.257 Bulldog

[Insanity]

Long .257 barrel making progress.  MAYBE some chrono numbers next week....



35.5" barrel, 42" overall length.

Now this makes me wonder how my .257 brod will look like with its 36" barrel... My guess silly.

[mackeral5]

Long .257 barrel making progress.  MAYBE some chrono numbers next week....



35.5" barrel, 42" overall length.

Now this makes me wonder how my .257 brod will look like with its 36" barrel... My guess silly.

Not silly, just LOOONNGGG....  you will need to help the breech out however you can, it may want to flex in the mag slot.. 

[Insanity]

I will likely have support the barrel some how to help with that. I plane on single shot tray so maybe some sort or top rail  that dont interfere with loading and the scope.

[YEMX]

Whew!  That is really coming along!  Even though it's long, I bet it handles far better than a conventional rifle would, with the same length barrel! 

[mackeral5]

Things are moving pretty slow, but I did manage to rough in the barrel port and barrel screw indentions.  Barrel port is at .200 and slightly elongated to approximately .250 long.  I still plan to take it to .300 but doing this all by hand requires me to do it in stages, and only doing it when it feels "right." 

This meant that the barrel is now secure and the air passage is clear so hey, why not send a few rounds into the trap? 

All I have is 3200psi of nitrogen, so that's as high as I tested.  Here are some quick max velocity numbers. 

With MP 257-640 HP's dropping at 68gr  max velocity 1125fps 191fpe

With some 257420 boat tails from Apex, weighing in at 71gr, max velocity 1075fps.  182fpe


A regulated tune is intriguing to me.  A bit of testing found that it will send the 68gr 985fps on a miserly 2300psi.  Of course this is with a 340cc tube as a plenum.  later today I will assemble with 160cc of plenum and 340cc HPA storage and see how many of these 145fpe shots I can wring out of it. 

That long 35.5" barrel makes a BIG difference.  Once i swap out tanks we can see what kind of numbers 3500psi will produce.

[YEMX]

How long of a projectile can a BD mag hold again?

[mackeral5]

The wheel measures .675 thick.

[YEMX]

The wheel measures .675 thick.

Hmmmmm...

[Scotchmo]

...
All I have is 3200psi of nitrogen, so that's as high as I tested.  Here are some quick max velocity numbers.
...
With some 257420 boat tails from Apex, weighing in at 71gr, max velocity 1075fps.  182fpe

...

My Armada has a 36" TJ 25-20 liner and with 73gr RL 257420 slugs at 3200psi, averaging 1058fps, 181fpe

So seems about right.

[mackeral5]

...
All I have is 3200psi of nitrogen, so that's as high as I tested.  Here are some quick max velocity numbers.
...
With some 257420 boat tails from Apex, weighing in at 71gr, max velocity 1075fps.  182fpe

...

My Armada has a 36" TJ 25-20 liner and with 73gr RL 257420 slugs at 3200psi, averaging 1058fps, 181fpe

So seems about right.

Yes, very similar results between the very similar barrels.  Big difference in powerplants though..  Mine is old school PCP.  ~102 gram hammer and stiff spring, ~.400 peek poppet on a .375 throat.  Multi-caliber gun, .257 and .357.

[rkr]

I would say you need a barrel band when you proceed to accuracy testing stage. CF sleeving might also be a good idea. With the power you have there I'd also try 257388 bullets. 

[mackeral5]

I would say you need a barrel band when you proceed to accuracy testing stage. CF sleeving might also be a good idea. With the power you have there I'd also try 257388 bullets.

Agreed on the sleeving and barrel band.  Read a few posts up, the pic with the barrel hanging in the wind was merely a mock-up...  It has now been sleeved to 19mm with CF, and will be supported  forward of the breech.

Thanks for the recommendation on bullets to try.  for now I have a 65-75gr assortment of cast and swaged from the various manufacturers.  I'm not sure I will ultimately run it hard enough for heavier ammo.  But, in the early phases it is fun to see how much energy it can produce. 

My only mold is the MP 257-640 GC.    In deep hollowpoint it drops at 68gr, flat point 72gr.  I hope it proves to be accurate.   

[rkr]

I would say you need a barrel band when you proceed to accuracy testing stage. CF sleeving might also be a good idea. With the power you have there I'd also try 257388 bullets.

Agreed on the sleeving and barrel band.  Read a few posts up, the pic with the barrel hanging in the wind was merely a mock-up...  It has now been sleeved to 19mm with CF, and will be supported  forward of the breech.

Thanks for the recommendation on bullets to try.  for now I have a 65-75gr assortment of cast and swaged from the various manufacturers.  I'm not sure I will ultimately run it hard enough for heavier ammo.  But, in the early phases it is fun to see how much energy it can produce. 

My only mold is the MP 257-640 GC.    In deep hollowpoint it drops at 68gr, flat point 72gr.  I hope it proves to be accurate.   

Well those 257420s seem a bit fast to me, I wouldn't go over 1050 fps. 257388 mold is available from Arsenal and drops around 85 grains. That should be around 1000 fps with your setup which to me sounds quite perfect. I was shooting them at 920 fps and I got a feeling that a bit more speed would have helped. Arsenal also has BT version of 257420 but that likes a bit lower speed, they are very accurate at 920 fps from my Evanix and groups start to open up with more speed.

[mackeral5]

I would say you need a barrel band when you proceed to accuracy testing stage. CF sleeving might also be a good idea. With the power you have there I'd also try 257388 bullets.

Agreed on the sleeving and barrel band.  Read a few posts up, the pic with the barrel hanging in the wind was merely a mock-up...  It has now been sleeved to 19mm with CF, and will be supported  forward of the breech.

Thanks for the recommendation on bullets to try.  for now I have a 65-75gr assortment of cast and swaged from the various manufacturers.  I'm not sure I will ultimately run it hard enough for heavier ammo.  But, in the early phases it is fun to see how much energy it can produce. 

My only mold is the MP 257-640 GC.    In deep hollowpoint it drops at 68gr, flat point 72gr.  I hope it proves to be accurate.   

Well those 257420s seem a bit fast to me, I wouldn't go over 1050 fps. 257388 mold is available from Arsenal and drops around 85 grains. That should be around 1000 fps with your setup which to me sounds quite perfect. I was shooting them at 920 fps and I got a feeling that a bit more speed would have helped. Arsenal also has BT version of 257420 but that likes a bit lower speed, they are very accurate at 920 fps from my Evanix and groups start to open up with more speed.

That's great feedback, thanks for sharing your experience.  What you've done with the Evanix is very impressive.

[mackeral5]

Here is another mock-up.  it is a functioning gun at this point, however with a few temporary parts.  The bolt probe is cobbled together and the shroud supports are roughly machined.  An caliber swappable, interchangeable probe bolt system and a set of precisely machined barrel supports are in USPS possession.  Hopefully I'll have those parts this week. 

Barrel is sleeved in 19mm CF, tube is equipped with Matt's 160cc extension bringing air capacity to ~500cc. 

I forgot to install my depinger, will add it when it comes time to replace the bolt/probe system. 

A DonnyFL KOI does a surprising job of making the 165fpe bark a little more tame.  Not backyard friendly, but still quieter than the PINGGGGGG!

Total length is 48" with the KOI.

[mackeral5]

During lunch I was able to shoot a few initial groups using freshly cast MP Molds 257-640's, cast with the deep hollow point pins.  The batch used for this testing dropped at 68.7-68.8gr and were sized at .257.  At this stage I've cast probably 300ish bullets of various molds and probably melted down half of those, so I have a long ways to go in learning proper technique, etc.  I lubed with 10wt silicon RC shock oil. 



This mold was  a bit of a gamble as it isn't the most popular, I only found one reference to it on the airgun forums, but no real performance data.  I liked the fairly large flat point/hollowoint and it didn't appear to have much surface area of contact with the bore, so I rolled the dice. 

Here is a target with groups of 5 shots.  The center bull was the sighter.  Shots were taken at 75 yards, all the distance I have setup right now, 



These shots were shot standing with the pressure tube resting on a Tack Driver bag.  Not a bad start, especially considering all of the variables at play.  I did notice the long barrel requires more careful follow-through. 

The current tune is 7 shots 1023, 1044, 1049, 1052, 1045, 1042, 1028fps, a 7 shot average of 1040fps, 165fpe.  3100psi fill.  It uses about 500 psi of air. 

I am enjoying casting my own ammo, thanks to all the guys that freely share their experience i was able to get off to a bit less shaky of a start than anticipated. 

I expect groups to tighten up as I get more experience with this long barrel and better at casting.  Also, the barrel isn't fully secured in the shroud, I have some additional parts arriving hopefully this week which should further stabilize the barrel. 

[Hobbyman2007]

You must be ecstatic of the results, I know I would be with groups like that from an untested mold, untested rifle , and only sizing once. Very promising indeed. Looking forward to see some more. Glad to see this barrel is a performer.

[mackeral5]

You must be ecstatic of the results, I know I would be with groups like that from an untested mold, untested rifle , and only sizing once. Very promising indeed. Looking forward to see some more. Glad to see this barrel is a performer.

Yes sir indeed.  I don't feel quite as bad about splitting that other barrel down the middle now that things are going in the right direction. 

There are a lot of personal "firsts" going on with this one..  After watching one of Sean Perro's vidieos I created my first lead lap for this barrel.  I ended up swapping ends from the way it was labeled as the end labeled muzzle felt more loose to me when I slugged prior to lead lapping.  Also, there were more inclusions towards the end labeled as the muzzle.  So I rolled the dice and swapped ends.  It was a gamble, but so far it appears to have paid off.....

One thing I noticed about these .257 TJ's barrels---they are not as close to "perfect" as my .357's and .300's.  Even after a thorough lap job, there are still some spots in it that I am not happy with.....

I am really happy with the performance untethered with a 3100psi fill.  But, with 500cc of air and 35.5" of barrel I guess it shouldn't be surprising...

More to come.  Working on getting a mag to function....

[Lani52]

Great work Mike, really satisfying isn’t it.  Imagine what it will do with bullets sorted to specific weights and tethered.

I am just tickled your doing that, it will only get better.

Regards,

Roachcreek

[Airgun-hobbyist]

That's some work to be proud of right there.  If you regulated it those groups will likely tighten up even further.  Fine job Sir!