First big bore build

[Scotchmo]

I'm using my 100+fpe .22 HP build as the basis for a .257 long range gun. I'm looking to get in the 180fpe range.

The base rifle is/was an Armada .22 but there are few original parts remaining (receiver, handrail, modified air tube and gauge block, plug/endcap). It still looks like an Armada.

Electronic hammer/trigger
Cothran Powerhouse valve
Custom single shot breech with 0.250" ports
36" bull barrel (0.875" dia) with TJ 25-20 liner
215cc plenum
2000cc, 300bar bottle
Ninja Flex regulator (3000psi max)

It's for bench rest. Weight will be ~19lbs without scope or bipod.

Currently using a 450cc tank. Waiting on the 2000cc tank. I have the barrel blanks. I just need to make some time to get to the shop. I ordered an Arsenal 257420 Boat Tail mold (70gr), but they are backed up with orders so that won't be in for several weeks.

[Hobbyman2007]

Sounds like fun . Love the flat shooting 257 . Too bad it’s way overkill for hunting. I think you’ll  really like the 257420 mold. Keep us posted

[mackeral5]

This one should be very interesting.  Big plenum, LOOONNNNGGG barrel. 

I have a 35" TJ's 25-20 in process for one of my Bulldogs, it will be used both regulated and unregulated, should be interesting to compare notes.  The gun previously did a little over 165pe with 72gr at 3000psi, but with a 27" barrel.  Hoping for similar energy levels as you but not having to run it near as hard as was required with the 27" barrel. 

[rsterne]

Sounds like a great project.... 180 FPE on 3000 psi will be a good power level, if it can be done with decent efficiency.... The 36" barrel will, of course, help in that regard.... I would be looking at a heavier slug, however, that works out to 1075 fps with a 70 gr.... 

Bob

[JuryRigger]

Watching,
Jesse

[Scotchmo]

I plan on finishing the barrel tomorrow. I machined down the first 5.3" of the 7/8" DOM tubing to fit the breech. And then I was tried to sand out the bore to accept the liner. It was a lot easier to sand down the liner a tiny amount (< .001"). The liner is a smooth snug slip fit with no perceptible clearance. I have Loc-tite 641 to use to bond the liner in place - unless I hear a reason not to. I'll crown the liner first and then bond it in with the crown recessed about 1/6" to 1/8" into the muzzle end. Then cut the small excess off the breech end and chamfer/ream the chamber if needed. Finally, cold blue the exterior.

My 257420 mold won't be shipped for several weeks, so I ordered some Griffin 84gr RBT slugs for initial testing.

[rkr]

I was getting 1030 fps with 257420s from 31" barrel at 3050psi in my Evanix, at 2900psi it does 990 fps and the limit is more or less the barrel length as I've played with it quite a lot. Since you have 5" longer barrel you should be very close to that 1075 fps at 3000 psi if you just make it flow enough and tune the hammer strike right.

[Scotchmo]

I did some initial tests over the chronograph. I have not cut the lead-in yet, so I had to tap the .257 slugs in with a hammer and drift. The skirts of the smaller .25 pellets snapped in easily:

2900psi
34.95gr JSB
1253fps
1257
1242

82gr Griffin
959fps
949

I have a small taper reamer that works well for .22. I'll probably order a slightly larger taper reamer to cut the .257 chamber area. I want it optimized for the 257420 cast slugs, for a nice fit. I think I'll be able to get the 257420 slugs up to 1060fps at 3000psi.

[rsterne]

Sounds about right for a 36" barrel.... Tapered Pin Reamers are great for cutting chambers.... They are 1/4" taper per foot.... From another post I wrote....

A #5 tapered pin reamer starts at 0.2407" and ends at 0.2994".... A #4 starts at 0.2071" and ends at 0.2600".... Either would work for a .25 cal or .257 cal.... but the #4 could also be used in a .22 cal or .224 cal.... Since you probably would want to grind away the flutes after it reaches chamber diameter you would need two anyways.... A #3 will also work for .22 cal or .224 cal, it starts at 0.1813" and ends at 0.2294".... A #2 would be the size for .177 cal, it starts at 0.1605" and ends at 0.2010".... A #6 would work for .30 cal or .308 cal, it starts at 0.2773" and ends at 0.354".... As mentioned above, the #7 is for .35 and .357 cal....

Bob

[Scotchmo]

Sounds about right for a 36" barrel.... Tapered Pin Reamers are great for cutting chambers.... They are 1/4" taper per foot.... From another post I wrote....

A #5 tapered pin reamer starts at 0.2407" and ends at 0.2994".... A #4 starts at 0.2071" and ends at 0.2600".... Either would work for a .25 cal or .257 cal.... but the #4 could also be used in a .22 cal or .224 cal.... Since you probably would want to grind away the flutes after it reaches chamber diameter you would need two anyways.... A #3 will also work for .22 cal or .224 cal, it starts at 0.1813" and ends at 0.2294".... A #2 would be the size for .177 cal, it starts at 0.1605" and ends at 0.2010".... A #6 would work for .30 cal or .308 cal, it starts at 0.2773" and ends at 0.354".... As mentioned above, the #7 is for .35 and .357 cal....

Bob

I have the #3, so I just ordered a #2, #4, and #5.

[Scotchmo]

I tried some different pressures with the 82gr. When tapping it into the uncut chamber area, it shears off about 2gr of lead, so I'll call it an 80gr slug for fpe calculations:

2600psi - 920fps, 150fpe
3000psi - 966fps, 166fpe
3500psi - 1021fps, 185fpe

3000psi is the maximum that I will be running at in the long term.

The lead of the Griffin slugs seems very hard. It takes considerable force to push a slug completely through the barrel. Slugging the barrel gives me .249" land x .256" groove, as best as I can measure. I'm thinking that the 82gr Griffins at .697" long might not be the best for the 1:14 liner. The 257420 BT molds shows 0.6" long so should be a better match. But it's several weeks out for my backorder. Anyone have a .257 mold that they want to sell? Prefer 60gr-80gr.

Not sure if this liner can shoot .25 pellets accurately. I just tuned it down to shoot JSB 34gr pellets at 980fps. I'll try that at the range tomorrow.

[rsterne]

You may be finding that the slugs being hard and with a long bearing area are losing velocity.... or maybe not, since you are tapping them into the bore to start with....  Nice numbers, in any case....

Bob

[Scotchmo]

We had a very calm day today. I kept the regulator pressure at 2800-3000psi (creepy!) and swapped the 0.25 port (1250fps) for a 0.14 port (980fps). The 34gr JSB pellets at 980fps shot surprisingly well in the .257 barrel. Even at 100 and 135yds. This was going to be a dedicated slug barrel and I have a couple of .22 pellet barrels already for this gun, but am now thinking of getting more .25 pellets and also going that route. It will take some more testing.

I also picked up 50 or so slugs from a friend. The hand written label says R+L 0.257 FN. They weigh in at 73gr and look very similar to the Lee and Arsenal 257420. I'll try these soon but still waiting on the taper reamer for the chamber (do next week).

[rkr]

Sounds about right for a 36" barrel.... Tapered Pin Reamers are great for cutting chambers.... They are 1/4" taper per foot.... From another post I wrote....

A #5 tapered pin reamer starts at 0.2407" and ends at 0.2994".... A #4 starts at 0.2071" and ends at 0.2600".... Either would work for a .25 cal or .257 cal.... but the #4 could also be used in a .22 cal or .224 cal.... Since you probably would want to grind away the flutes after it reaches chamber diameter you would need two anyways.... A #3 will also work for .22 cal or .224 cal, it starts at 0.1813" and ends at 0.2294".... A #2 would be the size for .177 cal, it starts at 0.1605" and ends at 0.2010".... A #6 would work for .30 cal or .308 cal, it starts at 0.2773" and ends at 0.354".... As mentioned above, the #7 is for .35 and .357 cal....

Bob

What would be the correct reamer for .45?

[mackeral5]

Sounds about right for a 36" barrel.... Tapered Pin Reamers are great for cutting chambers.... They are 1/4" taper per foot.... From another post I wrote....

A #5 tapered pin reamer starts at 0.2407" and ends at 0.2994".... A #4 starts at 0.2071" and ends at 0.2600".... Either would work for a .25 cal or .257 cal.... but the #4 could also be used in a .22 cal or .224 cal.... Since you probably would want to grind away the flutes after it reaches chamber diameter you would need two anyways.... A #3 will also work for .22 cal or .224 cal, it starts at 0.1813" and ends at 0.2294".... A #2 would be the size for .177 cal, it starts at 0.1605" and ends at 0.2010".... A #6 would work for .30 cal or .308 cal, it starts at 0.2773" and ends at 0.354".... As mentioned above, the #7 is for .35 and .357 cal....

Bob

What would be the correct reamer for .45?

I have used a #8.  This chart shows the size ranges.

[rkr]

Thanks! Metric sizes are more common at Aliexpress and Mcmaster has a size chart: https://www.mcmaster.com/taper-reamers/metric-size-hand-reamers-for-taper-pin-holes/

[mackeral5]

Thanks! Metric sizes are more common at Aliexpress and Mcmaster has a size chart: https://www.mcmaster.com/taper-reamers/metric-size-hand-reamers-for-taper-pin-holes/

Great info on Aliexpress, I haven't considered them.  Typically I pay $20-25 per reamer on ebay....

[rkr]

Thanks! Metric sizes are more common at Aliexpress and Mcmaster has a size chart: https://www.mcmaster.com/taper-reamers/metric-size-hand-reamers-for-taper-pin-holes/

Great info on Aliexpress, I haven't considered them.  Typically I pay $20-25 per reamer on ebay....

I just ordered four for 21$!

[BigBird]

Is using a smaller taper reamer and running it in at the edge of the bore at an angle with aluminum siding tape at the tip to prevent scratches bad form?

[Scotchmo]

Still awaiting my Arsenal 257420 mold but managed to get my hands on some 73gr RL 257420 slugs. Full ports at 3200psi averages 1058fps, 181fpe.

The Cothran valve is tunable via either pressure or transfer port. Not so much using the hammer/solenoid settings. I'm setting this up for benchrest. I need a very consistent pressure in order to get consistency between shots. I originally chose Ninja Flex regulator because it goes to 3000psi, and is externally adjustable, but it suffers from a little more creep and inconsistency than I like to see. I might take a shot a fixing it later. For now, I've decided to go with a generic Chinese bottle regulator. I tried a couple of the new designs that go up to 3000psi but I was not impressed. The common style regulator is only available up to 2200psi, but they seem more stable at those lower output pressures. My spreadsheet calculations show that should put me in the 980fps, 150-160fpe range with the 72gr 257420 slugs. I can settle for that if it's consistent.

I also plan on shooting JSB 34gr pellets. Transfer ports are easy to swap out, so that will be the likely way that I tune it down. Optionally, I'll have different bottles with different regulators.

With the 2000cc tank, I should get lots of shots. Overall length is 54".