Author Topic: airguns barrels TJ,S (Read 4568 times))

Airgun-hobbyist · « **Reply #20 on:** December 30, 2019, 12:11:58 PM »

Quote from: dyotat100 on December 30, 2019, 11:49:45 AM

Quote from: Airgun-hobbyist on December 30, 2019, 01:21:39 AM
Quote from: rsterne on December 30, 2019, 12:36:22 AM
I can't imagine building a 7mm with purposely a low enough power to require a light slug.... but I suppose it could be done.... I'm guessing the .30 cal FX slugs will be under 60 gr.... but I could be wrong.... That guess is based on the lack of commercially available .30 cal PCPs over 100 FPE, let alone 120....

Bob

I don't know if this can be done, but with smaller caliber coupled with the available power I was thinking of not lowering the power, but utilizing air pressure and volume to produce a slug speed close to 1300 FPS at the muzzle. At 100 yards a 65 grain slug is still moving 1087 fps and has 171 ft lbs. energy so it stays in a flight speed where it shouldn't be effected by going in and out of mach zones until nearly the 200 yard mark.

What gun do you think will do this? When you step down in size you loose fps. Smaller surface to push on.

I don't know anything that will shoot a slug that fast unless helium is used

I see. So it is like getting deminishing returns going smaller in size. It was just a thought for an experiment, having the power/pressure of a dedicated big bore and putting the smaller barrel in there to up the speed into the sweet spot of another Mach zone.

PakProtector · « **Reply #21 on:** December 30, 2019, 12:40:14 PM »

Alright, TJ has nothing past 26" in twist for the 30 pellet. So I'll get a new mandrel. One in 44" twist. three grooves, .080 wide each. Bore of .294 +0/-.0005. Groove .2997 +0/-.0003.

Grooves are 75% of bore circumference, and the grooves are a wee bit under the .300 pellet heads to get certain engagement all the way around. I was tempted to do two grooves, but those shot best when quite tight compared to pellet head, and I don't think it is required. A compromise to get solid head engagement should do. PT&G will be making the mandrel.
cheers,
Douglas

rsterne · « **Reply #22 on:** December 30, 2019, 12:41:52 PM »

There are at least two problems with the idea of trying to shoot an airgun Supersonic.... First, the internal efficiency drops off extremely fast as you approach and exceed Mach 1, unless you use Helium.... Second, the slug slows so quickly after it leaves the muzzle that the wind drift increases instead of decreases.... Yes, you can deliver more energy to the target, with a flatter trajectory, but if the wind makes it harder to hit things until you get the velocity above 2500 fps, are you really gaining usefulness?....

https://hardairmagazine.com/ham-columns/the-external-ballistics-of-slugs-in-airguns/

Read that article, the last chart in it shows what happens to wind drift as you increase the velocity....

Bob

rsterne · « **Reply #23 on:** December 30, 2019, 12:45:42 PM »

Douglas, I assume you mean that the lands will be 0.080" wide, not the grooves.... or are you talking about the grooves in the mandrel?.... Sounds like a good barrel design for pellets only.... I wonder how slow we can go?....

Bob

PakProtector · « **Reply #24 on:** December 30, 2019, 01:11:30 PM »

yes, the lands will be .080 wide. the grooves about 3x that. IOW, there will be .080-wide grooves in the pellet from the lands...

Hair splitting and proper terminology is critical here. Got a pic from PT&G just to be sure.
cheers,
Douglas

dyotat100 · « **Reply #25 on:** December 30, 2019, 01:37:33 PM »

Another thing is to try and figure is the barrel has spring back. So mandrel needs to be adjusted.

The new 7mm is .28460" after slugging barrel. I don't have the mandrel to measure.

On .50 cal I had the mandrel made at .50960". Barrel samples came out at .51140". So I had to have mandrel ground down. I haven't seen the mandrel but my barrel is .5100" now.

I know that the TJ 1:14 7mm barrel was .2850" when I built Cedrics 7mm. I had him Mike grind the mandrel down when he was adjusting the 308 1:14 to come out .3080".

So not sure how much is needed but it does have spring back.

rsterne · « **Reply #26 on:** December 30, 2019, 01:51:01 PM »

Thicker barrel wall may spring back differently as well.... I like having my barrels made with a 14mm OD, because of the readily available CF tubing with that ID and a 20mm OD (over 3/4")…. Todd at TJ's seems to be making quite a few 14mm OD barrels now.... I gave him a sample of the CF sleeve so that he could easily check the OD....

Bob

dyotat100 · « **Reply #27 on:** December 30, 2019, 01:57:40 PM »

I have a thinner 7mm also I will slug when I get home to see if it is any different.

The 50 cal barrel is not that thick. It is only .685" OD.

There is spring back in all of them or the mandrel wouldnt come out.

Just figuring out how much is the fun part.

Kinetic45^ · « **Reply #28 on:** December 30, 2019, 04:00:39 PM »

Doug, did you happen to verify we got 18" twist on the new 7mm mandrel when you slugged the barrels?

PakProtector · « **Reply #29 on:** December 30, 2019, 04:22:54 PM »

Yeah, spring back...I did make sure to state that on the RFQ that the specified dimensions are for the formed barrel, and not the mandrel itself. I wish I could have gotten LW to eat some of the research $$ for a polygon, long twist rate .300 pellet barrel. 44" should do a darned fine job on pellets, even ones going very quickly...

and more importantly, ones that will slow considerably on their way to the target.

Mandrel due in some 9-12 weeks...

cheers,
Douglas

dyotat100 · « **Reply #30 on:** December 30, 2019, 04:46:03 PM »

Quote from: Kinetic45^ on December 30, 2019, 04:00:39 PM

Doug, did you happen to verify we got 18" twist on the new 7mm mandrel when you slugged the barrels?

No I just slugged it

Insanity · « **Reply #31 on:** December 30, 2019, 05:29:38 PM »

Quote from: KnifeMaker on December 28, 2019, 12:11:01 AM

TJ's list for the public.

FWIW I just bought a 36" long barrel liner 1/2" OD .257 in a 14" twist so he may have more options. Unless he keeps a stock of everything on hand I got the barrel sooner than I thought I would get it.

rsterne · « **Reply #32 on:** December 30, 2019, 05:32:44 PM »

The .257 with a 14" twist is the liner for a 25-20, and one of his most popular barrels.... You will find it in the PB list.... You can get it in 1/2", 14mm and 9/16" OD, and possibly also 5/8"....

Bob

Insanity · « **Reply #33 on:** December 30, 2019, 05:35:13 PM »

I thought it was that liner but on the list I must have over looked the OD as a option as the list columns get jumbled up for me. That would explain why it got here so quick.

K.O. · « **Reply #34 on:** December 31, 2019, 02:02:56 AM »

1-44 twist sounds like a round ball/maxi ball black powder compromise barrel... just might be pretty good with subsonic round ball..

https://www.trackofthewolf.com/Search.aspx?search=%20.283

Tiroflojo · « **Reply #35 on:** December 31, 2019, 05:57:40 AM »

Greetings.
Now I have recovered my crony, after the breakdown, so I used an afternoon to test my slugs 6.35 / 66 grains and the LW 1/16 twist cannon.
The deposit was filled to 290 bars and down to 150.The result was:
281mxsg ------ 168J
282
282
283
281
279
--- shots out of crony
--- "
--- "
274
275
273
273 ------- 159J
The slug is from Noebulletmolds.
The grouping is good at 50m (the only one tested). The grouping tests made with 74 grains boattail hollow point from Noebulletmolds, were good obtaining the same POI. And instead the tests with the tips of 95 grains .257 "Noble "of the Arsenalmolds were not good, obtaining lateral breaks.
I decided to ask Antony (Talon Tunes) a TJ 257 1/14 twist barrel, with the idea of having better results with the long slugs of 95 g.
The confuiguration of my rifle is 115 grams of hammer and spring tension (10 cm in length / 2mm thread) is between two and three. So there is still room to raise power, if necessary. I hope Antony returns to activity soon to have the TJ in my Condor.

PakProtector · « **Reply #36 on:** December 31, 2019, 08:57:07 AM »

Quote from: K.O. on December 31, 2019, 02:02:56 AM

1-44 twist sounds like a round ball/maxi ball black powder compromise barrel... just might be pretty good with subsonic round ball..

https://www.trackofthewolf.com/Search.aspx?search=%20.283

I'll not be the one to load round ball in it. Probably.

So KO, where would you put the FX skid-thru barrels that have a twist rate of 120-150"? Balls with negative curvature?
cheers,
Douglas

rsterne · « **Reply #37 on:** December 31, 2019, 12:15:34 PM »

Enrique.... I would think that the 1 in 16" twist of your LW barrel would be too slow for a 95 gr. in .257 cal.... What LW barrel do you have, their pellet barrels are a 17.7" twist?....

Bob

Tiroflojo · « **Reply #38 on:** January 01, 2020, 06:11:22 AM »

Bob, I don't have an LW barrel of pellets. I have unchoked and 1/16 twist. It also shoots the pellets very well, as long as they stay at a speed between 290/260 mxsg. Up to 250m xsg for pellets. Slugs need a little more speed to be stable.
These are the LW barrels available in Europe:

https://www.lothar-walther.com/gun-barrel-blanks/airgun-barrels/?p=2

I have also tried lime. 30 1/16 twist with slug up to 150 g, the 135 g boattails were the best groups to do (tests at 50m).
I hope you are right and the TJ of 1/14 makes the right turn for the long slug of .25 / 95 grains. I will also get rid of the ugly task of passing the slug with a hammer blow from 257 to 252 in two sessions. It is very slow work and greatly deforms the original design of these slugs.

PakProtector · « **Reply #39 on:** January 01, 2020, 12:05:01 PM »

Based on a sample of about one, and half a decade ago, a gentleman with a .257 Scandalous found about 80 gr the limit of what a 1:14 barrel could stabilize and went to 1:10" twist rate for heavy slugs. Shooting at 286 yards across his vineyard. Not to say you will have the same, just a note.
cheers,
Douglas

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airguns barrels TJ,S

Author Topic: airguns barrels TJ,S (Read 4568 times))