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Author Topic: .257 Bulldog  (Read 4173 times))

Offline mackeral5

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.257 Bulldog
« on: December 18, 2020, 01:02:00 PM »
I've had this TJ's 25-20 barrel laying around for some time now and always wanted to try it in one of my Bulldogs.  It is a .500 od, 1:14 twist, a little over 27" long.  One hurdle in making this happen was the desire for a barrel mounted breech oring.  I have become pretty creative in using my very limited fabrication tools and skills, however cutting an internal oring groove is an operation that my hammer and chisels just aren't quite up to task for.  Recently a forum member agreed to help me out with this operation, so I am now out of excuses. 

The barrel is sleeved with a 11/16 OD thimble of 4130 tubing on the breech end, which mates up to 2 layers of CF tubing--a 15x13 then a 15x17.  The transition from 4130 to CF occurs under the rear shroud adapter.  The 4130 and CF tubing is bonded with Loctite 680.





The .257 barrel will actually end up as a swappable complete "upper" with the barrel/shroud semi-permanently attached, there is no reason to separate the 2.  Here is a picture of my .357 upper and a possible shroud length.  I will be installing a 17mm slip on 1/2-20 adapter once it arrives from Poland.   The shroud will end up somewhere between the 2 shown.  A second rear shroud adapter will be mounted at the front of the shroud, with side screws added to make the barrel/shroud one rigid unit. 



The bulldog's design makes caliber swaps challenging, if the caliber swap system requires interchangeable bolt probes.  To remove the OEM bulldog bolt, it requires almost complete disassembly, at minimum some of the trigger sear/pins must be removed to access the cocking lug/bolt.  Long term, I hope to have a bolt system made very similar to the WAR style which will allow for simple caliber swaps.

I've read a lot of posts from Marco over the years where he gives advise along the lines of "build the powerplant for a .357 and put a .257 barrel on top of it."  That is what we have here.  The bottom end is ported .310 with full bore porting in the .257 barrel.  A bolt probe is in the way, but I have tried to minimize it's size. 

I've also read where it takes a lot of plenum and pressure to get .257 bullets up to speed.  This experiment has taught me that there are no exceptions to physics.....  Initially I tested with a regulated tube and the Huma set around 125bar.  71 gr slugs would not break 900fps, using approximately 120cc of plenum at this reg setting.  I didn't invest much time here, and I may revisit this but for now I will ditch the reg.

Next I put on an unregulated tube and found a twin spring combination that worked pretty well. 

Filling to 3000psi, and dialing up HST until it will just barely cock---

Hunters Supply 87gr  930fps  167fpe
Hunters Supply 71gr  1030fps  167fpe

There may be a little more in it with hammer weight, or spring, but right now I don't really see any need to push it harder.

Dialing HST back a bit gives a 4 shot string 982, 983, 984, 972 fps with Hunters Supply 71gr.    Call it 4 shots of 150fpe. 

I'm not quite sure where this one will end up, but I like the data I see so far.  For example, when using this same barrel on my QB .257 build with a powerhouse valve, it maxed out with the 87gr at 935fps, but it took 3500psi to do so whereas the Bulldog is getting 930fps on 3000psi.  I am assuming this is  largely due to the Bulldog having almost double the air storage of the QB .257 build, thus maintaining a much higher average pressure during the shot.  I also note the barrel was cut down approximately 1/2" when converting it fitting it to the Bulldog.

Once I get an LDC mounted I will put some lead on target.  That may be a week or two while waiting on the adapter to arrive from Poland.   
« Last Edit: December 18, 2020, 01:07:26 PM by mackeral5 »
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Offline redlined_b16a

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Re: .257 Bulldog
« Reply #1 on: December 18, 2020, 01:26:04 PM »
I was brewing up a plan in my head last week for a .257 or .308 barrel on the Bd platform.

Outstanding work!
Thinking a longer .357 barrel could be used as well.
I did come across a .357 1:16 twist 34" long blank.

But I have no clue where to start to make the lead in.
Barrel blank was a 1" o.d.
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Offline mackeral5

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Re: .257 Bulldog
« Reply #2 on: December 18, 2020, 02:00:18 PM »
I was brewing up a plan in my head last week for a .257 or .308 barrel on the Bd platform.

Outstanding work!
Thinking a longer .357 barrel could be used as well.
I did come across a .357 1:16 twist 34" long blank.

But I have no clue where to start to make the lead in.
Barrel blank was a 1" o.d.

Thanks for the compliment.  The chamber/lead is one of the easier parts, IMO.....  search for posts about a taper pin reamer.    Regarding barrel length---I wish I would have had 30+" of barrel, but all I had was a little over 27"....
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Offline FuzzyGrub

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Re: .257 Bulldog
« Reply #3 on: December 18, 2020, 02:29:43 PM »
Nice work, Mike.  Thx for posting.  Cal changes on BD's looked very challenging to me.  Glad you tackled it and provided the info for everyone.  :)

Look forward to seeing that bolt set-up. 

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Offline rsterne

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Re: .257 Bulldog
« Reply #4 on: December 18, 2020, 02:30:46 PM »
Impressive.... It is always easier to go smaller on caliber to get big (relative) power than the other way....

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Offline Hobbyman2007

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Re: .257 Bulldog
« Reply #5 on: December 18, 2020, 02:44:43 PM »
Canít wait to see some pics of it completed. Thatís some real good power . Make sure you get yourself some 257420 bullets . These barrels absolutely love them. I did something similar with the 70-35 Winchester and it was much easier to get power out of than the .257 disco. I really need to get out and shoot it some time . Itís just a bit overkill for rabbits and partridge inside 30 yards .
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Offline steveoh

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Re: .257 Bulldog
« Reply #6 on: December 18, 2020, 05:12:30 PM »
This is great. I love my .257 Texan and .257 Citrus, but holy cow they are both long and front heavy. I've love a powerful bullpup in .257 for more ease in handling.
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Offline mackeral5

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Re: .257 Bulldog
« Reply #7 on: December 18, 2020, 06:53:50 PM »
Thanks for the encouraging words. 

The Bulldog is a great all around platform.  it has a sidelever, ample, versatile hammer system (105 gram OEM hammer, plenty of room for more spring/stroke, OEM hammer can be whittled down below 50 grams), over 300cc of air storage, and a .375 valve throat.  There is plenty of room in the valve pocket for Cobra chambers, even adapted in a Cothran Powerhouse valve in one.  At some point I may see how the Cothran works in this one. 

Currently the gun is running a peek poppet from the Cobra valve I use in regulated applications, with no return spring.  Initially I tested the .257 with the Cobra chamber, but I removed it for testing max FPE.  An observation on Cobra valves....whether low power, or high, it seems the air spring effect drops max velocity by about 25fps.  Disable the cobra chamber and velocity increases by approximately 25fps.  I saw that effect with this gun.  I will likely reinstall the Cobra chamber for further testing.

I have completed 2 BD barrels conversions, with a 3rd still in process--a TJ's 1:26 .357 and this TJ's .257 1:14.  The third is 32" of TJ's .457 in process for another BD build.  I expected the .457 to be ready by now, but sometimes things take a bit longer than expected.....

Once the muzzle adapter arrives I'll be ready to fully assemble and put rounds on paper. 

Here is a random observation....  When you are used to regulated guns, shooting an unregulated big bore seems so much more extreme....I think the word violent is a fair descriptor... 

Have to order more ammo.  I like the 71gr from Hunter Supply but their pricing has gotten to be very unreasonable.  Can anyone recommend a similar bullet/source? 
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Offline Hobbyman2007

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Re: .257 Bulldog
« Reply #8 on: December 18, 2020, 07:41:12 PM »
Mike ,

Are you modifying the magazines for each caliber ? I wonder if thereís someone out there that would print new ones .
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Offline mackeral5

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Re: .257 Bulldog
« Reply #9 on: December 18, 2020, 07:51:20 PM »
Mike ,

Are you modifying the magazines for each caliber ? I wonder if thereís someone out there that would print new ones .

Denis, I haven't modded any magazines yet, and it won't be a simple task to do a caliber conversion. 

IMO the OEM mag is a good enough design and caliber swaps are so rare, I don't see it being worth anyone's  while to print a mag.  Darko's mags are awesome, and I know he could do it, but I don't thing it being a very profitable venture.

Something strange about the BD platform and my shooting habits----so far I have only punched paper for that I rarely use the mags.and never use the single shot trays.  Someday I would like to hunt with the platform, then magazines will become more of a priority.   
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Offline mackeral5

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Re: .257 Bulldog
« Reply #10 on: December 18, 2020, 09:23:13 PM »
A picture of the lead which was cut with a modified taper pin reamer, cut by hand, mounted in a tap handle.  Later it will be polished with JB bore paste.



Now a pic of the modified #4 reamer.  If you look closely near the pencil tip you can see where I relieved/sanded down the cutters to stop the cutting at my desired diameter. 



For those that are curious about taper pin reamers, here is a chart of sizes.  For .250/.257 I chose a #4, I think because that is what I found the best price on at the time.  As you see in the chart, both a #4 and a #5 could have been used.  Note you can use straight or spiral flutes and both will work, however spiral flutes do a better job of not digging into the rifling. 

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Offline redlined_b16a

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Re: .257 Bulldog
« Reply #11 on: December 18, 2020, 10:18:37 PM »
Did you check
gtbullets
Rimrockbullets
Western bullets

Gt has some 55 grain .257 and will be the cheapest.
Casted in .258
http://www.westernbullet.com/25caliber.html
« Last Edit: December 18, 2020, 10:23:41 PM by redlined_b16a »
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Offline mackeral5

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Re: .257 Bulldog
« Reply #12 on: December 18, 2020, 11:06:29 PM »
Did you check
gtbullets
Rimrockbullets
Western bullets

Gt has some 55 grain .257 and will be the cheapest.
Casted in .258
http://www.westernbullet.com/25caliber.html

Thanks for the suggestions
  I've got some GT 55gr, which I do like, but a little light for this one.  Have some of the Western 65gr in route, even though they are a tad light for my preference.   Will report back on how they do.
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Offline Blutroop

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Re: .257 Bulldog
« Reply #13 on: December 19, 2020, 05:24:18 AM »
Has anyone been shooting a .257 in a 1-10 twist? Iím looking for advice on bullet weights.
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Offline mackeral5

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Re: .257 Bulldog
« Reply #14 on: December 19, 2020, 09:36:46 AM »
Has anyone been shooting a .257 in a 1-10 twist? Iím looking for advice on bullet weights.

Bob's cast bullet database is a pretty good guideline around bullet length and twist requirements as well as how a boat tail or gas check effects this relationship.
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Offline FuzzyGrub

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Re: .257 Bulldog
« Reply #15 on: December 19, 2020, 10:53:29 AM »
Mike,

Thanks for the detailed pictures on the pin reamers.   Looks like I need a #7 for the 357 to go with the #6 you recommended for the 30.   

Am I correct that the leade would start at back of where the pellet/slug at bolt closed position?  Ideally this would be just past the barrel port?

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Offline mackeral5

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Re: .257 Bulldog
« Reply #16 on: December 19, 2020, 11:29:29 AM »
Hi John, I can't say for certain where the lead should start ideally.  But I do like to make mine start at the barrel port, as you described.  I really just run the cutter in, remove, clean chips, insert preferred projectile and see how deep it seats into the chamber.  Then I repeat the process until I have the depth I want.  You will want to remove the cutter and clean out chips frequently and use some type of cutting oil, I just use 3 in one oil.  If you don't remove chips frequently and do not go slowly, you WILL smear the rifling and it will take a lot of work to clean it up, if even possible without cutting off that section and starting over.

I may be wrong doing it this way, but with a sidelever I don't mind a shallow lead where I essentially swage the bullet into the rifling by closing the bolt.  With a bolt this isn't practical.  I'm sure there is a right way and a wrong way, but I'm not necessarily qualified to say which. 

A shallow lead can always be cut deeper.....

Another use for the modified reamer is to modify pellet leads from a hard corner to a more gradual lead.  I've done that on a .25 GM barrel, it works very well. 

Sizing the reamer----I run it into the barrel until I get the right chamber diameter, by test fitting the base of a pellet/slug.  Then I mark the reamer and relieve the cutters beyond the desired diameter.  I relieve the cutters by chucking in a drill and spinning it against a 1" belt sander.  I have one of those little Ken Onion Work Sharp units, combining it and a drill is used for many of my caveman "lathe" operations.....
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Offline Sbak

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Re: .257 Bulldog
« Reply #17 on: December 19, 2020, 12:09:16 PM »
Thank you for the reamer idea and tips. I'm going to have to make one up. Very clever
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Offline Lani52

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Re: .257 Bulldog
« Reply #18 on: December 19, 2020, 03:20:37 PM »
Mike,

Fantastic!

One of the best and most dependable platform out there.

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Offline mackeral5

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Re: .257 Bulldog
« Reply #19 on: December 19, 2020, 05:20:01 PM »
The taper pin reamer idea came from various forum members talking me out of wasting a couple hundred bucks buying something that wasn't going to work for its intended job.  I believe this happened across multiple threads, but here is one of them. 

https://www.gatewaytoairguns.org/GTA/index.php?topic=166984.msg155874793#msg155874793

Most every DIY mod I share is based on information freely shared by others.  Sometimes it's an outright plagiarism of others work, sometimes it's my own crazy idea.  Some pan out others don't.  I try to share both when things work and when they don't, but I don't think there is enough forum bandwidth for me to memorialize all of my mistakes and bad ideas, lol.

For a DIY hack, I think the taper pin reamers  work great.  If I were taking people's money for services I would probably have to invest in something with greater precision/repeatability. 

RC---Thank you and I agree.  A great platform.  .

« Last Edit: December 19, 2020, 05:31:48 PM by mackeral5 »
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