12 Bore rifle project

First off, hello to everybody and thanks for developing a community such as this wherein I can discuss questions, such as the following, without necessarily being regarded as 'a little off.' First off, I've been handloading for a few years now (I've also been shooting 12 gauge slugs since I was in grade school). I recently purchased an H&R Ultra Slug in 12 ga and soon began customizing (I'm first and foremost a rifle shooter, as the following will suggest). By weighting the stock, adding a Harris Bipod and a comically powerful scope, throwing in a Limbsaver Barrel De-Resonator and a few other personalized customizations to improve the harmonics of the barrel, I've gotten some meticulously loaded BPI sabot slug rounds to shoot satisfactory groups at 100 yards (I went with the H&R single shot instead of the Savage bolt action because of its simplicity). I'm still not happy, though, and this project is really just about making me smile (yes, I am aware that it's a little ridiculous). Here's my goal: a .729" +1,000 grain slug at transonic speeds for accuracy and knockdown out to, let's say, 300 yards. If I could get consistent six inch groups at that range and if I knew that the slug was still carrying 60% of its muzzle energy, I'd be happy. Now, I've read the '12 Gauge From Hell' thread and have garnered a fair amount of useful information, but I'm not looking for a 20mm cannon, here (1,200 grains at 1,000 fps is 2,664 ft/lbs). Nor am I looking for Sierra match king BTHP precision, but I am looking for a projectile with a ballistic coefficient better than a flying sieve, hence the heavyweight slug. I understand that I'm obviously in custom mold territory and may soon be contacting Stever Brooks for such a mold and Rocky Mountain Cartridge for some brass shells. I also may have my H&R rechambered to 3 1/2", if the situation dictates. My primary concerns right now are pressure, stabilization, powder, etc. The Greenhill Formula says that my 1:35 twist may stabilize a 1,200 grain bullet, such as a bullet that would be cast by NEI's .715 mold (and yes, I've heard about what happened to NEI's quality control after the company lost it's patriarch). I'll probably just go with a Brooks mold, but I wonder how the .715 in pure lead will obturate. I'd also like to stick to plastic shells if possible, for a number of reasons, but even a 3 1/2" shell may not solve all my problems, if Mr. Hubel's posts are any indications. So...thoughts?

Greg5278 had a 1000 gr. TC full bore mould made. Not sure where he got it but if you contact him he has been working on a variety of slug projects and will likely be able to help you with mould and load info for heavyweights. He was loading to 1100 to 1200 FPS with it so pretty much what you are looking for.

Longbow

You need to slug your barrel first. Most of the rifled barrels I checked a .715 is very loose I settled on a .728. That give full engraving on a 870 rem
300 yds is a long way to push 2+ oz of lead

Good morning VMX1200 I use the 300 yards as the max limit for my .300 Weatherby Mag rifle.
If you check carefully here most deer are shot between 10 to 50 yards. The smoothbore shot gun with scope is accurate to 50 to 70 yards, with a proper rifled barrel and slug combo good to 70 to 100 yards. You can streatch the range from time to time to 120 yards or a little more.
Dont forget the cross wind can and will shift your point of impact as much as 30 inches at 175 to 200 yards.
With that heavy a slug your gun will shoot both ways.
It still dont change the fact that most deer are shot between 10 to 50 yards. Hunting is a sport where you out wit the animal by approaching him carefully up close.
I wish I could have been more positive.
Just my 2 cents and now I'm broke!
Ajay Madan
www.PreciousVideoMemories.Com

That's a big order.

I have 5 of the H&R's and they are fun. You do need to slug your bore. 3 of mine rune .730 and one is .731. one is ,729.

It's an interesting project but I doubt you'll reach your 300 yard goal. 200 maybe and 150 definately. Don't get discouraged...work at it.

PS, I'd have gone with the Savage for long range work. Just my opinion.

What you want to do can be done. There are two main things I see so far that I can add beyond what you have done so far based on your OP is all good except for messing with those sabots (waste of time compared to full bore slugs).

First, I didn't see you mention anything about doing something about the forcing cone section of your gun. Properly dealing with this bump in the road is a paramount step to obtaining what your trying to do (73-cal., 1,000+ grain projectile / 1,000-1,200 fps. Muzzle Velocity / 300 yards Min. of N.A. big game chest cavity accuracy). A forcing cone as commonly used in a shotgun is very, very different from the throat of a rifle or pistol.

A throat is basically where the first portion of a guns rifling is reamed out to just enough to remove the rifling lands and maybe just a little more metal so as to make a snug little pocket for the bullet to sit in ideally with the nose just touching the beginning of the rifling in the bore or be a very short jump like less then 0.10" to the beginning of the rifling in a tightly contained short section of smooth bore (often referred to as “free bore”) nearly the same diameter as the bullet. This is how rifles and pistols are set-up.

A forcing cone is like a funnel section in a shotgun's bore that starts right after the chamber where the mouth of the opened, un-crimped shot shell is. At this point at it's beginning it's the same diameter as the end of the chamber which is slightly larger then the OUTSIDE diameter of the plastic section of a shot-shell and then it slowly tapers down to regular bores size. When I say slowly I’m talking about low single digit degree measurements on the taper angle. This works great for shooting shot loads especially when the shot isn’t contained in the petals of a modern plastic wad however for slugs its not good at all because the slug has to literally jump a whole section of barrel that is oversize diameter and more often then not will enter the rifling on the other end of the forcing cone at an off angle kilt and will not be centered true with the bore. This is especially bad when the forcing cone is longer then the slug is which often times can be the case. Also the excessive “free bore” hurts the accuracy as well in another way just like rifles that have excessive “free bore” in that the slug is already moving at farely high velocities when it slams into the rifled section of the bore and thus the initial engraving of the rifling profile into the slug is a rather violent occasion rather then a smooth swaging which is most desirable for accuracy. Almost every handloader that loads rifle loads for best accuracy is well aware of the fact that making cartridges with a long enough OAL (sometimes excessively so) so that the bullet is touching the rifling grooves is the best for accuracy and shorter OALs that make the bullet “jump” to the rifling will have reduced accuracy. Often times the distances they concern themselves are less then a quarter inch at best. So with that in mind how much more effect is this going to have on a shotgun slug that’s crimped a 1/2” deep inside the hull so it’s already got at least a 1/2” of excessive “free bore” plus it might have an inch or more distance in the forcing cone to jump as well before it ever touches the rifling in the barrel ------ Not Good for Accuracy!

Long story short, you don’t want to cut your chamber deaper to 3-1/2” just for the extra powder and wadding space. You also are doing it to remove at least most of that darn forcing cone. To accomplish this you will need to have the chamber reamer you buy modified or have a custom chamber reamer made so that it doesn’t just cut another nasty forcing cone in front of the new chamber and you’ve got the same problem as before only with a longer chamber to take bigger shells so you can miss your target with slugs that go faster. Now exactly how to modify the reamer and what shape it should make for best accuracy is certainly debateable. Some like to go all the way and make it just like a rifle or pistol throat with a nearly square edge where the end of the hull is, this has numberous problems among which include the fact that at least with conventional plastic shotgun hulls the length of a supposably 3-1/2” hull can very nearly plus or minus a 1/16” at least. Secondly, if you ever fire a shorter hull in your lengthened chamber cut this way or you have a slug graze the edge of this nearly square edge because one side of the plastic hull was thicker then the other it’s going to put some significant lead deposits in your chamber which if not dealt with properly could lead to big problems. Ever hear of the guy who fire several boxes of 45-colt loads with soft lead bullets in a 460-mag revolver and then went back to shooting full power 460-mag loads without cleaning the lead out of the chambers first and blew his gun up ????? Same problem could develop with a throat so cut. Granted we are dealing with a lot less pressure --- but still. The other method is to still use a forcing cone set up but make it much, much shorter by using a far steaper angle. The main problem with this method is that your not completely eliminating the problem just significantly reducing it’s severity. Angles of between 20 and 45 degrees seem with the chamber cut to standard depth seems to be the general idea for still having a little bit of a cone as a safety thing but making the gap the slug must jump as short as possible.

Second, you do realize that at the velocity and range we are discussing that drop and wind drift compensation are going to be the name of the game. A lot of people that are used to shooting modern rifles often think that such things cannot be manually compensated for under field conditions ---------- They are dead wrong. Drop and wind drift can be accurately and predictably accomidated for by a dedicated marksman. I strongly suggest you start hanging around with the BPCR (Black Powder Cartridge Rifle) crowd. Basically for you and your 12-bore gun as so described in your OP to do what you want it to do your going to have to treat it like it was a BPCR. Not the whole blow tubing and fowling thing but how you actually perceive your target and the bullet’s (in this case slug’s) path of travel from the moment the powder starts burning until it hits the target and thus your over all shooting and sighting technique. If your going to use a scope I strongly suggest a fixed magnification model so that the size of your cross hairs doesn’t change with magnification settings so you can get used to doing proper “hold over” and compenstation for all different distances, wind situations, and shooting angle from horizontal (shooting up hill and down hill), better yet would be some kind of mechanical screw system which would allow you to raise and lower the rear mounting point of the scope with micro-meter like precision but that would definently have to be ultra custom.

I got to say tommygirlMT, I always enjoy your posts! You certainly know your stuff! Well written that.

Longbow

I've been thinking on the Paradox bore 12 bores the British liked for African game use.
They often built these on a heavy 10 gauge sized frame to allow more meat at the breech. They rifled the last six inches or so of the bores.

Anyway I got to thinking that if you wanted to spin stabilize a slug but still get a decent shot pattern from the same barrel it might work better if the rifling was from the throat to about half way up the tube, and smoothbore from there to the muzzle.
A slug spun up by the rifling should maintain its spin relatively well through a long freebore section before exiting the muzzle, but a charge of shot, not confined by a shot cup at least, should lose any spin induced by the rifling, at least the shot in the center of the charge. The shot on the outside of the charge would not transfer the spin to the rest of the shot efficiently.
An add on choke like that used by the Thompson Center 410/.45 pistol should be more effective that way at any rate.

VMX, I do have some of the bullet you are lookign for, 1043Grains in 12ga. The diameter is .729" as sized and lubed. Please PM me or email me if you are interested. I do have other slugs of different weight also.
Thanks,
Greg
gksappington@aol.com

First off, I just want to thank everybody for responding to my post and giving me some great advice. What I keep coming back to, in terms of difficulty with this project, is consistency. Again, yes, I know that I'm basically asking a shotgun to be a rifle, and it just isn't, but why not see how far I can push this whole thing, right? Simplicity and uniformity equal accuracy and, again, I find myself realizing that the reason rifles shoot like rifles, instead of shotguns, is because people have come to the same conclusions I'm coming to. I need brass shells of precisely unifrom dimensions (and a 12 gauge brass shell case trimmer, I guess), I need to eliminate as much wadding as I can, and as far as the forcing cone/throat goes, I need to do what I do with my bench rifles and seat the slug not 1" off the lands but .010" (ideally, not in practice). I'll see what I can do through customization, but even with that long 1200 grain slug and what I believe I first measured to be a .6" forcing cone, there will be complications. Then there's the powder - I know I can't, but I'd really like to start getting out my 4064. The casting, too, is going to be an intense process, I imagine, when it comes to unifromity, with a .729 1200 grain slug. Of course, intensity is kind of the point when it comes to this project. I guess the question now is how close can I come to these ideals with the available resources. Wind drift and drop are of course issues, but I've already accepted/dealt with these issues through optics and technique, to some extent (through sabots I orginally wanted to match the ballistics of the .510 Whisper). For the foreseeable future, at least until I work these problems out, this gun is strictly a bench project and not meant for the field. Regardless, thanks again everybody and if anybody has any more thoughts at all, I'd be happy to hear them.

Take Greg up on his offer to buy heavy weight solid cast slugs from him and experiment with those before you go get your own mold cut.

When you are ready for your own mold have Brooks or Old West cut it for you not NEI and be real nice and accomidating to Brooks and/or Old West. Send them a drawing showing the basic shape and intended diameter. Dimension key details such as the over-all length and nose length with generous tolerances (example: 0.49" to 0.50" = Nose Length). Basically both of those guys can cut great molds but you need to kind of gently herd them in the direction you want them to go and not try to slap a tightly toleranced mold drawing on them with every little nook and cranny of the mold exactly specified down to the thous. and tightly toleranced at plus or minus a thous. on every single little detail. DO Specify your "as cast" diameter to exactly what you want to the thous. (example: 0.731") and either put a tolerance on it or better yet gently suggest to them in your communications that -0.000/+0.002 is what you expect on that one critical dimension, everything else specify the dimensions to two decimal places (0.00) and give a one one hundredth (0.01") of slack room between the upper and lower limits like I did in my nose length example. They both do excellent work but you need to give them some slack and wiggle room to let them do their best otherwise they will start bucking and snorting like a pissed off stud horse and start thinking of you as a PITA and they will be less motivated to go the extra mile for you and produce an excellent mold. Also, let them cut the mold in their own mold blocks --- you would not believe the little tantrum they threw when I once made the mistake of trying to talk them into doing a custom mold I wanted in a magma machine casting mold block.

Great guys but don't go trying to push their buttons. It's not just them by the way --- a lot of machinists that are their own bosses and have their own business have that kind of temperament. James at Dixie Slugs is kind of that way too. They all are great guys and do exceptional work but you can't try to put them on a leash you have to let them do it their way for things to work out.

I like your idea of putting the slug right up against the rifling of the barrel. If your forcing cone is only 0.6" long then it's probably do-able but it would be a lot easier if you bored that chamber out to 3-1/2" and brought that forcing cone down to about 0.1-0.2" by modifying the 3-1/2" reamer to do a sharper angle and thus shorter forcing cone. The only problem I see is that some of the best powders for what your trying to do such as Reloader-17, IMR-4759, and IMR-4227 do require a high "shot start pressure" to work correctly. Usually this is done with a firm wad column and a nice tight roll crimp. I think if the slug was tight up against the rifling lands that would provide adequate shot start pressure as good or better then a tight roll crimp.

As far as using metallic shells exclusively --- might not be completely necessary. The boys over at hoeningbigboresouth.com with their HBBS 410ga. rifled slug gun have been using plastic cases with the end of the slug hanging out the end un-crimped no problem for quite a while now. How they do it is by squeezing down the diameter of the plastic hulls at the end and then seating the slugs inside so the slugs stretch the plastic back out to full size and thus grab tightly to the slugs with neck tension similar to what brass hulls would give. I would think some kind of "short length of pipe" like bit in a drill press with a tapered opening would be the way to do this to the much larger 12ga. plastic hulls for about the first 1" of their length at the mouth. The rotary motion would heat the plastic so it would hold its new smaller diameter after cooling back down --- sort of like the heat generated with a roll crimper bit helps produce the holding power of a conventional roll crimp. Of course if such a method worked out and you did eventialy get your own slug mold cut a slightly tapered base might be advantages for seating the slugs in the tightened up plastic hulls. Since you will still be using wadding since it is still a shotgun there shouldn't be any of the usual disadvantages to a tapered base cast bullet as experienced by pistol and rifle bullets which have the gas pressure acting directly against their bases.

As for wadding my suggestion would be a plastic gas seal or two directly over the powder. The stackable original BPGS from BPI would be excellent or just make your own by taking a razor knife to regular one piece plastic shot wads. I wouldn't suggest BPI's newer style "X" gas seal --- IMO they are far inferior to the original BPGS. On top of that I would use a stack of the tougher, harder 1/4" thick nitro cards from circlefly.com --- prefereably waxed to whatever height put me just short of the over all length I wanted to put the slug tight up against the rifling. Then I would use 1/8" & 0.07" thick nitro cards as well as 0.03" thick paper card material overshot cards to fine tune the wad column length to put that slug within a hair width of the rifling if not right on it tight kissing it.

As far as casting your own, if and when you do get a mold if you go with a Postel or Creedmoor type of nose shape for your slug mold which would probably give you the best possible B.C. for long range shooting then 50/50 WW-alloy/pure-lead is fine for punching paper but for shooting actual game you would want to do a two step pore with an exact capacity micro dipper of pure lead in first to form the nose followed by the 50/50 mix from a bottom pore to do the main slug body would allow you to maintain an aerodynamic nose profile and still get a good permanent would cavity on game. Usually I do this by making dippers using straight wall pistol cases and a length of hanger wire to do the handle up and keep the pure lead in one of those Lee pots that’s the smallest, simplest and cheapest they sell and you can pick up for like $30. The reason I suggest 50/50 instead of pure WW alloy is because at the ranges your talking about I think you will actually get a little better accuracy by using a slightly softer alloy then pure WW. I’m pretty sure the slugs Greg is offering you are a truncated cone flat nose style. Not quite as good of B.C. but you don’t need to do any fancy soft nose casting for game due to their flat tips which will give you a good permanent wound cavity because the nose is already flat and doesn’t need to be soft like a more aerodynamic nose shape which needs to flatten out on impact to give good performance on game.

VMX you might want to look back in history at the British Bore rifles and see what you can learn.Sometimes it beats trying to reinvent the wheel. The British bore rifle were pure hunting guns and sure weren't meant for 300 yards but in their day they were the heavey weight stopping rifles.

VMX, I have the slugs, and trying them is a great deal cheaper than investing in a custom Mold. I think I have around $300 in my Mold, and I had to make the blocks myself. I had a falling out with Brook molds, after he F---up my blocks, and charged me about $65 per the mistake. After the mistake, he told me mu Blocks were heat treated, and started cursing at me. That didn't go over too weel.

Anyway the accuracy of the slug, and gun is greate rthan you can hold. I had a Law Enforcement sniper fire 3 MOA groups with a Tarhunt shotgun using 3 different slugs of mine. Two types were cast, and one was Lathe turned. None were sorted my weight, and the powder charges were thrown, not weighed. I do have a 3" reamer with minimum tolerances if you could find a 2 3/4" gun to rechamber.
Please give me a shout when you need the help.
Greg

VMX for powder choices you can use IMR 4759, 4227, and possibly Accurate XMP 5744. I think Vihtavuori N110 could work too, but I haven't finished my work with it. It seems to burn around the same speed as 4759 in the 12ga low pressure. I do like the IMR powders for the shotgun loads, they are more forgiving in the way of pressure spikes, and such. I would stay away from BAll powders for working up test loads.
Greg

Quote:

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Originally Posted by Cheshire Dave

VMX you might want to look back in history at the British Bore rifles and see what you can learn.Sometimes it beats trying to reinvent the wheel. The British bore rifle were pure hunting guns and sure weren't meant for 300 yards but in their day they were the heavey weight stopping rifles.

---

i would suggest the same thing. i personally think the modern manufacturers use way too fast a twist in their slug guns unless the manufacturer's intention is to use those sabot slug loads. i have no idea about that kind of load and personally think that is an exercise in sillyness. the old British 12 bore rifles that i have seen had twists in the 1-70" to 1-102" range. you can learn about the old rifles by examining the loading tools supplied with the rifle when sold. i saw a WW Greener rifle that shot .736" round balls (original mould) with the 1-102" twist. an Alex Henry 12 bore rifle i saw with original mould for a 1100gr. conical had a 1-78" twist. i am interested to see your testing and results. 12 bore rifles were general purpose hunting rifles. think deer, elk, blackbear in N. American terms. 8 bore and 4 bore were the stopping rifles.

I saw a very nice double in a small museum in san francisco years ago. It had belonged to a photographer who's photos recorded the Gold rush in Alaska.
He of course also spent much of his time panning for Gold and hunting to stay alive.
The Shotgun was a Wesley Richards under lever, it looked to be a Tropical version, a 12 bore on a ten bore frame, but I couldn't tell it it had a paradox bore or not.
Theres a Wesley Richards at my local shop that I've had my eye on, looks to be in great shape. The owner hasn't put a price on it yet.

A slow twist is generally best for a heavy bullet with little bearing surface and large diameter, like a round ball or short conical slug, at least at the standard velocities you'd expect from a 12 bore.

Tests on Springfield muskets indicated that those shot much tighter groups with a patched round ball than with the standard minie' ball.

If a round ball looses stability down range it simply reverts to the same sort of roll it would have had if fired from a smooth bore. A conical bullet on the otherhand becomes much more inaccurate when it begins to first osilate then tumble end over end scrubbing off velocity at several times the rate of a rolling round ball.

Another way is to not go quit so heavy. Use 715gr, RG Henson jacketed
slugs in a 3.5" RMC brass case at higher speeds, that is your best
chance at getting over 250 yard accuracy. Or a cast and lubed
slug with pointed shape of same weight. You have to cut down the
time of flight. To do anything at 250-300 yds you must get rid of
the shotput trajectory in the first 200 yds.

RG's Slugs are buck fifty each and you just deepen chamber.
Use the loads of 4759,4227, RE17 that we've used. You can easily start
them over 2000 fps, in 3.5" brass.Ed

I wasn't clear when I typed the one post. I forgot to put the - in the line. I meant to type that the LE Sniper fired 3-1 MOA groups at 100 yards with an 8.9# Tarhunt shotgun.
Sorry for any mistake.
Greg S

TommyGirl, you're a wealth of information. I was being chastised the other day for saying my Handi's didn't have a forcing cone and the ones I;ve checked, don't. It's because they were rechambered to 3.5 and FH.

I haven't checked the 3" because I plan on rechambering anyway.

Thanks for the compliment Peter Nap. In truth --- I can not claim to be the original finder of most of the information I have posted. I've learned a lot from others and try to continue the cycle and spread the info around for another cycle.

As far as why I am interested in such topics --- Well lets just say I've got an incurable case of Magmamitis along with a basic thought pattern process that generally assumes bigger is better. I didn't get into slug shooting and reloading because I have any real need for a slug gun as a big game hunting instrument but rather because a rifled bore 12ga. is a 73-caliber power house that you can legally own and load for without having to get a tax stamp as is normally required for any rifle larger then 60-caliber.

I will not deny for one minute that at its beginning the Magmamitis started as an ego thing where when I was a kid I could successfully handle bigger guns then the guys my same size and age or even bigger could. I will never forget the first time I realized this when one of my guy buddies got nocked on his ass literally by my deer hunting rifle way back when I was still in grade school and it was the first year I could legally hunt. God, the respect I earned in their eyes felt good when that story finished its trip through the grape-vine. I've mainly grown out of the whole "dare devil" ego trip thing now that I'm much older and wiser and had few humbling (or was that humiliating) experiences when I tried to push things a little too far over the years growing up --- but I still like big guns, the bigger the better. I shoot a lot of cast boolit loads at reduced velocity now days from my big bores and I'm not so much into building the most powerful load I can at least for my big bore bottle-neck cartridge guns but with my shotgun slug loads for rifled bores and other-wise I'm still trying to push the envelope.

I just found this thread and am working on the same type project with the same basic gun. How have you progressed?

All I see here is pain,,, and plenty of it.

A 2.25 oz. slug at 1000 fps from a 6lb gun? Do you have any idea how much recoil you are talking about?

This gun needs to weigh 12lbs + just to be able to shoot it twice in one day.

The British 12, and 8 bore double guns, some fully rifled and some with Paradox barrels where only the last two inches were rifled, weighed upwards of 16-18 lbs.

You needed cajones about that big to pull the trigger on one of those guns. The 8 bore guns shot boolits weighing 1250 gr.

I applaud your idea, however if I was you I'd let someone else fire that gun the first time.

On another note,,,, It might be a good idea to work your way up to those loads, slowly,,, and stop when you can't take it anymore.

My .02

Randy

I built up one of those H&R super slug guns. I think I have a thread on it here somewhere. I called it the .73 caliber Talleywhacker. I had RCC make me some custom everlast 12 ga. cases 3.5" long. I had done a lead slug of the chamber and throat and found that a 3.5" hull was the way to go. I then had a custom mould made for a 1300 grain +/- .730 cal slug. I cast it 1/20 tin to lead. I use 150 grains of 2F compressed, a 11 gauge over powder card wad, two greased felt wads and I do a light roll crimp on the case mouth. Recoil is brutal but not impossible. However a 300 yard gun? No way in heck. This thing is a 50 yard gun with 100 being the max I'd try and hit with it.

It seems to me that it would be better to stay below transonic velocities. Most bluff nosed projectiles experience incredible drag as they approach Mach 1 and it doesn't improve much until well into the supersonic region. Below transonic the drag remains remarkably stable throughout the flight regime. With such a heavy projectile high velocity would not be needed to assure deep penetration. The effectiveness of the old big bore guns depended on heavy high sectional density bullets not high velocities.