Improving accuracy

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Don Eigler
Posts: 6
Joined: Mon Jan 05, 2015 8:00 pm

Improving accuracy

Post by Don Eigler » Sun Jun 21, 2015 5:47 pm

The challenge I face is to tighten up the groups I achieve when firing my Rolling Block. I thought maybe the readers of this forum might be able to offer suggestions about what to try next. Here’s the story.

My RB is a Type 1, so-called “transformed,” Military gun. It was re-barreled in Belgium sometime between 1877 and 1892. The Belgian made barrel is 35 3/16” long, 5 lands, roughly 21:1 twist and the bottom side of the barrel is stamped with the number 10.6, which, to the best of my knowledge, indicates that the caliber is .43 Spanish. The inside of the barrel shows some pitting or wear. I don’t know whether to call it light, medium or heavy pitting/wear as I have no experience that allows me to make such a judgement. For what it’s worth, the outside of the barrel is in near perfect shape (comparing to images in George Layman’s book).

I did two chamber castings, a muzzle casting and I slugged the bore. I measured the groove-to-groove dimension using a 108 degree V-anvil micrometer. The slug measured 0.4525”, the muzzle cast measured 0.4522”, and the chamber cast measured 0.4557” (all groove-to-groove dimensions). Many of you may now be asking yourself whether my RB is a .43 Spanish that got converted into a .43 Reformado. The answer is no. I’ve test fit Reformado cartridges and they do not fit. The chamber has a bottleneck that is much more pronounced than the nearly straight sides of a Reformado cartridge.

I started out by shooting store-bought (Buffalo Arms) .43 Spanish cartridges. As one would expect, the .439” bullet of a .43 Spanish cartridge did not give very satisfying results going through a .452” bore. The best result was 3.3 MoA radial standard deviation shooting bench-rest at 100 yards. I’m a newbie to shooting black powder cartridges and while I was working my way through my batch of store-bought rounds I was also building my skills and learning what my RB liked and didn’t like. A more experienced shooter would almost certainly have achieved a better result with the same cartridges and rifle. I routinely achieve much tighter groups with my other iron-sighted guns, so I have some confidence that the accuracy was not limited by my ability to aim and squeeze the trigger.

I read that it is quite often the case that the actual bore of .43 Spanish Rollers is considerably larger than the spec .439” and that people approach this problem by loading larger diameter bullets (I have yet to hear of a .43 Spanish with a bore as large as mine, but I wouldn’t be surprised if there was one). My next step was to reload my .43 Spanish brass with 385 grain flat nose and 520 grain round nose .446” diameter bullets. My best results have been with the 520 grain bullets, achieving a 2.5 MoA radial standard deviation – a step in the right direction but still nothing close to what I would like to achieve.

One of the issues that may be limiting accuracy is how far the bullet has to jump to come into contact with the lands. I have read that some guns like to have the bullet kissing the lands and others like to have the bullet jump. With the .43 Spanish brass the longest overall length cartridges I have loaded (to date) still fall .250” short of putting the bullet up against the lands. To address this issue I did a search of cartridges and found that the .43 Mauser case would fit quite nicely into my Rolling Block’s chamber, only requiring fire-forming to move the bottle neck forward a bit. The .43 Mauser is a longer case than the .43 Spanish and so would allow me to get the bullet closer to the lands. So I purchased some .43 Mauser brass, fire-formed it, loaded it up with 520 grain round nose .446” diameter bullets with two exposed lube grooves and at last had achieved a cartridge with an overall length that allowed the bullet to just reach the lands (overall length was 3.433”… a monster). The results however were no better than what I have achieved with the 520 grain bullet and the .43 Spanish brass.

So where do I go from here? I’ve been experimenting around with different loads, varying the amount of powder, the compression, the thickness of the wad and, as mentioned above, the weight of the .446” bullet. I can certainly continue to explore this space, but I have also been thinking about how to get a .452” or .453” bullet into this gun. There are two possibilities that I have been able to think of.

One possibility is to ream out the neck of a .43 Spanish or .43 Mauser case to accommodate a .452” bullet. Doing so would reduce the wall thickness of the neck to about .0065” for the Mauser case and just a tiny bit larger for the shorter Spanish case. In practice the wall thickness would most likely have to be .0060” as the .0065” does not allow for any clearance. Is such a thin wall feasible?

Another possibility is to have a bullet mould made that would yield a heeled bullet with a .446” shank that fit into the brass and then a step up to .452” once in front of the brass. Does anyone have any experience shooting heeled bullets from black powder cartridges? Will the lube in the lube bands on the shank be adequate or would one need a lube band(s) at the .452” diameter section in front of the brass? How does one go about designing a heeled bullet? Would a heeled bullet need to go through a sizing die? If so, then the shank wouldn’t be sized. Does that matter?

I’d very much appreciate your thoughts about what step(s) (other than getting a new barrel or a new gun) I might take to improve accuracy. Suggestions about shooting technique would also be most welcome.

Finally, I would be remiss if I didn’t mention just how much fun the process has been. I love this gun.

Dick Hosmer
Posts: 158
Joined: Thu Jul 03, 2008 8:15 pm

Re: Improving accuracy

Post by Dick Hosmer » Tue Jun 23, 2015 9:23 am

Absolutely wonderful post, showing a great deal of thought!

Are you trying to make the rifle shoot as well as possible absolutely without ANY alteration at all, or are you open to small modifications? If the latter, I would suggest some work on the trigger and lightening the mainspring. With NO disrespect to your comments about squeezing ability, most, if not all, military RBs have terribly heavy trigger pulls, not conducive to good accuracy. You might also consider lightening the hammer - the smashing blow originally delivered is not required to ignite today's primers.

I'm guessing that the front sight is one-piece with a tapered top portion, thus you cannot replace the blade, as on a (late) trapdoor Springfield? If you do not care about the gun, you could file the sight block to a nice squared post, which could also be blacked and provided with a snap-on (Springfield) cover. If you also added a tang sight, you should effectively remove the sighting component (whatever small part it may be) of the group size. Of course, mounting a pistol scope to the existing screw holes would take sighting error out of the equation entirely.

As to the barrel, etc., you want fairly soft lead, sized to groove diameter, and minimal bullet jump. How you achieve that (heeled bulet, etc.) is up to you. Recall that a lot of the old-time target shooters seated their bullets from the muzzle and used a separate case and wad. Warning - if attempting this with black powder, make SURE that you leave NO air-space! Top of wad column definitely needs to contact base of seated bullet!

I don't think it would have much effect at short range - and two-piece stocks are not the best anyhow - but you might try shimming the bands (if there is any loosesness) and/or removing the forend entirely. I would remove the cleaning rod before shooting in any case.

Just some thoughts. Basically, it will boil down to a LOT of trial and error. Have fun, and let us know how things work out!

Added: To clarify the above bit about breech/muzzle loading - yes, I AM well aware that such procedure was normally done with ultra-heavy barrels and false muzzles, but, if need be, a simple starter/aligner could be made with very little effort or expense.

Don Eigler
Posts: 6
Joined: Mon Jan 05, 2015 8:00 pm

Re: Improving accuracy

Post by Don Eigler » Tue Jun 23, 2015 1:05 pm

Reply to Dick Hosmer’s reply of June 23, 2015.

First off, thanks for your reply. It contains multiple ideas I had not considered.

I am quite open to suggestions for modifications as long as those modifications allow me to return the gun to its original state.

Your recommendation about lightening up the trigger pull is something that I have already implemented by purchasing a light trigger spring from Kenn Womack. It certainly was a step in the right direction. The accuracy numbers I posted were achieved with the light trigger spring.

Prior to your reply I had not considered “lightening up the hammer.” I presume what you mean is to reduce the strength of the hammer spring rather than actually removing mass from the hammer (both strategies would be effective in reducing the reactive motion of the gun). I’ll have to look into purchasing or fabricating a lighter hammer spring as I do not want to alter the original. If, on the other hand, you actually meant reducing the mass of the hammer… well in that case I would have to find a hammer that I could whittle down or fab a new hammer from scratch.

Your words “smashing blow” just caused me to think along another line. My firing pin is the kind that is spring loaded. As near as I can discern, the sole intended function of the spring is to retract the firing pin, as the spring is so weak that it does virtually nothing to slow down the hammer. One possibility would be to replace the spring with a stronger spring that was effective in cushioning the “smashing blow.” Is there anyone out there with experience or thoughts along these lines?

Your guess about the front sight is correct. It is a military “barleycorn” sight. I have tried changing its coloring by painting the tip with a tiny white dot of enamel paint. This provided no significant improvement in sighting. Perhaps a black dot would be better. Painting the sight is easily reversed with solvent and a cloth so I was willing to give it a try. Snapping on a cover might be helpful. My preference is to not irreversibly alter the gun in any way, so adding a tang sight or a pistol scope is off the table. But as I mentioned in my original post, I don’t believe that the size of my groups is limited by my sighting capabilities.

The lead I’ve been shooting is 20:1. Would you recommend trying softer stuff? If so, what alloy? I’ve read and heard that the softer the lead alloy the more likely it is to run into lead fouling. Speaking of lead fouling: I’ll be the first to admit that I don’t know how lead fouling affects accuracy. Just what are the symptoms of lead fouling (other than lots of lead on your cleaning patches)? How would I know if my barrel is fouled with lead to the point where it is limiting accuracy? If you have a lead-fouled barrel, how do you go about un-fouling the barrel? Solvents? Brushes? Heat? All of the above?

I am not familiar with the practice of seating bullets from the muzzle unless you are referring to muzzle loading muskets and rifled-muskets. But if this is a practice that was done with cartridges can you tell me a bit more about it or point me to a source?

The barrel bands are tight. I routinely remove the cleaning rod before firing.

I’ve never thought of entirely removing the forend. Even if I don’t want to regularly shoot with the forend removed, it poses an interesting question: does the gun shoot better with or without the forend attached? The answer might be useful in guiding me towards better accuracy. I’ll run the experiment.

Speaking of the forend, how one best supports the forend is a matter I am slowly playing with. My current practice is to rest the forend on bench cross sticks placed about one inch in front of the rear barrel band. Rather than try to pull the gun down forcibly into the cross sticks using my left hand, I let gravity do the job and instead use my left hand to cradle the receiver just in front of the trigger guard. This allows me to use my left hand to pull the gun into my shoulder, relieving my right hand and arm from a good deal of that duty. This reduces the stress on my right hand and arm, and I suspect allows me to achieve a more uniform squeeze of the trigger. I started out shooting this RB in the way I shot all guns prior to this, that is, supporting the forend with my left hand. I soon realized that the geometry of an RB, specifically, the large moment arm between the line of the barrel and the middle of the butt plate causes it to have a whopping upward recoil. Holding the forend down is fine if you can do it reproducibly. On this last point I had, and continue to have, doubts about my abilities, so my decision was to let gravity hold down the forend. Yes, the gun jumps upwards more this way, but gravity is very reproducible from shot to shot. But if you press me on this point I’ll have to scream “uncle”: I cannot yet say with certainty that I shoot better with my left hand holding down the forend or back at the receiver. I’d be most appreciative to learn about the experience of readers of this forum.

Has there been a “Best Shooting Practices” thread in this forum? Are the various Rolling Blocks and their ammunition so different from one another that the wisdom developed on one model is wholly inapplicable to another model?

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