the forum!
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Re: R243MBS Problem

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I have checked all the things mentioned, switched the scope to a known good Weaver 2x10 and the problem continues. The lock up is tight with no lateral or vertical play. It just will not shoot anything over 85 grains with any degree of accuracy. It handles 70 grain Sierra Matchkings into less than 3/4" groups at 100 yards, all day long. Anything over 85 grains the accuracy deterioration increases the heavier and longer the bullets get. 100 grain Sierra semi-pointed string out up to 5" from point of aim, spitzer bullets even more. I feel the problem is simply the 12 inch twist!! It may even be slower then that, because my measurements are based on a cleaning rod and tight fitting patch. It will make a good coyote gun but not much good for deer size game at 100 yards. I don't intend to do anything else to the gun. So if you're thinking of buying one of these for deer or antelope size game, there are better choices out there. Thank you all for the suggestions.

Again, why would Rossi choose a 12 inch twist after all the information out there about the Remington problems with the 244/6mm. Are shorter heavy bullets available in Brazil?
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Re: R243MBS Problem

Post by akuser47 »

I would find someone with a bore scope or do a barrel pour/cast to see if there are imperfections with in it something is not right. Basically you would need to do a cast of the barrel/chamber so we could see what the rifling is like inside you could then measure your chamber to see if it is out of spec and so on. Please keep us posted.
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Re: R243MBS Problem

Post by Ranch Dog »

tchepone wrote:Again, why would Rossi choose a 12 inch twist after all the information out there about the Remington problems with the 244/6mm. Are shorter heavy bullets available in Brazil?
The catalog indicates the R243MBS has a 1:10. This is from the current catalog and the 2012 catalog. Prior to 2012, they did not list the twist on the single shot rifles and this goes back to the Braztech acquisition in 2008. Only they could tell you what ROT was used on the earlier rifles but it would help to know what year your rifle is prior to contacting them and that can be done via the "Find My Model" link on their website. May be earlier rifles used a 1:12 :?:
Clipboard0_RR_01.jpg
If you are certain about the rate of twist, call Rossi. I would probably call them anyway as when it gets to things that you can no longer check or correct it is their turn to fix it.
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Re: R243MBS Problem

Post by tchepone »

First off, this is the MBS, not the HBS model.
There are not many Hawkeye borescopes around where I live, in fact I don't know of any. The fired cases come out within expected dimensions, when compared with other 243's which I have shot in a Remington 700. I may do a chamber cast, I have Cerrosafe.
It does have what I consider a long freebore. Using the Stony Point tool with a 100 grain Sierra Semi-pointed bullet, the end of measuring rod comes to within .032" from the case mouth. That flat base bullet will barely stay the case.
The rifle was purchased new from a Rossi dealer in February of 2013 and it was ordered out by that dealer. I don't know how long it sat in the distribution pipeline but I am guessing it is a late 2012 or early 2013 manufacture. It is definitely not a 10" twist!
I am convinced the problem is the slow barrel twist. It will shoot 60, 70, 75 & 80 grain bullets with very good accuracy. Beginning with 85 grain and continuing through 100 grain, the vertical dispersion gets progressively worse. 105 & 107 gainers cannot be counted on to stay on paper. Brand of bullet doesn't seem to matter. I have tried all the major brands. The chronograph tells me the loads I am using are appropriate, low ES and low Sd.
I have not had much luck calling any manufacturer, so I will forgo that until I have exhausted every other possibility.
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