TC Seneca Hoyt Re Bore From .36 to .40

[Idaholewis1]

Cooked up another Project I have owned 2 Thompson Center Seneca’s in .36 Cal for quite sometime now, Unfortunately both bores were Rough when i got them. Both rifles shot ok, but as anyone familiar with Blackpowder Rifles know, it is TOUGH to maintain a Rough pitted bore from getting worse over time. Both of my Seneca’s have the Rare to find Seneca/Cherokee Tang mounted peeps, And Both rifles are in excellent condition exterior wise.
Skip ahead a bit, i ended up trading 1 of these Seneca’s to Forum member willfish4fud, I fully explained to him the Bore condition, and what my future plans were, He and i have become good friends through here, He is a Darn Good guy, But a BAD INFLUENCE!! 
My idea with 1 of these little Seneca’s has always been to strip the Barrel down and send it to Bob Hoyt for a Re Bore to .40 Cal and Twist it to shoot .40 Cal Pistol Bullets, But i have stalled on doing it (To Many Irons in the Fire!) Both Little Seneca’s have just Sat around in Idle, After Explaining my idea to Forum member willfish4fud he and I decided to get the project underway! I played around with Rifle Twist figures and Bullet weights, 1:36-1:38 Twist Looked really good for the Pistol Bullets, And Velocities we plan to shoot, so we went 1:37 Twist   I spoke with Hoyt, We both shipped our Barrels Off to him. Hoyt told me the Bore Diameters will end up at .400, and no larger than .402, He will Bore and Rifle our Barrels at the same time (1 after the other)
This will be the First bullet we work with, this one should end up around 180 Grains with my 1-40 Alloy, for safety I am having the Mold Cut to .403 using Tom’s Positive tolerance (+.002/-.000) Which means the diameter will be AT LEAST .403, and with Tom’s Tolerance window of .002 it could end up .405, We also ordered a Lee .401 Push through Bullet Sizer so I can Customize bullet fit to our Bores. I am Looking forward to both of us getting our Barrels back and “Wringing them out” i will post updates as things progress along

[font=Roboto, sans-serif]The Bullet Mold i am having made, should be here any day now[/font]
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[Idaholewis1]

Velocity wise i plan to stay in the 1300-1400 FPS Range, 50-60 Grains of Swiss 2F should get me right in there. I really put Thought in to the Seneca Rifle itself in this Build, You that have, or have handled them know the Seneca’s are a Slim/Trim Little Rifle and not meant to Push Hard (Heavy Bullets/Charges), i went off of TC’s Load data for the 45 Seneca and Maxi Ball/Maxi Hunter, Those 2 bullets are in the 240-250 Grain Range, TC lists the Hottest end at 80 Grains of 2F with a Velocity of 1,541, I have never been a Fan of the .45 in the Seneca due to the Slim/Trim design of the Seneca, i know a few guy’s that have cracked their Stocks when pushing the 45 Maxi Ball/Maxi Hunter with upper end Hot loads. So by going with a .40 Cal Bullet under 200 Grains, and Staying in the 1300-1400 FPS Range i will be well under their .45 load Data for the Seneca. These little Rifles will be able to digest this Day in, and Day out
I used JBM’s Stability Calculator, A number of 1.5 is the military Standard for Stability, As you can see by the Bullet length, Weight, Twist Rate, and Velocity i chose in this build, it puts me right in there

 

[Idaholewis1]

I already got my .36 Seneca Re bore to .40 Barrel back from Mr. Hoyt, That was Fast! And it looks AWESOME!! I just did a Quick bore polish, Cleaned it thoroughly, and oiled it up. Waiting on the Accurate Mold, i have the .401 Sizer, Willfish4fud and i are Close to Making Smoke with these! Put back together and ready for it’s Maiden Voyage    This one has the Seneca Tang Peep, and of course i added a Lyman 17 Globe so i can use my Shaver’s BPCR inserts. I bet there aren’t many 1:37 Twist .40 Cal TC Seneca’s around?   

 

[Idaholewis1]

I got tired of waiting on the new .40 Cal Mold from Accurate, i had to come up with a Way of shooting this new Rebored Seneca Barrel?   I picked up a Box of Cheap Blazer .40 S&W 180 FMJ loaded Shells and pulled them apart with my Kinetic Bullet puller. I checked them with a Magnet to make sure, They were non magnetic as i figured, They are Copper with a Lead Core, They Measure .6 in length and weigh 180 Grains (same as the mold i have coming) The Diameter kinda threw me off, they were .399 on the Dot (i was thinking they would be .400) I Drop tested one on my Concrete basement floor and it dinged Easily, I was confident they would “Bump up” in my Bore, But i was sure they would be fairly loose? Nope! They just grabbed the Rifling (This bore is .399) I loaded up and headed for the Sandpit, I foul shot the 1 Bullet that i dinged on my Basement floor off Target, Swabbed the Bore good, Reloaded, and Started my Group. My powder Charge was 60 Weight Grains of Swiss 2F, and i used a .45 Cal Wool Felt Over Powder Wad. The Bullets Slid down the Bore no problem.

Box of shells i pulled the bullets from
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My Frankford Arsenal Kinetic Bullet Puller i used to pull the Bullets

The Bullets, 180 Grains FMJs

A size comparison, next to a 350 Grain .45 Cal Lyman Gould Bullet, These .40s are Cute Little things 

[font=Roboto, sans-serif]Where i shot these from[/font]
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It was REALLY cold here yesterday morning, -4 Degrees! I waited til it warmed up to a Sultry 10 Degrees or So   It was also Breezy, Not a Great day for Shooting! But I couldn’t Resist trying this out. I had forgot Tools to make sight adjustments, I had no choice but to Go with it, My first 2 Shots were high, just above the Target and a Little right, but about a 1/2” Apart, it was looking good 

 i pulled my 3rd Shot slightly, it went left and a little Lower. My folks live just up the Rd about 1/4 mile from here so i loaded up and headed there to use my Dads Wrenches to make a Quick Sight adjustment, I headed back to the Pit and Shot my last 2 Shots, They were a 1/2” Apart, Stil a Little high, and maybe a Smidge right, But she’s Close! I was impressed with results since i was using a Complete Odd Ball Bullet, This Little rifle is gonna shoot!  :ttups:

 

[Marty1]

No need yesterday Idaholewis to wait long for the barrel to cool between shots :lol:   
Very interesting read.  Will this rifle be for fun target or hunting :?:   Yotes and fox come to mind for this small bore.

 

[Idaholewis1]

No need yesterday Idaholewis to wait long for the barrel to cool between shots :lol:   
Very interesting read.  Will this rifle be for fun target or hunting :?:   Yotes and fox come to mind for this small bore.

Marty, It was really to Restore a Pitted Bore, These TC Seneca Rifles are really nice little guns, and Quite Sought after. I had 2 of them, Both in .36 Caliber, But both had Pitted Bores when i got them :x I’ve always said, These Poor Ole Muzzleloaders sure have a HARD time finding a good Home!!

Having this .36 Bored out to .40 Cal Would allow me to Deer Hunt with it here in Idaho. It would be VERY adequate for it!! The Mold i am Waiting On will be in the 180 Grain Range. At 1300-1400 FPS this thing would be DEADLY on Deer!! And it’s a LOT of fun to Shoot! Just a Bump to the Shoulder, Gotta love it! 

 

[exMember]

excellent shooting!

How does the rifling look? Any way to take a pic of the rifling work?

 

[Marty1]

No need yesterday Idaholewis to wait long for the barrel to cool between shots :lol:   
Very interesting read.  Will this rifle be for fun target or hunting :?:   Yotes and fox come to mind for this small bore.

Marty, It was really to Restore a Pitted Bore, These TC Seneca Rifles are really nice little guns, and Quite Sought after. I had 2 of them, Both in .36 Caliber, But both had Pitted Bores when i got them :x I’ve always said, These Poor Ole Muzzleloaders sure have a HARD time finding a good Home!!

Having this .36 Bored out to .40 Cal Would allow me to Deer Hunt with it here in Idaho. It would be VERY adequate for it!! The Mold i am Waiting On will be in the 180 Grain Range. At 1300-1400 FPS this thing would be DEADLY on Deer!! And it’s a LOT of fun to Shoot! Just a Bump to the Shoulder, Gotta love it! 

I didn't realize you can use a .40 for deer out your way.   Here in MA you need at least a .44 MLer for deer.

 

[Idaholewis1]

excellent shooting!

How does the rifling look? Any way to take a pic of the rifling work?

I tried to get a Pic of this new Rifling, But this darn new Phone just WON’T Focus up, I played around with this thing for 30 minutes or more trying, My Old Samsung Galaxy Phone Camera did Good with Bore pics, But this new Phone is HORRIBLE for it. A green Bore light works best, But I only have that in 45-50 Cal, I have a little Red light (Lighted Archery Arrow Nock) that is Small and will drop right in, But my Phone just won’t Focus.

I REALLY need to get a Bore/endoscope, preferably one that would hook to my Ipad, Actually my Android Phone might be better? There are a BUNCH of them out there, Is there 1 you would Recommend? How did get the Bore pics of your “Shoot Out” Before and after Pics? That’s what i want!! Those pics look AWESOME!

 

[Idaholewis1]

Update on my little .36 Seneca Re bore to .40 Cal

 I did some playing with the Chronograph, I was wanting to find what it took to get 1300-1400 FPS? Turns out VERY LITTLE :ttups: 

Accurate molds <a href='/tags/40-172L' rel='nofollow' title='See all tagged subjects with: #40-172L'>#40-172L</a>, Bullet weighs 177 Grains when poured from 1-40 Alloy, and 178 Grains Pure Lead

 

This is 30 Grains of Swiss 2F, Recoil is COMICAL , Just Bumps the Shoulder

40 Grains of Swiss 2F

60 Grains of Swiss 2F, Accuracy wasn’t all that great here with Lead bullets, But it Shoots Copper Jacketed REALLY well at this Velocity

 

[Idaholewis1]

You can see it’s gonna Shoot :ttups: I dropped Shot number 3 way out somehow? I am pretty sure I discovered why Last night, There was a Tiny movement in the Hooked Breech to Tang Fit when i pushed on it Loading, I knew it was there and ignored it (My Bad!) Yesterday Told on it! I had 2 Shots Cutting eachother Low, and 3 Shots Cutting eachother about 6” higher, It was Shifting! I have it Fixed now and Ready to go :ttups:  We are getting BOMBARDED with Snow again Right now, If it Quits tonight i will get out first thing in the Morning and Check my Work, I am Confident i got it

<iframe width="560" height="315" src="https://www.youtube.com/embed/Na__kDkfvec" frameborder="0" loading="lazy" allowfullscreen ></iframe>

 

[Marty1]

Really nice range report Idaholewis on that new .40 bore.   It's always a plus to see a chrono at work on new load testings !  Thanks also for taking the time to show us a video.   :ttups:
I alway ignore shots like <a href='/tags/3' rel='nofollow' title='See all tagged subjects with: #3'>#3</a> and go for a group of five like you did.

I've taken many whitetails with a sabotted.40 caliber projectile.

 

[bronko220002]

I had a Seneca in .45 years ago and have since been trying to get another. I also had a .32 cal Cherokee. And like a dummy I sold both. I've seen a couple at on line auctions and bid as high as I dare without holding and seeing it personally. They are a joy to shoot and carry in the field. The .45 will give you a nice bump on the shoulder with a stout hunting load but it isn't bad. That looks like a fun caliber and is a good shooter. Bob does nice work for sure.

 

[Idaholewis1]

I had a Seneca in .45 years ago and have since been trying to get another. I also had a .32 cal Cherokee. And like a dummy I sold both.  I've seen a couple at on line auctions and bid as high as I dare without holding and seeing it personally.  They are a joy to shoot and carry in the field.  The .45 will give you a nice bump on the shoulder with a stout hunting load but it isn't bad.  That looks like a fun caliber and is a good shooter.  Bob does nice work for sure.

We have actually had a tough time with these little .40s, Neither of us have been able to get the little Lead Bullet to Shoot that Great? I started playing around with Sabotless Jacketed, Turned Willfish4fud on to them as well. We have Gotten pretty Decent Accuracy that way. I need to pick this little Rifle back up and Work with it More, I got Burned out with it and Set it aside for Awhile. 

  Willfish4fud spoke with Rice Barrels, They mentioned Harmonics in the Little 13/16” Barrel possibly being the Culprit, They Told Willfish4fud that they would not Build a 13/16 Bullet Barrel for that Reason. I believe they are correct, I played with some Friction points in the Stock (Light Barrel contact) rear of the Wedge Key, and Forward of it, Those Groups were HORRIBLE!! By FAR the worst mine has Shot. My 1” Barrels are NOT finicky like this, Not in the least.

 I am actually thinking about trying some PRB in this thing, .390 RB, Even Though the Twist is 1:37, I believe i can get it to Shoot by Lowering the Powder Charge